APS Homepage

Poster: Biology & Disease Mgmt: Chemical Control


Fungicide resistance profiles and virulence of Stagonosporopsis species isolates from watermelon and melon in eastern China
M. NEWARK (1), N. Dufault (1), M. Paret (2), L. Pingfang (3), X. Yang (3) (1) University of Florida, U.S.A.; (2) University of Florida, U.S.A.; (3) Jiangsu Academy of Agricultural Science, China

Stagonosporopsis spp. (syn: Didymella bryoniae) is a major pathogen on cucurbits. China is the largest producer of watermelon in the world with 22% of the seed imported to the US is coming from China. The purpose of this study was to examine fungicide resistance and virulence profiles of Stagonosporopsis spp. isolates in China as a first step in understanding potential global movement of novel strains. Sixty-nine mono-conidial isolates from 4 provinces in east China were collected between 2011 and 2015. Fungicides azoxystrobin, boscalid, difenoconazole, tebuconazole, and thiophanate M were tested using an amended agar assays at the rates of 0.096, 0.034, 0.032, 0.128, and 100mg/L, respectively. Virulence was examined using a detached leaf assay with the watermelon (Citrullus lanatus) var: ‘Sugar Baby’. Leaves were inoculated with the pathogen and evaluated using a disease scale. Statistical analysis was done using R version 3.2.3 examining frequencies and distributions of fungicide resistance and virulence. All isolates found in East China were pathogenic on a US variety with many isolates having moderate (67%) or even high virulence (29%). In total, 92% of the isolates were resistant to two or more classes of fungicides. Based on these findings, it is apparent that fungicide resistance is present in eastern China and could pose a risk to the global movement of resistant strains.