Reproductive performance of C abernet S auvignon and M erlot ( V itis vinifera L .) is affected when grafted to rootstocks

Background and Aims C abernet S auvignon and M erlot are V itis vinifera cultivars known to be susceptible to poor fruitset in cool climates ( MJT 19° C –20.9° C ). The importance of rootstocks in viticulture is well documented, particularly in relation to yield, salinity and water relations; little is known, however, about how rootstocks affect reproductive performance. This study assessed the reproductive performance of C abernet S auvignon and M erlot grafted to rootstocks. Methods and Results C abernet S auvignon and M erlot grafted to rootstocks, R amsey, 5 C T eleki, S chwarzmann and 1103 P aulsen, were assessed for reproductive performance over three consecutive growing seasons. This was measured by assessing the following: bud fruitfulness, flower number per inflorescence, fruitset (%), berry number per bunch, coulure index ( CI ), and millerandage index ( MI ). Fruitset was higher when grafted to rootstocks compared to that of ungrafted vines which corresponded to a decrease in MI and CI . For C abernet S auvignon, there were no observed differences in fruitset, however, fruitfulness and bunch number were higher when grafted to rootstocks compared to ungrafted vines. Conclusion Rootstocks affect fruitfulness and fruitset in C abernet S auvignon and M erlot, however, reproductive performance differs between cultivars when grafted to the same rootstock. Significance of the Study Rootstocks may be used as a management tool to manipulate the reproductive performance of C abernet S auvignon and M erlot in cool climates.