Genotypic and phenotypic correlations for reaction to five foliar pathogens in alfalfa

Genotypic and phenotypic correlations for reaction to five foliar pathogens were estimated from analyses of variance and covariance in eight, five-parent diallel crosses each in Saranac, MSA-C4, and MSB-C4 alfalfa (Medicago sativa L.). The foliar pathogens wereUromyces striatus, Schroet. var.medicaginis (Pass.) Arth.,Stemphylium botryosum Wallr.,Pseudopeziza medicaginis (Lib.) Sacc.,Phoma herbarum West var.medicaginis Fckl., andLeptosphaerulina briosiana (Poll.) Graham and Luttrell.Genotypic correlations for reaction toU. striatus andP. medicaginis were significant and positive in Saranac and MSB-C4, but were significant and negative in MSA-C4. Genotypic correlations involvingL. briosiana,S. botryosum, andP. medicaginis were positive and significant in MSA-C4 and MSB-C4, but were not significant in Saranac. Significant positive genotypic correlations were observed for reaction toU. striatus andP. herbarum, and toP. herbarum andS. botryosum in Saranac and forU. striatus andL. briosiana in MSA-C4. Correlated responses in selection experiments involving the above, or closely related cultivars, confirmed most of the significant genotypic correlations. Phenotypic correlations were generally much smaller than the genotypic correlations.