Tree and fruit traits of progenies from the cross between (Annona cherimola Mill. × A. squamosa L.) × A. reticulata L. and approaches for the introgression of valuable genes from A. reticulata L.

Abstract

Annona reticulata L. possesses many traits desirable in other edible annonas, and hybridization is the simplest means to combine desirable features of related species. In this study, A. reticulata was hybridized with atemoya (A. cherimola Mill. × A. squamosa L.), and 250 trispecies hybrids were studied for 28 traits (12 tree traits and 16 fruit traits) with the objective of salvaging useful genes from the three edible annonas and determining the extent of variation in the progeny. The heterozygous nature of Annona spp. and simultaneous segregation of three distant genomes resulted in a tremendous heterogeneity in the progenies. The fitness of the progenies ranged from very vigorous to very weak, with a wide range of values for tree height (1.75–5.9 m), canopy spread (1.15–5.07 m) and trunk circumference (11–38.5 cm). The occurrence of diverse and novel segregants for tree shape and branching pattern suggested the possibility of identifying efficient ideotypes. Variation in fruit shape, skin colour and skin surface in addition to wide range of values for total soluble solids (17–32°B), acidity (0.16–2.2%) and number of seeds per/100 g fruit (3–49) showed that exciting opportunities existed in terms of selecting for desirable traits. Among the segregating population were slow-fruit-ripening genotypes that required up to 12 days from harvesting to ripening. Interestingly, some recombinants produced fruits resembling A. glabra and A. muricata fruits, suggesting that one or the other parental species of the trihybrid could be progenitor of these two non-parental species. These results demonstrate that A. reticulata is potentially a valuable source of a variety of novel traits. However, the F₁ trihybrids exhibited reduced fertility with pronounced undesirable traits of A. reticulata, and the survival of F₂ trees was poor, with those that did survive being extremely weak and failing to flower or set fruit. Consequently, backcrossing may be more suitable approach than advancing trihybrid generation for transferring desirable genes from A. reticulata. Backcrossing F₁ progeny of [(A. cherimola × A. squamosa) × A. reticulata] to A. squamosa, a highly fertile species, is expected to yield productive introgressants in which the contribution of the A. squamosa genome will be extended from 25 to 62.5% in the F₁BC₁ generation. The genetics is described herein based on the expressions of certain tree and fruit traits in the progeny.