ORIGINAL ARTICLE Heterosis and genetic diversity for selection of papaya hybrids for resistance to black spot and phoma spot Marcelo Vivas 1 & Helaine C. C. Ramos 2 & Pedro H. D. Santos 1 & Silvaldo F. Silveira 1 & Telma N. S. Pereira 2 & Antonio Teixeira do Amaral Jr. 2 & Messias G. Pereira 2 Received: 3 February 2016 /Accepted: 26 October 2016 /Published online: 21 November 2016 # Sociedade Brasileira de Fitopatologia 2016 Abstract In this work, two experiments were set up in order to select papaya hybrids and verify heterosis ex- pression 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 dam- aged area by black spot was estimated. These character- istics were used to estimate genetic distance with com- plement 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. Keywords Asperisporium caricae . Carica papaya . Stagonosporopsis caricae . Genetic resistance . Hybrid vigor . Top cross Introduction Phoma spot, caused by Stagonosporopsis caricae (Sydow & P. Sydow) Aveskamp, Gruyter & Verkley [Syn. Phoma caricae-papayae (Tarr) Punith] (Aveskamp et al. 2010), is considered the second most important post-harvest disease of papaya in Brazil (Rezende and Martins 2005). The fungus is widespread in tropical regions (Hunter and Budderhagen 1972) and shows various symptoms. Another fungal disease that currently constitutes the main papaya disease is black spot caused by Asperisporium caricae (Speg.) Maubl (Rezende and Martins 2005). It causes severe losses by reducing the photosynthetic area of leaves and by depreciating the fruits for the market (Rezende and Martins 2005). The incidence and severity levels of these diseases can be so high that chem- ical control is mandatory to achieve profitable production at certain times of the year. The main measure adopted to control these diseases is the use of fungicides (Dianese et al. 2007; Vivas et al. 2010). The selection of resistant genotypes is a sustainable alternative for disease control; however, in papaya, complete resistance has not been observed in elite genotypes (Vivas et al. 2010, 2012b). In field assessments, different levels of disease were observed (Vivas et al. 2015), probably due to a polygenic control of resistance. Crop improvement can be achieved by selection of resistant genotypes or by the best hybrid Section Editor: Rosana Rodrigues * Marcelo Vivas mrclvivas@hotmail.com 1 Lab. de Entomologia e Fitopatologia, Centro de Ciências Tecnológicas e Agropecuárias, Universidade Estadual do Norte Fluminense Darcy Ribeiro, Campos dos Goytacazes, RJ 28013-600, Brazil 2 Lab. de Melhoramento Genético Vegetal, Centro de Ciências Tecnológicas e Agropecuárias, Universidade Estadual do Norte Fluminense Darcy Ribeiro, Campos dos Goytacazes, RJ 28013-600, Brazil Trop. plant pathol. (2016) 41:380–389 DOI 10.1007/s40858-016-0109-1