Selection for papaya resistance to multiple diseases in a base population of recurrent selection

Papaya has a narrow genetic base concerning disease resistance, with few genetically distinct cultivars for planting in the world. Losses in crop production caused by fungal and viral diseases, added to the absence of resistant cultivars available to producers, have reduced the competitiveness of crops. Therefore, this study aimed to select promising individuals for resistance to phoma spot and black spot based on direct or combined genetic gains in the base population of the recurrent papaya selection. The population used in this study originated from the crossing of dioecious, female individuals and holders of a gene pool for resistance to phoma spot and black spot. These were crossed with elite individuals with a gene pool for production traits and fruit quality. The experiment was carried out without an experimental design, containing one plant per plot. Three measurements were taken on 255 individuals for five traits of disease resistance, being: four associated with black spot (incidence and severity on the leaf and fruit) and one associated with phoma spot (severity on the leaf). With the observations obtained, the REML/BLUP procedure was performed to estimate the temporary and permanent environmental effects. Such values were used to know the genetic parameters of the population and to elaborate a combined selection index, as well as to compare the gains with the direct selection. The results indicate environmental variance was relatively high witch low repeatability for the traits. Both selection strategies provide gains in reducing the diseases studied. Combined selection is recommended as it provides greater expected gain than direct selection. However, direct selection can be considered for the development of lines per se, as it offers the opportunity to already select superior individuals during the process of breeding the recurrent population or, to be part of the recombination phase.