Sensitivity of Venturia inaequalis Populations to Anilinopyrimidine Fungicides and Their Contribution to Scab Management in New York

Abstract

Sensitivities of Venturia inaequalis isolates to the anilinopyrimidine fungicides (APs) pyrimethanil and cyprodinil were determined for nine populations by measuring the growth of colonies formed from germinating conidia derived from single scab lesions. At the discriminatory pyrimethanil dose of 0.2 μg ml-1, the mean relative growth range measured for eight V. inaequalis populations (n = 39 to 74) never treated with AP fungicides varied from 18.1 to 48.2, translating into an approximately sixfold difference in mean baseline sensitivities. For the composite of all 469 isolates tested, sensitivities to pyrimethanil and to the sterol demethylation inhibitor (DMI) myclobutanil were significantly correlated. When isolates were organized into subpopulations based on their sensitivities to an individual fungicide, sensitivities to both fungicides declined in parallel through the highly and moderately sensitive spectra of subpopulations, but they diverged for isolates in subpopulations least sensitive to either fungicide. The result suggested that at least one of the multiple genes conferring DMI resistance also lowered the sensitivity to AP fungicides. The relative contribution of AP fungicides to scab management was evaluated at an experimental orchard representative of the Great Lakes region of the United States. Frequencies of DMI-resistant isolates of V. inaequalis had progressed to the stage of practical resistance at the site, and the sensitivity to pyrimethanil was similar to several commercial orchard populations never treated with APs. For management programs at the experimental site involving the AP fungicides cyprodinil and pyrimethanil and conducted from 1996 to 2000, the level of fruit and terminal leaf scab control was inferior to that of nonspecific protectants such as mancozeb or captan. For the control of scab on cluster leaves, the efficacy of AP fungicides equaled the performance of nonspecific protectants. This modest contribution of AP fungicides to scab management might have been caused by a lack of the extended cool temperature conditions that were conducive to AP performance in northern Europe in previous studies, and/or by the reduced sensitivity to AP fungicides in this DMI-resistant V. inaequalis population.

Sensitivity of Magnaporthe grisea to the Sterol Demethylation Inhibitor Fungicide Propiconazole

“…The EC 50 values of 52 isolates to propiconazole ranged from 0.145 to 1.446 μ g/ml. Similar variation in sensitivity to DMI fungicides has also been reported from other plant pathogens (Reynolds et al., 1997; Zehr et al., 1999; Köller et al., 2005). Thus, the selection pressure of a DMI fungicide might be favourable for the less sensitive isolates to propagate in the population.…”

“…The relative amount of cyp51 mRNA of each isolate was compared with the mRNA level from isolate 04-006. Each bar represents a mean of two experiments (Zehr et al, 1999;Ko¨ller et al, 2005), to our knowledge, the hypersensitive isolates have never been characterized before. In this study, we characterized the PHS isolates of M. grisea by determining their pathogenicity, sensitivity to other fungicides, and structure and expression of cyp51 gene.…”

Sensitivity of Venturia inaequalis Chilean Isolates to Difenoconazole, Fenarimol, Mancozeb, and Pyrimethanil

“…Narrower distributions were described by Köller et al (2005) in a sensitivity study of 22 isolates from New York which could result from the small number of tested isolates. A very similar distribution of sensitivities was observed in this study for the orchard population which ranged from 0.0061 to 3.2 µg mL -1 with a separation factor of 524 (Table 2, Figure 1).…”

“…A discriminatory dose of 0.2 µg mL -1 is suggested for in vitro determination of sensitivity to pyrimethanil. The same dose was determined by Köller et al (2005) for the New York isolates.…”

The dissipation rates of myclobutanil and residue analysis in wheat and soil using gas chromatography-ion trap mass spectrometry

“…As a broad spectrum fungicide, myclobutanil acts by interfering with ergosterol biosynthesis by inhibiting demethylation of steroids [9][10][11]. It was extremely active against the powdery mildew and rust of grain, and some reports related the use and efficacy of myclobutanil in crops, fruits and vegetables to improve their yield and quality [12][13][14].…”