Genotype-Ideotype distance index and multivariate analysis to select sources of anthracnose resistance in Capsicum spp

The challenges of plant breeding for disease resistance include identifying genotypes that are resistant to more than one pathogen isolate and defining adequate methods for measuring resistance. We report the identification of Capsicum spp. genotypes resistant to anthracnose caused by two Colletotrichum scovillei isolates using the Genotype-Ideotype Distance Index (GIDI) and multivariate analysis. Forty-one genotypes of chili peppers from three Capsicum species considering unripe and ripe fruits were evaluated for resistance to anthracnose. For inoculation, 20 μL of a suspension containing 1 × 10⁶ conidia/mL were applied in each fruit. Analyses were performed daily for eight days using a scale from 1 (resistant) to 9 (susceptible). Area under the disease progress curve (AUDPC), incubation period, and latent period were evaluated in unripe and ripe fruits, and analyzed using a non-parametric test with ANOVA-type statistic and correlated using the Spearman method. Genotypes were classified using the GIDI and Ward’s hierarchical clustering method. There was variability in germplasm resistance to anthracnose considering the resistance variables and the stage of fruit development. GIDI allowed identifying nine C. baccatum var. pendulum genotypes resistant to isolate 13, and eight C. baccatum var. pendulum plus one C. annuum genotypes resistant to isolate 8. GIDI and Ward’s clustering method identified the same genotypes resistant to isolate 8. Finding resistance in Capsicum genotypes representing different genic complexes means that breeders would be able to introgress resistant alleles from non-cultivated or semi-domesticated into cultivated plants. One genotype, UENF 1628 (C. baccatum var. pendulum), was resistant to two pathogen isolates representing a very interesting source of resistance to anthracnose caused by C. scovillei.