Effects of four physiologically active substances on the control of gray mold and fruit quality of blueberries

【Objective】Due to climate and other factors, gray mold outbreak of blueberries in South China has occurred for many years, seriously affecting blueberry fruit yield, quality and economic benefits. Emerald is one of the varieties susceptible to gray mold disease, which could suffer complete crop failure in severe cases. Chemical control is widely used in the control of gray mold of blueberries due to its low cost and fast effectiveness. However, with the abuse of chemical agents, the pathogens have developed serious resistance. Currently, using natural plant physiological active substances to induce plant resistance against gray mold disease is regarded as a new method for disease control. However, there has been few research on the use of physiological active substances in blueberry. The study aimed to screen the green control measures of gray mold in Emerald blueberry (Vaccinium spp.) in southern Anhui Province in order to improve the fruit yield and quality.【Methods】The natural plant physiological active substances effectively inhibiting the important causal organism of gray mold, Botrytis cinerea were screened through the plate confrontation test. Then, the selected four active agents salicylic acid (SA), methyl jasmonate (MeJA), chitooligosaccharide, and Bacillus subtilis were applied to field- cultivated blueberry, with a total of (0.1 mmol·L-1 , 0.5 mmol·L-1 , 1 mmol·L-1 ) SA, (0.01 mmol·L-1 , 0.1 mmol·L-1 ,0.5 mmol·L-1 ) MeJA, (1.5 g ·L-1 , 5.0 g ·L-1 ) chitooligosaccharide, 2 g ·L-1 Bacillus subtilis and the control group were applied four times in flowering stage and before the color-changing period of the fruits (the flowering period: March 22 and April 1, 2024; the period of young fruit: April 20, 2024; and the period of fruit expansion: May 10, 2024) to investigate the effects of different treatments on the incidence of gray mold in blueberry, and the effects of different treatments on the development and quality of blueberry fruits. The best group was selected by correlation analysis and principal component analysis.【Results】The four physiologically active substances could significantly inhibit the growth of gray staphylococcus mycelium. The higher the concentration of chitooligosaccharides and salicylic acid, the better the inhibition effect. And the overall inhibition effect on gray mold in the field was 0.1 mmol·L-1 SA, 5 g·L-1 chitosan, (0.50, 0.01 mmol · L- 1 ) MeJA, and 2 g · L- 1 Bacillus subtilis, in descending order. All treatments (except 5 g · L- 1 chitooligosaccharides) could significantly improve the transverse diameter and weight of blueberries in the ripening stage, and maintain their hardness without significant changes. By inhibiting the expression of the gray mold in the field and its influence on fruit development, we selected 0.1 mmol · L- 1 SA, 1.5 g · L- 1 chitooligosaccharides and 0.5 mmol· L- 1 MeJA as three treatment groups with excellent comprehensive performance. 11 key indexes were screened by principal components of 16 indexes related to the internal and external quality of ripening fruits, and further evaluated comprehensively through the weighted average of the subordinate function, which showed that the treatment groups with the effect of improving the quality of fruits from the highest to the lowest were, in descending order, 0.1 mmol·L-1 SA, 1.5 g·L-1 chitooligosaccharides and 0.5 mmol·L-1 MeJA, and all three treatments could significantly increase the glucose, fructose, total soluble sugar content, total phenolic content, as well as the DPPH free radical clearance rate of blueberry, and significantly decrease the malondialdehyde content of the fruits, and basically remain the titratable acid content unchanged. The antioxidant capacity of the fruits was mainly affected by the content of proanthocyanidins. 0.1 mmol·L-1 SA affected the enzyme activity, while 0.5 mmol· L- 1 MeJA and 1.5 g · L- 1 chitooligosaccharides could regulate the antioxidant capacity and appearance quality of the fruits by affecting the sugar content and flavonoids. All the three treatments could regulate the sweetness of the fruits through flavonoids.【Conclusion】For the prevention and control of gray mold in the field, the effect of 1.5 g ·L-1 chitooligosaccharides on reducing incidence rate of wilting inflorescence was optimal; 0.5 mmol·L-1 MeJA for reducing the ratio of moldy flowers, enhancing the effect of DPPH free radical clearance rate of ripe fruit was optimal; for the enhancement of the ripe fruit weight, transverse diameter, proanthocyanidins, total flavonoids, and total phenolic content, 0.1 mmol·L-1 SA was optimal with a small increase in the hardness of the fruits. The effect of 1.5 g·L-1 chitooligosaccharides on the total sugar, titratable acid, and glucose of the ripe fruits in each period was optimal. This study could provide theoretical and practical guidance for coping with gray mold and improving the quality and yield of the blueberry fruits in cultivation.