Genetic diversity between papaya lines and their correlation with heterosis in hybrids for disease resistance and morpho-agronomic traits

Abstract

This study aimed to verify if the genetic divergence between papaya lines, obtained by means of molecular markers, is correlated with heterosis in the hybrids for characteristics related to production, fruit quality and disease resistance. Eight parents and 56 hybrids obtained from diallel crosses were evaluated in randomized blocks, with four replicates. The number of commercial fruits (NCF), the average fruit weight (AFW), the productivity (PROD), the fruit firmness (FIRM) and the total soluble solids (TSS) were evaluated, as well as the severity of black spot on leaves (BSS) and fruits (BSSFr), phoma spot (PSS) and powdery mildew on leaves (PMS). Correlations were estimated between genetic divergence, obtained based on Vivas, M.; Cardoso, D.L.; Ramos, H.C.C.; Santos, P.H.D.; Silveira, S.F.; Moraes, R.; Pereira, M.G. Genetic diversity between papaya lines and their correlation with heterosis in hybrids for disease resistance and morpho-agronomic traits. Summa Phytopathologica, v.44, n.1, p.110-115, 2018. SSR, and heterosis, estimated for each characteristic in four possibilities of crossings within the diallel: i) all crossings; ii) between parents of the 'Solo' group; iii) between parents of the 'Formosa' group; and iv) between parents of 'Solo' with 'Formosa' group and 'Formosa' with 'Solo' group. Results indicate the possibility of exploring heterosis both in crossings between groups and in crossings within groups. The low magnitude of the estimates of correlation between heterosis and morphological characteristics of the hybrids with genetic distance obtained by SSR in the parents indicates that the behavior of hybrids cannot be inferred based on the genetic divergence between parents.Keywords: Carica papaya, diallel, hybridization, plant breeding.Papaya (Carica papaya L.), one of the tropical plants with major importance for the national and world's fruit production, is cultivated in several Brazilian states. One of the bottlenecks of this crop is the lack of commercial varieties and hybrids that meet the requirements of the domestic and external market; thus, breeding programs with this attempt should be intensified. Breeding programs in papaya aim to obtain lineages and use them in hybridization programs with the focus on hybrid vigor or heterosis, a phenomenon that provides great productivity to hybrids from the crossing of highly divergent parents.In papaya, the possibility of exploring heterosis is already reported for morpho-agronomic characteristics (5, 17), physiological seed quality (19) and disease resistance (13,27,29,26). Falconer (9) suggests that, at any degree of dominance above zero, heterosis is a function of allele frequency between the parents; therefore, there is a positive correlation between genetic divergence and heterosis. For this reason, lineage diversity estimates can be used as a predicting tool of superior crosses in plant breeding programs (14). Studies with lineages obtained from the populations BR-105 and BR-106, correlating productivity and genetic divergence es...

Genetic advance and regression analysis in sunflower

“…Most often there is a close correspondence between the magnitude of genetic variability and heterosis (LALITHA REDDY et al 2000;FUZATTO et al 2002;RAO et al 2004;OLIVEIRA et al 2004). Further, there are also studies reporting that heterosis will not always occur when divergent parents are crossed (DIXIT and SWAIN, 2000;VIVAS et al 2018). For an effective breeding strategy heritability estimates are important indicator about transferability of economically important quantitative traits.…”