The Use of Mentor Pollination to Facilitate Wide Hybridization in Blueberry

Two diploid yellowleaf Vaccinium elliottii Chapmn. clones were pollinated with pollen from the tetraploid southern highbush cultivar `Misty' (largely V. corymbosum L). These interspecific crosses, which normally yield few hybrids because of a triploid block, were made with and without the use of V. elliottii mentor pollen mixed with V. corymbosum pollen. Mentoring had no effect on the number of hybrids produced when V. elliottii `Silverhill' was the seed parent, but when V. elliottii `Oleno' was the seed parent, no hybrids were produced unless mentor pollen was utilized. The difference was postulated to be a greater ability to produce one-seeded berries in `Silverhill' than in `Oleno'.

An efficient interspecific hybridisation protocol for Carica papaya L. × C. cauliflora Jacq.

Summary. A protocol for interspecific hybridisation between Carica papaya and C. cauliflora is necessary for gene introgression between these 2 incompatible species. Carica papaya × C. cauliflora hybrids were successfully created using a new, efficient hybridisation protocol. This protocol includes the use of highly viable pollen of C. cauliflora produced during summer, autumn and/or spring, the use of an isolation time ranging from 90 to 120 days post-pollination of hybrid embryos, and the use of the most compatible C. papaya cultivar 2001 for crossing with C. cauliflora. Two types of interspecific hybrid embryos, namely single and multiple, were isolated in all resulting fruit. The application of gibberellic acid (0.6 or 0.8 mol/L) or 2,4- dichlorophenoxyacetic acid (1.5 or 2.0 mol/L) to freshly cross-pollinated flowers and pollination by mentor pollen did not promote either the rate of successful crosses or the production of hybrid embryos. Using this efficient protocol, hybridisation between C. papaya and C. cauliflora conducted in 3 locations in south-east Queensland produced 338 crosses which generated 43 736 seed. From these seed, 2100 hybrid embryos were recovered resulting in the production of 485 morphologically normal interspecific hybrid plants. Studies reported elsewhere show that these hybrids are resistant to papaya ringspot virus type P.

ATTEMPTS TO OVERCOME THE BARRIER OF INTERSPECIFIC HYBRIDIZATION BETWEEN CUCUMIS MELO AND C. METULIFERUS

The crossability ofCucumis meloandC. metuliferuswas studied in order to find ways to effect the cross between the two species. In cross-pollination withinC. melo, the pollen tubes entered the ovarian cavity within 24 h, and fertilization occurred within 48 h. Pollen germinated well after cross-pollination between the species, but pollen tubes grew slowly.C. metuliferuspollen tubes were arrested in the stigma or the upper style ofC. meloflowers.The influence of 100-, 150-, and 200-krad gamma radiation on in vitro germination, pollen tube growth ofC. meloandC. metuliferus, and on in vivo fertilization ofC. melowas studied. Pollen ofC. metuliferusappeared to be much less sensitive to gamma rays than that ofC. melo.Higher radiation doses were found to reduce fruit set ofC. melo.Irradiation of pollen ofC. meloalways resulted in “pseudo-fertilization”.We attempted to overcome the prefertilization crossing barrier betweenC. meloandC. metuliferusby using techniques of bud pollination, benzyladenine (BA) treatment, and irradiated mentor pollen. Ten lines ofC. meloand 6 accessions ofC. metuliferuswere used as female and male parents, respectively. The techniques of BA and bud pollination were ineffective. Numerous fruits with few embryos were obtained on some of theC. melolines after using the irradiated mentor pollen technique. Embryos, which were isolated at the age of 20–25 days and cultured on medium consisting of 1/3 Murashige and Skoog medium, were observed to provide normal development. All nine surviving plants were similar to the maternal parent and were not interspecific hybrids.