Sensitivity and cross-resistance of pathogen of Amomum tsao-ko leaf spot to new low-toxic fungicides

【Objective】 To screen environmentally friendly low-toxic pesticides to prevent and control leaf spot diseases of Amomum tsao-ko，so as to provide scientific basis for A.tsao-ko leaf spot prevention and control and planting of A.tsao-ko.【Method】 Pathogens of 3 kinds of A.tsao-ko leaf spot（anthracnose，leaf blast and leaf spot disease），Colletotrichum sp.，Pyricularia grisea，and Phoma sp.were taken as material.Mycelial growth rate method was used to determine the sensitivity and virulence coefficient of variation of 6 medicaments（pyrimethanil，myclobutanil，prochloraz，mancozeb，azoxystrobin and penthiopyrad）；through cross-resistance analysis between medicaments，combinations of medica-ments with better synergistic effects were screened.【Result】Penthiopyrad and prochloraz had the strongest virulence to Colletotrichum sp.and P.grisea，and their EC₅₀ was significantly different from that of other medicaments（P<0.05）.The average EC₅₀ values of penthiopyrad and prochloraz against Colletotrichum sp.were 0.04 μg/mL and 0.08 μg/mL，respectively，mycelial growth inhibition rate of penthiopyrad on Colletotrichum sp.was above 61.68%，and its highest value was 93.57%.Six medicaments had strong virulence to Phoma sp.，with a EC₅₀ of 0.17-4.99 μg/mL，among which prochloraz and azoxystrobin had the strongest virulence.The results of virulence variation coefficient analysis of 6 medicaments against 3 pathogens showed that penthiopyrad and prochloraz had strong virulence，but their variation coefficients were high，indicating they worked differently for pathogens.Based on the correlation analysis of the lgEC₅₀ of penthiopyrad，prochloraz and myclobutanil，these 3 medicaments had high cross-resistance（P<0.01）；penthiopyrad and prochloraz had little interaction resistance with pyrimethanil，mancozeb and azoxystrobin.【Conclusion】Compound agent of single agent of penthiopyrad or prochloraz with pyrimethanil，mancozeb and azoxystrobin can be used as a new low-toxicity control agent for prevention and control of A.tsao-ko leaf spot in planting.