An Improved Embryo-Rescue Protocol for a Carica Interspecific Hybrid

Abstract

An improved embryo-rescue protocol was developed for embryos (90 days old) of Carica papaya L. (Clone 2001), and subsequently was utilised for efficient production of interspecific hybrids of C. papaya × C. cauliflora Jacq. from 90- to 120-day-old embryos. Pre-incubation of C. papaya embryos for 7 days on a germination medium containing half-strength De Fossard nutrients supplemented with gibberellic acid (10 μM), 6-benzylamino-purine (0.25 μM), alpha-naphthalene-acetic acid (0.25 μM). sucrose (58 mM) and agar (8 g L-1) supported 100% germination. Subsequent transfer of germinated embryos to a nutrient medium that was identical, except that it was free of plant growth regulator, allowed good growth but induced shoot etiolation and callus production. Reducing the pre-incubation of C. papaya embryos on this medium to 5 days before transfer to the medium free of plant growth regulator produced similarly high germination (96%), but allowed for the production of good quality seedlings that were unetiolated and free of unwanted callus. For interspecific hybrids, a 5-day pre-incubation of the embryos on a liquid formulation was better than the solid formulation as it promoted better growth and vigour of the normally abortive interspecific hybrid embryos. Using the improved protocol, 1981 of 2100 (94%) interspecific hybrid embryos consisting of single and multiple forms were germinated. In all cases, the germinating multiple embryos underwent further embryogenesis that allowed for the production of 485 (25%) morphologically normal hybrid plants grown in soil in the glasshouse.

Maternal inheritance of cytoplasmic organelles in intergeneric hybrids of Carica papaya L. and Vasconcellea spp. (Caricaceae Dumort., Brassicales)

“…In the initial crosses, the recovery of intergeneric hybrids was limited due to ovule abortion and/or faulty endosperm development (Manshardt & Wenslaff, 1989;Magdalita et al, 1997). Introduction of embryo-rescue techniques helped to overcome these incompatibility barriers and significantly enhanced the pace and scope of wide hybridization (Magdalita et al, 1996;Drew et al, 1998). Nowadays, these biotechnological approaches can be routinely used to overcome the constraints to sexual hybridization and currently several of these hybrids are under evaluation to verify introgression of desired traits (Rod Drew, personal communication).…”

Screening Carica papaya × C. cauliflora hybrids for resistance to papaya ringspot virus‐type P

“…papaya × C. cauliflora hybrid seedlings produced via hybridization and embryo rescue (Magdalita et al, 1996) and true-to-type seedlings of C. papaya and C. cauliflora were used. The 120-day-old hybrid and parent seedlings were grown in a glasshouse at Redlands Research Station, Cleveland, Queensland and then transferred to a glasshouse in the Plant Protection Unit, Indooroopilly, Queensland for PRSV-P screening.…”

ISSR markers for genetic relationships in Caricaceae and sex differentiation in papaya

“…However, they are drastically reduced in crosses with C. papaya (Warmke et al 1954, Jimenez and Horovitz 1958, Horovitz and Jimenez 1967, Mekako and Nakasone 1975, Manshardt and Wenslaff 1989. Some interspecific crosses using embryo rescue were successful (Magdalita et al 1996, Manshardt and Drew 1998. For a better understanding of the genetic relationships in Caricaceae, several molecular studies have been performed, suggesting a considerable genetic distance between Carica and Vasconcellea (Jobin-Decor et al 1997, Aradhya et al 1999, Olson 2002, Van Droogenbroeck et al 2004, Kyndt et al 2006 (Hofmeyr 1938, Storey 1938.…”