Productivity and Fruit Composition of Dry-On-Vine Raisin Grapes Pruned to 15- or 20-Node Canes on an Overhead Trellis

Abstract

Summary Goals: Dry-on-vine (DOV) raisin grapes are cane-pruned to allow for cane severance, which initiates the DOV process, and to maximize yield potential. Yield components of Thompson Seedless raisin grapes, including the number of clusters per node, cluster and berry weight, and soluble solids per berry, have been shown to follow particular patterns with respect to node position, and this has informed pruning practice. However, DOV raisins in California are made from varieties that ripen earlier than Thompson Seedless, and they may have different fruiting characteristics. Therefore, we conducted a study to determine how the number of nodes per cane, and node position, affected yield components of DOV raisin grape varieties. Key findings: Basal nodes produced the fewest clusters due to poorer bud break and lower fruitfulness. Fiesta was the most fruitful variety, followed by Selma Pete, and then Thompson Seedless and DOVine. Cluster fresh weight increased whereas berry soluble solids (Brix) decreased with node position, regardless of cane length. Fruit from longer canes had less soluble solids (Brix) than the fruit from shorter canes, thus cane length did not usually affect total soluble solids (fruit fresh weight x soluble solids (Brix)) per cane. Fiesta produced more fresh fruit and total soluble solids per cane than other varieties. Impact and significance: Cane length had contrasting effects on fresh fruit weight and soluble solids, with shorter canes producing less fruit with higher soluble solids, whereas long canes produced more fruit of lower soluble solids. Harvested on the same date, these effects sufficiently countered each other such that canes of different lengths produced similar amounts of total soluble solids (sugar per cane) in two of three years. In California, where early maturity is preferred to ensure adequate drying time, shorter canes may be better than longer ones. However, if cane severance can be delayed to allow the berries to accumulate more sugar, which might be possible in other growing regions, or when drying emulsion may be used to hasten drying, longer canes could potentially increase raisin yield.