Backcrossing in passion fruit: generation advance and selection of genotypes resistant to Cowpea aphid-borne mosaic virus
The woodiness disease induced by the Cowpea aphid-borne mosaic virus (CABMV) is regarded as a limiting factor for passion fruit production. We estimated genetic parameters for resistance and agronomic performance-related traits and selected genotypes resistant to CABMV in segregating populations of passion fruit. The experiment was a randomized-block design with four replicates, consisting of six full-sibling first backcross genotype families, in which 319 genotypes were evaluated. The disease symptoms were evaluated based on spontaneous occurrence of CABMV, using a scale of scores in young leaves, plant and fruits. Based on these scores, we estimated the area under the disease progress curve (MAUDPC). Agronomic traits were also assessed: fruit weight per plant and number of fruits per plant. The variance components and genetic value of each genotype were estimated for each variable via mixed models. The MAUDPC values ranged from 401.25 to 1192.5, indicating considerable genetic variability. The high individual narrow-sense heritability value for the MAUDPC trait (0.95) indicates the possibility of genotypic selection within CABMV-resistant families. For the production-related traits, even with low heritability values, it was possible to obtain genetic gains in individual selection, which ranged from 4.99 to 6.24% for fruit weight and 22.64 to 28.70% for number of fruits. The genotypes chosen to compose the next backcross generation should be selected based on resistance to CABMV, which is the main objective of the program, since agronomic traits can be recovered from backcrosses. Of the 30 individuals ranked for CABMV tolerance, genotypes 501, 506, and 597 were selected to compose the next generation of backcrosses. These had the lowest values for MAUDPC.