Effects of prohexadione calcium on growth and fruit quality of Fuji apple

Abstract:【Objective】In order to provide a theoretical basis for reasonable growth of Fuji apple trees, the tree growth and fruit quality after treatments with growth retardants were compared【. Methods】Sev- en treatments were set up: CK (clean water), T1 (PBO diluted with 100 times water), T2 (PBO diluted with 200 times water), T3 (PBO diluted with 300 times water), T4 (100 mg·L-1 prohexadione calcium), T5 (300 mg · L- 1 prohexadione calcium) and T6 (500 mg · L- 1 prohexadione calcium). In the mid- June, the leaves of the whole trees were sprayed until the solution on leaves was dripping. Each tree served as one plot, and each treatment was repeated for three times. Before spraying, ten current shoots from each tree were selected and marked, and the length and diameter were measured. The diameter was measured at the position 1cm away from the base. The growth of the shoots was photographed one month after spraying. The length and diameter of the 10 shoots of each tree were measured after fruit harvest. The chlorophyll content was determined by the SPAD-502 chlorophyll meter in mid-August. Healthy and mature leaves were taken from the middle part of the sprayed shoots, and 10 leaves were taken from each replicate. The photosynthesis index was measured by the CIRAS-3 portable photosynthesis instru- ment (PP system company in the United States) from 8:00 to 10:00 in the morning of a sunny day. Fruit samples were collected in late October during fruit ripening period and taken back to the laboratory to determine single fruit weight, L/D index, soluble solids content, fruit hardness, titratable acid content, etc.. Single fruit weight was measured by a balance, L/D index was measured by a vernier caliper, solu-ble solids content was measured by the atagopal-1 digital sugar meter, fruit firmness was measured by the Gy-1 fruit firmness meter, Vc content was measured by 2, 6-dichlorophenol indophenol titration method, titratable acidity was measured according to GB/T 12456—2008. Ten fruits were randomly selected from each replicate. The fruit color was measured by NR60CP, and the C, h, L*, a*and b* were calculated. The average value of each data measured at 3 points of each fruit was taken. Excel was used to sort out the experimental data, SPSS 22.0 was used to analyze the variance. The fuzzy membership function method was used to evaluate the effect of different treatments.【Results】The effect of 300 mg·L-1prohexadione calcium treatment was better than that of others. Compared with the control, the current shoot length decreased by 50.88% and the shoot diameter increased by 400%; the relative chlorophyll content increased by 3.66%, net photosynthetic rate increased by 15.09%, stomatal conductance in- creased by 24.74%, transpiration rate increased by 20.97%, and intercellular CO2 concentration de- creased by 6.06%; the single fruit weight, soluble solids content and Vc content increased by 26.24%, 2.36% and 53%, respectively, the fruit surface brightness value L* increased by 2.18%, the fruit hard- ness, titratable acid content, yellow saturation b*, color saturation C, hue angle h and other indicators had no significant difference, compared with other treatments. The fuzzy membership function method was used to rank the main measurement indexes. The rank in a descending order was T5 (300 mg · L- 1prohexadione calcium) > T3 (PBO diluted with 300 times water) > T4 (100 mg·L-1 prohexadione calci- um) > T6 (500 mg·L-1 prohexadione calcium) >T2 (PBO diluted with 200 times water)>T1 (PBO dilut- ed with 100 times water)>CK (clean water). Among the treatments, PPO diluted with 300 times water was the second. Compared with the control, the current shoot length decreased by 8.38%, the shoot di- ameter increased by 167%, the relative chlorophyll content increased by 2.74%; the net photosynthetic rate increased by 16.78%, the stomatal conductance increased by 28.49%, the transpiration rate in- creased by 30.40%, the intercellular CO2 concentration decreased by 13.18%; the single fruit weight in- creased by 8.96%, the soluble solids content increased by 3.46%, the VC content increased by 143%; and the fruit surface brightness value L* increased by 1.04%, red saturation a* increased by 2.19%, and yellow saturation b* increased by 2.69%.【Conclusion】The examined indexes of the treatments were ba- sically better than those of the control to varying degrees. Spraying PPO and prohexadione calcium at different concentrations, the current shoot length was less than the control, the shoot thickness was greater than the control, the net photosynthetic rate, the relative chlorophyll content, the single fruit weight, the Vc content and the peel brightness value L* were better than those of the control to varying degrees. The results showed that PPO and prohexadione calcium can control tree growth and improve some physiological indicators and fruit quality. Among them, spraying 300 mg · L- 1prohexadione calci- um can increase the currentshoot thickness, inhibit shoot vigorous growth, increase chlorophyll content, single fruit weight and L/D index, and improve fruit finish, it was the best to evaluate by membership function method.