Mating type and sensitivity of Phytophthora nicotianae from tobacco to metalaxyl and dimethomorph in Henan province, China

Abstract

Phytophthora nicotianae causes black shank, one of the most important diseases of tobacco worldwide. Metalaxyl and dimethomorph are two fungicides which have been used widely for control of this disease in Henan province, China. A study was conducted to determine the level of metalaxyl and dimethomorph sensitivity in isolates of P. nicotianae from tobacco in Henan province and mating type structure of the pathogen population. A total of 32 isolates were isolated from 11 cities in Henan province. Sensitivity of all isolates to metalaxyl and dimethomorph was tested in vitro, and mating types of all isolates were determined by pairing known A1 and A2 testers. For metalaxyl, EC50 values of 32 P. nicotianae isolates ranged from 0.08 to 2.82 mg/L. Sixteen isolates were sensitive, and the rest were intermediate to metalaxyl. None were classified as resistant isolates. For dimethomorph, EC50 values of 32 P. nicotianae isolates ranged from 0.07 to 0.59 mg/L. All isolates were sensitive to dimethomorph. Thirty‐one isolates were A2 mating type, and one isolate was A0 mating type. No isolate was identified as A1 mating type. These results suggested that the P. nicotianae population in Henan province has already exhibited intermediate resistance to metalaxyl and was still sensitive to dimethomorph, and asexual reproduction was the major form of reproduction for the P. nicotianae population.

Phylogeography of the wide‐host range panglobal plant pathogen Phytophthora cinnamomi

“…In Vietnam, highly unbalanced A1:A2 ratios ranging from 1:3 to 1:5 of the introduced pathogen P. capsici were found in four provinces (Truong et al, 2010). In China's Henan province all isolates of the introduced P. nicotianae recovered from tobacco plantations belonged to the A2 mating type (Cui et al, 2018) whereas all isolates of the Asian pathogen P. colocasiae obtained from taro fields in Hawaii were of the A1 mating type (Ko, 1979). An extensively studied pathogen is P. ramorum with two A2 lineages and one A1 lineage introduced into North America and two A1 lineages introduced into Europe (Grünwald et al, 2012;Van Poucke et al, 2012).…”

“…In China’s Henan province all isolates of the introduced P . nicotianae recovered from tobacco plantations belonged to the A2 mating type (Cui et al, 2018) whereas all isolates of the Asian pathogen P . colocasiae obtained from taro fields in Hawaii were of the A1 mating type (Ko, 1979).…”