Genetic resistance of grape genotypes to rust.
An experiment was conducted to evaluate the genetic resistance of grape genotypes to rust, caused by Phakopsora euvitis, and the infection efficiency in relation to leaf age and inoculum concentration. The evaluation was conducted on 15 genotypes, based on the following resistance components: number of pustules (uredia) per cm2; size of pustules; number of urediniospores produced per pustules; and latent period. The resistance components, except for the latent period, presented considerable quantitative variation. The multivariate analysis of resistance components discriminated 5 groups of genotypes. The more resistant genotypes were the rootstock cultivars IAC3I3, 1AC572, and 1AC766, in which the infection efficiency was low, with small pustule sizes, and less urediniospores production, aside from hypersensivity response on tissue surrounding the pustules. The infection increases with an increase in inoculum concentration. The rust colonizes young and mature grape leaves.