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The soil-borne pathogens, particularly Fusarium oxysporum f. sp. niveum (FON) and southern root-knot nematode (RKN, Meloidogyne incognita) are the major threats to watermelon production in the southeastern United States. The role of soil micronutrients on induced resistance (IR) to plant diseases is well-documented in soil-based media. However, soil-based media do not allow us to determine the contribution of individual micronutrients in the induction of IR. In this manuscript, we utilized hydroponics-medium to assess the effect of controlled application of micronutrients, including iron (Fe), manganese (Mn), and zinc (Zn) on the expression of important IR genes (PR1, PR5, and NPR1 from salicylic acid (SA) pathway, and VSP, PDF, and LOX genes from jasmonic acid (JA) pathway) in watermelon seedlings upon inoculation with either FON or RKN or both. A subset of micronutrient-treated plants was inoculated (on the eighth day of micronutrient application) with FON and RKN (single or mixed inoculation). The expression of the IR genes in treated and control samples was evaluated using qRT-PCR. Although, significant phenotypic differences were not observed with respect to the severity of wilt symptoms or RKN galling with any of the micronutrient treatments within the 30-day experimental period, differences in the induction of IR genes were considerably noticeable. However, the level of gene expression varied with sampling period, type and concentration of micronutrients applied, and pathogen inoculation. In the absence of pathogens, micronutrient applications on the seventh day, in general, downregulated the expression of the majority of the IR genes. However, pathogen inoculation preferentially either up- or down-regulated the expression levels of the IR genes at three days post-inoculation depending on the type and concentration of micronutrients. The results demonstrated here indicate that micronutrients in watermelon may potentially make watermelon plants susceptible to infection by FON and RKN. However, upon infection the IR genes are significantly up-regulated that they may potentially aid the prevention of further infection via SA- and JA-pathways. This is the first demonstration of the impact of micronutrients affecting IR in watermelon against FON and RKN infection.

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.

Shade nets can be an effective technology for producing bell pepper (Capsicum annuum L.) under hot climatic conditions. However, the effects of shading on fruit quality are still unclear. The objectives were to evaluate the effects of shade level on fruit mineral nutrient content, physiological disorders, and postharvest water loss. Trials were conducted in the spring–summer of 2016, 2017, and 2018 in Tifton, Georgia, USA, following a randomized complete block design with five shade levels: 0% (open field), 30%, 47%, 63%, and 80%. Shading increased the bell pepper fruit dimensions (length, diameter, and weight) in 2016 and mineral nutrient content in 2017. Fruit sunscald incidence decreased with increasing shade level, while blossom-end rot showed inconsistent responses. Postharvest fruit water loss and transpiration rates were highest in fruits from the unshaded treatment in 2016; there were no differences in fruit water loss among the shade levels. NONEXPRESSOR OF PATHOGENESIS-RELATED 1 (NPR1) and PATHOGENESIS-RELATED 1 (PR1) genes expressed more than 1.5-fold and 10-fold, respectively, at 47% shade level compared to 80%, though not significantly. Therefore, plants grown under shading had fruit with greater size, increased mineral nutrient content, and reduced sunscald incidence compared with the unshaded control.

Members of the bacterial genus Burkholderia are a routine threat to onion production worldwide. In addition to the common onion‐pathogenic species, Burkholderia cepacia, Burkholderia orbicola and Burkholderia gladioli, other Burkholderia species have the potential to cause onion disease. Despite their impacts and long‐known association with onion disease, the virulence mechanisms of onion‐pathogenic Burkholderia are far less well understood than Burkholderia in human and murine infection models. In this review, we will focus on genetically characterized virulence factors in species that contribute to symptom production in onion and other plant hosts. Specifically, we will focus on the variable roles of specialized protein secretion systems (T2SS, T3SS and T4SS) and secreted proteins, thiosulphinate tolerance gene (TTG) clusters and the well‐characterized phytotoxin toxoflavin in virulence. The regulation and roles of LuxI/LuxS quorum‐sensing system and IclR‐type transcriptional regulator, qsmR, as master regulators of secondary metabolite production and virulence factors will also be discussed. The TTG clusters, involved in bacterial tolerance to thiosulphinate defence compounds, exhibit onion tissue‐specific contributions to virulence. This suggests that Burkholderia onion pathogens have tissue‐specific virulence strategies for causing disease. [ABSTRACT FROM AUTHOR]

Disease outbreaks of bacterial leaf spot and blight of pepper and tomato often occur in both transplant- and field-production systems worldwide. In some cases, the outbreaks are caused by novel bacterial species. Characterization of these novel bacterial species are critical in developing diagnostic assays and identifying management options for pathogen monitoring and sustainable production, respectively. We characterized strains belonging to novel Pseudomonas species that are responsible for outbreaks in pepper and tomato both in transplant-houses and in production fields in Georgia, USA. Phylogenomic analyses and whole genome sequence indices demonstrated that the pepper and tomato strains belonged to P. capsici. The whole-genome comparison revealed that 13 Pseudomonas strains from diverse isolation sources that were curated in NCBI were indeed P. capsici indicating a potential wide-host range for this bacterial species. Our greenhouse-based host-range assay also indicated that P. capsici strains were pathogenic on pepper, tomato, eggplant, cabbage, lettuce, and watermelon corroborating a wide-host-range. A phylogenetic tree inferred from the whole genome sequence data showed that the P. capsici strains from Georgia (pepper and tomato) were genetically diverse, and were closely related to tomato P. capsici strains from Florida. Genomic presence of traditional bacterial virulence factors in P. capsici strains was also determined. Pseudomonas capsici strains encode one set of type I secretion system, two sets of type II secretion systems, one set of type III secretion system, two sets of type V secretion systems, three sets of type VI secretion systems, and various secondary metabolite gene clusters including lipopeptides. In in-vitro assays, it was demonstrated that six out of seven P. capsici strains (pepper and tomato strains from Georgia) were not sensitive to 0.8 mM CuSO4. When the genomes of copper-tolerant strains were compared with the copper-sensitive strains, it was observed that the former strains encode a cluster of genes related to copper tolerance, which were absent in the genomes of copper-sensitive strains. Considering the ability of P. capsici strains to infect a range of vegetable hosts and possession of a wide range of bacterial virulence factors, secondary metabolites, and copper-tolerance genes, we envision that the management of this pathogen might potentially be a challenge. [ABSTRACT FROM AUTHOR]

Plant defense traits such as trichomes along with biocontrol agents may provide alternatives to insecticide use in tomatoes, Solanum lycopersicum L. (Solanaceae). However, plant‐herbivore‐natural enemy interactions are not always complementary. In a series of greenhouse and field experiments, we explored whether augmented defense traits (i.e., production of acylsugars) in tomato plants could reduce sweet potato whitefly, Bemisia tabaci Gennadius (Hemiptera: Aleyrodidae), populations and aid the establishment of the predatory mite Amblyseius swirskii Athias‐Henriot (Acari: Phytoseiidae). In the field experiment, commercial tomato cultivars and acylsugar‐producing tomato lines received no predatory mites or mites released via three methods: dusting on top, dusting on bottom, or slow‐release sachets. In the first greenhouse experiment, predatory mites were released onto the commercial and acylsugar‐producing tomato plants via sachets. In the second greenhouse experiment using a similar design, we augmented the mite diet with an alternative non‐prey resource (i.e., cattail pollen). Our results indicated that acylsugar‐producing tomato plants supported significantly fewer whiteflies than the commercial lines in all experiments. However, in the field, despite lower whitefly numbers, Tomato yellow leaf curl virus (TYLCV) (Geminiviridae, Begomovirus) was detected at higher frequencies in acylsugar‐producing lines. Few mites were recovered from all commercial and acylsugar‐producing lines in the field or greenhouse experiments suggesting A. swirskii does not establish well on tomatoes, and acylsugar lines successfully decreased whitefly populations but not a viral disease transmitted even at low whitefly abundance. [ABSTRACT FROM AUTHOR]

Onion bulb rot can be caused by multiple plant pathogens including bacterial pathogens. During our routine survey of commercial onion farms in 2014, 2020, and 2021, seven putative Rouxiella spp. strains were isolated from symptomatic onion samples in Georgia, United States. Upon fulfilling Koch's postulates on onion, a genome analysis was conducted. Whole-genome indices (ANI and dDDH) showed that the strains belonged to Rouxiella badensis. Although the seven R. badensis strains were not pathogenic on onion foliage, the strains were able to cause bulb rot and could also produce necrotic lesions in a red onion scale assay. R. badensis populations increased significantly and to a level comparable to P. ananatis PNA 97-1R in a red onion scale infection assay. The core-genome analysis grouped all onion R. badensis strains from Georgia together, and distinct from R. badensis strains isolated from other sources and locations. Based on the genome analysis of strains (from the current study and available genomes in the repository), type I, III (Ssa-Esc and Inv-Mxi-Spa types), and V secretion systems are present in R. badensis genomes, while type II, IV, and VI secretion systems are absent. However, various secondary metabolite gene clusters were identified from R. badensis genomes, and a thiol/redoxassociated enzyme gene cluster similar to the Pantoea alt cluster mediating thiosulfinate tolerance was also present in onion strains of R. badensis. This is the first report of R. badensis as a plant pathogen. [ABSTRACT FROM AUTHOR]