Characterization of the reproductive performance of a collection of grapevine cultivars

Abstract

Genetic, physiological and environmental factors interact to determine the number of flowers in the inflorescence and the fruitset rate of grapevine. Abnormal behavior in reproductive performance may cause coulure or millerandage, which may affect yield. In this work, the reproductive performance of a set of 120 wine-grape and table-grape cultivars was studied in two consecutive growing seasons (2016 and 2017). Reproductive performance was measured in ten inflorescences from different plants in each cultivar. It included flower number per inflorescence, berry number per bunch, fruitset rate, coulure index, and millerandage index. The number of flowers per inflorescence was estimated from the number of flower caps collected in fine mesh bags set just before bloom. After flowering, flower caps from each individual bag were scanned and the digital images were used for manual or automatic counting, using a specially dedicated tool developed with ImageJ software. The same clusters used for flower counting, conveniently tagged, were cropped at harvest time, and several bunch components were measured. The average fruitset rate among all the cultivars was about 44%. The range of variation among cultivars was very high for fruitset, more than 90% every year. Differences in fruitset between seasons were also very variable among cultivars, with an average difference of around 9-10% and a range of 0-40%. Regarding coulure and millerandage, there was also great variability among cultivars, while, between seasons, they were stable: on average, about 1 point of difference on a scale of 0-10. The results obtained for these reproductive performance variables allowed us to establish a preliminary clustering of the cultivars in three separate classes. The high variability found for these key parameters between grapevine cultivars provides a very suitable base to study the genetic processes involved in grapevine reproductive performance.