YIELD FORMATION IN MIXTURES OF RUST RESISTANT AND SUSCEPTIBLE PLANTS OF COMMON BEAN (PHASEOLUS-VULGARIS L)

In a two-factorial trial, conducted in 1986 at the CIAT farm in Palmir a (Colombia), the performance of nine tropical bean lines differing in resistance to rust and seven mixtures obtained by combining these lin es on the basis of equal proportions in seed number was evaluated in a rust inoculated treatment and in a fungicide treated control. Compare d to the fungicide treated control, rust attack significantly reduced the yield of all susceptible lines by 24 to 56 % in pure stands. In ru st inoculated mixtures containing resistant, intermediate and suscepti ble genotypes, mixture effects on yield increased only by 3.3 % compar ed to the fungicide treated control. In mixtures of common bean a high er proportion of resistant lines appears to be required compared to ce reals for comparable reductions in the spread of rust due to lower pla nt density and correspondingly higher autodeposition rate of uredospor es.