Agronomic traits affecting resistance to white Mold in common bean

Resistance to white mold [caused by Sclerotinia sclerotiorum (Lib.) de Bary] in common bean (Phaseolus vulgaris L.) is complexly inherited, and highly influenced by environmental factors. The identification of agronomically desirable avoidance mechanisms in advanced or elite lines and segregating populations is essential. The objectives of this study were to determine the relationship between nine agronomic traits (growth habit, days to flower, canopy height and width, branching pattern, lodging, days to maturity, seed size, and yield) and resistance to white mold in the field, corresponding heritabilities of resistance and agronomic traits, and the effect of the agronomic traits on disease and seed yield. A group of elite lines, and two recombinant populations derived from crosses between two resistant navy bean cultivars, Bunsi and Huron, to a susceptible cultivar, Newport, were evaluated for disease severity index (DSI) and agronomic traits in multiple field seasons. Heritability estimates for DSI were moderate (0.47) in the Bunsi/Newport population and high (0.82) in the Huron/Newport population. All agronomic traits displayed moderate to high heritability estimates. The agronomic traits that associated significantly with DSI in the three populations differed greatly. The most important agronomic trait that reduced DSI and contributed to yield was indeterminate growth habit. Increased canopy height, width, and lodging were generally associated with an increase in DSI, whereas traits such as days to flower and maturity varied in relation to DSI and yield across environments and populations. The complexity of the relationship of agronomic traits to DSI and yield highlights the difficulties bean breeders face in selecting among elite lines and within segregating populations for resistance to white mold in the field.