Brassinosteroids and gibberellic acid: effects on in vitro pollen germination in grapevine

Many physiological processes related to plant growth and development are under the influence of growth regulators, which also have an impact on pollen germination. In this study, the effects of two brassinosteroid compounds, epibrassinolide and 22S,23S-homobrassinolide, and gibberellic acid (GA3) on in vitro pollen germination of two table grape cultivars, ‘Italia’ and ‘Cardinal’ (Vitis vinifera L.), were determined. A total of 28 treatments, alone and in combination, were applied to freshly collected pollens which were sown on a basic medium with 1% agar and 20% sucrose. Petri dishes were kept at 26±1°C for 24 hours. Counting of the germinated pollens revealed that the effects of these plant hormones were cultivar- and substance-specific. The cultivar ‘Italia’ was not influenced by the treatments (the highest germination ratio being 44.4% from 0.001 mg L-1 epibrassinolide) as opposed to the cultivar ‘Cardinal’. The highest germination ratio in ‘Cardinal’ was about 50% in pollens treated with 25 mg L-1 GA3 + 0.01 mg L-1 epibrassinolide. The control group resulted in 32.38% germination. Combining GA3 with epibrassinolide provided slightly higher germination ratios compared to combining GA3 with 22S,23S-homobrassinolide.