Effect of Brassinosteroids and chilling on bud break release in Vitis labrusca L. cuttings

Abstract

In tropical regions, grapevine plants are not usually exposed to extreme low temperatures over the production cycle. As a result, bud break is nonuniform and sprouting is inconsistent. To cope with this, Hydrogen Cyanamide (Dormex^®) is used to break bud dormancy and provide uniformness to the vineyard. In this work, we tested Brassinosteroids (BRs) with the purpose of surpassing the process of dormancy. We also tested the influence of temperature and photoperiod on bud sprouting. Cuttings were harvested in March (Summer) and August (Winter) and the following treatments were applied: Control (C); Cooling (15 days at 5ºC, F); Dormex^®(D); Cooling before (FD) or after Dormex^® (DF);0.1 mg L^-1 BRs (BR1); 1.0 mg L^-1 BRs (BR2); Cooling after BR 0.1 (BR11) or BR1.0 (BR21); Cooling before BR 0.1(BR12) or BR 1.0 (BR22). The cuttings were maintained at 25°C±1°C and 14 h photoperiod for 60 days. In the summer, the BR₅₀ of all treatments varied from 7,6 to 20,8 days. Branches which were collected in Summer received additional 254 hours of photoperiod than the branches collected in the winter, and this may have influenced the dormancy as most treatments in winter did not present satisfactory bud break apart from Dormex-applied treatments (FD, DF and D) and BR21. BRs did not contribute to accelerate the process of sprouting but it might have some protective effect on the bud as the cooling treatment applied after BRs was the only BR-treatment that reached BR₅₀ in the winter.