Development of Resources for Lima Bean (Phaseolus lunatus ) Breeding and Genetics Research

Abstract

Lima bean (Phaseolus lunatus) is a semi-perennial, leguminous species characterized by large flat, crescent-moon-shaped pods and trifoliate leaves with generally vigorous growth habit. Lima bean is naturally distributed from the southern United States to northern Argentina, from sea level to over 2,700m and has been grown commercially in California since the late 1800’s. The objective of the University of California Davis Lima bean breeding program is to develop improved large and baby, bush- and vine-type dry bean varieties with lygus (L. hesperus) and nematode (M. incognita ) resistance and to develop breeding tools such as genetic maps and molecular markers linked to important traits to facilitate future breeding efforts. To broaden the genetic base of the California Lima bean breeding program and add novel sources of stress resistance, 313 exotic accessions of Lima beans were field-tested at UC Davis (38.54N, -121.79W). Only nine percent of accessions produced seed and were evaluated for a second season for yield and lygus tolerance relative to ‘UC Haskell’, a leading baby-vine cultivar. Ten accessions outperformed the check for either yield or insect damage and may be good candidates to incorporate into California breeding. To facilitate breeding and research at a genetic level, several tools were developed for this semi-orphan crop, including the first large Recombinant Inbred (RI) population (n ∼300) derived from California cultivars originating from the conspecific Mesoamerican and Andean gene pools which show transgressive segregation for most agronomic traits. Traits including flowering time, inflorescent position, plant height, pod position and pod density showed correlation with yield that varied with and without lygus pressure, indicating potential tolerance mechanisms, which should be studied in more depth. This population was used to create a genetic linkage map containing 515 SNPs spanning 1622 cM across 13 linkage groups with synteny to common bean. This genetic map in combination with two seasons of field phenotypic data were used for composite interval mapping of 27 QTLs for germination rate, plant height, seed weight, yield, flowering time, inflorescence position, growth habit, and hydrogen cyanide potential in Lima bean. Seven of the new Lima bean QTLs for flowering time, plant height and seed weight are in similar locations to common bean QTLs. This research has increased our scientific and agronomic knowledge of Lima bean, a semi-orphan crop that has potential for increased utilization in California and globally.