Pathogen, Incidence Regulation And Chemical Control Of Peach Shoot Blight

Peach shoot blight is an increasingly serious disease in southern China such as Jiangsu and Zhejiang provinces in recent years. In order to control the disease effectively, the pathogen was identificated, and its biological characteristics, the infection and occurrence regulation and the chemical control of the disease were studied in this paper.The isolates were obtained by tissue isolation of the diseased twigs in peach orchards of Wuxi, Jiangsu and Nanhu, Zhejiang. According to their cultural characteristics and morphology of pycnidia and conidia, these isolates were identificated as Phomopsis amygdali, which was verified by ITS analysis of rDNA. The ITS sequences (GenBank Accession No. JX081273 and JX182974) had 99% similarity with P. amygdali isolate FAU1052 (Accession No. AF102998) causing the disease in the southeastern United States of America. The isolates could cause typical symptom of peach shoot blight by the wound inoculation in the laboratory and in the filed, and could also cause peach fruit rot, but could not infect peach leaves.The biological characteristics of the pathogen such as mycelial growth and conidial germination were detected. The results showed that the optimum temperature for the mycelial growth was 25℃. Potato dextrose agar (PDA) medium was the best among the 4 media. The optimum pH value was 6.0 to 7.0, and 12 hour illumination each day was suitable for the mycelial growth. The optimum carbon source of the mycelial growth was sucrose and glucose, and the optimum nitrogen source was peptone and beef extract. PDA was the best for pycnidia and conidia production. The rate of conidial germination was highest in the condition of 25℃, pH 6.0～7.0,12 hour illumination each day, and more than 95% relative humidity.The field investigation in Wuxi, Jiangsu showed that there was obvious difference in the disease incidence among peach varieties, for example, "Liutiaobaifeng" (the diseased twig rate of 42% in 2013 and the rate of 13% in 2014) was more susceptible than "Hujingmilu" (the diseased twig rate of 28% in 2013 and the rate of 5% in 2014). The disease incidence in the below part of the trees was significantly higher than in the upper. The peak period of the disease incidence occurred in late June to July.The pathogen could overwinter on diseased twigs in the field trees, indoor, on soil surface and in soil tillage layer (20 cm). In general, the pycnidia and conodia were formed on diseased twigs in early March. The spore capture results showed that the conidia begined to be released in middle March, and the peak period for the release was from late March to middle April. After that, the released spores decreased gradually. The spores released were obviously increased after the rain. The spores above-mentioned were initial infection source. The pycnidia and conodia were in the field observed to form second time in late June, and might make secondary infection, but the spores was negligible to the disease epidemic, because they could only infect twigs.The virulence of 15 fungicides against the pathogen was tested in the laboratory by the method of mycelial growth inhibition, and some fungicides with high virulence were selected to be used in the field control trials. Among these fungicides, prochloraz had the strongest virulence, with EC50 value of 0.0047 μg/mL, and carbendazim, difenoconazole and diniconazole had better antimicrobial effects, with EC50 values of 0.0276 μg/mL,0.0692 μg/mL and 0.0762 μg/mL, respectively. The field control trials showed that prochloraz 40% EW (800-fold dilution) was the best to prevent diseased twigs and blight ones, with the control efficacy of 95.7% and 89.4% 15 days after three times of the spray, respectively, and with the efficacy of 90.4% and 88.5% 40 days after the spray. The control efficacy of carbendazim 50% WP (500-fold dilution) and difenoconazole 10% SC (600-fold dilution) was 70%～80% 40 days after the spray.