Resistance to multiple foliar diseases in papaya genotypes in Brazil

Abstract

The absence of cultivars with satisfactory levels of genetic resistance justifies the search for genotypes incorporating disease-resistance genes in the papaya-breeding program. In this study, two field-plot experiments were carried out in the municipality of Linhares, Espirito Santo State, Brazil, to evaluate resistance to foliar diseases in a papaya germplasm collection. The variables incidence and severity of leaf diseases and black spot incidence and severity on fruits were considered for uni- and multivariate variance analyses. The Mahalanobis distance was calculated for each pair of genotypes, and the distance matrix was used for clustering methods. Papaya genotypes were grouped by the Tocher method and the hierarchical method of Un-weighted Pair Group with Arithmetic Mean (UPGMA) was used for dendrogram construction. Although no immune reaction was observed among the genotypes for any of the leaf diseases, the data analyses highlight the following genotypes as potential sources of resistance genes for use in a papaya breeding program: ‘STZ 23 PL’, ‘Maradol’, ‘Maradol GL’, ‘JS 11’, ‘Americano’, ‘Caliman SG’, ‘Sekati’, ‘Sekati FLM’, ‘Waimanalo’, ‘Caliman AM’, ‘Papaya 46’, ‘Tailândia’ and ‘SH 12-06’. This is the first time multivariate analyses were employed to evaluate multiple disease resistance in a papaya crop.