Influence of canopy management on grapevine reproductive performance

Abstract

Grapevine reproduction is an intricate process that extends over two growing seasons. There is an overlap of two reproductive cycles; while the shoots are growing and inflorescences are developing into bunches for the first cycle (season one), the compound buds at the axil of lateral leaves are developing the potential crop for the next reproduction cycle (season two). The conditions of the first season not only influence reproductive growth of the current year, but also affect bud fruitfulness and hence potential yield for the following year. Canopy management practices play a vital role in commercial vineyards. A range of techniques have been developed and widely applied on grapevine canopies to achieve a desired yield and fruit quality. Grapevine reproductive performance response to different canopy management practices varies as source-sink relationship and microclimate are manipulated at different levels. Therefore a better understanding of vegetative and reproductive development in relation to the practices is imperative for sustainable production in vineyards. The aim of this thesis was to investigate the effects of different canopy management practices on the reproductive performance of two winegrape varieties, Semillon and Shiraz (Vitis vinifera L.). Five commonly used canopy management treatments including bunch thinning, shoot thinning, leaf removal at the bunch zone and at the middle third part of shoots, and leaving more buds after light winter pruning were applied on vines grown under field conditions. Canopy architecture was assessed by measuring leaf area index and canopy porosity. Light microclimate was measured as light interception at the whole canopy level and bud renewal zone. Reproductive performance was comprised of yield components (bunch number per vine, berry number per bunch and berry weight), bunch architecture (bunch length, width and compactness), berry uniformity and berry maturity during ripening. Bud fruitfulness was assessed using bud dissection analysis to record the number and area of inflorescence primordia and incidence of primary bud necrosis. Other measurements included shoot vigour parameters and carbohydrate contents of buds and canes. Results showed that grapevine reproductive performance was influenced by canopy management practices at different levels. Specifically, shoot thinning had the strongest effects on yield components, bunch architecture and bud fruitfulness through a greater modification of canopy architecture and light interception. Berry weight, berry number and bunch weight were significantly increased by shoot thinning. Leaf area index was decreased and canopy porosity and light interception were increased by shoot thinning and leaf removal. The number of inflorescence primordia was increased in the two treatments when an increase in the bud light microclimate was measured. Berry ripening was positively affected by shoot thinning and bunch thinning, while leaf removal and light pruning delayed the process. Leaf removal had relatively minor impact on reproductive parameters, while shoot thinning and bunch thinning showed compensation effects in yield components and bunch architecture, and light pruning decreased berry weight. In addition, bunch compactness was found to be increased by shoot thinning and was correlated with bunch rot (Botrytis cinerea) incidence for Semillon. This study improved our understanding of the role of canopy management practices on reproductive performance of grapevine, particularly for bunch architecture and bud fruitfulness. These insights may be used by practitioners to make more informed vineyard management decisions when manipulating yield.