Papaya germplasm evaluation for resistance to papaya ringspot virus using artificial inoculation

Papaya ringspot disease, caused by papaya ringspot virus P (PRSV-P), is restricting the commercial cultivation of papaya worldwide. Several measures have been taken to control the disease, including the application of aphicides, identification of host plant resistance, and the use of transgenics. However, only genetically engineered papayas carrying the viral coat protein have been found to effectively control the disease. Transgenic papayas are not cultivated worldwide due to ethical regulations. Assessing the diverse papaya germplasm for resistance to PRSV-P could be a suitable alternative. Therefore, the present study was undertaken to assess PRSV resistance in 79 accessions, including commercial hybrids/ varieties and wild accessions. To identify novel resistant sources, the accessions were mechanically inoculated with PRSV under controlled conditions. The inoculated plants were continuously monitored for the appearance of PRSV-like symptoms and scored for disease severity on a scale of 0 to 5. Additionally, PRSV-P infection was confirmed by performing RT-PCR with coat protein-specific primers. The presence of the ~900 bp amplicon confirmed PRSV-P infection in the inoculated plants. Among all the accessions tested, only two accessions, HCAR 46 (Vasconcellea pubescens) and HCAR 177 (V. stipulate), did not show any symptoms. All Carica papaya accessions were susceptible to PRSV-P, whereas only Vasconcellea sp. showed resistance. The PRSV-resistant genotype identified in the present study could be used in breeding programs to breed PRSV-resistant cultivars.