Abstract
Hormonal regulatory processes controlling in vitro morphogenesis of grapevine inflorescence primordia, excised from latent buds from November to April, were investigated. Cytokinin (benzylaminopurine, BAP), gibberellin (GA3) and auxin (3-indolebutyric acid, IBA) were used at 1 mg/L. BAP induced branch development and flower calyx differentiation. GA3 first promoted the elongation of inflorescence rachis and then promoted flower differentiation up to the formation of normal calyx and calyptra (the fused petals), while anthers and pistils were also present but not functional. IBA did not seem to be directly involved in these morphogenetic processes. After culturing for 6–7 weeks, explants became either necrotic or formed friable callus. Excision between November (leaf fall) and April (bud burst) led to different morphogenetic development in both Pinot Noir and Chardonnay explants. Overall, Chardonnay explants were better able to develop, especially in December and January. There were differences in the organogenesis of Pinot Noir and Chardonnay during this period. These differences seem related to variation in the endogenous state of inflorescences at the time of excision, be it due to the activity of growth regulators or of other compounds. Aptitude for development was best in November, when 63% of explants developed, and worst in December, when only 26% developed.
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