Increase of fruit set and yield of 'Rocha' pear trees

Low fruit set is one of the main factors leading to low yields of the pear orchards in Brazil. Exogenous application of plant growth regulators (PGRs) shows great potential to overcome this problem. Recent studies have shown great promise of several ethylene inhibitors in increasing fruit set and yields of several fruit species. The objective of this study was to evaluate the effect of several PGRs sprayed at different timings on fruit set, yield, and fruit quality of 'Rocha' pear in southern Brazil. The study was performed during the 2016/2017 growing season using five-year-old 'Rocha' pear trees on 'BA29' quince rootstock. Treatments consisted of an untreated control, aminoethoxyvinilglycine (AVG) 60 mg L-1 applied 1+2 weeks after full bloom (WAFB); cobalt (Co) 25.6 mg L-1 + molybdenum (Mo) 38.4 mg L-1 sprayed at full bloom (FB), 1 WAFB, 2 WAFB, 1 + 2 WAFB or FB + 1 + 2 WAFB; and kinetin (Ki) 0.18 mg L-1 + gibberellic acid (GA(3)) 0.1 mg L-1 + indolebutyric acid (IBA) 0.1 mg L-1 sprayed at FB or FB + 1 WAFB. Fruit set, number of fruit tree(-1), yield, average fruit weight, fruit length (L), fruit diameter (D), L/D ratio, seed number, flesh firmness and soluble solids content were assessed. Fruit set and yield were increased by all treatments except Ki + GA(3) + IBA sprayed at FB in total number of fruit at harvest, number of thinned fruit and yield compared to control trees. The greatest increase in yield was observed with AVG. Average fruit weight of all treatments, except Co + Mo (FB), was reduced compared to control trees, likely due to the increased crop load.