Preharvest Watersprout Removal Influences Canopy Light Relations, Fruit Quality, and Flower Bud Formation of `Redskin' Peach Trees

Three separate blocks of mature, nonirrigated trees of 'Redskin' peach ( Prunus persica (L.) Batsch) on 'Lovell' rootstock, all uniformly dormant-pruned to an open center, were summer pruned 43, 31, and 21 days before harvest (DBH) in 1988, 1989, and 1990, respectively, and compared to unpruned controls in respect to light penetration and fruit characteristics. Summer pruning consisted of watersprout removal (WSR), selectively including all shoots more upright than 45° on scaffolds from the crotch to the top of the tree. WSR increased photosynthetic photon flux density (PPFD) in the center of the fruiting zone of the canopy to four times the level measured in unpruned trees, but only to an average of 16% of above-canopy PPFD. The greatest effect of WSR on PPFD occurred in the center of the tree, increasing light levels from <10% full sun before WSR to 90% full sun following WSR. WSR resulted in higher PPFD in the center of the tree for the remainder of the season. Fruit ground color and red pigmentation were not affected by WSR. WSR increased the percentage of fruit that exceeded 62 mm in diameter and decreased the percentage of fruit < 55 mm in diameter in 1988 and 1990. In 2 of the 3 years, WSR increased flower count per cm shoot length in the fruiting zone of the canopy. Optimum fruit production involves maximizing distribution of photosynthates to fruit for optimum yield and quality while con- trolling vegetative and root growth at minimum plant level require- ments (Chalmers et al., 1981). In fruit trees, control of photosyn- thate distribution is attempted by genetic, growth regulator, and cultural manipulation. In the absence of genetic or growth regula- tor control, peach trees in many production areas are characterized by an inefficient distribution of photosynthate s to fruit compared to vegetative growth (Walsh et al., 1989). The open-center tree training system, still common in many production areas, promotes the distribution of photosynthate s to vegetative growth (Myers, 1988). This system involves training primary scaffolds out at various orientations, primarily with prun- ing. By design, the tree center is open, with no central axis above the origin of the scaffolds from the trunk. In the absence or reduction of apical control, coupled with use of severe pruning, open center peach trees tend to restore a rounded tree crown via apical response, resulting in the production of vigorous watersprouts along the upper side of scaffolds concentrated at pruning cuts and horizontal areas. The architecture of open center peach trees influences the canopy light environment, with light levels highest at the tree periphery, intermediate in the tree center, and lowest halfway between the tree center and periphery (Marini and Marini, 1983). Peach redness has been correlated linearly with the percentage of full sun to which fruit was exposed (Rom et al., 1984). Light exposure of fruit in the final stages of fruit development increased red pigmentation, possibly due to increased fruit sink strength (Erez and Flore, 1986). The greatest negative effect on peach fruit weight and quality occurred when fruit were shaded during the