First Report of Broad Bean Wilt Virus 2 Infecting Balsam (Impatiens balsamina) in China.

Balsam (Impatiens balsamina L.) is an ornamental plant cultivated extensively in China and elsewhere, but it has also been used as a medicinal plant for thousands of years (Qian et al., 2023). In 2022, an examination of 10 garden-grown I. balsamina plants in Chaoyang, Beijing, China revealed eight plants with blotches, mosaic symptoms, and deformed leaves (Fig. S1A). Total RNA was extracted from the symptomatic leaf tissue of these eight plants using the TRIzol reagent (Invitrogen, USA). Four RNA preparations (high quality and quantity) were combined for the small RNA sequencing analysis (TIANGEN Biotech Co., China). A total of 16,509,586 clean reads (18-30 nt) were obtained and assembled into larger contigs using Velvet 1.0.5. A search of the National Center for Biotechnology Information non-redundant database using BLASTX indicated 72, 24, and 19 contigs were homologous to broad bean wilt virus 2 (BBWV2), cucumber mosaic virus (CMV), and impatiens cryptic virus 1 (ICV1) sequences (Zheng et al., 2022), respectively. To verify the next-generation sequencing data, the following three sets of primer pairs were designed according to the contig sequences of these three viruses: CMV-F:5'-ATGGACAAATCTGAATCAACCAGTGC-3'/CMV-R: 5'-CCGTAAGCTGGATGGACAACC-3'; BBWV2-F:5'-CAATTTGGACAACTACAATTTGCC-3'/ BBWV2-R: 5'-GCTGAGTCTAAATCCCATCTATC-3'; and ICV1-F: 5'-CGCACAACT CTACAAT GACATGGTC-3'/ICV1-R: 5'-AGTTCCATCGTCCAGTAGGCG-3'. The primers were used to amplify CMV, BBWV2, and ICV1 sequences by reverse transcription-polymerase chain reaction (RT-PCR), with individual RNA preparations serving as the template. The CMV, BBWV2, and ICV1 target sequences were amplified from eight, four, and four samples, respectively (Fig. S1B). To evaluate virus infectivity, Nicotiana benthamiana seedlings were inoculated using a leaf tissue extract prepared from an infected I. balsamina plant. At 7 days post-inoculation, disease symptoms were detected on N. benthamiana systemic leaves (e.g., deformation and apical necrosis) (Fig. S1C). Confirmation tests involving RT-PCR indicated the N. benthamiana plants were infected with BBWV2 and CMV, but not with ICV1 (Fig. S1D). To obtain the complete BBWV2 genome sequence (RNA1 and RNA2), virus-specific PCR primers (Table S1) were designed to produce the terminal sequences via 5' and 3' rapid amplification of cDNA ends (RACE), which was completed using the SMARTer RACE 5'/3' Kit (Clontech, China). The RNA1 and RNA2 sequences comprised 5,957 nt (GenBank: OQ857921) and 3,614 nt (GenBank: OQ857922), respectively. The BLAST analyses revealed RNA1 and RNA2 were similar to sequences in other BBWV2 isolates (sequence identities of 78.88% to 95.15% and 80.83% to 91.51%, respectively). Using the neighbor-joining method and MEGA 7.0, the phylogenetic relationships between the BBWV2 isolated in this study and other isolates were determined on the basis of the full-length RNA1 and RNA2 sequences (Kumar et al., 2016). According to the RNA1 and RNA2 sequences, the BBWV2 isolated in this study was most closely related to the BBWV2 isolate from Gynura procumbens (GenBank: KX686589) and the BBWV2 isolate from Nicotiana tabacum (GenBank: KX650868), respectively (Fig. S1E). To the best of our knowledge, this is the first report of I. balsamina naturally infected with BBWV2 in China. The study findings may be useful for detecting BBWV2 in I. balsamina and for diagnosing and managing the associated disease. The authors declare no conflict of interest. Yanhong Qiu and Haijun Zhang contributed equally to this paper. Funding: This research was supported by the Beijing Academy of Agriculture and Forestry Foundation, China (KYCX202305, QNJJ202131, and KJCX20230214). References: Qian H.Q., et al. 2023. J Ethnopharmacol. 303. Zheng Y., et al. 2022. Arch Virol. 167: 2099-2102. Kumar et al. 2016. Mol Biol Evol. 33: 1870-1874.

Morphological and molecular analyses reveal two new species of Microcera (Nectriaceae, Hypocreales) associated with scale insects on walnut in China.

The fungal genus Microcera consists of species mostly occurring as parasites of scale insects, but are also commonly isolated from soil or lichens. In the present study, we surveyed the diversity and assess the taxonomy of entomopathogenic fungi in Sichuan Province, China. Two new species of Microcera, viz. M.chrysomphaludis and M.pseudaulacaspidis, were isolated from scale insects colonising walnut (Juglansregia). Maximum Likelihood and Bayesian Inference analyses of ITS, LSU, tef1-α, rpb1, rpb2, acl1, act, tub2, cmdA and his3 sequence data provide evidence for the validity of the two species and their placement in Nectriaceae (Hypocreales). Microcerapseudaulacaspidis primarily differs from similar species by having more septate and smaller cylindrical macroconidia, as well as DNA sequence data. Meanwhile, Microcerachrysomphaludis has elliptical, one-septate ascospores with acute ends and cylindrical, slightly curved with 4-6 septate macroconidia up to 78 µm long. Morphological descriptions with illustrations of the novel species and DNA-based phylogeny generated from analyses of multigene dataset are also provided to better understand species relationships.

Trunk rot of Juglans regia caused by Myrmaecium fulvopruinatum in China.

Walnut (Juglans regia) is a deciduous tree of the Juglandaceae family, widely cultivated in China, and provides value in a variety of ways, including the usage of the wood and nuts, and offers substantial economic, social, and environmental advantages (Wang et al, 2017). Nevertheless, a fungal disease of causing walnut trunk rot was observed in approximately 30% of 50 counted ten-year-old J. regia in Chongzhou City (30°33'34″N, 103°38'35″E, 513 m), Sichuan Province, China, and this disease has greatly delete healthy growth of walnut. The infected bark exhibited purple necrotic lesions, and the sick parts were surrounded by water-soaked plaques. From 10 trunks of the 10 diseased trees, 20 isolated fungal colonies were the same. The ascospores placed in 60 mm plates were almost entirely covered with mycelium within 8 days, colonies on the PDA changed from initial pale to white, ad then turned yellowish to light orange or rosy to yellow-brown (25℃, 90% relative humidity, 12-h photoperiod). On the host, Ectostromata were immersed to erumpent, globose to subglobose, purple and brown, and measured 0.6 - 4.5 × 0.3 - 2.8 mm (x̄ = 2.6 × 1.6 mm, n = 40); Ascomata were flask-shaped to subglobose, dark brown, and measured 0.1 - 0.6 × 0.1 - 0.4 mm (x̄ = 0.35 × 0.25 mm, n = 40); Asci were numerous, cylindrical to subclavate, contained 8 uniseriate ascospores, and measured 80 - 150 × 10 - 20 µm (x̄ = 115 × 15 µm, n = 40), and Ascospores were ellipsoid, 2-celled, dark brown to black, plump or attenuated towards, apices with 1 large drop per cell, and measured 14 - 20 × 6.5 - 9 µm (x̄ = 17 × 7.8 µm, n = 40). These morphological characteristics are consistent with the species Myrmaecium fulvopruinatum (Berk.) Jaklitsch & Voglmayr (Jaklitsch et al. 2015). The genomic DNA of a representative isolate SICAUCC 22-0148 was extracted. The ITS, LSU region, tef1-α, rpb2 genes region were amplified using the primer pairs ITS1/ITS4 primers (White et al. 1990), LR0R/LR5 (Moncalvo et al. 1995), EF1-688F/986R (Alves et al. 2008), fRPB2-5f/fRPB2-7cr (Liu et al. 1999), respectively. The sequences were deposited in NCBI with accession numbers ON287043 (ITS), ON287044 (LSU), ON315870 (tef1-α), and ON315871 (rpb2), rspectively, which showed 99.8, 99.8, 98.1, and 98.5% identities with M. fulvopruinatum CBS 139057 holotype (accession numbers KP687858, KP687858, KP688027, and KP687933 respectively). Based on the analyses of phylogenies and morphologies, the isolates were identified as M. fulvopruinatum. The pathogenicity of SICAUCC 22-0148 was tested by inoculating surface-sterilized trunk wounds of four-year-old trees of J. regia with a mycelial plug (Desai et al. 2019). Sterile PDA plugs were used as controls. Wounds were covered with a film, to ensure humidity and prevent contamination. Each inoculation was repeated twice and included two plants, control and inoculated. A month later, the symptoms observed on inoculated trunks were similar to those in the wild, and M. fulvopruinatum was re-isolated from the inoculated trunk, confirming Koch's postulates. Previous research has reported M. fulvopruinatum as an important fungal species that cause canker delete symptoms on Chinese sweet chestnut in China (Jiang et al. 2018). We carried the taxonomy work of the fungi that caused trunk rot on walnut, and this is the first time that M. fulvopruinatum has been linked to walnut trunk rot on J. regia. Trunk rot of walnut will not only cause weakening of trees, but also affect the yield and quality of walnuts, bringing huge economic losses. This study was supported by the Sichuan Science and Technology Program under Grant 2022NSFSC1011. References: Alves, A., et al. 2008. Fungal Diversity 28:1-13. Desai, D.D., et al. 2019. International Journal of Economic Plants 6:147-149. Jaklitsch., W.M., et al. 2015. Fungal Diversity 73(1):159-202. Jiang, N., et al. 2018. Mycosphere 9(6):1268-1289. Liu, Y.L., et al. 1999. Mol Biol Evol 16:1799-1808. Moncalvo, J.M., et al. 1995. Mycologia 87:223-238. Wang, Q.H., et al. 2017. Australasian Plant Pathology 46:585-595. White, T.J., et al. 1990. Page 315 in: PCR Protocols: A Guide to Methods and Applications. Academic Press, San Diego, CA.

Identification and pathogenicity analysis of leaf brown spot of Juglans regia in China.

English walnut (Juglans regia), has high economic and ecological value. As an important tree species for eliminating poverty, it is planted in many Provinces of China. In 2021, new pathogenic fungi were observed in English walnut in Guangyuan City, Sichuan Province, China. The initial symptom of leaf infection is that the leaves are covered with small black spots, which gradually expand into larger brown spots. Most of the spots appeared at the edges of the leaves, and yellow whorls were observed at the junction between the spots and the healthy leaves. The pathogenic fungi were isoalted form collecting disease samples and purified by single-spore culturing. In vitro and field experiments showed that the pathogen could cause brown spots on walnut leaves. The inoculation experiment showed that the symptoms in the field experiment were the same as those observed on the spot; however, slight differences were observed in the in vitro experiment. Ten isolates were obtained from walnut leaves with brown spot symptoms, and these were further characterized based on morphology and DNA sequencing. ITS (internal transcribed spacer), LSU (large sub-unit rDNA), rpb2 (second largest subunit of RNA polymerase) and tub2 (beta-tubulin) gene regions were used to construct phylogenetic trees and determine the evolutionary relationships among the collected strains. The isolate was identified as Nothophoma quercina by morphological and polygene analyses. As far as we are aware, the brown spots on walnut leaves caused by N. quercina is the first report of its kind.

Leaf spot disease on Juglans regia caused by Ragnhildiana diffusa in China.

Juglans regia L. is commercially important for its edible nuts, which is a major species of walnut trees in Sichuan Province (Luo et al. 2020). In September 2021, brown leaf spot symptoms were observed on roughly 75% of 60 J. regia trees surveyed in an orchard of Chongzhou city (30°40'6''N, 103°40'18''E). Initially, the lesions measuring 2-10 mm were reddish to brown with a yellowish halo, then increased in size and coalesced to cover the whole leaf, eventually resulting in severe defoliation. Six symptomatic leaves from different trees were collected, and a single fungal isolate was obtained from each of the sampled leaves using single-spore isolation (Chomnunti et al. 2014). The isolates were incubated on potato dextrose agar (PDA) with a 12h photoperiod at 25 ℃, and deposited at the Culture Collection of Sichuan Agricultural University. Colonies were identical with black center and reddish-brown periphery, and the diameter reached 2 cm after 7 days. On the host, conidiophores were mostly reduced to conidiogenous cells, with prominent and thickened conidiogenous loci. Conidia were light green to light brown, and curved with a thickened and darked hilum at the base, 0-17 septate, tapering toward the distal end, and measuring 20-120 × 3-5 µm ((x ) ̅= 56 × 4, n = 30). Morphological characteristics fit the description of Ragnhildiana diffusa (Heald & F.A. Wolf) Videira & Crous (Synonym: Sirosporium diffusum (Heald & F. A. Wolf) Deighton) (Poletto et al. 2017). The internal transcribed spacer (ITS) region, the large subunit of the nrDNA (LSU), and RNA polymerase II second largest subunit (rpb2) were amplified by polymerase chain reaction and sequenced with primers ITS5/ITS4 (White et al. 1990), LR0R/LR5 (Vilgalys & Hester 1990), fRPB2-5F/Rpb2-R3 (Liu et al. 1999, Videira et al. 2017), respectively. The nucleotide blast of the two isolates (SICAUCC 22-0077, SICAUCC 22-0078) showed 99.7% and 99.5% (ITS, 472/473 bp, 471/473 bp), 100% (LSU, 725/725 bp, 725/725 bp), 99.8% (rpb2, 866/867 bp, 866/867 bp) identities with the ex-type strain of Ragnhildiana diffusa (CBS 106.14). The phylogenetic tree combined with ITS, LSU, and rpb2 genes and morphological characteristics confirmed the identification as R. diffusa. These sequences of the three gene regions of two isolates were deposited in GenBank with accession numbers ON409525 and ON409526 (ITS), ON409559 and ON409560 (LSU), ON417473 and ON417474 (rpb2), respectively. The isolate SICAUCC 22-0077 was used for pathogenicity test to fulfill Koch's postulates. Three leaves of each walnut seedlings (2-year-old seedlings) were inoculated by placing a mycelium plug onto fresh wounds on the upper leaf surface punctured via a fine needle (0.7 mm in diameter), and three replicate seedlings were inoculated. For the control, a sterile PDA plug was placed on the same number of replicate leaves on the plants. The inoculated and control plants were placed in a growth chamber at 25°C with relative humidity >80% and a 12-h photoperiod. Irregular light to dark brown spots developed on inoculated leaves after twenty days, and no symptoms were observed on controls. The re-isolation and examination of the fungus showed it to be morphologically and phylogenetically identical to the originally isolated pathogen. R. diffusa has been described on J. regia in Mexico (Farr & Rossman 2022). To our knowledge, this is the first report of R. diffusa causing brown leaf spot on J. regia in China. The identification of the pathogen will provide a basis for disease management in walnut planting areas.

Morphology and phylogeny of ascomycetes associated with walnut trees (Juglans regia) in Sichuan province, China.

In Sichuan province, walnuts, consisting of Juglans regia, Juglans sigillata, and the hybrid J. regia × J. sigillata, are commercially important edible nuts, and J. regia is the most widespread plant. To date, the diversity and distribution of fungi inhabiting on Juglans have not received enough attention, although there have been studies focusing on pathogens from fruit and stem. In order to update the checklist of fungi associated with Sichuan walnuts, a survey on fungi associated with the three Juglans species from 15 representative regions in Sichuan was conducted. In this article, ten fungi distributed in two classes of Ascomycota (Dothideomycetes and Sordariomycetes) were described based on morpho-molecular analyses, and two novel species, Neofusicoccum sichuanense and Sphaerulina juglandina, a known species of Ophiognomonia leptostyla, and seven new hosts or geographical records of Cladosporium tenuissimum, Diatrypella vulgaris, Helminthosporium juglandinum, Helminthosporium velutinum, Loculosulcatispora hongheensis, Periconia byssoides, and Rhytidhysteron subrufulum were included. Morphological descriptions and illustrations of these fungi are provided.

Culm blight on Phyllostachys aureosulcata 'Spectabilis' caused by Apiospora locuta-pollinis in China.

Phyllostachys aureosulcata McClure 'Spectabilis' C.D. Chu. et C.S. Chao is predominantly native to subtropical to warm temperate areas and is widely cultivated for landscaping in China (Neményi et al. 2015). In November 2020 (10 - 16 ℃), culm blight symptoms were observed on P. aureosulcata 'Spectabilis' in Wangjiang Tower Park (all kinds of plant areas are about 9.8 ha), Chengdu City (104°09'30.42″ E, 30°63'18.89″ N). Fifty plants were surveyed, and disease incidence was recorded as approximately 30%. Initially, chlorotic necrotic patches appeared on the culms, and gradually the patches became white, expanded to both ends, and encircled the whole culm with black edge and conidiomata, which eventually led to wilt and death. Five samples from different bamboos were collected and one of them were used for morphological observation. Five single conidia isolates were carried out on potato dextrose agar (PDA) at 25±1℃ (Chomnunti et al. 2014). Colonies were initially white and then yellowish in the center with abundant aerial mycelia. On the culm, conidiomata were dry, black, and filamentous. Conidiophores were reduced to conidiogenous cells. Conidiogenous cells were smooth, hyaline, ampulliform to doliiform. Conidia were ellipsoid to globose, dark brown, smooth and aseptate, measuring 5.2 to 9.4 × 4.4 to 7.3 µm, (=8.2 × 6.5µm, n=50). On the PDA medium, conidia were globose to subglobose, olive green to pale brown, and smooth, larger than those from the host in size, measuring 9.0 to 18 × 7.5 to 9.5 µm ( =36.6 × 18.8 µm, n=50). These asexual structures were extremely similar to Apiospora locuta-pollinis (F. Liu & L. Cai) X.G. Tian & Tibpromma (Zhao et al. 2018). DNA was extracted from the representative strain (SICAUCC 22-0036), and the internal transcribed spacer (ITS), translation elongation factor 1-alpha (tef1-α), beta-tubulin (tub2), 28S large subunit rDNA (LSU) were amplified and sequenced with primers ITS1/ITS4 (White et al. 1990), EF1-728F (Carbone & Kohn 1999)/EF2 (O'Donnell et al. 1998), T1 (O'Donnell & Cigelnik 1997)/Bt2b (Glass & Donaldson 1995) and LR0R/LR5 (Rehner & Samuels 1994). The newly generated sequences were deposited in GenBank with accession nos. ON228609 (ITS), ON324018 (tef1-α), ON237657 (tub2), and ON228665 (LSU). Nucleotide blast showed 98.97%, 100% and 99.46% identities with A. locuta-pollinis (LC11683, ex-holotype) (accession nos. MF939595, MF939622, MF939616), and LSU data missing. Phylogenetic analyses using maximum likelihood showed a 92% bootstrap support value in a clade with A. locuta-pollinis (Fig 2). Eight healthy plants (2-year-old) were used for the pathogenicity test. Culms of four healthy bamboos were wounded via sterile double-edged blade and sprayed with conidial suspension (105 conidia/ml) prepared from 4-week-old cultures that were incubated on PDA at 25℃. The other four bamboos were sprayed with sterile distilled water as controls. Inoculated plants were placed in a growth chamber (25℃, 90% relative humidity, 12-h photoperiod). About 60 days later, necrotic patches similar to those observed in the field were found on the inoculated culms, and no symptoms were observed on the controls. The pathogen was reisolated from the diseased culms with identical morphology as previously described. To our knowledge, this is the first report of culm blight on P. aureosulcata 'Spectabilis' caused by A. locuta-pollinis. The risk of this pathogen needs further evaluation, and effective control measures should be taken.

Trunk canker of Juglans sigillata caused by Lasiodiplodia pseudotheobromae in China.

Iron walnut (Juglans sigillata Dode) is a temperate deciduous tree indigenous to China. It is mainly distributed in southwestern China, and valued for its wood and nuts (Feng et al. 2018). In September 2020, symptoms of canker on J. sigillata were observed in an orchard measuring 2 hectares located in Chongzhou City, Sichuan Province (31°5' 25″N, 105°27'36″E, 365 m altitude). Twenty percent of plants showed canker symptoms during the 50 surveyed plants. The infected trunk showed necrotic lesions with black pycnidia, that led to necrosis of branches and death of the whole plant in severe cases (Fig. 1). Six specimens from different diseased plants were collected for pathogen isolation and morphological observation. Pure cultures were obtained from single conidium on potato-dextrose agar (PDA) media according to the method described by Chomnunti (Chomnunti et al. 2014). Colonies grew fast and reached 3 cm after 5 days. The aerial mycelium was abundant, which was initially white and then grayish. Conidiomata on the host were measured 160-280 µm × 140-190 µm (average: 220 × 165 µm, n = 20), stromatic, uniloculate, dark brown to black, immersed, and erumpent when mature. Pycnidial walls 32-58 µm wide, were composed of 5-7 layers of brown to dark brown cells. Conidia were hyaline, and ellipsoidal with rounded apex and base, widest at the middle, thick-walled, and unicellular, with a size 21.5-31 µm × 11.5-15.7 µm (average: 27 × 13.5 µm, n = 50). Morphological characteristics fit the description of Lasiodiplodia pseudotheobromae A.J.L. Phillips, A. Alves & Crous (Aives et al. 2008). The internal transcribed spacers (ITS), 18S small subunit rRNA (SSU), 28S large subunit rDNA (LSU), translation elongation factor 1-alpha (tef1-α), and beta-tubulin (tub2) were amplified by polymerase chain reaction and sequenced with primers ITS1/ITS4, NS1/NS4, LR0R/LR5, EF1-728F/EF1-986R and Bt2a/Bt2b, respectively (Li et al. 2018). The sequences of the representative isolate (SICAUCC 22-0079) were deposited in NCBI with accession numbers ON090365 (ITS), ON090406 (SSU), ON090418 (LSU), ON112377 (tef1-α), and ON112378 (tub2), respectively. Nucleotide blast showed 100% similarity of all the analyzed and NCBI submitted isolates with L. pseudotheobromae (CBS116459; holotype) (accession numbers EF622077, EU673199, EU673256, EF622057, EU673111). Phylogenetic analyses based on a combined dataset showed 100% bootstrap support values in a clade with L. pseudotheobromae complexes (Fig. 2). Based on morphological and molecular analyses, the fungal pathogen was identified as L. pseudotheobromae. To conduct Koch's postulates, four 2-year-old healthy plants of J. sigillata were inoculated with 10 µL spore suspension (105 conidia/mL) onto the wounded sites via sterile pin. As control, four healthy plants were treated with sterile distilled water. The inoculated and untreated plants were placed in a growth chamber at 25°C with relative humidity >90% and 12-h photoperiod. Trunk canker symptoms appeared on inoculated plants after 15-20 days, and the pathogen was re-isolated and the controls were symptomless, confirming Koch's postulates. L. pseudotheobromae is widely distributed in various plants all over the world, usually as a pathogen associated with damping-off, wilt, die-back, root rot, collar rot, witches' brooms, or fruit rots (Zhao et al. 2010). To our knowledge, this is the first report of trunk canker on J. sigillata caused by L. pseudotheobromae in China. Trunk canker caused by L. pseudotheobromae is becoming a potential threat to walnut production, and some necessary measures for integrated management should be made.

Morpho-Molecular Characterization of Microfungi Associated with Phyllostachys (Poaceae) in Sichuan, China.

In the present study, we surveyed the ascomycetes from bamboo of Phyllostachys across Sichuan Province, China. A biphasic approach based on morphological characteristics and multigene phylogeny confirmed seven species, including one new genus, two new species, and five new host record species. A novel genus Paralloneottiosporina is introduced to accommodate Pa. sichuanensis that was collected from leaves of Phyllostachys violascens. Moreover, the newly introduced species Bifusisporella sichuanensis was isolated from leaves of P. edulis, and five species were newly recorded on bamboos, four species belonging to Apiospora, viz. Ap. yunnana, Ap. neosubglobosa, Ap. jiangxiensis, and Ap. hydei, and the last species, Seriascoma yunnanense, isolated from dead culms of P. heterocycla. Morphologically similar and phylogenetically related taxa were compared. Comprehensive descriptions, color photo plates of micromorphology are provided.

First report of tomato spotted wilt virus infecting water dropwort in China.

Water dropwort (Oenanthe javanica) is an aquatic perennial plant that has been cultivated in many regions in Asia for thousands of years. In China, it is an economically important vegetable that has been consumed as food, while also being used as a folk remedy to alleviate diseases (Liu et al., 2021). In 2021, during a disease survey of a greenhouse in Beijing, China, chlorotic spots were detected on many water dropwort plants (Fig. S1A). Twenty-seven water dropwort samples were collected for the extraction of total RNA using the TRIzol reagent (Invitrogen, USA). High-quality RNA samples from three water dropwort plants were combined and used as the template for constructing a single small RNA library (BGI-Shenzhen Company, China). The Velvet 1.0.5 software was used to assemble the clean reads (18 to 28 nt) into larger contigs, which were then compared with the nucleotide sequences in the National Center database using the BLASTn algorithm. Thirty-eight contigs matched sequences in the tomato spotted wilt virus (TSWV) genome. No other viruses were detected. Twenty-seven leaf samples were analyzed in an enzyme-linked immunosorbent assay (ELISA) with anti-TSWV antibody (Agdia, USA), which revealed 17 positive reaction. Two sets of primer pairs targeting different parts of the S RNA (Table S1) was used to verify the TSWV infection on water dropwort by reverse transcription (RT)-PCR followed by Sanger sequencing (BGI-Shenzhen, China). The TSWV target sequences were amplified from 17 samples, which was consistent with the ELISA results. The sequenced 861-bp PCR product shared 99.8% nucleotide sequence identity with TSWV isolate MR-01 (MG593199), while the 441-bp amplicon shared a 99.2% nucleotide sequence identity with MR-01 (MG593199). To obtain the whole genome sequence of TSWV (S, M, and L RNA sequences), specific RT-PCR primers were designed (Table S1) and used to amplify their respective fragments from one representative sample (TSWV-water dropwort). The amplified products were inserted into PCE2TA/Blunt-Zero vector (Vazyme Biotech Co., Ltd, China) and then sequenced (BGI-Shenzhen, China). The S, M, and L RNA sequences were determined to be 2,952 nt (accession no. OM154969), 4,776 nt (accession no. OM154970), and 8,914 nt (accession no. OM154971), respectively. BLASTn analysis demonstrated that the whole genome sequence was highly conserved. The nucleotide identities between this isolate and other TSWV isolates ranged from 98.6% to 99.6% (S RNA), 98.9% to 99.2% (M RNA), and 97.3% to 98.7% (L RNA). Using MEGA 7.0, the phylogenetic relationships of TSWV were determined on the basis of the S, M, and L RNA full-length sequences (Kumar et al., 2016). In the S RNA derived phylogenetic tree, the water dropwort isolate was closely related to the MR-01 isolate from the USA (MG593199). In the M RNA and L RNA derived phylogenetic trees, the water dropwort isolate formed a branch with only a TSWV isolate from eggplant. Additionally, the M and L RNA sequences were most similar to sequences in TSWV isolates from China and Korea, respectively (Fig. S1B). To the best of our knowledge, this is the first report of water dropwort as a natural host for TSWV in China and the second report worldwide since the first finding in the Korea (Kil et al. 2020). TSWV has caused serious problems on many crops in the world, and the infection of TSWV on water dropwort in a greenhouse should not be looked lightly. Firstly, the virus can be passed on from generation to generation in infected water dropwort due to the vegetative propagation mode of the plant in production, thus threaten the production of this vegetable crop. In addition, infected water dropwort may serve as a reservoir for the virus, thus potentially posing a threat for causing TSWV spread in the affected greenhouses. The author(s) declare no conflict of interest. Funding: This research was supported by the Beijing Academy of Agriculture and Forestry Foundation, China (QNJJ202131, KJCX20200212, and KJCX20200113). References: Kil et al. 2020. Plant Pathol. J. 36: 67-75 Kumar et al. 2016. Mol Biol Evol, 33: 1870-1874 Liu et al. 2021. Horticulture Research. 8:1-17.

Branch blight of Juglans sigillata caused by Juglanconis appendiculata in China.

Juglans sigillata Dode, an endemic walnut species native in southwest China, is mainly used as nuts in Sichuan Province (Jin et al., 2019). In May 2021, symptoms of branches blight were observed in an orchard measuring 10 hectares located in Mianyang City, Sichuan Province (31°5' 25″N, 105°27'36″E, 365 m above sea level). About 40% of plants were diseased in the quadrat consisting of twenty walnut trees, and 20% of branches were dead on each affected tree. Initially, light brown spots appeared; then, the spots expanded to surround the whole branches; finally, the branches changed from brown to reddish-brown and died. Four symptomatic branches were sampled randomly from different trees. Next, four fungal isolates were obtained from the acervuli of each branch using the single-conidium isolation (Chomnunti et al. 2014) and cultured on potato dextrose agar (PDA). The Petri dishes were placed in an incubator and cultured at 25 °C under a 12-h photoperiod. Colonies were initially white with thin aerial mycelia and gradually turned dark grey with irregular margins. Conidiomata were acervular, black and scattered, with a diameter of 0.3 - 0.7 mm. Conidiophores were narrowly cylindrical, simple or branched at the base, 30 - 43 × 3 - 8 µm (x = 36.5 × 5.5 µm, n = 40). Conidiogenous cells were annellidic with distinct annellations. Conidia were unicellular, brown when mature, narrowly ellipsoid with gelatinous sheaths and truncate scars at the base, 17 - 32 × 7 - 12 µm (x = 27 × 9 µm, n = 40). The genomic DNA of a representative isolate SICAUCC 22-0064 was extracted, and the internal transcribed spacer (ITS) region, guanine nucleotide-binding protein subunit beta gene (ms204), translation elongation factor 1-alpha (tef1-α), and partial sequences of ß-tubulin (tub2) were amplified by polymerase chain reaction and sequenced with primers V9G/LR5 (de Hoog & van den Ende 1998), MS-E1F1/MS-E5R1 (Walker et al. 2012), EF1-728F (Carbone & Kohn 1999)/TEF1LLErev (Jaklitsch et al. 2005), and T1/BtHV2r (Voglmayr et al. 2017), respectively. The sequences of ITS, ms204, tef1-α, and tub2 were deposited in NCBI with accession numbers ON000068, ON112376, ON112374, and ON112375, respectively. With the consideration of the sequence lack of ms204 and tub2 in the ex-type strain (D96) of Juglanconis appendiculata Voglmayr & Jaklitsch, the isolate D140 was used for nucleotide blast. The results showed 99.68%, 100%, 100%, and 100% identities of ITS, ms204, tef1-α, and tub2 with D140 (accession numbers KY427138, KY427157, KY427207, KY427226). Phylogenetic analysis based on a combined dataset showed 100% bootstrap with J. appendiculata, and the morphology was consistent with the asexual stage of J. appendiculata (Voglmayr et al., 2017). To verify Koch's postulates, five branches wounded by pin-prick were sprayed with conidial suspension (1 × 105 conidia/mL) in each plant, and three repetitions were performed on healthy 2-year-old potted plants. The same number of branches were sprayed with sterile distilled water as controls. The plants were placed in a greenhouse at 25 ℃ under 90% relative humidity and a 12-h fluorescent light/dark regime. After five weeks, all the inoculated branches showed brown necrosis similar to that observed in the field, and no symptoms occurred on the controls. The pathogens were re-isolated from the necrotic lesions and identified by morphology and phylogeny. J. appendiculata has been reported on Juglans nigra and J. regia in Austria, France, Spain and Greece (Farr & Rossman 2022). This paper is the first report of branch blight on Juglans sigillata caused by J. appendiculata in China. This result may develop the understanding of walnut diseases and lay a foundation for further management.

Branch blight of Juglans regia caused by Palmiascoma qujingense in China.

Juglans regia L. is one of the major cultivated walnut species in China for nuts and wood (Pollegioni et al. 2012). In June 2020, branches with blight symptoms were observed in an orchard at Chongzhou City (30°33'34″N, 103°38'35″E). In an orchard of 30 hectares, disease incidence was around 50%. A total of 15 plants were sampled and 40% of their branches were affected by this disease. Firstly, brown and irregular spots appeared, then the spots gradually expanded and encircled the branch, which eventually killed the branch. Five samples of diseased branches from different trees were collected and a single fungal isolate was obtained from each of the five samples using the single ascospore isolation (Chomnunti et al. 2014). Colonies of the five isolates on potato dextrose agar (PDA) were identical that initially appeared white on the top, becoming light to dark brown with age. On the host, ascostroma were black, globose to subglobose, short-papillate, ostiolate, 260 - 410 × 210 - 320 µm (x = 335 × 265 µm, n = 20). Asci were 8-spored, bitunicate, cylindrical, short pedicellate, 55 - 78 × 8 - 12 µm (x = 67.5 × 10 µm, n = 40). Ascospores were 1-septate, fusiform to ellipsoidal, slightly curved, guttulate, 12 - 17 × 3 - 5 µm (x = 14.5 × 4 µm, n = 40). These sexual morphological characteristics are consistent with the Palmiascoma qujingense Phook. & K.D. Hyde (Monkai et al. 2021). Asexual morphs were formed on PDA in incubator after 17 days (25℃, 90% relative humidity, 12-h photoperiod). Conidiomata were black, globose to subglobose, 220 - 300 × 240 - 380 µm (x = 270 × 310 µm, n = 20). Conidia were oblong to ellipsoidal, aseptate and smooth-walled, 3 - 7 × 2 - 4 µm (x = 4.9 × 3 µm, n = 50). The genomic DNA of a representative isolate SICAUCC 21-0013 was extracted, and the internal transcribed spacers (ITS) region, large subunit rDNA (LSU) region, small subunit rDNA (SSU) region, and the largest subunit of RNA polymerase II (rpb2) gene were amplified and sequenced with primers ITS5/ITS4 (White et al. 1990), LR0R/LR5 (Rehner et al. 1994), NS1/NS4 (White et al. 1990), and fRPB2-5F/fRPB2-7cR (Liu et al. 1999), respectively. The sequences were deposited in NCBI with accession numbers MZ983549, MZ959419, MZ951112, and MZ818772, respectively, which showed 100%, 100%, 99.14%, and 99.59% identities with P. qujingense KUMCC 19-0201 (holotype) (accession numbers MT477185, MT477186, MT477183, MT495782respectively). Phylogenetic analysis (maximum likelihood) based on a concatenated dataset showed 93% bootstrap support values with P. qujingense. To verify Koch's postulates, 9 healthy branches from three 1-year-old seedlings were inoculated with conidial suspension (106 conidia/ml) from 4-week-old cultures via pin-prick inoculation (Desai et al. 2019), and the same number of seedlings and branches were inoculated with sterile water as controls. Plants were placed in a greenhouse at 25℃ and 90% RH on a 12-h fluorescent light/dark regime. After 28 days, brown spots were formed on P. qujingense-inoculated branches and similar to those observed in the field, while the controls remained asymptomatic. The pathogen was re-isolated from the lesions and identified by morphology and phylogeny. To our knowledge, this is the first report of P. qujingense causing branch blight on J. regia in the world. This disease potentially impacts the growth and yield of J. regia, and control measures should be made.

First report of squash leaf curl China virus infecting tomato in China.

Squash leaf curl China virus (SLCCNV) is a species in the genus Begomovirus that possess a bipartite genome. It is transmitted by the whitefly species Bemisia tabaci and infects cucurbit crops in various parts of the Old World (Wu et al., 2020). In 2020, tomato plants with curled, distorted and yellow leaves were found in a greenhouse in Shouguang, Shandong Province, China (Fig. S1). Leaves with these symptoms were collected from 11 plants and the total RNA was extracted with TRIzol reagent (Invitrogen, USA). Five RNA extracts of the highest quality were combined and a small RNA library was generated by the company (BGI-Shenzhen, China). About 22,338,920 clean reads (18-28nt) were acquired and assembled into larger contigs with the software Velvet 1.0.5. These were further compared against nucleotide sequences in the National Center for Biotechnology Information (NCBI) databases with BLASTn searches. Not unexpectedly, there were many assembled contigs that had high identities (90%-100% identities) with known tomato-infecting viruses, including 241 contigs matching tomato chlorosis virus, 26 contigs matching southern tomato virus, and 4 contigs matching tomato yellow leaf curl virus. However, 12 contigs had high identities (90%-100%) with the genomic DNA-A of SLCCNV, while 9 other contigs had high identities (90%-100%) with the genomic DNA-B of SLCCNV. To verify the presence of SLCCNV in tomato plants, two sets of primer pairs were designed according to the specific contigs assembled from derived small interfering RNAs (vsiRNAs). The primer pairs A742-F/A742-R (5'-GTAATACGAGCATCCGCACGGTAG-3'/5'-CGTGGAGGGCGAC AAACAGCTAACG-3') and B539-F/B539-R (5'-GCTACTTTCAAGGACGAAGAAGAGG-3'/5'-CG ACATAGATTTCTGGTCGGTGGGC-3') directed the amplification of 742 bp and 539 bp for DNA-A and DNA-B fragments, respectively, from the total genomic DNA of the 11 tomato samples. The DNA-A and DNA-B of SLCCNV were both detected from all of the tomato samples. After sequencing, the 742 bp PCR products shared 100% nucleotide sequence identity with the DNA-A of SLCCNV isolate GDXW (MW389919), whereas the PCR-amplified 539 bp fragments shared 100% nucleotide sequence identity with the DNA-B of SLCCNV isolate GDXW (MW389920). The full-length of DNA-A and DNA-B components were amplified with back-to-back primers A-F/A-R (Wu et al., 2020) and B-F/B-R (5'-GATAAACACGTCTCATTGCACCGC-3'/5'-GAGACGTGTTTATCAATATGGA CG-3'), respectively. The amplified fragments were further cloned into the PCE2TA/Blunt-Zero vector (Vazyme Biotech Co., China). After sequencing, the complete sequence of DNA-A was 2736 nt in length (MZ682117), while the DNA-B was 2718 nt in length (OK236348). The phylogenetic relationships of the DNA-A and DNA-B components were determined using MEGA 7 based on the full-length sequences of DNA-A and DNA-B, respectively (Kumar et al., 2016). Results showed that the DNA-A formed an independent cluster and was mostly related to the GDHY (MW389917) in the phylogenetic tree constructed using the neighbor-joining (NJ) method, while the DNA-B formed an independent cluster and was mostly related to the SLCCNV isolate BLDG (MW389928) and isolate GDBL (MW389922) (Fig. S2). The nt identities of DNA-A were also calculated with SDT v1.2 by comparison with other begomovirus sequences from the initial BLASTn analysis (Muhire et al., 2014), showing that the virus shared 99.4% sequence identity with SLCCNV isolate GDHY (MW389917). According to the current demarcation threshold for begomoviruses, recommended by the International Committee on Taxonomy of Viruses (ICTV) (91% nt identity) (Brown et al., 2015), this virus identified from tomato is a distinct strain of SLCCNV, designated SLCCNV-SDSG. To the best of our knowledge, this is the first report of a natural infection of SLCCNV on tomato in China. SLCCNV has caused serious problems in cucurbit production in some areas, so it will be important to investigate if tomato plays a role in the disease biology by serving as a reservoir host. The author(s) declare no conflict of interest. Funding: The funding for this research was supported by the Beijing Academy of Agriculture and Forestry Foundation, China (QNJJ202131, QNJJ201915, KJCX20200113). References: Brown et al. 2015. Arch Virol 160: 1593-1619 Kumar et al. 2016. Mol Biol Evol, 33: 1870-1874 Muhire et al. 2014. Plos One, 9 Wu et al. 2020. J Integr Agr, 19: 570-577.

Orbit-Engineered Anisotropic Magnetoresistive Effect for Constructing a Magnetic Sensor with Ultrahigh Sensitivity.

A strong anisotropic magnetoresistance (AMR) effect induced by spin-orbit coupling is the basis for constructing a highly sensitive and reliable magnetic sensor. Presently, effective AMR enhancement in traditional films focuses on the modulation of the lattice or charge degree of freedom, leading to a general AMR ratio below 4%. Here, we demonstrate a different strategy to strengthen the AMR effect by tuning the orbital degree of freedom. By inserting an oxygen-affinitive Hf layer into a Ta/MgO/NiFe/MgO/Ta multilayer film, Fe-O orbital hybridization at the MgO/NiFe interface was modulated to trigger an effective orbital reconfiguration of Fe. In turn, the number of holes in the in-plane symmetric d orbits of Fe increased substantially, facilitating the s-d electron scattering to enhance the AMR ratio to 4.8%. By further micromachining the film into a Wheatstone bridge, we constructed a sensing element that displayed an ultrahigh sensitivity of 2.7 mV/V/Oe and a low noise detectability of 0.8 nT/√Hz. These findings help to advance the development of orbit-governed AMR sensors and provide an alternative method for tuning other orbit-related physical effects.

Dual RNA-seq Reveals the Global Transcriptome Dynamics of Ralstonia solanacearum and Pepper (Capsicum annuum) Hypocotyls During Bacterial Wilt Pathogenesis.

Bacterial wilt, caused by Ralstonia solanacearum, is a serious disease in pepper. However, the interaction between the pathogen and pepper remains largely unknown. This study aimed to gain insights into determinants of pepper susceptibility and R. solanacearum pathogenesis. We assembled the complete genome of R. solanacearum strain Rs-SY1 and identified 5,106 predicted genes, including 84 type III effectors (T3E). RNA-seq was used to identify differentially expressed genes (DEGs) in susceptible pepper CM334 at 1 and 5 days postinoculation (dpi) with R. solanacearum. Dual RNA-seq was used to simultaneously capture transcriptome changes in the host and pathogen at 3 and 7 dpi. A total of 1,400, 3,335, 2,878, and 4,484 DEGs of pepper (PDEGs) were identified in the CM334 hypocotyls at 1, 3, 5, and 7 dpi, respectively. Functional enrichment of the PDEGs suggests that inducing ethylene production, suppression of photosynthesis, downregulation of polysaccharide metabolism, and weakening of cell wall defenses may contribute to successful infection by R. solanacearum. When comparing in planta and nutrient agar growth of the R. solanacearum, 218 and 1,042 DEGs of R. solanacearum (RDEGs) were detected at 3 and 7 dpi, respectively. Additional analysis of the RDEGs suggested that enhanced starch and sucrose metabolism, and upregulation of virulence factors may promote R. solanacearum colonization. Strikingly, 26 R. solanacearum genes were found to have similar DEG patterns during a variety of host-R. solanacearum interactions. This study provides a foundation for a better understanding of the transcriptional changes during pepper-R. solanacearum interactions and will aid in the discovery of potential susceptibility and virulence factors.

Insight into the Systematics of Novel Entomopathogenic Fungi Associated with Armored Scale Insect, Kuwanaspis howardi (Hemiptera: Diaspididae) in China.

This study led to the discovery of three entomopathogenic fungi associated with Kuwanaspis howardi, a scale insect on Phyllostachys heteroclada (fishscale bamboo) and Pleioblastus amarus (bitter bamboo) in China. Two of these species belong to Podonectria: P. kuwanaspidis X.L. Xu & C.L. Yang sp. nov. and P. novae-zelandiae Dingley. The new species P. kuwanaspidis has wider and thicker setae, longer and wider asci, longer ascospores, and more septa as compared with similar Podonectria species. The morphs of extant species P. novae-zelandiae is confirmed based on sexual and asexual morphologies. Maximum likelihood and Bayesian inference analyses of ITS, LSU, SSU, tef1-α, and rpb2 sequence data provide further evidence for the validity of the two species and their placement in Podonectriaceae (Pleosporales). The second new species, Microcera kuwanaspidis X.L. Xu & C.L. Yang sp. nov., is established based on DNA sequence data from ITS, LSU, SSU, tef1-α, rpb1, rpb2, acl1, act, cmdA, and his3 gene regions, and it is characterized by morphological differences in septum numbers and single conidial mass.

First report of leaf blight on Magnolia coco caused by Nothophoma quercina in China.

Magnolia coco (Lour.) DC. is an ornamental shrub and widely cultivated in southern China (Nana et al. 2017). In April 2020, leaf blight symptoms were observed on the leaves of M. coco in the Chengdu campus of Sichuan Agricultural University (30°42'19.92″N, 103°51'30.61″E, 493 m) where didn't have great protection, with roughly 70% leaves per plant were diseased. The initial symptoms presented on the leaf apex, which was manifested as dark brown spots surrounded with obvious yellowish halo (Fig. 1). As the disease progressed, spots gradually enlarged and coalesced covering the leaf, and severe infection finally caused leaf necrosis and plant decline. Four specimens from different diseased plants were used for pathogen isolation and morphological observation. Four fungal isolates were obtained from four specimens, following Chomnunti et al. (2014). Colonies on potato dextrose agar (PDA) medium were initially white and then light brown to dark brown. Pycnidia measured 284-427 × 326-554 µm (x=372.8 µm × 476.1 µm, n=20), and were brownish-black to black, broadly globose to irregular. The pycnidial wall measured 16-27 µm wide (n=20) and was composed of hyaline to brown cells of textura angularis. Conidiophores were absent, and the conidiogenous cells are pear-shaped, colorless, and smooth. Conidia measured 5-8 × 4-6 µm (x=6.5 µm × 4.6 µm, n=50), and were elliptical or subglobose, thick-walled, aseptate, hyaline, smooth, brown. These asexual structures were similar to Nothophoma quercina (Syd. & P. Syd.) Qian Chen & L. Cai described by Chen et al. (2017). The genomic DNA of representative isolate SICAUCC 21-0011 was extracted, and the internal transcribed spacers (ITS), 28S large subunit rDNA (LSU), RNA polymerase II large subunit 2 (RPB2), and beta-tubulin (TUB2) regions were amplified using the primer pairs ITS5/ITS4, LR0R/LR5, FRPB2-5F/FRPB2-7cR, and T1/BT4R, respectively. The accession numbers deposited in GenBank were MW541930 (ITS), MW541934 (LSU), MW883395 (RPB2), and MW883394 (TUB2). Nucleotide BLAST showed high homology with the sequences of N. quercina, viz. GU237900 (ITS, 485/486, 99.79%), EU754127 (LSU, 862/862, 100%), KT389657 (RPB2, 593/596, 99.49%), and GU237609 (TUB2, 333/335, 99.40%). Phylogenetic analyses based on a combined dataset showed 100% bootstrap support values in a clade with N. quercina complexes (Fig. 2). Four healthy potted plants (2-years-old) with 15 to 20 leaves per plant were sprayed with conidial suspension (105 conidia/mL) prepared from 4-week-old cultures of SICAUCC 21-0011, which incubated on PDA at 25℃, onto the wounded sites via pin-prick inoculation described by Desai et al. (2019). Another four plants were sprayed with sterilely distilled water as controls. Inoculated plants were cultured in a growth chamber (25℃, 95% relative humidity, and 12-h photoperiod). About 30 days later, brown spots were found on the inoculated leaves, which were similar to those observed in the field. There were no symptoms on the control plants, and the pathogen was re-isolated from the diseased leaves and characterized morphologically. N. quercina has been reported on Photinia × fraseri Dress, Aucuba japonica, Malus micromalus, and Chaenomeles sinensis (Mohamed et al. 2019, Lv et al. 2020, Zou et al. 2021). To our knowledge, this is the first report of leaf blight on M. coco caused by N. quercina. M. coco is one of the important ornaments in the courtyard, street, and park in China, and the risk of this pathogen needs further exploration and effective control measures should be made. Qian Zeng, Yicong Lv, and Xinyue Li contributed equally to this work.

First Report of Brown Leaf Spot of Juglans hybrid Caused by Ophiognomonia leptostyla in China.

"Chuanzao 2" is a walnut variety derived from the hybridization of Juglans regia L. and J. sigillata Dode distributed in southwest China, where it is an economically important tree species in rural regions (Xiao et al. 2012). In April 2020, the variety in a walnut garden showed symptoms of brown leaf spot in Beishan Town (107°21'43.93″E, 31°28'12.34″N), Dazhou City in Sichuan, China, with 5% to 10% of leaves per plant affected (5 plants). Symptomatic leaves showed brown to dark brown spots (2 to 5 mm) with a dark brown to black halo and grayish-tan center. The spots were subcircular to irregular in shape, and gradually expanded and formed necrotic spots. A single conidium isolation was performed (Senanayake et al. 2020) and transferred to Potato Dextrose Agar (PDA). Five isolates were obtained from five different infected leaves. Colonies of five isolates were subcircular, erose or dentate, flat or effuse, white initially, gradually becoming yellowish with white margins, developed and fluffy aerial mycelia, and conidiogenensis was produced underneath mycelia after 25-days-incubation. Conidiogenous cells were subcylindrical to cylindrical, or irregular in shape, and hyaline. Macroconidia were lunate, reniform, hyaline, basal cell bluntly rounded, apical cell with acute end, 1-septate, rarely aseptate, sometimes slightly constricted at septum, basal cell equal or larger than apical cell, and measured 16.5 to 30.5 × 5 to 8.5 µm (mean = 23.2 × 6.3 µm, n = 50). Microconidia were not observed. These morphological characteristics resembled those of Ophiognomonia leptostyla (Fr.) Sogonov (Walker et al. 2012a). For molecular identification, genomic DNA (isolates SICAUCC 21-0008 and SICAUCC 21-0010) was extracted, and the internal transcribed spacers (ITS) region, guanine nucleotide-binding protein subunit beta (MS204) gene, and translation elongation factor 1-alpha (tef1-α) were amplified and sequenced by using the primers ITS5/ITS4 (White et al. 1990), E1F1/E5R1a (Walker et al. 2012a), and EF1-728F/EF1-1567R (Walker et al. 2012b), respectively. Phylogenetic analyses (maximum likelihood) based on a combined dataset showed 100% bootstrap support values in a clade with O. leptostyla. The sequences of ITS, MS204, and tef1-α genes were deposited in GenBank with accession numbers MW493111/MZ026300, MW495270/MZ031975, and MW495271/MZ031974, respectively. To fulfill Koch's postulates, five healthy hybrid plants (2 to 3 years old) with 5 to 8 leaves per plant were spray inoculated with conidium suspensions (104 conidia/mL; isolate SICAUCC 21-0008) prepared from 40-days-old cultures onto the wounded sites via pin-prick inoculation. Similarly, five noninoculated plants sprayed with sterile water served as controls. Plants were placed in a growth chamber at 25℃ on a 12-h fluorescent light/dark regime and daily sprayed with sterile distilled water. After two weeks, observed symptoms were similar to those from natural infections. No disease symptoms were found on control plants. The fungus O. leptostyla was reisolated from the diseased leaves and characterized morphologically. O. leptostyla is a global pathogen and has been reported to cause the leaf spot in many walnut trees, viz. J. ailantifolia, J. californica, J. cinerea, and J. major, etc. To our knowledge, this is the first report of O. leptostyla causing brown leaf spot on Juglans hybrid (J. regia × J. sigillata) in China. The increasing risk of this pathogen in the walnut-growing areas of Sichuan Province of China needs a further exploration and outreach effort to develop effective control measures. Chunlin Yang, Feng Liu, and Qian Zeng contributed equally to this paper.

First report of brown leaf spot on Juglans sigillata caused by Ophiognomonia leptostyla in Sichuan, China.

Juglans sigillata Dode (Iron walnut) is mostly distributed in southwestern China, and valued for wood and nuts (Feng et al. 2018). In April 2020, we surveyed a walnut garden located in Baisha Town, Wanyuan City, (Sichuan, China), where brown spot symptoms were observed on leaves of ten trees among of 100 plants, and this disease can result in a reduced growth potential when trees are severely infected. Necrotic and subcircular lesions with conidiamata were observed on diseased leaves. Symptomatic leaves were collected and taken back to the laboratory forfurther analysis. Using the single spore isolation technique developed by Chomnunti et al. (2014), five isolates were grown from the infected leaves on Potato Dextrose Agar medium (PDA). The five isolates had similar colony morphology, which was initially white, suborbicular, gradually turning yellowish with black spots, developing fluffy aerial mycelium. Morphological characteristics were examined using light microscopy on the PDA. Conidiogenous cells were subcylindrical to cylindrical, or ampulliform, hyaline, rarely branched. Macroconidia were lunate, reniform, hyaline, 1-3-septate, mostly 1-septate, distinctly constricted at the septum, the basal cell was bluntly rounded, the apical cell had an acute end, and the basal cell was equal to or larger than the apical cell, measuring 22 to 40.5 × 2.5 to 8.3 µm (mean = 32 × 6.2 µm, n = 50). Microconidia were botuliform, or subfusiform, hyaline, both ends were rounded, straight or curved, aseptate, and measured 10 to 28.5 × 1.9 to 3.7 µm (mean= 17.2 × 2.7 µm, n = 20). A multilocus approach was conducted for precise identification of a representative isolate SICAUCC 20-0012. The internal transcribed spacer regions (ITS), guanine nucleotide-binding protein subunit beta gene (MS204), and translation elongation factor 1-alpha (tef1-α) of isolate SICAUCC 20-0012 were amplified and sequenced as described by Sogonov et al. (2008) and Walker et al. (2012a). GenBank Accession Nos. for ITS, MS204, and tef1-α are MW250303, MW246773, and MW246775, respectively. Phylogenetic analyses showed 100% support with Ophiognomonia leptostyla (Fr.) Sogonov, and the morphology was consistent with the asexual stage of O. leptostyla documented by Walker et al. (2012b). To test Koch's postulates, five healthy plants of J. sigillata (2- to 3-year-old) with 5-8 leaves per plant were inoculated with conidial suspensions (104 conidia/mL) after wounded with a small pin as described by Desai et al. (2019), and the same number of healthy plants were wounded and sprayed with sterile distilled water as controls. Plants were sprayed regularly with distilled water every day and placed in a growth chamber at 25℃ with a 12-h fluorescent light/dark regimen. After 15 days, typical brown spot symptoms developed on inoculated leaves, but not on the controls. The fungus O. leptostyla was reisolated from the lesion as described above but not from non-inoculated leaves. O. leptostyla has been reported on some walnut trees; for example: J. ailantifolia, J. californica, J. cinerea, J. hindsii, J. major, J. mandshurica, J. nigra, and J. regia (Farr & Rossman 2020). However, to our knowledge, this is the first report of O. leptostyla causing brown leaf spot on J. sigillata. J. sigillata is an economically important tree in southwest China, and fungicide treatments should be considered to prevent the spread of this fungus before it becomes more widespread. Chunlin Yang, Yu Deng, and Feihu Wang contributed equally to this work. This research was supported by the Key Research and Development Project of Sichuan Province (2021YFYZ0032).