Identification and fungicide screening of fungal species associated with walnut anthracnose in Shaanxi and Liaoning provinces, China

Abstract

Walnut is cultivated around the world for its precious woody nut and edible oil. Recently, walnut infected by Colletotrichum spp. resulted in a great yield and quality loss. In August and September 2014, walnut fruits with anthracnose were sampled from two commercial orchards in Shaanxi and Liaoning provinces, and five representative isolates were used in this study. To identify the pathogen properly, four genes/region (internal transcribed spacer, glyceraldehyde-3phosphate dehydrogenase, actin, and chitin synthase) were sequenced and used in phylogenetic studies. Based on multi-locus phylogenetic analysis, five isolates clustered with C. fioriniae including its ex-type with 100% bootstrap support. The results of multi-locus phylogenetic analyses, morphology and pathogenicity confirmed that C. fioriniae was one of the walnut anthracnose pathogens in China. All 13 fungicides tested inhibited mycelial growth and spore germination. Flusilazole, fluazinam, prochloraz, and pyraclostrobin showed the strongest suppressive effects on the mycelial growth than the others, the average EC50 values were from 0.09 to 0.40 μg/mL, and there was not any significant difference (P < 0.05). Pyraclostrobin, thiram, and azoxystrobin were the most effective fungicides on spore germination (P<0.05), and the EC50 values ranged from 0.01 to 0.44 μg/mL. Pyraclostrobin, azoxystrobin, fluazinam, flusilazole, mancozeb, thiram, and prochloraz exhibited good control effect on walnut anthracnose caused by C. fioriniae, and preventive activities were greater than curative activities. Pyraclostrobin at 250 a.i. μg/mL, and fluazinam 500 a.i. μg/mL provided the highest preventive and curative efficacy and the values were from 81.3% to 82.2%, from 72.9 % to 73.6 %, respectively. As a consequence, mancozeb and thiram could be used at the preinfection stage, pyraclostrobin, azoxystrobin, flusilazole, fluazinam, and prochloraz could be selected at the early stage, for effective prevention and control of walnut anthracnose caused by C. fioriniae. The results will provide more significant instruction for controlling the disease effectively in Northern China.