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 1.5×4.8m, grafted onto Pyrus calleryana. Different P-Ca rates were applied (100, 200, 300, 400mgL−1) in different biological stages: first in early spring (shoots ∼2.5 and 5cm 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 ∼90days 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 200mgL−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 30days of regular air cold storage (RACS)+3days of ripening period (RP) in both seasons. These results implicate P-Ca as a potential tool to manage vigor of ‘Le Conte’ pear tr