Evaluation of indexes for the quantitative and objective estimation of grapevine bunch compactness

Bunch compactness is a key factor on the determination of grape quality. The use of qualitative visual systems for its determination is quite controversial, hindering some studies that require objective and quantitative measures of the trait. Here, eleven indexes published in literature and eight designed in this survey were tested with three different criteria to determine their usefulness for the estimation of bunch compactness. A sample of 110 grape bunches of different morphology, from 11 different varieties, were classified by a panel of 14 judges according to the visual OIV descriptor No 204. Besides, a number of measures were taken from the same bunches, which were used for the indexes’ calculations. Several indexes designed here proved to be more suitable to obtain quantitative estimations for this trait in a genetically diverse set of varieties than the indexes previously published. Two of the selected indexes, CI-18 and CI-19, are based on the combination of six metrics from bunches (bunch weight, number of berries per bunch, number of seeds per berry, bunch length, first ramification length and either pedicel length or number of ramifications per bunch, respectively). These two indexes are more suitable for intervarietal studies where obtaining quantitative data is critical. Other selected index (CI-12) is based on two easy-to-measure characteristics of the bunch (weight and length), and it is proposed as a fast estimator of bunch compactness for the viticulture sector.