Comparison of Rhizoctonia Foliar Blights of Soybean With Respect to Infection Process, Double-Stranded RNA Components, and Evaluation of Resistance.

Infection cushions were formed in a similar manner on soybean leaves by Rhizoctonia solani AG-1 IA (aerial blight) and AG-1 IB (web blight) isolates, however, AG-1 IB produced more mucilagenous material. Leaf topography did not induce infection cushion formation. More infection cushions were formed by isolates of AG-1 IA and IB on collodion membranes placed over leaves of susceptible compared to resistant cultivars. Glucose and 3-O-methylglucose repressed disease severity caused by AG-1 IA and IB isolates to the same extent. However, when the solutions were applied 40 h or longer after inoculation, no repression was observed. Disease severity and number of infection cushions were significantly correlated. Isolates of AG-1 IA formed more infection cushions and caused greater disease severity than AG-1 IB isolates at 35 C. There were no significant differences at 20, 25, and 30 C. Only isolates of R. solani AG-1 IA, IB, IC, AG-4, and AG-5 formed infection cushions, while other AG\u27s did not. More seedling infections occurred at 20-25 C, whereas, more leaf infections were observed at 25-30 C by both AG-1 IA and IB indicating that infection and colonization of different host parts are affected differently by temperature. Double-stranded RNA (dsRNA) was detected in 63% of R. solani AG-1 IA and IB isolates. Most AG-1 IA isolates had seven dsRNA components with molecular sizes ranging from 1.3-9.3 kb. Most AG-1 IB isolates had a large 12 kb dsRNA and these components appeared to be different from dsRNA of other AG\u27s. DsRNA components were stable through successive subculturing and were located in the cytoplasm. DsRNA was not detected in isolates of AG-1 IB (2 tested) and one isolate of AG-1 IA (2 tested) after 1 wk of growth at 35 C. The presence or absence of dsRNA in AG-1 IA or IB isolates did not correlate with virulence or mycelial growth. Disease severity determined with a detached leaf inoculation technique was correlated with Rhizoctonia foliar blight ratings of soybean cultivars in an inoculated nursery. The potential use of these two techniques for evaluation of resistance is discussed

The Transcriptomic Profile of Watermelon Is Affected by Zinc in the Presence of Fusarium oxysporum f. sp. niveum and Meloidogyne incognita

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

NMR Spectroscopy Identifies Metabolites Translocated from Powdery Mildew Resistant Rootstocks to Susceptible Watermelon Scions

Powdery mildew (PM) disease causes significant loss in watermelon. Due to the unavailability of a commercial watermelon variety that is resistant to PM, grafting susceptible cultivars on wild resistant rootstocks is being explored as a short-term management strategy to combat this disease. Nuclear magnetic resonance-based metabolic profiles of susceptible and resistant rootstocks of watermelon and their corresponding susceptible scions (Mickey Lee) were compared to screen for potential metabolites related to PM resistance using multivariate principal component analysis. Significant score plot differences between the susceptible and resistant groups were revealed through Mahalanobis distance analysis. Significantly different spectral buckets and their corresponding metabolites (including choline, fumarate, 5-hydroxyindole-3-acetate, and melatonin) have been identified quantitatively using multivariate loading plots and verified by volcano plot analyses. The data suggest that these metabolites were translocated from the powdery mildew resistant rootstocks to their corresponding powdery mildew susceptible scions and can be related to PM disease resistance

Micronutrients Affect Expression of Induced Resistance Genes in Hydroponically Grown Watermelon against Fusarium oxysporum f. sp. niveum and Meloidogyne incognita

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

Genome of ‘Charleston Gray’, the principal American watermelon cultivar, and genetic characterization of 1,365 accessions in the U.S. National Plant Germplasm System watermelon collection

Years of selection for desirable fruit quality traits in dessert watermelon (Citrullus lanatus) has resulted in a narrow genetic base in modern cultivars. Development of novel genomic and genetic resources offers great potential to expand genetic diversity and improve important traits in watermelon. Here, we report a high-quality genome sequence of watermelon cultivar ‘Charleston Gray’, a principal American dessert watermelon, to complement the existing reference genome from ‘97103’, an East Asian cultivar. Comparative analyses between genomes of ‘Charleston Gray’ and ‘97103’ revealed genomic variants that may underlie phenotypic differences between the two cultivars. We then genotyped 1365 watermelon plant introduction (PI) lines maintained at the U.S. National Plant Germplasm System using genotyping-by-sequencing (GBS). These PI lines were collected throughout the world and belong to three Citrullus species, C. lanatus, C. mucosospermus and C. amarus. Approximately 25 000 high-quality single nucleotide polymorphisms (SNPs) were derived from the GBS data using the ‘Charleston Gray’ genome as the reference. Population genomic analyses using these SNPs discovered a close relationship between C. lanatus and C. mucosospermus and identified four major groups in these two species correlated to their geographic locations. Citrullus amarus was found to have a distinct genetic makeup compared to C. lanatus and C. mucosospermus. The SNPs also enabled identification of genomic regions associated with important fruit quality and disease resistance traits through genome-wide association studies. The high-quality ‘Charleston Gray’ genome and the genotyping data of this large collection of watermelon accessions provide valuable resources for facilitating watermelon research, breeding and improvement

Psychostimulants

A current survey and synthesis of the most important findings in our understanding of the neurobiological mechanisms of addiction are detailed in our Neurobiology of Addiction series, each volume addressing a specific area of addiction. Psychostimulants, Volume 2 in the series, explores the molecular and cellular systems in the brain responsible for psychostimulant addiction, including both direct/indirect sympathomimetics and nonsympathomimetics. This volume introduces the readers to the history of psychostimulant use. The authors clearly differentiate the neurobiological effects into three distinct stages of the addiction cycle: binge/intoxication, withdrawal/negative affect, and preoccupation/anticipation. © 2020 Elsevier Inc. All rights reserved