2018 ASHS Annual Conference

Low fruit set is a major concern of pear orchards in warm-winter climates like Southern Brazil, often leading to poor yields. In major pear producing regions of the northern hemisphere, specific cultivars have a tendency for low fruit set, primarily during their early years, despite receiving adequate chill. Exogenous application of plant growth regulators (PGR) is one strategy employed to overcome this problem, though many compounds have been inconsistent. Aminoethoxyvinilglycine (AVG), an ethylene synthesis inhibitor, has shown promising results for several cultivars. The objective of this study was to evaluate different rates and timings of AVG on yield components of pear trees grown in two markedly different climates. In 2015, 20-year old ‘Packham’s Triumph’ (2 x 5 m; 1000 trees ha^-1) were sprayed with AVG (60 mg L^-1) 7 days after bloom (DAFB). In 2016, 5-year old ‘Rocha’ (0.7 x 3.5 m; 4082 trees ha^-1) were sprayed with AVG (60, 80 and 100 mg L^-1) 7 and 14 DAFB. Both orchards were located in Southern Brazil and were grafted on Pyrus calleryana rootstock. In Hood River, Oregon, twelve experiments were conducted between 2012 and 2016 using variable AVG rates and application timings to the cultivars ‘d’Anjou’ and ‘Comice’. Orchards varied in tree age and planting density. All experiments were arranged in randomized block designs generally comprising four to six single-tree replications. A nonionic surfactant [0.05% (v:v)] was used in all studies and solutions were sprayed to whole trees. Fruit set and yield components of ‘Packhams’s Triumph’ were increased by AVG. Similarly, AVG significantly and linearly increased fruit set and yield components of ‘Rocha’ regardless application timing. However, a greater increase was observed when treatments were sprayed 7 DAFB. Fruit size was slightly reduced as AVG rate increased, probably as an indirect result of crop load. In Oregon, AVG-treated trees had significantly greater fruit set in 65% of the experiments. Full bloom applications were ineffective. Natural ethylene production rates of non-treated flowers and fruitlets peaked at 14 DAFB, irrespective of cultivar or year, and were reduced considerably by AVG. The effect of AVG on ethylene production persisted for 10 to 20 days after application and was rate-responsive. AVG applications between 7 and 14 DAFB were, generally, efficacious. Based on these results, AVG is a promising PGR to improve fruit set and yield of ‘Packham’s Triumph’ and ‘Rocha’ pears grown in Southern Brazil, and ‘d’Anjou’ and ‘Comice’ pears in Northwest USA.