Differential responses of germinating Venturia inaequalis conidia to kresoxim‐methyl

Abstract

: A new class of agricultural fungicides derived from strobilurins act as respiration inhibitors by binding to mitochondrial cytochrome b. The e †ects of the strobilurin, kresoxim-methyl, on conidia germination, mycelial growth and the protection of apple leaves from scab development were investigated for two isolates of V enturia inaequalis randomly selected from a culture collection. Inhibition of mycelial growth required relatively high doses of kresoxim-methyl for both isolates. In comparison, germination of conidia was (ED 50 \ 1 lg ml~1) highly sensitive for one of the isolates while the level of (ED 50 \ 0É005 lg ml~1), inhibition achieved for the second isolate was 60-fold less (ED 50 \ 0É3 lg ml~1). As deduced from identical sequences of cytochrome b cDNAs prepared from both isolates, the di †erent responses of germinating conidia to kresoxim-methyl were not caused by di †erences in the sequence of cytochrome b as the target site for strobilurin action. Strong synergistic e †ects of salicylhydroxamic acid on kresoxim-methyl inhibitory potency suggested that the reduced kresoxim-methyl sensitivity observed for germinating conidia was caused by interference of the alternative respiratory pathway with inhibitor action. However, this mechanism of target site circumvention in germinating conidia had no adverse e †ects on the protection of apple leaves from scab infection by kresoxim-methyl. (

Effect of azoxystrobin on activities of antioxidant enzymes and alternative oxidase in wheat head blight pathogens Fusarium graminearum and Microdochium nivale

“…The relationship between sensitivity to strobilurin fungicides and the cyanide-resistant respiration pathway has been studied for several phytopathogenic fungi (AvilaAdame and Köller 2002; Miguez et al 2004;Olaya et al 1998;Schnabel et al 2003). Generation of the superoxide anion by strobilurins and the induction of AOX expression by H 2 O 2 have been reported for M. grisea (Mizutani et al 1996;Yukioka et al 1998).…”

“…AOX bypasses complexes III and IV in the cytochrome-mediated pathway and transfers electrons directly from ubiquinol to oxygen (Joseph-Horne et al 2001;Vanlerberghe and McIntosh 1997). AOX activity has been identified in several phytopathogenic fungi: Magnaporthe grisea (Avila-Adame and Köller 2002), Mycosphaerella graminicola (Miguez et al 2004), Botrytis cinerea (Tamura et al 1999) and Venturia inaequalis (Olaya et al 1998). The AOX inhibitors SHAM and nPG enhance sensitivity to strobilurin fungicides in these fungi (Ishii et al 1999;Wood and Hollomon 2003).…”

Fungicide-induced transposon movement in Monilinia fructicola

“…Control plates received no fungicide. Potato dextrose agar (PDA) amended with azoxystrobin also contained 100 μg/ml of SHAM, which is added to inhibit the alternative oxidase pathway and is routinely used for QoI resistance assessment (Olaya et al, 1998). Fungicide stock solutions (54.3 μl) were spread on solidified PDA in a Petri dishes (15 cm diameter; 50 ml PDA per dish) with a spiral plater (Neu-tec Group INC, Farmingdale, NY).…”

In vitro sensitivity of Corynespora cassiicola isolated from soybean to fungicides and field chemical control of target spot

“…Conidial germination is directly affected by QoI fungicides (25). Assessment of spore germination is a suitable method to evaluate the sensitivity to this fungicide group.…”