Use of metalaxyl against some soil plant pathogens of the class Peronosporomycetes - A review and two case studies

Upon its discovery and implementation in plant protection, metalaxyl became one of the most important fungicides against Phytophthora infestans, but its efficiency has also been proven against other soil pathogens of the class Peronosporomycetes. The most important genus - Phytophthora comprises more than 150 plant pathogens, which cause significant losses in crop production or damage to natural plant associations. Many species of related genera Pythium, Phytopythium and Globisporangium have a similar ability as the species of Phytophthora. Those pathogens are able to quickly spread in wet soils by actively movable zoospores or in the air by means of zoosporangia; they are able to persist in an environment for long periods once they are introduced into the locality, having durability from their resting structures (chlamydospores, hyphal swelling and oospores). Metalaxyl has proven to be very efficient against these pathogens. However, shortly after its release, the rapid development of resistance against this compound was recorded in many species of the class Peronosporomycetes. Such easily developed resistance is due to the monogenic nature of the resistance, which also determines any anti-resistant strategies. The solution of this issue rests in the cautious use of metalaxyl, with consideration given to these strategies, and should be based also on precise information about the environment and the present pathogenic agents.