Lignin Biosynthesis Gene Expression Is Associated with Age-related Resistance of Winter Squash to Phytophthora capsici

The Oomycete plant pathogen, Phytophthora capsici, causes root, crown, and fruit rot of winter squash (Cucurbita moschata) and limits production. Some C. moschata cultivars develop age-related resistance (ARR), whereby fruit develop resistance to P. capsici 14 to 21 days postpollination (DPP) because of thickened exocarp; however, wounding negates ARR. We uncovered the genetic mechanisms of ARR of two C. moschata cultivars, Chieftain and Dickenson Field, that exhibit ARR at 14 and 21 DPP, respectively, using RNA sequencing. The sequencing was conducted using RNA samples from ‘Chieftain’ and ‘Dickenson Field’ fruit at 7, 10, 14, and 21 DPP. A differential expression and subsequent gene set enrichment analysis revealed an overrepresentation of upregulated genes in functional categories relevant to cell wall structure biosynthesis, cell wall modification/organization, transcription regulation, and metabolic processes. A pathway enrichment analysis detected upregulated genes in cutin, suberin monomer, and phenylpropanoid biosynthetic pathways. A further analysis of the expression profile of genes in those pathways revealed upregulation of genes in monolignol biosynthesis and lignin polymerization in the resistant fruit peel. Our findings suggest a shift in gene expression toward the physical strengthening of the cell wall associated with ARR to P. capsici. These findings provide candidate genes for developing Cucurbita cultivars with resistance to P. capsici and improve fruit rot management in Cucurbita species

Epidemiology and Population Biology of Pseudoperonospora cubensis: A Model System for Management of Downy Mildews

The resurgence of cucurbit downy mildew has dramatically influenced production of cucurbits and disease management systems at multiple scales. Long-distance dispersal is a fundamental aspect of epidemic development that influences the timing and extent of outbreaks of cucurbit downy mildew. The dispersal potential of Pseudoperonospora cubensis appears to be limited primarily by sporangia production in source fields and availability of susceptible hosts and less by sporangia survival during transport. Uncertainty remains regarding the role of locally produced inoculum in disease outbreaks, but evidence suggests multiple sources of primary inoculum could be important. Understanding pathogen diversity and population differentiation is a critical aspect of disease management and an active research area. Underpinning advances in our understanding of pathogen biology and disease management has been the research capacity and coordination of stakeholders, scientists, and extension personnel. Concepts and approaches developed in this pathosystem can guide future efforts when responding to incursions of new or reemerging downy mildew pathogens.Keywords: disease management, mating type, pathotype, Bayesian prediction, risk assessment, genomic

Mature pepper fruit phenotypic diversity in size, shape, end shape, and pericarp thickness of a worldwide collection.

<p>Mature pepper fruit phenotypic diversity in size, shape, end shape, and pericarp thickness of a worldwide collection.</p

Population structure of pepper (<i>Capsicum annuum</i>) grouped by country of origin.

<p>Only countries represented by more than four individuals are included. Individuals are represented by their proportionate membership (0 to 1) in cluster 1 (purple), cluster 2 (light yellow), cluster 3 (sky blue), cluster 4 (steel blue), or cluster 5 (orchid). A white space and black tick marks separate subgroups of individuals.</p

Fruit thickness, perimeter, area and fruit shape compared among countries and continents.

<p>Fruit thickness, perimeter, area and fruit shape compared among countries and continents.</p

Broad sense heritability of fruit phenotypic characteristics.

<p>Broad sense heritability of fruit phenotypic characteristics.</p

Genetic diversity, population structure, and resistance to Phytophthora capsici of a worldwide collection of eggplant germplasm.

Eggplant (Solanum melongena L.) is an important solanaceous crop with high phenotypic diversity and moderate genotypic diversity. Ninety-nine genotypes of eggplant germplasm (species (S. melongena, S. incanum, S. linnaeanum and S. gilo), landraces and heirloom cultivars) from 32 countries and five continents were evaluated for genetic diversity, population structure, fruit shape, and disease resistance to Phytophthora fruit rot. Fruits from each line were measured for fruit shape and evaluated for resistance to two Phytophthora capsici isolates seven days post inoculation. Only one accession (PI 413784) was completely resistant to both isolates evaluated. Partial resistance to Phytophthora fruit rot was found in accessions from all four eggplant species evaluated in this study. Genetic diversity and population structure were assessed using 22 polymorphic simple sequence repeats (SSRs). The polymorphism information content (PIC) for the population was moderate (0.49) in the population. Genetic analyses using the program STRUCTURE indicated the existence of four genetic clusters within the eggplant collection. Population structure was detected when eggplant lines were grouped by species, continent of origin, country of origin, fruit shape and disease resistance

Genetic differentiation of pepper lines when grouped by fruit shape categories^A.

<p>Genetic differentiation of pepper lines when grouped by fruit shape categories<a href="http://www.plosone.org/article/info:doi/10.1371/journal.pone.0156969#t006fn001" target="_blank">^A</a>.</p

Pepper lines evaluated for fruit characteristics.

<p>Pepper lines evaluated for fruit characteristics.</p

Population structure of pepper (<i>Capsicum annuum</i>) grouped by fruit end shape categories.

<p>Individuals are represented by their proportionate membership (0 to 1) in cluster 1 (purple), cluster 2 (light yellow), cluster 3 (sky blue), cluster 4 (steel blue), or cluster 5 (orchid). A white space and black tick marks separate subgroups of individuals.</p