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 Palmira (Colombia), the performance of nine tropical bean lines differing in resistance to rust and seven mixtures obtained by combining these lines on the basis of equal proportions in seed number was evaluated in a rust inoculated treatment and in a fungicide treated control.
Compared to the fungicide treated control, rust attack significantly reduced the yield of all susceptible lines by 24 to 56% in pure stands. In rust inoculated mixtures containing resistant, intermediate and susceptible genotypes, mixture effects on yield increased only by 3.3% compared to the fungicide treated control. In mixtures of common bean a higher proportion of resistant lines appears to be required compared to cereals for comparable reductions in the spread of rust due to lower plant density and correspondingly higher autodeposition rate of uredospores.