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Watermelon is an important cucurbit vegetable crop grown in most of the United States. Phytophthora fruit rot of watermelon caused by Phytophthora capsici has been a major factor, limiting production for the past 15 years in the southeastern United States. The U.S. Department of Agriculture, Agricultural Research Service released five Phytophthora fruit rot-resistant germplasm lines for use in breeding programs. These lines were developed by phenotyping using a local isolate of P. capsici from South Carolina. The present study was undertaken to determine if these resistant lines had broad resistance to diverse P. capsici isolates collected from different states and crops. Five resistant germplasm lines (USVL020-PFR, USVL203-PFR, USVL782-PFR, USVL489-PFR, and USVL531-MDR) and two susceptible cultivars, Sugar Baby and Mickey Lee, used as checks were grown in a field in 2014 and 2015 to produce fruit for evaluation. Mature fruit were harvested and placed in a walk-in growth chamber and inoculated with 20 different P. capsici isolates. The chamber was maintained at 26 ± 2°C and high relative humidity (>95%) using a humidifier. All five resistant germplasm lines were significantly more resistant than the two susceptible checks to all 20 P. capsici isolates. Among the five resistant germplasm lines, USVL020-PFR, USVL782-PFR, and USVL531-MDR had broad resistance. Some P. capsici isolates induced minor lesions and rot on USVL489-PFR compared with the other resistant lines. Variation in virulence and genetic diversity among the 20 P. capsici isolates was also observed. The five watermelon germplasm lines will be useful for developing commercial watermelon cultivars with broad resistance to P. capsici.

Phytophthora capsici is an oomycete pathogen causing economically important diseases in a wide range of hosts worldwide including cucurbitaceous, solanaceous, and fabaceous crops. All plant parts, crown and roots, or only the fruit may be affected depending on the host, and symptoms can range from wilting to rot and plant death. Considered a hemibiotroph, P. capsici can be cultured in artificial media and maintained in long-term storage. In this diagnostic guide, we describe methods to identify P. capsici infection based on disease symptoms and pathogen signs. We also outline methods for molecular identification, pathogen isolation, storage of single-sporangium cultures, and pathogenicity testing.

Diseases caused by oomycete plant pathogens result in devastating losses to agriculture and native forests, despite the significant research efforts that have advanced our understanding of these organisms. Limiting these pathogens has been challenging to plant pathologists and plant health practitioners. In this first focus issue , titled Managing Stubborn Oomycete Plant Pathogens, Plant Health Progress has assembled an array of manuscripts on the biology and management of Phytophthora, Pythium, Pseudoperonospora, Peronospora, and Aphanomyces spp. This focus issue has 28 peer-reviewed papers including three diagnostic guides, three mini-reviews, three briefs, two surveys, and 17 research papers. Of the 28 papers, 20 are on diseases caused by Phytophthora, four on Pythium, three on downy mildews, and one on Aphanomyces. All advance our understanding of these stubborn oomycete pathogens.

Butternut squash (Cucurbita moschata) is an important vegetable crop grown and consumed in most states in the United States. C. moschata lines and interspecific hybrids between Cucurbita species are also used as rootstocks for grafting watermelon and melon. However, currently most commercially available C. moschata squash varieties are highly susceptible to crown and root rot caused by the oomycete pathogen Phytophthora capsici, especially in the southeastern United States. All available plant introductions (PIs) of C. moschata (319 PIs) were evaluated for resistance to crown rot. Four-week-old plants were inoculated with 104 zoospores from a local South Carolina isolate of P. capsici. Plants were rated for disease severity 3 weeks after inoculation using a 0 to 5 rating scale (0 = no symptoms and 5 = plant dead). The majority (87%) of the C. moschata PIs were highly susceptible to crown rot in the first evaluation and were rated as 5. Reevaluation of the promising PIs identified several potential new sources of resistance (e.g., Grif 935, PI 442272, PI 442264, PI 512142, PI 438724, PI 438778, and PI 442280). Variability in resistance reaction among plants within a PI was also observed, and not all plants exhibited resistance. Further evaluation of S1 generation from the most resistant plants (rated ≤1) demonstrated that highly resistant plants could be selected from these PIs to develop lines for use in breeding programs. These new sources of resistance can be utilized for developing new crown and root rot resistant rootstocks for watermelon grafting and for developing resistant varieties for human consumption.

Epidemics of tomato yellow leaf curl virus (TYLCV; species Tomato yellow leaf curl begomovirus) have been problematic to tomato production in the southeastern United States since the first detection of the virus in Florida in the late 1990s. Current strategies for management focus on farm-centric tactics that have had limited success for controlling either TYLCV or its whitefly vector. Areawide pest management (AWPM)—loosely defined as a coordinated effort to implement management strategies on a regional scale—may be a viable management alternative. A prerequisite for development of an AWPM program is an understanding of the spatial and temporal dynamics of the target pathogen and pest populations. The objective of this study was to characterize populations of whitefly and TYLCV in commercial tomato production fields in southwestern Florida and utilize this information to develop predictors of whitefly density and TYLCV disease incidence as a function of environmental and geographical factors. Scouting reports were submitted by cooperating growers located across approximately 20,000 acres in southwestern Florida from 2006 to 2012. Daily weather data were obtained from several local weather stations. Moran’s I was used to assess spatial relationships and polynomial distributed lag regression was used to determine the relationship between weather variables, whitefly, and TYLCV. Analyses showed that the incidence of TYLCV increased proportionally with mean whitefly density as the season progressed. Nearest-neighbor analyses showed a strong linear relationship between the logarithms of whitefly densities in neighboring fields. A similar relationship was found with TYLCV incidences. Correlograms based on Moran’s I showed that these relationships extended beyond neighboring fields and out to approximately 2.5 km for TYLCV and up to 5 km for whitefly, and that values of I were generally higher during the latter half of the production season for TYLCV. Weather was better at predicting whitefly density than at predicting TYLCV incidence. Whitefly density was best predicted by the number of days with an average temperature between 16 and 24°C (T16to24), relative humidity (RH) over the previous 31 days, and vapor pressure deficit over the last 8 days. TYLCV incidence was best predicted by T16to24, RH, and maximum wind speed over the previous 31 days. Results of this study helped to identify the extent to which populations of whitefly and TYLCV exist over the agricultural landscape of southwestern Florida, and the environmental conditions that favor epidemic growth. This information was used to propose an approach to AWPM for timing control measures for managing TYLCV epidemics.

Powdery mildew, caused by the fungus Podosphaera xanthii, is one of the most important diseases of melon. Although there are several pathogenic races of P. xanthii, race 1 is the predominant race in South Carolina and in other parts of the United States. We used a densely genotyped recombinant inbred line melon population for traditional quantitative trait loci (QTL) mapping, to identify two major (qPx1-5 and qPx1-12) and two minor (qPx1-4 and qPx1-10) QTLs (named according to race – chromosome number) associated with resistance to P. xanthii race 1. QTL mapping of disease severity in multiple tissues (hypocotyl, cotyledons, true leaves, and stems) identified the same genetic basis of resistance in all tissue types. Whole-genome resequencing of the parents was used for marker development across the major QTLs and functional annotation of single nucleotide polymorphisms (SNPs) for candidate gene analysis. Kompetitive allele-specific PCR (KASP) markers were tightly linked to the QTL peaks of qPx1-5 (pm1-5_25329892, pm1-5_25461503 and pm1-5_25625375) and qPx1-12 (pm1-12_22848920 and pm1-12_22904659) in the population and will enable efficient marker-assisted introgression of powdery mildew resistance into improved germplasm. Candidate genes were identified in both major QTL intervals that encode putative R genes with missense mutations between the parents. The candidate genes provide targets for future breeding efforts and a fundamental examination of resistance to powdery mildew in melon.

Zinc (Zn) accumulation and deficiency affect plant response to pests and diseases differently in varying pathosystems. The concentrations of Zn in plants aid in priming defense signaling pathways and help in enhanced structural defenses against plant pathogens. Studies are lacking on how concentrations of Zn in watermelon plants influence defense against two important soil-borne pathogens: Fusarium oxysporum f. sp. niveum (FON) and southern root-knot nematode (RKN, Meloidogyne incognita). In this study a comparative transcriptomics evaluation of watermelon plants in response to high (1.2 ppm) and low (0.2 ppm) levels of Zn were determined. Differential transcript-level responses differed in watermelon plants when infected with FON or RKN or both under high- and low-Zn treatment regimes in a controlled hydroponics system. Higher numbers of differentially expressed genes (DEGs) were observed in high-Zn-treated than in low-Zn-treated non-inoculated plants, in plants inoculated with FON alone and in plants inoculated with RKN alone. However, in the co-inoculated system, low-Zn treatment had higher DEGs as compared to high-Zn treatment. In addition, most DEGs were significantly enriched in hormone signal transduction and MAPK signaling pathway, suggesting an induction of systemic resistance with high-Zn concentrations. Taken together, this study substantially expands transcriptome data resources and suggests a molecular potential framework for watermelon-Zn interaction in FON and RKN.

Watermelon is an important vegetable crop and is widely cultivated in USA with an approximate global production of >100 million tons. Powdery mildew (PM) caused by Podosphaera xanthii is a major production-limiting factor on watermelon and other cucurbits. Numerous PM and multiple disease resistant (MDR) watermelon germplasm lines have been developed by the USDA in Charleston, SC. To gain a better understanding of the innate and activated molecular defense mechanisms involved during compatible and incompatible PM-watermelon interactions, we inoculated PM susceptible (USVL677-PMS) and resistant (USVL531-MDR) watermelon plants with 10(5) conidia ml(-1) of P. xanthii. RNA-seq profiling was done on leaf samples collected at 0, 1, 3, and 8 days post inoculation (DPI). A total of 2,566 unique differentially expressed genes (DEGs) were identified between compatible and incompatible interactions with P. xanthii. The compatible interactions resulted in distinct plant gene activation (>twofold unique transcripts, 335:191:1762 SCRI Vegetable Grafting Grant award [2016-1498-08]; SCRI CuCAP Grant award [2015-51181-24285]; ORISE This research was funded in part by a SCRI Vegetable Grafting Grant award 2016-1498-08 and the SCRI CuCAP Grant award 2015-51181-24285 to C. S. Kousik. Mihir Mandal acknowledges the fund provided by ORISE. The whole genome sequencing of USVL531-MDR and USVL677-PMS was performed at the Duke Center for Genomic and Computational Biology, Durham, NC, USA with Illumina HiSeq 4000 (Illumina, Inc., San Diego, CA, USA) while RIL lines were performed at Novogene Corporation, Sacramento, CA, USA using HiSeq X Ten platform. The authors would also like to acknowledge Dr. Jason Holliday, Associate Professor, Department of Forest Resources and Environmental Conservation, Virginia Tech for his valuable suggestions on analyzing our transcriptomic and whole genome sequencing data. The authors would also like to acknowledge the use of Virginia Tech Advanced Research Computing Center for clustering and bioinformatic sequence data analysis. The authors wish to acknowledge the technical assistance provided by Jennifer Ikerd and summer undergraduates in conducting many of these experiments. We also thank Dr. William Rutter, Plant Pathologist, USVL-USDA Charleston for critical review and suggestions to improve the manuscript prior to submission. Disclaimer: The use of trade, firm, or corporation names in this publication is for the convenience of the reader. Such use does not constitute an official endorsement or approval by the United States Department of Agriculture or the Agriculture Research Service of any product or service to the exclusion of others that may also be suitable. Public domain – authored by a U.S. government employee

COVID 19 caused by SARS-CoV-2 is spreading worldwide and affected 10 million people with a mortality rate between 0.5 % to 5%. Medicinal plants from China, Morocco, Algeria, Africa and India were tested for antiviral efficacy in SARS-CoV-2. Ayurveda Medicine described many medicinal plants. The Nimba (Azadirachta indica A. Juss) is used in fever, bacterial and viral infections, and Amrita (Tinospora cordifolia (Thunb.) Miers) is used as antiviral, antipyretic, and anti-inflammatory purposes. The combination of both these plants is called Nimbamritam, and it is widely used in pyrexia, dermatitis, viral infections, etc. Spike protease (PDB ID 6VXX) and Mpro (PDB ID 6LU) were retrieved from RCSB and 16 ligands from A. indica and 6 ligands from T. cordifolia were obtained from IMPPAT and PubChem. AutoDock Vina embedded PyRx was used for docking. Remdesivir was taken as a reference drug. In silico study of Cordifolide A of T cordifolia showed the highest scores with -8.2 Kcal/mol and -10.3Kcal/mol with Mpro protease and Spike protease respectively. Cordifolide A had 4 H bonds and Kaempferol had 7 non-conventional bonds, including van der Waal with Mpro (6LU7) protease. The interactions with 6VXX had 5 H bonds in each ligand Cordifolide A and Azadirachtin B. The prevention of virus entry by targeting spike protease host receptor ACE2 and restricting replication of the viral genome by targeting Mpro residues were identified in our study. A. indica and T. cordifolia are promising therapeutic agents in COVID 19.