GENETIC MECHANISMS OF RESISTANCE TO FUSARIUM ROOT ROT IN PEA (PISUM SATIVUM L.)
BODAH, ELIANE THAINES
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Pea (Pisum sativum L.) is an important cool season food legume grown worldwide. High protein and nutritional value, nitrogen fixation, lower water usage and easy growth are some of the benefits of pea production. Despite several breeding efforts, pea yields continue to be compromised by Fusarium root rot. One of the most frequent causal pathogens is Fusarium solani (Mart.) Sacc. f. sp. pisi (F.R. Jones) W.C. Snyder & H.N. Hans (Fsp). The aim of this work was to establish a foundation for phenotypic evaluation of Fusarium root rot and utilize the phenotypic platform to unravel the underlying genetic mechanisms of Fsp resistance and sensitivity in pea. Phenotypic evaluation and classification of pea accessions and commercial cultivars showed significantly different levels of resistance in the pea germplasm utilized in this study. Fsp resistance was previously suggested to be linked to pigmented-flowered peas. However, a pigmented-flowered pea, PI 180693, was observed to be susceptible. From all the parameters investigated, root diseases severity (RDS) and dry root weight were found to be the most effective phenotypic parameters to identify partial resistance to Fusarium root rot.In order to unravel the underlying genetic mechanisms related to resistance or susceptibility, eight white-flowered pea genotypes were selected for a time course pathogen challenge experiment followed by quantitative transcriptome analysis. Samples were harvested at 0, 6, and 12 hours after pathogen challenge. From the transcriptome dataset, several polymorphic sequence features with emphasis on SNPs were identified. As a proof of concept genes known to be involved in disease resistance were further investigated. Two F7 populations were used for SNP validation. Statistical analysis revealed that the six NBS-LRR type genes found to be polymorphic in the first population explained only a small portion of the investigated phenotype (R2= 0.03082). Evaluation of SNPs embedded in the additional 8,218 differentially expressed genes identified in this work is expected to enrich the disease associated Fsp gene-linked markers.