Genetic control of partial resistance to Asian soybean rust

The genetic control of rust resistance was studied using the Caiaponia x IAC-100 and Luziania x Potenza crosses. The F-2 and F-3 generations were evaluated. Rust severity was quantified through visual assessment of the middle third of three leaflets per plant and performed by three different evaluators; the average score was calculated for each individual plant. From these data, we estimated the mean and variance of the genetic components by employing the weighted least squares method. The estimated number of genes and broad-and narrow-sense heritabilities were also obtained. It was concluded that rust resistance is a characteristic controlled by 2 to 23 genes that are predominantly dominant. The estimate of narrow-sense heritability was greater than 70% for the Caiaponia x IAC-100 cross, and the wide-sense heritability was greater than 60% for the Luziania x Potenza cross; thus, it is possible to successfully select resistant individuals in early generations.