Stenospermocarpic Seedlessness Research Articles

Effect of culture medium, genotype, and year of cross on embryo development and recovery from in vitro cultured ovules in breeding stenospermocarpic seedless grape varieties

A highly efficient embryo rescue technique using in ovulo culture is critical for maximising success when using stenospermocarpic female parents to breed new seedless grape varieties. The effects of medium composition, pollen parent, and year of cross on embryo development and recovery in cultured ovules were investigated to improve in ovulo embryo rescue from stenospermocarpic parents commonly used in breeding seedless grapes for the Australian table and dried grape industries. Increasing CaCl2 concentrations in the culture medium improved embryo recovery, but embryo emergence from ovules and germination rates were unaffected by varying FeEDTA concentrations. A casein hydrolysate supplement in the culture medium improved embryo recovery, emergence, and germination. Embryo recovery varied with parental genotype and ranged from 5% to 14% in 4 self-pollinated genotypes. Mean embryo recoveries from ovules cultured 50 days after controlled cross-pollination from berries of the pollen-sterile, stenospermocarpic variety ‘Carina’ were 36% and 26% where the pollen parents were seeded (11 crosses) and seedless (6 crosses), respectively. Embryo recovery and germination were affected by the year in which a cross was made and there was a significant cross × year interaction. The results indicated that in ovulo embryo rescue can be improved by increasing CaCl2 concentrations and incorporating a casein hydrolysate supplement in the basal medium, by exploiting genotypic differences through the use of seedless parents that yield greater proportions of rescued hybrids, and possibly by understanding environmental effects on female parents to maximise the numbers of hybrids produced.

Seedless-Seedless Grape Hybridization via In-Ovulo Embryo Culture.

The effect of berry sampling time and genotypic difference in stenospermocarpic seedless grapes on the recovery of viable embryos through in ovulo embryo culture was examined. In 5 open-pollinated seedless cultivars, berry weight increased consistently as the fruit developed, but the ovule length did not correspondingly increase, being either constant or shrinking. The recovery rate of viable embryos significantly increased as the days after anthesis proceeded, especially on the 40th day. During the culture, polyembryony was occasionally observed in some ovules. At the micropylar end of the ovule, most multiple embryos emerged adventitously from the hypocotyl-root axis of zygotic embryo. In 5 open-pollinated selections and 6 cultivars, veraison ranged from 49 to 66 days after anthesis. Varietal difference in the recovery of viable embryos from ovules sampled at veraison was significant, ranging from 0 to 24.7%. In a total of 20 crosses between seedless accessions, the recovery rate of viable embryos significantly varied from 2.7 to 47.0%. The rate of plant recovery in vitro ranged from 0.6 to 24.9%. F1 progenies produced through in ovulo embryo culture in seedless x seedless crosses segregated as follows ; completely seedless : perceptible seed traces : seeded=24 : 56 : 21.

Somatic embryogenesis and plant development from immature zygotic embryos of seedless grapes (Vitis vinifera L.)

Somatic embryo formation occurred from immature zygotic embryos within ovules of stenospermocarpic seedless grapes (Vitis vinifera L.), when cultured for two months on liquid Emershad/Ramming medium. Somatic embryos continued to proliferate after excision and transfer to Emershad/Ramming medium supplemented with 1 μM benzylaminopurine and 0.65% TC agar. Plant development from somatic embryos was influenced by genotype, medium, phase (liquid, agar), stage (torpedo, mature) and their interactions. Optimal plant development occurred on Woody Plant Medium supplemented with 1.5% sucrose + 1 μM benzylaminopurine + 0.3% activated charcoal and 0.65% TC agar.