Multilocus Sequence Analysis and Detection of Copper Ion Resistance of Xanthomonas phaseoli pv. manihotis Causing Bacterial Blight in Cassava.

Cassava (Manihot esculenta Crantz) is an important tropical tuber crop around the world. Cassava bacterial blight, caused by Xanthomonas phaseoli pv. manihotis, is a key disease that influences cassava production worldwide. Between 2008 and 2020, 50 X. phaseoli pv. manihotis strains were isolated from diseased plant samples or acquired from China, Uganda, Cambodia, Colombia, Malaysia, and Micronesia. Using multilocus sequence analysis, the genetic diversity of X. phaseoli pv. manihotis strains was evaluated. A neighbor-joining phylogenetic dendrogram was constructed based on partial sequences of five housekeeping genes (atpD-dnaK-gyrB-efp-rpoD). The strains clustered into three groups whose clusters were consistent with atpD and RpoD gene sequences. Group I contained 46 strains from China, Uganda, Cambodia, and Micronesia, and the other two groups were comprised of strains from Colombia and Malaysia, respectively. The resistance of all these strains to copper ion (Cu2+) was determined, the minimal inhibitory concentration was between 1.3 and 1.7 mM, and there was no significant difference between strains from different geographic region. During genome annotation of the X. phaseoli pv. manihotis strain CHN01, homologous gene clusters of copLAB and xmeRSA were identified. The predicted amino acid sequences of two gene clusters were highly homologous with the copper-resistant protein from Xanthomonas strains. CopLAB and xmeRSA were amplified from all these strains, suggesting that the regulation of copper resistance is associated with two distinct metabolic pathways. CopLAB and xmeRSA were highly conserved among strains from different geographic regions, possibly associated with other conserved function.

Whole genome resequencing reveal patterns of genetic variation within Colletotrichum acutatum species complex from rubber trees in China.

The Colletotrichum acutatum species complex possesses a diverse number of important traits, such as a wide host range and host preference, different modes of reproduction, and different strategies of host infection. Research using comparative genomics has attempted to find correlations between these traits. Here, we used multi-locus techniques and gene genealogical concordance analysis to investigate the phylogenetic relationships and taxonomic status of the Colletotrichum acutatum species complex using field isolates obtained from rubber trees. The results revealed that the dominant species was C. australisinense, followed by C. bannaense, while strain YNJH17109 was identified as C. laticiphilum. The taxonomic status of strains YNLC510 and YNLC511 was undetermined. Using whole-genome single nucleotide polymorphism data to analyze population structure, 18 strains of C. australisinense were subsequently divided into four populations, one of which was derived from an admixture of two populations. In addition, the strains LD1687, GD1628, and YNLC516, did not belong to any populations, and were considered to be admixtures of two or more populations. A split decomposition network analysis also provided evidence for genetic recombination within Colletotrichum acutatum species complex from rubber trees in China. Overall, a weak phylogeographic sub-structure was observed. Analysis also revealed significant differences in morphological characters and levels of virulence between populations.

Isolation and Identification of Secondary Metabolites Produced by Phytopathogenic Fungus Corynespora cassiicola from Hevea brasiliensis.

The secondary metabolites of the phytopathogenic fungus Corynespora cassiicola CC01 from Hevea brasiliensis were investigated. As a result, two new compounds, 5-acetyl-7-hydroxy-6- methoxybenzofuran-2(3H)-one (1) and (S)-2-(2,3-dihydrofuro [3,2-c]pyridin-2-yl)propan-2-ol (2), together with seven known compounds, 4,6,8-trihydroxy-3,4-dihydronaphthalen-1(2H)-one (3), 3,6,8-trihydroxy-3,4-dihydronaphthalen-1(2H)-one (4), curvulin acid (5), 2-methyl-5-carboxymethyl- 7-hydroxychromone (6), tyrosol (7), p-hydroxybenzoic acid (8) and cerevisterol (9), were isolated from the fermentation extract by comprehensive silica gel, reverse phase silica gel, Sephadex-LH20 column chromatography and high-performance liquid chromatography (HPLC). The structures of these compounds were identified by using high-resolution electrospray mass spectrometry (HRESIMS), nuclear magnetic resonance spectroscopy (NMR), optical rotation, ultraviolet and infrared spectroscopy techniques and a comparison of NMR data with those reported in the literature. Compounds 1 and 2 were new compounds, and compounds 3-9 were discovered from this phytopathogenic fungus for the first time. Compounds 1-9 were tested for phytotoxicity against the fresh tender leaf of Hevea brasiliensis, and the results show that none of them were phytotoxic. Additionally, these compounds were subjected to an antimicrobial assay against three bacteria (E. coli, methicillin-resistant Staphylococcus aureus and Micrococcus luteus), but they showed no activity.

Characterization and necrosis-inducing activity of necrosis- and ethylene-inducing peptide 1-like proteins from Colletotrichum australisinense, the causative agent of rubber tree anthracnose.

Colletotrichum australisinense, a member of the Colletotrichum acutatum species complex, is an important pathogen causing rubber tree anthracnose. Genome-wide comparative analysis showed this species complex contains more genes encoding necrosis- and ethylene-inducing peptide 1-like proteins (NLPs) than other Colletotrichum species complexes, but little is known about their necrosis-inducing roles in host. The aim of this study was to analyze NLPs number and type in C. australisinense, and characterize their necrosis-inducing activity in host or non-host. According to phylogenetic relationship, conserved the cysteine residues and the heptapeptide motif (GHRHDWE), 11 NLPs were identified and classified into three types. Five of the eleven NLPs were evaluated for necrosis-inducing activity. CaNLP4 (type 1) could not induce necrosis in host or non-host plants. By contrast, both CaNLP5 and CaNLP9 (type 1) induced necrosis in host and non-host plants, and necrosis-inducing activity was strongest for CaNLP9. CaNLP10 (type 2) and CaNLP11 (type 3) induced necrosis in host but not non-host plants. Substitution of key amino acid residues essential for necrosis induction activity led to loss of CaNLP4 activity. Structural characterization of CaNLP5 and CaNLP9 may explain differences in necrosis-inducing activity. We evaluated the expression of genes coding CaNLP by reverse transcription polymerase chain reaction (RT-PCR) and quantitative real-time PCR (qRT-PCR) at different time-points after pathogen infection. It was found that genes encoding CaNLPs with different activities exhibited significantly different expression patterns. The results demonstrate that CaNLPs are functionally and spatially distinct, and may play different but important roles in C. australisinense pathogenesis.

Antifungal activity of volatile compounds generated by endophytic fungi Sarocladium brachiariae HND5 against Fusarium oxysporum f. sp. cubense.

The soil-born filamentous fungal pathogen Fusarium oxysporum f. sp. cubense (FOC), which causes vascular wilt disease in banana plants, is one of the most economically important Fusarium species. Biocontrol using endophytic microorganisms is among the most effective methods for controlling banana Fusarium wilt. In this study, volatile organic compounds (VOCs) showed strong antifungal activity against FOC. Seventeen compounds were identified from the VOCs produced by endophytic fungi Sarocladium brachiariae HND5, and three (2-methoxy-4-vinylphenol, 3,4-dimethoxystyrol and caryophyllene) showed antifungal activity against FOC with 50% effective concentrations of 36, 60 and 2900 µL/L headspace, respectively. Transmission electron microscopy (TEM) and double fluorescence staining revealed that 2-methoxy-4-vinylphenol and 3,4-dimethoxystyrol damaged the plasma membranes, resulting in cell death. 3,4-dimethoxystyrol also could induce expression of chitin synthases genes and altered the cell walls of FOC hyphae. Dichloro-dihydro-fluorescein diacetate staining indicated the caryophyllene induced accumulation of reactive oxygen species (ROS) in FOC hyphae. FOC secondary metabolism also responded to active VOC challenge by producing less fusaric acid and expressions of genes related to fusaric acid production were interrupted at sublethal concentrations. These findings indicate the potential of S. brachiariae HND5 as a biocontrol agent against FOC and the antifungal VOCs as fumigants.

Genomic Characteristics and Comparative Genomics Analysis of Two Chinese Corynespora cassiicola Strains Causing Corynespora Leaf Fall (CLF) Disease.

Rubber tree Corynespora leaf fall (CLF) disease, caused by the fungus Corynespora cassiicola, is one of the most damaging diseases in rubber tree plantations in Asia and Africa, and this disease also threatens rubber nurseries and young rubber plantations in China. C. cassiicola isolates display high genetic diversity, and virulence profiles vary significantly depending on cultivar. Although one phytotoxin (cassicolin) has been identified, it cannot fully explain the diversity in pathogenicity between C. cassiicola species, and some virulent C. cassiicola strains do not contain the cassiicolin gene. In the present study, we report high-quality gapless genome sequences, obtained using short-read sequencing and single-molecule long-read sequencing, of two Chinese C. cassiicola virulent strains. Comparative genomics of gene families in these two stains and a virulent CPP strain from the Philippines showed that all three strains experienced different selective pressures, and metabolism-related gene families vary between the strains. Secreted protein analysis indicated that the quantities of secreted cell wall-degrading enzymes were correlated with pathogenesis, and the most aggressive CCP strain (cassiicolin toxin type 1) encoded 27.34% and 39.74% more secreted carbohydrate-active enzymes (CAZymes) than Chinese strains YN49 and CC01, respectively, both of which can only infect rubber tree saplings. The results of antiSMASH analysis showed that all three strains encode ~60 secondary metabolite biosynthesis gene clusters (SM BGCs). Phylogenomic and domain structure analyses of core synthesis genes, together with synteny analysis of polyketide synthase (PKS) and non-ribosomal peptide synthetase (NRPS) gene clusters, revealed diversity in the distribution of SM BGCs between strains, as well as SM polymorphisms, which may play an important role in pathogenic progress. The results expand our understanding of the C. cassiicola genome. Further comparative genomic analysis indicates that secreted CAZymes and SMs may influence pathogenicity in rubber tree plantations. The findings facilitate future exploration of the molecular pathogenic mechanism of C. cassiicola.

First Report on Neopestalotiopsis aotearoa of Rubber Tree in China.

Natural rubber is an important industrial raw material and an economically important perennial in China. In recent years, A new leaf fall disease, caused by Neopestalotiopsis aotearoa Maharachch., K.D. Hyde & Crous, has occurred in Indonesia, Malaysia, Thailand, Sri Lanka, and other major rubber planting countries. In May and July of 2020, this disease was first found on 2-year-old rubber seedlings in two plantations located in Ledong and Baisha counties in Hainan Province, China. In the two plantations of approximately 32 ha, 15% of the rubber seedlings had the disease and the defoliation was more than 20%. The infected leaves turned yellow and watery, and dark brown and nearly round lesions of 1-2 mm in diameter were formed on the leaves. When the humidity was high, the center of the lesion was grey-white, and the lesions had many small black dots, black margins and surrounded by yellow halos. When the disease was severe, leaves fell off. To identify the pathogen, leaf tissues were collected from lesion margins after leaf samples were surface-sterilized in 75% ethanol, rinsed with sterile water for three times, and air dried. The leaf tissues were plated on potato dextrose agar (PDA) and incubated at 28°C for seven days. Fungal cultures with similar morphology were isolated from 90% of tested samples and two isolates (HNPeHNLD2001 and HNPeHNLD2002) were used in pathogenicity and molecular tests. Rubber leaves (clone PR107) were inoculated with conidial suspension (106 conidia/ml), and inoculated with PDA were used as the control, Each treatment had 3 leaves, and each leaf was inoculated with 3 spots and incubated at 28oC under high moisture conditions. Five days later, leaves inoculated with conidial suspension showed black leaf spots resembling the disease in the field, whereas the control leaves remained symptomless. The fungal cultures isolated from the inoculated tissues, had identical morphology compared with the initial isolates. Colonies on PDA were 55-60 mm in diameter after seven days at 28°C, with undulate edges, pale brown, thick mycelia on the surface with black, gregarious conidiomata; and the reverse side was similar in color. Black conidia were produced after eight days of culture on PDA. Conidia were fusoid, ellipsoid, straight to slightly curved, 4-septate, ranged from 18.35 to 27.12 µm (mean 22.34 µm) × 4.11 to 7.03 µm (mean 5.41 µm). The basal cells were conic with a truncate base, hyaline, rugose and thin-walled, 4.35 to 6.33 µm long (mean 4.72 µm). Three median cells were doliform, 12.53 to 18.97 µm long (mean 15.26 µm), hyaline, cylindrical to subcylindrical, thin- and smooth-walled, with 2-3 tubular apical appendages, arising from the apical crest, unbranched, filiform, 14.7 to 25.3 µm long (mean 19.94 µm). The basal appendages were singlar, tubular, unbranched, centric, 3.13 to 7.13 µm long (mean 5.48 µm). Morphological characteristics of the isolates were similar to the descriptions of N. aotearoa (Maharachchikumbura et al. 2014). The rDNA internal transcribed spacer (ITS) region, translation elongation factor 1-αgenes (TEF), and beta-tubulin (TUB2) gene were amplified using the primer pairs ITS1/ITS4, EF1-728F/EF1-986R and T1/Bt-2b (Pornsuriya et al. 2020), respectively. The sequences of these genes were deposited in GenBank (ITS Accession Nos.: MT764947 and MT764948; TUB2: MT796262 and MT796263; TEF: MT800516 and MT800517). According to the latest classification of Neoprostalotiopsis spp. (Maharachchikumbura et al. 2014) and multilocus phylogeny, isolates HNPeHNLD2001 and HNPeHNLD2002 were clustered in the same branch with N. aotearoa. Thus, the pathogen was identified as N. aotearoa, which is different from N. cubana and N. formicarum reported in Thailand (Pornsuriya et al. 2020; Thaochan et al. 2020). The Neopestalotiopsis leaf spotdisease of rubber tree (H. brasiliensis) was one of the most serious and destructive leaf diseases in major rubber planting countries in Asia. ( Tajuddin et al. 2020) The present study of leaf fall disease on rubber tree caused byN. aotearoa is the first report in China. The finding provides the basic pathogen information for further monitoring the disease and its control.

Pathogenic Adaptations Revealed by Comparative Genome Analyses of Two Colletotrichum spp., the Causal Agent of Anthracnose in Rubber Tree.

Colletotrichum siamense and Colletotrichum australisinense cause Colletotrichum leaf disease that differ in their symptoms in rubber tree (Hevea brasiliensis), and pathogenicity of these two fungal species is also not identical on different cultivars of rubber tree. This divergence is often attributed to pathogen virulence factors, namely carbohydrate-active enzymes (CAZymes), secondary metabolites (SM), and small-secreted protein (SSP) effectors. The draft genome assembly and functional annotation of potential pathogenicity genes of both species obtained here provide an important and timely genomic resource for better understanding the biology and lifestyle of Colletotrichum spp. This should pave the way for designing more efficient disease control strategies in plantations of rubber tree. In this study, the genes associated with these categories were manually annotated in the genomes of C. australisinense GX1655 and C. siamense HBCG01. Comparative genomic analyses were performed to address the evolutionary relationships among these gene families in the two species. First, the size of genome assembly, number of predicted genes, and some of the functional categories differed significantly between the two congeners. Second, from the comparative genomic analyses, we identified some specific genes, certain higher abundance of gene families associated with CAZymes, CYP450, and SM in the genome of C. siamense, and Nep1-like proteins (NLP) in the genome of C. australisinense.

Genomic characteristics and comparative genomics analysis of the endophytic fungus Sarocladium brachiariae.

BACKGROUND: Sarocladium brachiariae is a newly identified endophytic fungus isolated from Brachiaria brizantha. A previous study indicated that S. brachiariae had antifungal activity; however, limited genomic information restrains further study. Therefore, we sequenced the genome of S. brachiariae and compared it with the genome of S. oryzae to identify differences between a Sarocladium plant pathogen and an endophyte. RESULTS: In this study, we reported a gapless genome sequence of a newly identified endophytic fungus Sarocladium brachiariae isolated from Brachiaria brizantha. The genome of S. brachiariae is 31.86 Mb, with a contig N50 of 3.27 Mb and 9903 protein coding genes. Phylogenomic analysis based on single copy orthologous genes provided insights into the evolutionary relationships of S. brachiariae and its closest species was identified as S. oryzae. Comparative genomics analysis revealed that S. brachiaria has 14.9% more plant cell wall degradation related CAZymes to S. oryzae, and 33.3% more fungal cell wall degradation related CAZymes, which could explain the antifungal activity of S. brachiaria. Based on Antibiotics & Secondary Metabolite Analysis Shell (antiSMASH) analysis, we identified a contact helvolic acid biosynthetic gene cluster (BGC) for the first time in S. oryzae. However, S. brachiaria had seven fewer terpene gene clusters, including helvolic acid BGC, compared with S. oryzae and this may be associated with adaptation to an endophytic lifestyle. Synteny analysis of polyketide synthases (PKS), non-ribosomal peptide synthetases (NRPS), and hybrid (PKS-NRPS) gene clusters between S. brachiariae and S. oryzae revealed that just 37.5% of tested clusters have good synteny, while 63.5% have no or poor synteny. This indicated that the S. brachiariae could potentially synthesize a variety of unknown-function secondary metabolites, which may play an important role in adaptation to its endophytic lifestyle and antifungal activity. CONCLUSIONS: The data provided a better understanding of the Sarocladium brachiariae genome. Further comparative genomic analysis provided insight into the genomic basis of its endophytic lifestyle and antifungal activity.

Colletotrichum Species Causing Anthracnose of Rubber Trees in China.

Anthracnose caused by Colletotrichum is one of the most severe diseases of Hevea brasiliensis. However, research on the diversity and geographical distribution of Colletotrichum remains limited in China. In this study, we investigated the phylogenetic diversity of Colletotrichum isolates associated with symptomatic tissues of H.brasiliensis from four provinces of China (Hainan, Guangdong, Guangxi, and Yunnan). Based on multi-locus phylogenetic analyses and phenotypic characteristics, five species were distinguished, including two known species (C. fructicola, C. siamense), one novel species of C. gloeosporioides species complex (C. ledongense), and two novel species of C. acutatum species complex (C. bannanense and C. australisinense). Of these, C. siamense and C. australisinense have been recognized as major causative agents of anthracnose of H. brasiliensis.

Cloning of insertion site flanking sequence and construction of transfer DNA insert mutant library in Stylosanthes colletotrichum.

Stylosanthes sp. is the most important forage legume in tropical areas worldwide. Stylosanthes anthracnose, which is mainly caused by Colletotrichum gloeosporioides, is a globally severe disease in stylo production. Little progress has been made in anthracnose molecular pathogenesis research. In this study, Agrobacterium tumefaciens-mediated transformation was used to transform Stylosanthes colletotrichum strain CH008. The major factors of the genetic transformation system of S. colletotrichum were optimized as follows: A. tumefaciens' AGL-1 concentration (OD(600)), 0.8; concentration of Colletotrichum conidium, 1 × 10(6) conidia/mL; acetosyringone concentration, 100 mmol/L; induction time, 6 h; co-culture temperature, 25 °C; and co-culture time, 3 d. Thus, the transformation efficiency was increased to 300-400 transformants per 106 conidia. Based on the optimized system, a mutant library containing 4616 mutants was constructed, from which some mutants were randomly selected for analysis. Results show that the mutants were single copies that could be stably inherited. The growth rate, spore amount, spore germination rate, and appressorium formation rate in some mutants were significantly different from those in the wild-type strain. We then selected the most appropriate method for the preliminary screening and re-screening of each mutant's pathogenic defects. We selected 1230 transformants, and obtained 23 strains with pathogenic defects, namely, 18 strains with reduced pathogenicity and five strains with lost pathogenicity. Thermal asymmetric interlaced PCR was used to identify the transfer DNA (T-DNA) integration site in the mutant that was coded 2430, and a sequence of 476 bp was obtained. The flanking sequence of T-DNA was compared with the Colletotrichum genome by BLAST, and a sequence of 401 bp was found in Contig464 of the Colletotrichum genome. By predicting the function of the flanking sequence, we discovered that T-DNA insertion in the promoter region of the putative gene had 79% homology with the aspartate aminotransferase gene in Magnaporthe oryzae (XP_003719674.1).

Identifying pathogenicity genes in the rubber tree anthracnose fungus Colletotrichum gloeosporioides through random insertional mutagenesis.

To gain more insight into the molecular mechanisms of Colletotrichum gloeosporioides pathogenesis, Agrobacterium tumefaciens-mediated transformation (ATMT) was used to identify mutants of C. gloeosporioides impaired in pathogenicity. An ATMT library of 4128 C. gloeosporioides transformants was generated. Transformants were screened for defects in pathogenicity with a detached copper brown leaf assay. 32 mutants showing reproducible pathogenicity defects were obtained. Southern blot analysis showed 60.4% of the transformants had single-site T-DNA integrations. 16 Genomic sequences flanking T-DNA were recovered from mutants by thermal asymmetric interlaced PCR, and were used to isolate the tagged genes from the genome sequence of wild-type C. gloeosporioides by Basic Local Alignment Search Tool searches against the local genome database of the wild-type C. gloeosporioides. One potential pathogenicity genes encoded calcium-translocating P-type ATPase. Six potential pathogenicity genes had no known homologs in filamentous fungi and were likely to be novel fungal virulence factors. Two putative genes encoded Glycosyltransferase family 28 domain-containing protein and Mov34/MPN/PAD-1 family protein, respectively. Five potential pathogenicity genes had putative function matched with putative protein of other Colletotrichum species. Two known C. gloeosporioides pathogenicity genes were also identified, the encoding Glomerella cingulata hard-surface induced protein and C. gloeosporioides regulatory subunit of protein kinase A gene involved in cAMP-dependent PKA signal transduction pathway.

HbMyb1, a Myb transcription factor from Hevea brasiliensis, suppresses stress induced cell death in transgenic tobacco.

Tapping panel dryness (TPD) is a complex physiological syndrome found widely in rubber tree (Hevea brasiliensis) plantations that causes severe yield loss in natural rubber-producing countries. In an earlier study, we confirmed that there is a negative correlation between HbMyb1 expression and TPD severity. To further investigate the function of HbMyb1 in TPD, HbMyb1 was over-expressed in tobacco controlled by a CaMV 35S promoter. In transgenic plants expressing HbMyb1, cell death induced by UV-B irradiation, paraquat and the hypersensitive reaction to necrotrophic fungal infection (Botrytis cinerea) was suppressed with a close correlation between HbMyb1 protein levels and the extent of suppression. In addition the nuclear condensation and degradation were observed in laticifer cells of TPD trees, while the nucleus of laticifer cells of healthy trees was morphologically normal. On the basis of the results described above, we propose that HbMyb1 maybe suppress stress induced cell death in rubber trees.

[Identification of a hrp-associated gene hpaB in the role of pathogenicity of Xanthomonas oryzae pv. oryzae].

Xanthomonas oryzae pv. oryzae (Xoo), a Gram-negative bacterium, is the causal agent of rice bacterial blight disease, which can cause severe yield loss of rice worldwide. To identify genes contributing to virulence and explore the possible mechanism of pathogenicity, transposon mutagenesis was used to isolate nonpathogenic mutants. By screening of a high-quality Tn5-like transposon (EZ: :TN) insertional mutant library of Xoo PXO99 against a host plant (rice cultivar IR24), one virulence-deficient mutant, XOG11, was identified. Genomic fragment flanking the insertion site of the mutant was amplified by thermal asymmetric interlaced polymerase chian reaction ( TAIL-PCR) and sequenced. The result of NCBI blast homologue searching of the fragment shows that the transposon was inserted into a hrp associated gene, hpaB. Xoo hpaB gene is one of the hrp gene cluster members that encode a type [I secretion system (TTSS) and locates at the downstream of hrpE. The product of hpaB in Xoo is a small (Molecular Weight, 17.6kDa), acidic (PI, 4.28) and Leucine-rich (14.4%) protein and shares high homology with corresponding proteins in other Xanthomonas. It suggests that HpaB may play as a TTSS chaperone. Mutant XOGl1 was confirmed both by PCR and Southern blotting: The PCR result by using primers upstream and downstream of hpaB respectively verified Tn5 insertion in hpaB and excluded the rare case of second transfer of the transposon associated with flanking sequence; Southern blot of digested genomic DNA with the probe of Km resistance gene aph proved that XOG11 was inserted by a single-copy transposon, indicating that the loss of pathogenicity in XOG11 was due to the Tn5 insertion in hpaB gene. Genetic complementation by cloning hpaB in the wide host range plasmid pHMI and transferring the recombinant plasmid into XOG11 restored its pathogenicity in IR24. These results suggest that the pathogenicity deficiency of XOG11 is due to the mutation of hpaB gene.

Association of decreased expression of a Myb transcription factor with the TPD (tapping panel dryness) syndrome in Hevea brasiliensis.

TPD (tapping panel dryness) is a complex physiological syndrome widely found in rubber tree (Hevea brasiliensis) plantations, which causes severe yield and crop losses in natural rubber-producing countries. The molecular mechanism underlying TPD is not known and there is presently no effective prevention or treatment for this serious disease. To investigate the molecular mechanism of TPD, we isolated and characterized genes for which the change of expression is associated with TPD. We report here the identification and characterization of a Myb transcription factor HbMyb1. HbMyb1 is expressed in leaves, barks, and latex of rubber trees, but its expression is significantly decreased in barks of TPD trees. Our results suggest that the expression of HbMyb1 is likely associated with TPD and that the function of HbMyb1 is associated with the integrity of bark tissue of rubber trees.