Development of PRSV-P resistant Carica papaya genotypes by introgression of genes from wild Vasconcella species
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This paper reports successful collaboration between researchers in the Philippines and Australia since 1993 on a project funded by ACIAR. Three intergeneric crosses were done between C. papaya and Vasconcella spp. resistant to Papaya Ring쳰ot Virus (PRSV-P). Production of F1 plants required embryo rescue and regeneration after an embryogenic phase in vitro. Eleven F1 plants from a cross between C. papaya and V. quercifolia were selected as being PRSV-P resistant and having some fertility, and 4 of these had sufficient fertility to produce embryos when backcrossed to papayas. Cytogenetic studies on one of these intergeneric hybrids revealed variable chromosome counts, presence of univalents, laggards and meiotic aberrations and pollen fertility of 0.2 - 2.2%. Segregating populations of first and second backcross plants were evaluated for PRSV-P resistance, fertility and morphological characteristics including fruit shape, size and quality. All first backcross plants were micropropagated in vitro before glasshouse and field evaluation. Variable reactions to the two viral strains in the two countries were observed. One plant (clone 54) demonstrated a high level of tolerance against multiple inoculations of PRSV-P in the glasshouse and stood up against aphid transmitted PRSV-P in the field for 9 months in Australia, however showed little resistance to PRSV-P in the Philippines. Results indicate that 3 backcrosses may be sufficient to produce fruit that are similar to papaya and commercially acceptable.