Mating Types of Phytophthora infestans Isolates and Their Responses to Metalaxyl and Dimethomorph in Korea

Abstract

Phytophthora infestans was isolated from potato leaves collected from main potato producing areas in Korea during 2009-2011. In 2009, 99 isolates tested were all A1 mating type. Two of 64 isolates in 2010 and two of 78 isolates in 2011 were A2 mating type and they were found only in Miryang area. Among 99 isolates examined in 2009, 13.1% was resistant to metalaxyl, 3.1% was intermediate resistant and 83.8% was sensitive. In 2010, 19.4% of 62 isolates was resistant, 4.8% was intermediate and 75.8% was sensitive. Metalaxyl resistant, intermediate and sensitive isolates collected in 2011 were 23.1%, 9.0% and 67.9%, respectively. Metalaxyl resistant isolates increased mainly in winter cropping areas and seed potato producing areas where fungicides were sprayed more often. Frequencies of isolates showing minimum inhibition concentration of dimethomorph at 1.0-5.0 mg/ml were 17.2% in 2009, 19.0% in 2010 and 15.4% in 2011. However, there was no evidence for occurrence of resistant isolate to dimethomorph because no isolate was able to grow at 5.0 mg/ml.

Genotypic and phenotypic characterization of Phytophthora infestans in South Korea during 2009–2016 reveals clonal reproduction and absence of EU_13_A2 genotype

“…No isolates resistant to dimethomorph were detected in different years and sample locations in the present study. Similarly, Kim et al (2014) reported that there were no isolates collected in South Korea from 2009 to 2011 that could grow on 5 µg/ml dimethomorph, while Gisi and Sierotski (2015) stated that, to date, no field isolates of any Phytophthora sp.resistant to CAA (carboxylic acid amide) fungicides (the group to which dimethomorph belongs) have been discovered. The South Korean P .…”

“…infestans genetic diversity than the other production regions. In this region, potatoes are grown in plastic tunnels during the winter season when late blight is more prevalent than in other regions because of high humidity and low temperatures (Kim et al , 2014). Frequently applied chemical control measures, including the use of metalaxyl, may have generated sufficient variable selection pressure to result in slightly more genetic diversity.…”

“…Intermediate isolates exhibited growth greater than 40% of the nonamended media control at 5 mg/L, but less than 40% of the nonamended media control with metalaxyl at 100 mg/L. Resistance was defined as over 40% growth on metalaxyl at 100 mg/L compared with nonamended media (Kim et al , 2014). Two replicates were included for each isolate.…”

“…All isolates were grown on Petri dishes containing 0, 1, or 5 mg/L dimethomorph as described above. The relative growth rate of dimethomorph‐sensitive isolates was reduced to below 40% on 1 mg/L dimethomorph (Kim et al , 2014).…”

“…Late blight management during the growing season is therefore primarily based on frequent applications of fungicides. Commonly, fungicides containing metalaxyl or dimethomorph are sprayed 5–10 times during cultivation of the summer‐ and winter crops to prevent or cure infection (Kim et al , 2014).…”