Lima beans with improved lygus bug tolerance

limaResearch adviser: Paul Gepts
Team Leader: Kimberly Gibson – kjgibson@ucdavis.edu

The SCOPE Lima bean team is focused on developing a large-seeded, bush-type Lima bean variety with resistance to the Western Tarnished Plant Bug (Lygus hesperus). Lygus is the most damaging insect pest for Lima bean (Phaseolus lunatus) in California. Yield losses attributable to Lygus feeding on flowers and young pods in unsprayed fields has been as high as 70% compared to sprayed fields. The necessity of insecticides prevents cultivation of P. lunatus within organic cropping systems.

Within the narrow genepool of elite California varieties, some lines of Lima bean are more resistant to Lygus than others, and there appear to be multiple mechanisms of resistance. We hope to add to this genetic resistance by diversifying the genepool with American heirloom varieties and germplasm from Centro Internacional de Agricultura Tropical (CIAT). We have specifically focused on making crosses with the elite large seeded bush cultivar UC 92 and other, more diverse germplasm. Additionally, we tested some F3 and F4 lines developed from crosses between Mexican landraces and Brazilian elite cultivars that have shown promise in the California environment.

Student with educational posterIn the summer of 2017, we grew F3 and F4 families at the UC Davis student farm. From these plots we made single plant selections. We planted 5 plants from each selection into the greenhouse for a winter generation advance. Each of these plants in the greenhouse will be harvested to plant a single plot in the 2019 field. We will make selections within and among these families.

Lima beans are an important food legume and a great rotation crop. Dry lima beans are typically row cropped, planted in early May and harvested in September, by windrowing then threshing. They come in a wide variety of shapes, colors, and sizes but the main market classes are white large and baby seeded types. Both the bush and vine type produce a tremendous amount of biomass. The main production constraint for Lima bean in the western US is the insect pest, Lygus hesperus, which causes significant reduction in both yield and grain quality by feeding on the flowers and developing pods. Our group has also initiated crosses with colorful patterned Lima beans which may be of interest to niche markets.

This project gives students experience in managing field trials at the UC Davis Student Farm, and in collaboration with organic growers, performing crosses and generation advances in greenhouses and fields and experience with in field selections.