Evaluation of the predictive capacity of different bunch compactness indexes during two consecutive vintages

Abstract

Bunch compactness can affect the quality of wine and table grapes by favoring certain conditions that promote the development ofimportant grape pests (i.e.: Botrytis cinerea, Lobesia botrana). Besides, high values of compactness may hinder an adequate sun irradiation of the berries, generating a heterogeneous ripeness of the bunch. Both effects rnay lead to a reduction of crop yield and fruit quality, which, consequently, may drop economic profits. In spite of its agronomic and commercial relevance, little is known of its genetic basis, partially due to the lack of a quantitative and objective system of evaluation needed for an accurate phenotyping. This trait is commonly evaluated according to the visual descriptor proposed by the O.I.V., which does not provide an adequate quantitative and objective measurement, hindering this type of studies. To sol ve it, different indexes based on different architectonical elements of the bunch are found in literature. In this survey, sorne ofthese indexes have been tested in a large sample ofbunches of different grapevine varieties during two consecutive vintages (2011 and 2012, 1040 and 1145 bunches, respective1y), together with new indexes designed here for the estimation of this trait, evaluating their correlation with the opinion given by a visual evaluation panel of experienced judges. Sorne indexes designed in this survey proved to be more suitable and consistent for the obtaining of quantitative, continuous and objective data of this trait than those previously reported in literature, so they are proposed as interesting tools for the phenotyping ofbunch compactness. One ofthem, based on the mathematical combination of two easy-to-measure characteristics of the bunch, could be useful for the rapid estimation of this trait, whereas the rest could be more suitable for research studies.