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

Abstract

We report the first successful production of PRSV-P resistant backcross (BC) papaya plants following intergeneric hybridisation between C. papaya and a Vasconcellea species after 50 years of reports on unsuccessful attempts. This follows our previous reports of PRSV-P resistant F 1 hybrids developed by intergeneric hybridisation between C. papaya and V. quercifolia. One PRSV-P resistant BC 1 (BC 1 ) plant was produced after 114,839 seeds were dissected from 940 fruits. The seeds yielded 1,011 embryos and 733 germinated in vitro from which 700 developed into plantlets that were screened in a glasshouse and in the field under high disease pressure and exposure to inoculation by viruliferous aphids. From the PRSV-P resistant backcross 1 (BC 1 ) male plant, 1465 plants [137 BC 2 , 546 SbC 2 (BC2 sib-crosses), 147 BC 3 , 379 SbC 3 and 256 BC 4 ] were grown from seed and inoculated with PRSV-P and virus resistant BC 3 and BC 4 plants were selected from these generations. Presence or absence of virus was confirmed by ELISA serological tests. BC plants generally developed mild symptoms of PRSV-P after periods ranging from 5 to 18 months in the field but many showed the ability to produce new growth free of symptoms. All control plants developed severe symptoms after 3 months in the field. Some BC 3 and BC 4 plants were free from viral infection after 18 months in the field. Subsequently they developed very mild symptoms on their leaves and a few ringspots on their fruit. They continued to grow vigorously and produce fruit for 3 years under high disease pressure provided by the infected controls and other susceptible plants. Good quality marketable fruit were produced on these plants. Application of these results should lead to restoration of the papaya industry in virus-infested regions of the Philippines and worldwide.

Molecular Phylogeny, Biogeography and an e-Monograph of the Papaya Family (Caricaceae) as an Example of Taxonomy in the Electronic Age

“…A morphological synapomorphy supporting this relationship is a unilocular ovary, while the remaining Caricaceae have 5-locular ovaries. Breeding efforts for papaya improvement should include the four species now revealed as the closest relatives, rather than focusing only on the highland papayas in the genus Vasconcellea (Sawant, 1958;Drew et al, 1998;Siar et al, 2011). So far, studies on the biology of the herbaceous Caricaceae are restricted to an investigation on the cultivation of the lowland species Jarilla chocola (Willingham and White, 1976).…”

“…Molecular data have revealed that the closest relative of papaya is a clade of four species in Mexico and Guatemala previously entirely neglected by ecologists and breeders . One of the main impediments for C. papaya production is the papaya ring spot virus, although some Vasconcellea are tolerant to the disease Siar et al 2011;. The lack of knowledge of the true closest relatives of papaya resulted in the assumption that the highland papayas (Vasconcellea species) are the best group to use in papaya improvement (Scheldeman et al 2011;.…”

“…Breeders have sought to introduce these features to C. papaya using traditional plant breeding techniques. However, although some experimental hybrids exhibit useful disease resistance, serious fertility barriers limit breeding efforts (Sawant, 1958;Dinesh et al, 2007;Siar et al, 2011). The commercial interest in papaya is reflected in more than 1300+ papers published on this species between 1970 and 2011 (Web of Science, accessed 25 September 2011), ca.…”

Resistencia de Vasconcellea cauliflora al Virus de la mancha anular de la papaya-potyvirus (PRSV-P) y su introgresión en Carica papaya

“…After mechanical inoculation with PRSV-P isolated in the Philippines, plantlets without symptoms (72.3% to 96.1%) under greenhouse conditions were recorded. After 18 months in the field, plants from the BC 4 backcross were analyzed using the ELISA technique but only 66% of them were resistant (Siar et al, 2011). In BC 3 plants, the ratio of resistant: susceptible segregants was 3:1, whereas in BC 4 plants two types of ratio were observed: 2:1 and 4:1.…”

Genetic Relationship between Vasconcellea and Carica Based on Their Chromosome Features

“…One way to do that is by using wide hybridization (Hajjar and Hodgkin 2007). However, attempts have been done since 1958 by Jimenez and Horovitz (1958) and Horowitz and Jimenez (1967) and the transference of resistance gene from wild to the cultivated papaya is not well succeeding unless embryo rescue technique is used (Magdalita et al 1996, Siar et al 2011.…”