Goldenseal (Hydrastis canadensis L.) Extracts Inhibit the Growth of Fungal Isolates Associated with American Ginseng (Panax quinquefolius L.).

American ginseng, a highly valuable crop in North America, is susceptible to various diseases caused by fungal pathogens, including Alternaria spp., Fusarium spp., and Pestalotiopsis spp. The development of alternative control strategies that use botanicals to control fungal pathogens in American ginseng is desired as it provides multiple benefits. In this study, we isolated and identified three fungal isolates, Alternaria panax, Fusarium sporotrichioides, and Pestalotiopsis nanjingensis, from diseased American ginseng plants. Ethanolic and aqueous extracts from the roots and leaves of goldenseal were prepared, and the major alkaloid constituents were assessed via liquid chromatography-mass spectrometry (LC-MS). Next, the antifungal effects of goldenseal extracts were tested against these three fungal pathogens. Goldenseal root ethanolic extracts exhibited the most potent inhibition against fungal growth, while goldenseal root aqueous extracts and leaf ethanolic extracts showed only moderate inhibition. At 2% (m/v) concentration, goldenseal root ethanolic extracts showed an inhibition rate of 86.0%, 94.9%, and 39.1% against A. panax, F. sporotrichioides, and P. nanjingensis, respectively. The effect of goldenseal root ethanolic extracts on the mycelial morphology of fungal isolates was studied via scanning electron microscopy (SEM). The mycelia of the pathogens treated with the goldenseal root ethanolic extract displayed considerable morphological alterations. This study suggests that goldenseal extracts have the potential to be used as a botanical fungicide to control plant fungal diseases caused by A. panax, F. sporotrichioides, or P. nanjingensis.

First Report of Leaf Spot of Panax quinquefolius Caused by Pestalotiopsis nanjingensis in Tennessee and the United States.

American ginseng (Panax quinquefolius L.) is an herbaceous perennial understory plant. It was listed as endangered species by the Convention on International Trade in Endangered Species of Wild Fauna and Flora (McGraw et al. 2013). Leaf spot symptoms were observed on 6-year-old cultivated American ginseng on a research plot (8 x 12 ft raised bed under a tree canopy) in Rutherford Co., TN in July 2021 (Fig. 1a). Symptomatic leaves were exhibiting light brown leaf spots with chlorotic haloes 0.5 to 0.8 cm in diameter, mostly confined within or bounded by veins. As the disease progressed, leaf spots expanded and coalesced into irregular shapes with necrotic centers, resulting in a tattered appearance of the leaf. Disease severity was about 50 to 80% of leaf area and incidence was 10% out of 20 plants. Plant tissues were surface sterilized with 10% NaOCl2 for 60s and washed thrice with sterile water and plated on potato dextrose agar (PDA). Colony growth of the isolates FBG880 and FBG881 on PDA were round, white, thick, and flocculent at the front of the plate and showed a yellowish-ringed shape on the back 10 days after incubation at 25°C (light/dark: 12/12h). Acervular conidiomata containing abundant conidia were observed on PDA. They were globose, 1.0 to 1.8 mm in diameter, and found as solitary or aggregated clusters. Conidia contained five cells (average 13.03±3.50 x 14.31±3.93 µm, n = 30). The middle three cells were light brown to brown. The basal and apical cells were nearly triangular, and transparent, with two to three (7:3 ratios, respectively) apical appendages (average 13.27±3.27 µm) and a basal appendage (average 4.50±0.95 µm, n = 30). To determine pathogen identity, total DNA was extracted using DNeasy PowerLyzer Microbial Kit from fungal colonies on PDA (isolates FBG880 and FBG881). The ribosomal internal transcribed spacer (ITS) region, beta-tubulin (BT), and translation elongation factors 1-α (EF1) genetic markers were amplified using ITS1/ITS4 (White et al. 1990), T1/T2 (Stefanczyk et al. 2016), and EF1/EF2 (O'Donnell et al. 1998), respectively. The sequences (GenBank accession nos. ITS: OQ102470 and OQ103415; BT: OQ107059 and OQ107061; and EF1: OQ107060 and OQ107062) are 100% similar to Pestalotiopsis nanjingensis (CSUFTCC16 and CFCC53882) (Jiang et al. 2022; Li et al. 2021) (Fig. 2). Based on morphology and molecular characteristics, the isolates were identified as P. nanjingensis. To conduct the pathogenicity trial, six healthy 1-year-old American ginseng plants, germinated from seeds and grown in the greenhouse were spray inoculated with a conidial suspension (1×106 conidia/ml) (FBG880). Six control plants were sprayed with sterile water. All plants were covered with plastic bags and incubated in a greenhouse set at 21 to 23°C, 70% relative humidity and 16-h photoperiod. After 48 h, bags were removed and plants were maintained under the same conditions. After one month, while control plants remained asymptomatic (Fig. 1b), inoculated plants started to exhibit symptoms resembling those in the research plot (Fig. 1c). Fungal isolates resembling P. nanjingensis in cultural characters were consistently recovered from inoculated plants and their identity as P. nanjingensis was confirmed by DNA sequencing. To our knowledge, this is the first report of leaf spot disease caused by P. nanjingensis on American ginseng. Identification of this pathogen and confirmation of its pathogenicity are fundamental to future disease management approaches.

First Report of Rusty Root of Panax quinquefolius Caused by Pseudomonas marginalis in Tennessee and the United States.

American ginseng (Panax quinquefolius L.) is one of the most valuable medicinal plants that is native to the U.S. This plant is naturally grown under hardwood canopies or artificially cultivated in fields covered with shade. Bacterial infections were observed on 5-year-old cultivated American ginseng roots in Rutherford Co., TN, in March 2022. Infected roots were exhibiting brown lesions in varying sizes. Under severe infection, the periderm of the root was ruptured, leaving a scabbed appearance on the root. The disease severity (percentage root area diseased) was nearly 20% and the disease incidence was nearly 10% out of 20 plants. Bacterial streaming from the infected tissue was observed under the microscope. Bacteria were isolated from surface-sterilized infected root tissue (0.525% NaOCl; 1 min) by plating 10-fold serial dilutions onto yeast dextrose carbonate and King's B (KB) media. Gram-negative, fluorescent bacterial colonies of the isolates FBG1141A and FBG1141B were milky white and translucent on KB at 28 °C. The biochemical and physiological tests including oxidase, levan, arginine dihydrolase, catalase, esculin, mobility test, and growth at 35°C were positive but gelatine and starch hydrolasis were negative. Bacterial suspension prepared with sterile distilled water (1×108 CFU/ml) resulted in soft rot on potato slices. The BIOLOG test showed positive results for the utilization of D-gluconic acid, D-glucuronic acid, D-galactose, D-glucose, L-serine and citric acid but negative results for the utilization of cellobiose and L-rhamnose. Bacterial identity was further confirmed by extracting the total genomic DNA using DNeasy PowerLyzer Microbial Kit directly from the two pure cultures. The small subunit ribosomal RNA (16S rRNA) and RNA polymerase sigma factor (rpoD) genes were amplified and sequenced by the primers 8F/1492R (Galkiewicz et al. 2008) and PsEG30F/PsEG790R (Mulet et al. 2009), respectively. The sequences (GenBank accession nos. OP549779, OP550133: 16S; OP554814, OP554815: rpoD) were 99.26% similar to 16S rRNA and 100% to rpoD genes of Pseudomonas marginalis (LC507983: 16S and MH49410: rpoD) from several hosts in multiple countries in the NCBI database. A phylogenetic analysis was performed by adding the concatenated sequences of 16S and rpoD from other closely related taxa obtained from GenBank (Fig. 1). Pathogenicity test was performed by spraying a suspension of the P. marginalis FBG1141A strain (108 CFU/ml) on six 2-year-old American ginseng roots wounded with a sterilized needle. Plants were covered with clear plastic for 24 h and maintained inside a greenhouse at 21 to 23°C, 70% RH, 16-h photoperiod. Six wounded roots were sprayed with sterilized water as controls and kept in the same condition. Inoculated roots showed rusty root symptoms after 4 weeks (Fig. 2a), while controls remained asymptomatic (Fig. 2b). The bacterium was re-isolated from the infected tissue and confirmed as P. marginalis using physiological and biochemical tests as well as sequencing. P. marginalis has been previously reported causing rusty-colored roots on Korean Ginseng (P. ginseng C.A. Mey)(Choi et al. 2005; Farh et al. 2018; Lee et al. 2011) but to our knowledge, this is the first report of rusty root caused by P. marginalis on American ginseng (P. quinquefolius) in Tennessee and the U.S. Identification of bacterial pathogen impacting the economic yield of American ginseng can be effective for developing correct disease management strategies.

First Report of Powdery Mildew of American Ginseng Caused by Erysiphe heraclei in Tennessee and the United States.

American ginseng (Panax quinquefolius L.), native to the forested regions of northeast U.S is a perennial herb valued as traditional Chinese medicine. It has been cultivated in North America for several decades due to high global demand. Powdery mildew symptoms were observed on 8-year-old cultivated American ginseng leaves (Fig. 1a, b) on a residential property in Rutherford Co., TN in May 2022. Disease severity was 40 to 60% of leaf area and incidence was 33% out of 30 plants. Affected plants exhibited white fungal colonies on the leaves. Under severe infection, the leaves were chlorotic and senescing. Microscopic observation revealed masses of conidia and mycelia on symptomatic tissue. Conidiophores were cylindrical and unbranched (2- or, rarely, 3-septate), measuring 66.7 ± 12.5 µm (n=78) with a range of 24.3 to 90.7 µm. Conidia produced singly or in pseudo-chains (Fig. 1c). Conidiophore foot cells measured 23.2 ± 4.3 µm long (n=54) and the width at the foot cell septum was 5.1 ± 0.6 µm (n=54). Hyphal width was 3.3 ± 0.6 um (n=59). Fresh vacuolated spores were oblong-elliptical to oblong (Fig. 1d) and measured 31.5 × 11.9 µm (n=55), lacked fibrosin bodies. The length-to-width ratio of conidia was 1.9 to 4.4 (avg. 2.7). Superficial mycelia and germinating spores displayed lobed appressorium (Fig. 1e). Detached spore surfaces were wrinkled (Fig. 1f). Morphological characteristics of the fungus matched the description of Erysiphe heraclei (Braun and Cook, 2012) and Erysiphe sp. (Cho et al. 2016) except for conidiophore length, which was shorter in our sample. To confirm pathogen identity, total DNA was extracted directly from single spore cultures (isolates FBG1668 and FBG1728). The ribosomal internal transcribed spacer (ITS) region was amplified using ITS4 and ITS5 primers (White et al. 1990). The sequences (GenBank accession nos. OP458196 and OP469994) showed 100% identity and 100% query coverage to E. heraclei (KY073878 and LC270862). The sequences were also 100% identical to the ITS sequences of E. betae and E. malvae. Solano-Báez et al. (2022) noted that the species in the E. malvae/E. heraclei/E. betae species complex are phylogenetically undistinguishable. E. betae and E. malvae infect plants in Chenopodiaceae and Malvaceae, respectively (Braun and Cook, 2012). However, E. heraclei has been reported to infect plants in Apiaceae. American ginseng belongs to Araliaceae which is a close family to Apiaceae and both belong to Apiales. Based on morphological and molecular identification, both isolates were identified as E. heraclei. Pathogenicity was confirmed by inoculating the adaxial leaf surface of six 2-year-old American ginseng plants. Spores from detached symptomatic leaves were tapped onto the adaxial surface of healthy leaves. Six non-inoculated and inoculated plants were maintained in a greenhouse at 21 to 23°C, 70%RH, with 16-h photoperiod. After 2 weeks, powdery mildew symptoms developed on the inoculated plants. The microscopy and molecular analysis confirmed infection and all control plants remained asymptomatic. Cho et al. (2016) reported powdery mildew on Korean ginseng (P. ginseng C.A. Mey) caused by Erysiphe sp., and Sholberg et al. (1996) reported Erysiphe sp. on P. quinquefolius in Canada, but to our knowledge, this is the first report of powdery mildew caused by E. heraclei on American ginseng in Tennessee and the U.S. Identification and timely management of powdery mildew on American ginseng will be necessary to control this disease in affected growing sites.

Efficient fluorescence-based localization technique for real-time tracking endophytes route in host-plants colonization.

Bacterial isolates that enhance plant growth and suppress plant pathogens growth are essential tools for reducing pesticide applications in plant production systems. The objectives of this study were to develop a reliable fluorescence-based technique for labeling bacterial isolates selected as biological control agents (BCAs) to allow their direct tracking in the host-plant interactions, understand the BCA localization within their host plants, and the route of plant colonization. Objectives were achieved by developing competent BCAs transformed with two plasmids, pBSU101 and pANIC-10A, containing reporter genes eGFP and pporRFP, respectively. Our results revealed that the plasmid-mediated transformation efficiencies of antibiotic-resistant competent BCAs identified as PSL, IMC8, and PS were up 84%. Fluorescent BCA-tagged reporter genes were associated with roots and hypocotyls but not with leaves or stems and were confirmed by fluoresence microscopy and PCR analyses in colonized Arabidopsis and sorghum. This fluorescence-based technique's high resolution and reproducibility make it a platform-independent system that allows tracking of BCAs spatially within plant tissues, enabling assessment of the movement and niches of BCAs within colonized plants. Steps for producing and transforming competent fluorescent BCAs, as well as the inoculation of plants with transformed BCAs, localization, and confirmation of fluorescent BCAs through fluorescence imaging and PCR, are provided in this manuscript. This study features host-plant interactions and subsequently biological and physiological mechanisms implicated in these interactions. The maximum time to complete all the steps of this protocol is approximately 3 months.