Thesis Abstract of AGS Students

Dong Ruihua (1997)

In Yunnan, the People’s Republic of China, low quality apple fruit accounts for 45% of total production. Preliminary data indicated that low fruit quality might be caused by boron (B) deficiency. A field experiment and a field survey were conducted to 1) evaluate effects of B fertilizer on apple B status and fruit quality; 2) establish the relationship between apple B status and fruit quality.

The field experiment was conducted in an apple (Malus domestica Borkn. cv.Golden Delicious) orchard in Yunnan. At full bloom, 4 levels of borax: 0 (B0), 40 (B40), 80 (B80) and 160 (B160) g tree^-1 were applied on 4 replicate trees. Fruit were harvested from each treatment when 50% of fruit skin area in B0 trees became yellow. Boron deficiency delayed fruit ripening as indicated by delays in fruit color development, and a reduction of fruit firmness. Thus, fruit in B40, B80 and B160 trees were harvested 2, 5 and 10 days respectively, beyond the same stage of ripening.

Increasing B supply generally increased B concentration in leaves, shoots and fruit; shoot length, fruit diameter, fruit length, fruit weight, fruit total sugar, seed number fruit^-1 and yield but decreased titratable acidity, soluble solids and fruit drop. Maximum yield, fruit weight, fruit size and high fruit quality were obtained in B80 trees, suggesting that 80 g borax tree^-1 was sufficient for maximum yield of high fruit quality. In addition, maximum net income, rate of return and borax efficiency were also obtained in B80 trees.

Trees with B concentrations in shoot, border and central flower and young open leaf at full bloom being equal to or lower than 37, 28, 32 and 24 mg kg^-1 dry wt., respectively exhibited with B deficiency at the late reproductive stage. Yield and total sugar at harvest reached maximum when leaf and fruit B concentrations at 4 weeks after full bloom (4W) were equal to or higher than 16 and 14 mg kg^-1 dry wt., respectively whereas they were below maximum when leaf and fruit B concentration were lower than 14 mg kg^-1 dry wt..

Fruit tended to drop when its B concentrations were lower than 13 and 9 mg kg ^-1 dry wt. at pea-size drop (4W) and June drop (8W), respectively. At harvest, yield and total sugar reached maximum when B concentrations in leaf and fruit core were equal to or higher than 21 and 22 mg kg^-1 dry wt, respectively whereas they were below maximum when leaf and fruit core B concentration were lower than 17 and 22 mg kg^-1 dry wt., respectively.

The field survey was undertaken in Zhaotong, Kunming and Lijiang districts of Yunnan province. At fruit maturity, fruit and leaves in 60 Golden Delicious apple orchards were sampled. Similar to the field experiment, weight, length, diameter of fruit and seed number per fruit increased with increasing leaf or fruit B concentration whereas fruit firmness and soluble solids decreased with increasing leaf or fruit B concentration. Only 22% of surveyed orchards had leaf B concentration being equal to or higher than 21 mg kg^-1 dry wt. being sufficient B level for high fruit quality.

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