Breeding for resistance against Papaya ringspot virus: history, present status and future prospects in India
Papaya ringspot virus (PRSV) strain PRSV-P is the main constraint in all papaya (Carica papaya L.) growing areas of the world. Since it is transmitted by aphid vectors in a non-persistent manner, there is no prophylactic or therapeutic control of the disease. Cross-protection against the virus is not effective, and transgenic resistance is successful in only limited areas. Presently, yield losses are minimized by managing cultural practices. Breeding for resistance against PRSV is challenging because of the absence of sources of resistance genes in the genus Carica. Introgression of genes of resistance against PRSV-P into C. papaya from its wild relatives (Vasconcellea species) is the only option for breeding resistant lines. Earlier attempts at crossing C. papaya with Vasconcellea species were not successful because the species chosen as the donor of resistant genes (Vasconcellea cauliflora) was cross-incompatible with C. papaya. In the case of rare seed formation or when this problem of incompatibility was overcome with the embryo rescue technique, the resultant F1 hybrids were infertile. The problem of incompatibility was overcome by spraying nutrient solution on the stigma when crossing. The fidelity of the hybrids was established with molecular markers. Recently, some dioecious papaya lines (Pune selections, PS) were developed from local collections at IARI RS Pune that exhibit tolerance for PRSV under field conditions. Although these lines showed good combining ability with susceptible papaya cultivars, they had severe limitations as breeding lines because of being dioecious. 'PS-1' (yellow pulp) and 'PS-3' (pink pulp), sister lines with delayed and mild PRSV infection and good marketable yield, were converted to gynodioecious lines 'PS-1-1' and 'PS-3-1', while retaining their PRSV tolerance. There is good potential for trying Vasconcellea quercifolia as a parent with C. papaya, because it is resistant against PRSV and cross-compatible with C. papaya. The Australian work involving Vasconcellea cundinamarcensis (immune to PRSV but cross-incompatible with C. papaya) with Vasconcellea parviflora as the bridge species can be taken forward against Indian isolates of PRSV. Recent advancements in papaya genomics have raised hopes for development of PRSV-P-resistant hybrids with commercially acceptable fruit quality in the near future.
Sharma, S.K., Tripathi, S. and Mitra, S.K. (2019). Breeding for resistance against Papaya ringspot virus: history, present status and future prospects in India. Acta Hortic. 1250, 45-54
Pune selection, resistance breeding, transgenic, Vasconcellea