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Laboratory studies to assess the risk of development of resistance to zoxamide
Author(s) -
Young David H,
Spiewak Sandra L,
Slawecki Richard A
Publication year - 2001
Publication title -
pest management science
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.296
H-Index - 125
eISSN - 1526-4998
pISSN - 1526-498X
DOI - 10.1002/ps.399
Subject(s) - oomycete , fungicide , phytophthora infestans , metalaxyl , biology , mutagenesis , phytophthora capsici , mutant , genetics , botany , pathogen , phytophthora , gene
Laboratory studies were conducted to evaluate the risk of developing field resistance to zoxamide, a new Oomycete fungicide which acts on microtubules. Zoxamide, metalaxyl and dimethomorph were compared with respect to the ease with which fungicide‐resistant mutants could be isolated and their level of resistance. Attempts to generate mutants of Phytophthora capsici and P infestans with resistance to zoxamide by mycelial adaptation on fungicide‐amended medium were unsuccessful. Similarly, changes in sensitivity to zoxamide were small (resistance factors ≤2.2) in mutants of P capsici isolated by chemical mutagenesis of zoospore cysts. In parallel experiments with metalaxyl, highly resistant mutants were obtained using both adaptation ( P capsici or P infestans ) and chemical mutagenesis ( P capsici ). For dimethomorph, chemical mutagenesis ( P capsici ) yielded moderately resistant mutants (maximum resistance factor = 20.9), and adaptation ( P capsici or P infestans ) did not induce resistance. It is proposed that failure to isolate mutants resistant to zoxamide results from the diploid nature of Oomycete fungi and the likelihood that target‐site mutations would produce a recessive phenotype. Our studies suggest that the risk of a highly resistant pathogen population developing rapidly in the field is much lower for zoxamide than for metalaxyl. However, as with any site‐specific fungicide, appropriate precautions against resistance development should be taken. © 2001 Society of Chemical Industry