Prohexadione calcium affects shoot growth, but not yield components, of 'Le Conte' pear in warm-winter climate conditions

Different studies describing Prohexadione calcium (P-Ca) as an efficient tool to reduce shoot growth have been extensively reported, but these studies are usually performed in typical temperate climate regions. However, a complete analysis of the effects of P-Ca in pear trees in regions of warm-winter climates has not been performed. Therefore, the objective of this study was to evaluate the effect of different rates of P-Ca on vegetative growth, production and fruit quality of 'Le Conte' pear trees, in warm-winter climate conditions. The experiment was conducted during the 2013/2014 and 2014/2015 seasons, in a six year old 'Le Conte' pear orchard, trained to a central-leader system, with spacing of 1.5 x 4.8 m, grafted onto Pyrus calleryana. Different P-Ca rates were applied (100, 200, 300, 400 mg L-1) in different biological stages: first in early spring (shoots 2.5 and 5 cm long) for all treatments and the others when shoot growth resumed (GR), but only for some treatments. Variables for vegetative growth, yield components and fruit quality at harvest and post-harvest were evaluated. Shoot length was measured on 10 one-year-old shoots evenly selected and tagged at the time of the first application and, then, at biweekly intervals until the end of the season. The use of P-Ca was effective to control vegetative growth in both seasons, at different rates. At 90 days after full bloom (DAFB), P-Ca treated shoots had a pronounced second flush of growth, requiring an additional application of P-Ca in both seasons. In the 2013/2014 season, the only time of P-Ca reapplication was at 93 DAFB for the rates of 100 and 200 mg L-1, which was "enough to check shoot growth throughout the season, but in the 2014/2015 season, three shoot growth flushes were observed according to P-Ca rate, requiring additional P-Ca applications. Unlike the first season, P-Ca reapplication was efficient to reduce shoot length relative to trees treated once with P-Ca. In both seasons, fruit set, number of fruits per tree, yield, average fruit weight, fruit diameter, estimated yield, return bloom, and return yield were not affected by P-Ca applications. P-Ca applications did not alter the qualitative attributes of the fruits of 'Le Conte' pear trees at harvest and when they were stored for a period of 30 days of regular air cold storage (RACS) +3 days of ripening period (RP) in both seasons. These results implicate P-Ca as a potential tool to manage vigor of 'Le Conte' pear trees in warm-winter conditions, given its efficiency to control vegetative growth without negatively affecting yield components. (C) 2016 Elsevier B.V. All rights reserved.