Breeding for Papaya ringspot virus resistance in Carica papaya via hybridisation with Vasconcellea quercifolia

Abstract

Papaya ringspot virus type P (PRSV-P) is a major threat to the papaya industry worldwide. F1 hybrids have been produced when Carica papaya L. female flowers have been pollinated with pollen of the PRSV-P resistant species Vasconcellea quercifolia. F1 plant production required embryo rescue 90 days post-pollination, and plantlet regeneration in vitro. Three hundred F1 hybrids were grown to maturity in the field and had morphological characteristics that were identical to 1 or both parents, were intermediate between those of the parents, or were greater than either parent. They had a sex ratio of 2 (male) : 49 (hermaphrodite) : 49(female). Eighteen plants (7 male and 11 hermaphrodite) produced some viable pollen. Pollen viability of these plants as measured by germination on agar medium varied between 1.1 and 6.1% (mean of 3.37 ± 0.18) compared with >90% for C. papaya. Cytogenetic studies showed limited homology between C. papaya and V. quercifolia genomes. The intergeneric hybrids varied in their reaction to strains of PRSV-P in Australia and the Philippines. Of the hybrids, 75% were resistant to PRSV-P while 25% produced virus symptoms.

Reproductive biology of Vasconcellea quercifolia A. St.-Hil. (Caricaceae), a moth-pollinated ‘highland papaya’

“…is one of the few species of the genus that apart from inhabiting high altitudes it also grows in lowlands and reaches the highest latitudes of distribution (Scheldeman et al 2007). This species has great attractiveness for human beings: it is resistant to PRSV-P C. papaya ringspot virus, it is capable of producing vigorous inter-generic hybrids with this species, and is a source of proteases with a proteolytic activity higher of genus (Drew et al 2006;Siar et al 2011;Torres et al 2010), although it is not cultivated nowadays.…”

Recent advances in the development of transgenic papaya technology

“…Reports of PRSV infestation of papaya farms were reported in Thailand [60], in Taiwan in 1975 [61] and in the Philippines in 1982 [62]. While PRSV is not a major problem in Australia, it is considered as an important threat to its papaya industry [4]. PRSV-infected papaya plants exhibit chlorotic leaves, ringed spots on the fruit and the upper part of the trunk, distortion of leaves which resembles the damage of mites, and depressed fruit production and eventually the infected plants die.…”

“…Interspecific hybridization studies, summarized in the consensus document on papaya [3], had limited success due to incompatibility problems and production of infertile hybrids. More recently, Drew et al [4] reported that their intergeneric crosses between Vasconcellea quercifolia and C. papaya have produced fertile hybrids. Moreover, backcrossing has produced several fertile intergeneric hybrids with PRSV resistance.…”

“…Attempts to hybridize wild relatives with Carica papaya had also been unsuccessful due to incompatibility and production of infertile hybrids [3]. It was only recently that the hybridization of C. papaya with Vasconcellea quercifolia resulted into fertile resistant hybrids [4].…”

Papaya ringspot virus resistance in Carica papaya via introgression from Vasconcellea quercifolia

“…Dioecious and hermaphrodite cultivars are grown in many tropical and subtropical countries for their vitaminrich fruits and their milky latex 2006a). Papaya is the best known member of the family Caricaceae that consists of five genera-Carica, Jacaratia, Jarilla, Cylicomorpha and Vasconcellea (Badillo 2000).…”