Study On Bacteriostatic Mechanism And Control Of Wood Tar On Apple Valsa Canker

Apple valsa canker, caused by Valsa mali, often lead to tree bark rot, hinder nutrient transport, affect the growth and development of trees, decrease yield and fruit quality of apple, even cause the death of fruit tree. Wood tar as the by-products of biomass pyrolysis contains rich antimicrobial active substances, and can inhibit the growth of many plant pathogens. What is more, it has good cohesiveness and waterproof properties, therefore is very suitable for controlling apple canker. This study used wood tar produced by waste fruit branches slow pyrolysis as supplied test fungicides, and explored its bacteriostatic mechanism. On the basis of the bacteriostatic test, the field experiment was carried out to study the comprehensive control effects of smearing once or twice different times dilution wood tar a year after disease spots treated in different ways. In addition, to study the effects of mixture fungicides mixed with wood tar, IAA and thiophanate-methyl for inhibiting the growth of Valsa mali, controlling apple canker in detached twigs and promoting wound healing on apple trunk. The research results are as following:(1) To study the bacteriostatic mechanism of wood tar for inhibiting the growth of Valsa mali. The results showed that the concentrations of wood tar were positively associated with the inhibition rates of hypha and residual duration. The inhibition rates of hyphal growth and residual durations were up to 100% and 7 days respectively with 2 and 5 times dilution wood tar. The morphological abnormalities were observed in the hyphae body of Valsa mali after 100 times dilution wood tar treatment, which significantly leaded to hyphae thinner and curvier, increased amount of vacuole, destroyed hyphal dissepiment, made local hyphae swollen and fractured with the outflow of small molecules, condensed cytoplasm, inflated hyphae tip. In the end, pathogenic bacteria could not normally grow and develop, and gradually became aging and died. The inhibition rates of conidium germination were up to 100% with 50 to 100 times dilution wood tar treatments. The conidium treated by 50 times dilution wood tar completely could not develop. However, the conidium treated by 100 times dilution wood tar only vertically elongated, could not normally swell and produce germ tubes.(2) To study the effects of wood tar for controlling apple canker on field experiment. The typical low management level orchard(Ⅰ place) and high management level orchard(Ⅱ place) were selected as test places to study the control effect of different times dilution wood tar on apple valsa canker, as lime sulfur and 3% thiophanate-methyl paste were used as control fungicides respectively. The results showed that the control efficiencies of treatments of smearing twice fungicides a year after striking off disease spots in Ⅰ place and striking off or crisscrossing scratches on disease spots in Ⅱ place gradually reduced with wood tar dilution ratio increasing. The control efficiencies of treatments of stock solution and 2 times dilution wood tar were up to 100%, compared with control fungicides, and were increased by 274.5%, 49.9% and 66.7% respectively; The wound-healing effects of treatments of striking off disease spots with smearing twice fungicides a year in Ⅰ place and Ⅱ place increased initially and then decreased with wood tar dilution ratio increasing. The effects of treatments of 10 and 5 times dilution wood tar were 95.44% and 91.75% respectively, compared with control fungicides, and were increased by 38.54% and 68.78% correspondingly; Except for 5 times dilution wood tar treatment, the effects of controlling disease spots development and wound healing of treatments of striking off disease spots with smearing once fungicides a year in Ⅰ place gradually reduced with wood tar dilution ratio increasing. The effects of controlling disease spots development and wound healing of stock solution wood tar treatment were 100% and 80.76% respectively, compared with control fungicides, and were increased by 274.5% and 34.44% correspondingly.(3) To study the effects of wood tar based mixture fungicide for controlling apple canker. A L16(45) orthogonal design method was used to study the control effect of fungicides mixed with wood tar, IAA and thiophanate-methyl on apple valsa canker. The results showed that, except for the treatment of mixture fungicide mixed with 100 times dilution wood tar, 0.50‰ mg·mL-1 IAA, 1.750 mg·mL-1 thiophanate-methyl inhibiting the callus formation, the treatments of other mixture fungicides inhibited the hyphal growths, decreased the incidences on detached twigs, controlled disease spots development, promoted callus formation. Except the dominant factors of the lesion area and control efficacy of disease spots of the curative effects test in detached twigs were IAA, the dominant factors of other test indicators were wood tar. The combined method of comprehensive ranking and range analysis was used to determine that the best mixture ratio was 2 times dilution wood tar, 0.50‰ mg·mL-1 IAA and 0.700 mg·mL-1 thiophanate-methyl, compared with 3% thiophanate-methyl paste, which inhibition rates of hyphal growth, protective efficacy, curative efficacy and width of callus formation were increased by 12.25%, 349.1%, 166.8% and 73.04% respectively.