Classification of reproductive performance of ten winegrape varieties

Background and Aims:  Flowering and fruitset are principal determinants of grapevine yield. Poor fruitset is said to limit the yield of many varieties in most regions in Australia; however, there is a lack of knowledge of the reproductive performance of most varieties under Australian conditions. Methods and Results:  The reproductive performance of Vitis vinifera winegrape varieties – Cabernet Sauvignon, Chardonnay, Merlot, Nebbiolo, Pinot Noir, Sangiovese, Sauvignon Blanc, Shiraz, Tempranillo, and Zinfandel – was studied in four consecutive growing seasons (commencing in 2004/05) across a range of climatic regions from cool (Adelaide Hills) to warm (Adelaide Plains). Measures of reproductive performance included flower number per inflorescence, fruitset (%), berry number per bunch, coulure index (CI), and millerandage index (MI). Principal component analysis and agglomerative hierarchical classification were used to group the varieties into three classes of reproductive performance. Conclusions:  Certain varieties have a reputation of having ‘poor fruitset’ that has been inferred from relatively low berry number per bunch; however, for some of these varieties, it is ‘low flower number per inflorescence’ rather than ‘poor fruitset’ that is the cause of low berry number. Significance of the Study:  An improved understanding of the reproductive performance of winegrape varieties has been achieved.