Ethephon as a blossom and fruitlet thinner affects crop load, fruit weight, fruit quality, and return bloom of 'summerred' apple (Malus xdomestica) Borkh.

摘要

Summerred apples are highly susceptible to biennial bearing if not properly thinned. This results in erratic yields and also affects fruit quality adversely. Between 2003 and 2005, summered/M9 trees were treated with ethephon at concn. of 250, 375 and 500 mg l--1 when most king flowers opened (20% bloom) or at concn. of 500, 625 and 750 mg l--1 when average fruitlet size was 10 mm in diam. The experiment was conducted with 2.5-m height slender spindle trees sprayed to the point of runoff with a hand applicator only when temp. exceeded 15 degrees C. Within 2 wk after the 2nd application, fruit set was reduced linearly with increasing concn. of ethephon to <1 fruitlet per cluster at the highest concn. used. Most thinning treatments reduced fruit set significantly compared with unthinned trees. Fruit numbers per tree decreased significantly with increasing ethephon concn., and the highest concn. of ethephon applied during bloom or when average fruitlet size was 10 mm in diam. resulted in overthinning. Yield results confirmed the fruit set response in which yield reductions were significant at the highest concn. of ethephon (2.1 kg/tree) compared with hand-thinned trees (7.3 kg/tree) in 2005. All thinning treatments resulted in a higher percentage of fruits larger than 60 mm in diam. compared with unthinned control fruit. Thinning resulted in significantly higher soluble solid contents, and this was especially so for hand-thinned trees. Other fruit quality parameters like yellow-green background colour did not show a clear response to thinning. Return bloom was, however, improved on all thinned trees. It is recommended that ethephon be applied at a rate of 375 mg l--1 when king flowers open or at a rate of 625 mg l--1 when average fruitlet size is 10 mm in diam. This thins summerred apples to a target of approx. 5 fruits/cm2 per trunk cross-sectional area or 50-70 fruits per 100 flower clusters without impacting on fruit quality, yield, or return bloom the next yr.