The effect of rootstock and water stress on the reproductive performance of Vitis vinifera L.

Abstract

The reproductive process in grapevines could arguably be the most important, as its success determines the yield for the current season and sets the potential crop for the coming season. In regions where poor reproductive performance exists, for example, poor fruitset in cool climates or in environments where water restrictions are likely, reproductive performance of grapevines may potentially be managed through the use of American Vitis rootstocks. The aim of this research was to assess the effect of American V. rootstocks on the reproductive performance of V. vinifera scions. Three scion cultivars commonly used in Australian viticulture, Cabernet Sauvignon, Shiraz and Merlot were investigated. The research identified that cultivars differ in their reproductive performance when grafted to the same rootstock. For Cabernet Sauvignon, rootstocks improved fruitfulness, for Merlot, rootstocks improved fruitset, while for Shiraz, the incidence of coulure— (an abnormal condition of fruitset), was more pronounced in rootstocks than for own-roots. A detailed investigation of rootstocks which incorporated analysis of carbohydrates, pollination, fertilisation, fruitfulness and fruitset on the cultivar Shiraz— (the most commonly planted red cultivar in Australian viticulture) was performed. Results showed that the quantity of pollen grains present on the stigma was important for successful fertilisation. As such, rootstocks associated with higher quantities of pollen grains on the stigma had higher percentage fruitset and seeded berry number. In addition, the levels of carbohydrates in roots and trunk were greater in rootstocks associated with greater vegetative growth. This research highlighted the importance of balance between vegetative and reproductive growth, as an imbalance in favour of reproductive growth was at the expense of carbohydrate accumulation which affected fruitfulness in the following season. The absence of irrigation affected reproductive development through yield losses which were attributed more to weight loss in bunches and berries through effects on berry size and dehydration, rather than low fruitset. A detailed analysis of the three cultivars enabled classification of rootstocks and cultivars based on their reproductive performance which will help identify reproductive traits for rootstock and cultivar combinations. In addition, there was an opportunity to assess the effect of rootstock and irrigation on grape and wine composition and wine sensory attributes of Shiraz. A novel sensory analysis technique enabled the discrimination of wine attributes between treatments and correlation with traditional wine quality assessments. For example, in one season, 1103 Paulsen with wine colour density, wine pH and the attributes “rich” and “black fruit”. 110 Richter with grape TA, wine phenolics and alcohol % and the attributes “astringent” and “black fruit” in the other season. In addition, low quality rootstocks Ramsey and 99 Richter were associated with ‘light’ and ‘simple’ attributes used by the expert winemaker panel. These findings have implications for rootstock selection management decisions and how we assess research wines for commercial application. This study has led to a greater understanding of how rootstocks impact reproductive performance and will help the Australian and international wine industries make decisions on rootstock selection, especially for sites and cultivars where reproductive development could be limited.