2019 ASHS Annual Conference

For snap bean (Phaseolus vulgarisL.) production, white-seeded cultivars are mostly used because colored seed results in anthocyanins in the seed and pods that impact visual appearance and reduce quality of the processed product. Some snap bean cultivars have been released with persistent color (pc), a member of the cosmetic stay-green gene family. These types are considered more desirable because the trait imparts a uniform dark green appearance to the pods. However, pcseeds show reduced germination and emergence compared to white-seeded types. Pleiotropic effects of pcare that dry seed is pale green in color, germinating seedling have bleached white cotyledons, and plant foliage and pods remain green even while senescing. Currently, pccultivars comprise about 40% of commercial acreage in the U.S. Seed fungicide treatments increase germination and emergence rates to levels almost the same as fungicide-treated white seed. The number of pccultivars would likely increase if the germination problem could be addressed. The objective of this research is to determine why and how germination and emergence is affected in pctypes compared to white- and colored-seeded types. A hypothesis is that seeds coats of pctypes are more fragile and may crack more easily (either from mechanical damage and/or imbibitional injury), thereby leaking solutes into the rhizosphere that attract pathogens that parasitize the germinating seed. In laboratory germination tests, no difference was observed among pc, white- and colored-seeded cultivars, and germination levels were generally high. We repeated field tests and observed that pctypes had a significantly lower ratio of untreated:treated seeds germinating compared to colored and white seeded types. Infected pcseeds were colonized by Fusarium oxysporumand more rarely, Waitea circinata. We also examined the anatomical structure of seed coat of genotypes with green (pp pcpc), white (pp PcPc) and colored (p^grip^griPcPc) seed. The outer testa layers were significantly thicker in ‘OR 91G’ (white) and GRI 2-1 (colored) than ‘Pascal’ (green) seeded types. These findings support the idea that pcseeds are more fragile and more likely to leak solutes into the rhizosphere. Breeding for reduced seed fragility in a pcbackground may be possible. These experiments can be supported with studies on solute leakage and susceptibility to mechanical and imbibitional damage.