Progress in introgression of Papaya ringspot virus resistance from Vasconcellea pubescens to Carica papaya

Abstract

An attempt to develop Carica papaya L. resistant to Papaya ringspot virus type P (PRSV-P) has been established via an intergeneric cross using Vasconcellea pubescens as the resistance donor. V. pubescens has consistently been reported to be resistant to PRSV-P, unlike the resistance in other species (d’Eeckenbrugge et al., 2014). The immunity to PRSV-P is also controlled by a single dominant gene (Dillon et al., 2006), which should be easy to transfer across crops. Because of the genetic distance between the two genera and genetic incompatibility, Vasconcellea parviflora was introduced as a bridging species to transfer the PRSV-P resistance gene(s) to papaya (C. papaya). Backcrossing has been achieved to BC4 in order to maximize the V. parviflora genetic background to improve fertility. The PRSV-P resistance genotype of the BC4 was determined with previously published sequences linked to the prsv-1 locus (Dillon et al., 2006). One of the heterozygous lines, BC4#113, was selected to use as a resistance donor to cross with C. papaya line 2.001. Embryos were rescued, initiated and multiplied in vitro. The cross was successfully micropropagated and produced 18 F1 lines [C. papaya × (V. parviflora backcrossed to V. parviflora × V. pubescens)]. These F1s were genotyped at the prsv-1 locus as previously mentioned. They were subsequently acclimatized and planted in a field in north Queensland. True hybridity was revealed through morphological characterization, including pink flowers, which is a dominant trait from V. parviflora. The hybrid F1s carrying the PRSV-P locus were then successfully backcrossed to C. papaya to generate BC1 generations. They were also sib-crossed with the F1 to generate F1:F2 generations. These lines will be planted in a quarantine laboratory at Griffith University, Nathan, for evaluation of virus resistance. Fertile plants that carry the virus-resistance alleles will be used as parental lines in future breeding strategies.