Potential for using Vasconcellea parviflora as a bridging species in intergeneric hybridisation between V. pubescens and Carica papaya

There have been numerous attempts to transfer Papaya ringspot virus type P (PRSV-P) resistance from wild Vasconcellea relatives to Carica papaya L. Success has been limited by the high degree of genetic divergence and thus incompatibility between Vasconcellea spp. and C. papaya. In the present work, intergeneric hybrid populations of C. papaya x V. pubescens Lenne et Koch, C. papaya x V. parviflora A. DC. and interspecific populations of V. pubescens x V. parviflora were produced and evaluated for morphological characteristics and PRSV-P resistance. F-2 and F-3 populations were produced from the V. pubescens x V. parviflora F-1 and PRSV-P resistant individuals with homozygous genotypes (RR) were selected with the aid of a co-dominant CAPS marker and backcrossed to V. parviflora or outcrossed to C. papaya. Leaf vein number (seven) from V. pubescens, flower colour (pink) from V. parviflora and petiole colour (red-green) and plant size from C. papaya were transferred as dominant traits in interspecific and intergeneric crosses. Other traits, e.g. flower shape and fruit size, were intermediate in hybrids. When the wild species or their hybrids were outcrossed to C. papaya, inheritance patterns did not always follow Mendelian ratios, suggesting abnormal pairing of chromosomes or preferential elimination of the Vasconcellea genes. For example, in crosses between C. papaya x V. pubescens, all flowers were female and in crosses between C. papaya x V. parviflora, the cream flower colour of C. papaya was dominant over the pink colour of V. parviflora. However, the PRSV-P resistance gene from V. pubescens was successfully backcrossed into V. parviflora from F-2 hybrids, and in the F-1 hybrids between C. papaya and V. parviflora, 45% pollen fertility was obtained thus V. parviflora is proposed as a potential bridging species between C. papaya and V. pubescens.