A functional association in Vitis vinifera L. cv. Cabernet Sauvignon between the extent of primary branching and the number of flowers formed per inflorescence

Abstract

The number of primary branches (those branches that arise directly from the rachis) and the total number of flowers were counted for inflorescences of Vitis vinifera L. cultivar Cabernet Sauvignon over a range of climates and a number of seasons as part of a yield prediction study. Regression analysis indicated that the number of primary branches per inflorescence exerted a strong control over the total number of flowers per inflorescence, with highly significant (P < 0.01) relationships explaining between 51 and 80% of the variation in flowers per inflorescence. Because the extent of primary branching is largely determined prior to grapevine buds entering dormancy, this strong functional association between branching and flower numbers, suggests that season-to-season differences in potential inflorescence size will be greatly affected by conditions during that phase of primordial differentiation in the previous growing season. A general tendency for the number of flowers per inflorescence to be positively related to other measures of vine fertility, supports this view. Lower orders of branching (secondary and tertiary) down to formation of individual flowers at budburst, also have the potential to influence eventual inflorescence size. As to the timing of such influences, we noted that increased severity of winter pruning significantly increased both flowers per inflorescence (by 9%) and the number of primary branches per inflorescence (by 21%). Such responses provide strong support for our contention that although the extent of primary branching is largely determined prior to grapevine buds entering dormancy, differentiation of new primary branches in Cabernet Sauvignon inflorescences continues to occur after the onset of dormancy.