Heterosis and genetic diversity for selection of papaya hybrids for resistance to black spot and phoma spot

In this work, two experiments were set up in order to select papaya hybrids and verify heterosis expression for black spot (Asperisporium caricae) and phoma spot (Stagonoparopsis caricae) resistance. Experiments were set up in randomized blocks with two replications. Black spot and phoma spot incidence and severity on leaves were evaluated, and fruit damaged area by black spot was estimated. These characteristics were used to estimate genetic distance with complement of Jaccard’s Index. For black spot resistance, 77 % of hybrids showed heterosis for at least one of three evaluated characteristics and 58 % of hybrids showed heterobeltiosis effect. For phoma spot severity, there was heterosis manifestation in 56 % of hybrids, and 30 % of them showed heterobeltiosis effect. Therefore, heterosis was found in most of the hybrids, emphasizing the possibility of using hybridization to develop resistant genotypes. We observed that the best estimates of heterotic effects were obtained by crossing genetically distant individuals, indicating the existence of a positive relationship between genetic distance and hybrid performance. Together, the results highlight the hybrid ‘Americano’ x ‘Waimanalo’ as having a strong potential to reduce the intensity of these two diseases.