Sugars, including fructose, glucose, and sucrose, contribute significantly to the flavor and consumer acceptance of snap beans (Phaseolus vulgaris L.). Little is known regarding differences in sugar content among snap bean and dry bean cultivars and the patterns of sugar accumulation with increasing pod size. Alcohol–soluble sugar concentration of five snap bean cultivars and one dry bean cultivar planted in field trials was assayed throughout pod development over 2 years using high-performance liquid chromatography. Significant differences in sugar accumulation patterns and quantity were observed among cultivars. In general, fructose and glucose content decreased, whereas sucrose increased with increasing pod size in snap beans. In contrast, fructose and glucose amounts increased, whereas sucrose concentration remained unchanged with increasing pod size in the dry bean cultivar. No year-by-genotype interactions were observed for sugar accumulation patterns or sugar amount. Results indicate that sieve size No. 3 (7.34 to 8.33 mm) or No. 4 (8.33 to 9.52 mm) pods are suitable for detecting differences in sugar concentration among genotypes.
Kyle M. VandenLangenberg, Paul C. Bethke, and James Nienhuis
Wesley Gartner, Paul C. Bethke, Theodore J. Kisha, and James Nienhuis
Sugars, including glucose, fructose, and sucrose, contribute significantly to the flavor and consumer acceptance of snap beans (Phaseolus vulgaris L.). Sugar accumulation and changes in sugar profiles during snap bean development contribute to overall assessments of quality for breeding lines and cultivars. Developing fruit from a diverse group of four snap bean cultivars containing Andean germplasm and one Mesoamerican dry bean cultivar were sampled at 5-day intervals from 10 to 30 days after flowering over 2 years. Glucose, fructose, and sucrose in pod and seed tissue was quantified using high-performance liquid chromatography. Percent seed mass relative to pod mass increased with days after flowering, but the rate of increase was heterogeneous among cultivars. Significant differences in sugar accumulation patterns of mono- and disaccharides were observed with time of development and between pods and seeds. Glucose and fructose decreased rapidly in pods and seeds with time after flowering. In contrast, sucrose concentration increased in pod tissue but remained constant in seeds of the snap bean cultivars with time after flowering. The patterns of changes in pod and seed sugar concentrations with time after flowering were similar among all snap bean cultivars. In contrast to the snap beans, seed sucrose increased with time after flowering in the Mesoamerican dry bean cultivar Puebla 152. No year by day after flowering interactions were observed for sugar accumulation patterns or sugar concentrations. Younger snap beans had the highest sweetness index based on observed sugar concentrations, percent seed mass, and perception of relative sweetness by the human palate. Although mean sweetness varied between cultivars, the rate of decrease in sweetness with time was the same for all five cultivars. These findings indicate that variation for sweetness exists in snap beans and can be exploited by breeding to develop cultivars with a potentially more desirable, sweet flavor.