Reduced fitness cost and increased aggressiveness in fenhexamid-resistant Botrytis cinerea field isolates from Chile

Abstract

Disease management programmes in Chilean table grape vineyards use the hydroxyanilide fenhexamid as a pivotal fungicide for Botrytis cinerea control. However, fenhexamid-resistant populations of this pathogen have progressively increased in vineyards under fungicide use. Botrytis cinerea isolates were collected in ‘Thompson Seedless’ vineyards under fenhexamid control programmes (>two sprays per season) from three regions of Central Chile, during the 2013-2014, 2014-2015 and 2015-2016 growing seasons. Focusing on the 2015-2016 growing season when the greatest level of resistance was measured, only 8% of recovered isolates were sensitive to fenhexamid with 92% of isolates exceeding the sensitivity threshold for mycelium growth. All fenhexamid resistant isolates analyzed carried a mutation in the Erg27 gene, which encodes for 3-keto reductase (3-KR) enzyme. The largest proportion of isolates presented a single-point mutation, leading to a substitution of phenylalanine by serine or isoleucine in the 412 residue of 3-KR (erg27^F412S, 27%; erg27^F412I, 48%). Substitution by valine in this position was observed in a lower proportion of isolates (erg27^F412V, 2%). In contrast to a previous report indicating high fitness cost in isolates carrying erg27^F412S or erg27^F412I, mycelium growth and sclerotia development under different restrictive temperatures were not affected compared to wildtype Erg27 ^F412  in Chilean mutant isolates. At 0°C, erg27^F412S and erg27^F412I generated larger lesions than erg27^F412V and Erg27^F412 isolates in wounded and unwounded berry assays. Another five mutations were detected in low-resistance Erg27 ^F412 isolates; one was  a previously unreported mutation: erg27^R330P. This study has demonstrated a significant loss of sensitivity to fenhexamid, limited fitness cost and high aggressiveness levels (erg27^F412S and erg27 ^F412I) in field isolates carrying Erg27 mutations, giving dirctions for the design of Botrytis control programmes based on fenhexamid.