Fungicide Resistance in Powdery Mildew Fungi.

Alejandra Vielba-Fernández,Alejandro Pérez-García,Antonio De Vicente,Álvaro Polonio,Dolores Fernández-Ortuño,Laura Ruiz-Jiménez

doi:10.3390/microorganisms8091431

Abstract

Powdery mildew fungi (Erysiphales) are among the most common and important plant fungal pathogens. These fungi are obligate biotrophic parasites that attack nearly 10,000 species of angiosperms, including major crops, such as cereals and grapes. Although cultural and biological practices may reduce the risk of infection by powdery mildew, they do not provide sufficient protection. Therefore, in practice, chemical control, including the use of fungicides from multiple chemical groups, is the most effective tool for managing powdery mildew. Unfortunately, the risk of resistance development is high because typical spray programs include multiple applications per season. In addition, some of the most economically destructive species of powdery mildew fungi are considered to be high-risk pathogens and are able to develop resistance to several chemical classes within a few years. This situation has decreased the efficacy of the major fungicide classes, such as sterol demethylation inhibitors, quinone outside inhibitors and succinate dehydrogenase inhibitors, that are employed against powdery mildews. In this review, we present cases of reduction in sensitivity, development of resistance and failure of control by fungicides that have been or are being used to manage powdery mildew. In addition, the molecular mechanisms underlying resistance to fungicides are also outlined. Finally, a number of recommendations are provided to decrease the probability of resistance development when fungicides are employed.

Highlights

The FRAC and the European and Mediterranean Plant Protection Organization (EPPO) have classified powdery mildew species depending on the risk of the pathogen developing resistance to fungicides under specific agronomic conditions [26]
In several surveys performed from 2001 to 2007 in the Czech Republic, benomyl was not effective in controlling any cucurbit powdery mildew, neither were P. xanthii or G. cichoracearum, with the frequency of resistant isolates being higher than 90% in most of the years sampled [70,71,72,73] (Table 2)
The most common powdery mildew fungi are high-risk pathogens, and as documented in this review, important cases of practical resistance have been reported in several parts of the world, such as Africa, Australia, Brazil, Canada, China, Europe (Austria, Belgium, Czech Republic, Denmark, France, Germany, Greece, Hungary, Italy, Portugal, Scandinavia, Spain and the Netherlands), Egypt, India, Iran, Japan, New Zealand, UK, and the US (California, Georgia, Michigan, New Jersey, New York, North Carolina, Ohio, South Carolina and Virginia)

Summary

Introduction

The FRAC and the European and Mediterranean Plant Protection Organization (EPPO) have classified powdery mildew species depending on the risk of the pathogen developing resistance to fungicides under specific agronomic conditions [26] In this regard, Blumeria graminis (wheat and barley powdery mildew), E. necator (powdery mildew of grape) and P. xanthii (cucurbit powdery mildew) are considered to be pathogens with high risk of resistance development because they show short disease cycles per season, their dispersal through conidia over time and space is high, and they have evolved resistance to several classes of fungicides after a few years of product use. For other powdery mildews, such as Podosphaera leucotricha (powdery mildew of apple), resistance against only a small number of chemical classes has been observed; this species is considered to be a low-risk pathogen with low importance in commercial market terms [26]

Current Fungicide Resistance Status in Powdery Mildew Fungi

Findings

Conclusions and Recommendations