Breeding for Papaya ringspot virus resistance in Carica papaya via hybridisation with Vasconcellea quercifolia

Abstract

Papaya ringspot virus type P (PRSV-P) is a major threat to the papaya industry worldwide. F1 hybrids have been produced when Carica papaya L. female flowers have been pollinated with pollen of the PRSV-P resistant species Vasconcellea quercifolia. F1 plant production required embryo rescue 90 days post-pollination, and plantlet regeneration in vitro. Three hundred F1 hybrids were grown to maturity in the field and had morphological characteristics that were identical to 1 or both parents, were intermediate between those of the parents, or were greater than either parent. They had a sex ratio of 2 (male)�:�49 (hermaphrodite)�:�49(female). Eighteen plants (7 male and 11 hermaphrodite) produced some viable pollen. Pollen viability of these plants as measured by germination on agar medium varied between 1.1 and 6.1% (mean of 3.37 � 0.18) compared with >90% for C. papaya. Cytogenetic studies showed limited homology between C. papaya and V. quercifolia genomes. The intergeneric hybrids varied in their reaction to strains of PRSV-P in Australia and the Philippines. Of the hybrids, 75% were resistant to PRSV-P while 25% produced virus symptoms.