Pathogen, Biological Characteristics And Chemical Control Of Peach Black Spot

Peach black spot is a new increasingly serious disease in Qin’an county, Tianshui City, Gansu Province in recent years. In order to control the disease effectively, the pathogen was identificated, and its biological characteristics 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 Qin’an, Gansu. According to their cultural characteristics and morphology of pycnidia and conidia, these isolates were identificated as Alternaria armeniacae, which was verified by internal transcribed spacer (ITS) analysis of rDNA. The ITS sequences (GenBank Accession No. KT154831) had 99%similarity with Alternaria spp. The isolates could cause typical symptom of peach black spot by the wound inoculation in the laboratory and in the filed, and could also cause peach fruit block spot, but could not infect peach leaves. The pathogen can infect not only peach but also plum, apricot and cherry fruit,but can’t infect pear and apple fruit.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 30℃. 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 maltose and starch, and the optimum nitrogen source was leucine and methionine. PDA was the best for conidial formation. The rate of conidial germination was highest in the condition of 25℃, pH 6.0-7.0,12 hour illumination each day.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 0.0929 ug/mL, and azoxystrobin of ammonia, hexaconazole and tebuconazole had better antimicrobial effects, with EC50 values of 0.1936ug/mL,0.2001ug/mL and 0.9917 ug/mL, respectively. In 2014 the field control trials showed that prochloraz 25%EW (500-fold dilution) was the best to prevent diseased twigs and blight ones, with the control efficacy of 98%12 days after the spray. The control efficacy of prochloraz 25%EW (1000-fold dilution) and hexaconazole 5%SC (1000-fold dilution) was 96.8%after the spray. In 2015 the field control trials showed that prochloraz 25%EW (1000-fold dilution) and hexaconazole 5% SC (1000-fold dilution) was the best to prevent diseased twigs and blight ones, with the control efficacy of 97.38%33 days after the spray. The control efficacy of prochloraz 25%EW (1000-fold dilution) was 95.89%after the spray.