The putative yield advantage associated with growing upright beans (Phaseohs vulgaris L.) at high planting densities in narrow (0.23-m) rows might he compromised by a higher risk of white mold [Sclerotinia sclerotiorum (Lib.) de Bary] because of reduced air flow through the crop canopy. This four-yeai-study was undertaken to compare the white-mold avoidance and agronomic attributes of upright bean lines and to determine whether their yields can he increased by raising planting density. Four upright lines and a viny line as a control were established in narrow rows at planting densities ranging from 25 to 60 plants/m* in a field artificially infested with sclerotia of S. sclerotiorum. On average, the four upright lines had lower incidence of white mold and smaller disease severity indices than the control, `UI36', indicating that the development of white mold is reduced in dense, erect canopies. There were differences in disease response among the upright lines, with `ISB82865' and `UI906' being the least and most susceptible entries, respectively. Increases in planting densities resulted in higher yields and influenced the development of white mold hut had no effect on vine length, lodging, and maturity. However, the planting density effect on the disease response was not consistent among entries in 2 of the 4 years. The results of this study indicate that upright beans can he grown at high planting densities without greatly increasing the risk of a white-mold outbreak. The choice of the most appropriate planting density for upright beans depends largely on the cost of seed.
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