Responses of fruit growth, quality, and productivity to crop load in apple cv. Ultra Red Gala/MM111

Abstract

The effects of three crop load densities (4, 6 and 8 fruit per cm 2 of the cross-section of each tree branch, BCSA) on fruit growth, yield, fruit quality and vegetative growth were studied in apples ( Malus × domestica Borkh) Ultrared Gala/MM111, from the fourth leaf (2006–2007 season) to the sixth (2008–2009 season). The maximum fruit growth rate was reached between 90 and 108 days after full bloom (DAFB), with values above 2.6 g day −1. Accumulated yields to the sixth leaf reached 181, 157 and 123 Mg ha −1 in the high, medium and low crop loads, respectively. Mean fruit weight decreased with increasing fruit crop load but the yields of fruit weight over 194 g were similar in all crop loads; the highest crop load exceeded the lowest crop load by 18.8 and 27.5 Mg ha −1 of fruit weight of more than 172 and 154 g, respectively. The yields of harvested fruit exceeding 75% with red coloring did not show major differences, while fruit classified as 50–75% with red coloring were less common in the low crop load. No major differences were found at the end of the study in vegetative growth in the different seasons, nor in plant size. The reduction in mean fruit weight and in the percentage of fruit with good coloring was compensated by the increase in yields, thus not resulting in an effective reduction in the quality of the harvested fruit. The level of plant development reached with a semi-vigorous rootstock and high fruit loads allowed obtaining high fruit yield earlier and of good quality.