INTERRELATIONSHIP OF PLANT ARCHITECTURE AND YIELD COMPONENTS IN THE PINTO BEAN IDEOTYPE

Ideotype breeding in common bean (Phaseolus vulgaris L.) has emphasized the selection of modified morphological traits that include upright, Type II (indeterminate) growth habit. Progress in the medium-seeded approximate to 40 g/100 seed) pinto bean appeared to have been limited by negative linkages between small seed size (approximate to 20 g/100 seed) and desired architectural traits. The objectives of this study were to determine the inheritance of seed weight and plant architecture, evaluate the genetic relationships among both traits, and to define a pinto bean ideotype for the humid midwestern USA. The genetic associations among three specific architectural traits, seed weight, and upright plant architecture were investigated in F-2 and F-2:3 generations at E. Lansing, MI, in 1990 and 1991, respectively. Upright plant architecture was estimated to be moderately heritable with narrow-sense es timates ranging from H-NS = 0.42 to 0.62. F-2 data from 1206 individuals indicated that plant architecture and seed weight are not linked (r = 0.05, P = 0.08). Directional selection for high (>30 g/100 seed) or low (<24 g/100 seed) seed weight resulted in significant differences in the average number of seeds per pod and the average number of seeds per plant. These directional selection results provide evidence that a pinto bean ideotype will differ from the small seeded navy bean ideotype by having fewer pods per plant and fewer seeds per pod. Selection for medium:seeded, upright (Type II) genotypes in other commercial classes would be greatly facilitated through the use of the pinto bean ideotype as a genetic bridge.