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Utilization of a diversity panel to address genetic bottlenecks in cultivars of lima bean while improving their resistance to Phytophthora phaseoli

Terence Mhora: University of Delaware

<div>Delaware and the Mid-Atlantic region are the largest producers of lima bean (<em>Phaseolus lunatus) </em>in the US. Downy mildew of lima bean, caused by the oomycete pathogen <em>Phytophthora phaseoli</em>, is the most important yield-limiting disease resulting in continued loss of profitable production. In 2004 the University of Delaware initiated a lima bean breeding program. Existing cultivars with quality characteristics required by the market have a narrow genetic diversity and more diverse germplasm must be used to improve disease resistance and agronomic traits. A diversity panel (DP) comprised of 261 accessions sampled from the major genepools of lima bean was obtained from the species’ centers of domestication. Accessions of the DP were evaluated for reactions to two major races (E and F) of <em>P. phaseoli</em> and to <em>P. capsici</em>, an emerging pathogen of importance. A population genetic analysis using genotyping-by-sequencing of the DP and crosses derived from it is being conducted to understand the extent of the genetic bottleneck in local cultivars and its effect on disease resistance. Concurrent resistance to races E and F has not previously been identified nor bred into existing cultivars. Phenotyping data revealed accessions that have resistance to one or both races and their geographic distribution suggests alternative resistance alleles. These data coupled with the lima bean genome recently completed by our group are being used to investigate these hypotheses.</div>