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

Abstract

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.

Efficacy of some plant resistance inducers against several sunflower downy mildew (Plasmopara halstedii (Farl.) Berl. et de Toni) isolates

“…Molinero-Ruiz et al (2008) reported a decrease on the effectiveness of two distinct active components (Metalaxyl and Metalaxyl-M) for controlling downy mildew in sunflowers is due to the ability of the novel strain to readily overcome P. halstedii resistance. Pánek et al (2022) indicated that the metalaxyl not limiting the pathogen penetration into a host plant but effectively reducing mycelial development. These findings are also consistent with our findings, which reveal that mefenoxam cannot restrict sporangia germination in vivo.…”

Efficiency of Rosemary Rosmarinus Officinalis and Chitosan in Controlling the Damping off Pathogen, Fusarium Spp., Identified Morphologically and Molecularly

“…The materials Tween 20, used as an aid dispersant to dissolve oil in water, and acetic acid as a solvent for chitosan, gave an inhibition rate of 20.5 and 32.2%, respectively. The fungicide's effectiveness may be due to the active substance Metalaxyl, as it works by its chemical effect to prevent and inhibit the synthesis of ribosomal RNA, as it does not prohibit the fungus from entering the plant tissues instead, it prevents the growth and reproduction of the fungus [16] or to the active substance Hymexazole, which has a role in inhibiting the biosynthesis of proteins and nucleic acids, or in the processes of oxidation and reduction, and thus in the energy production [17].…”

Evaluation of the Ability of Seven Active Ingredients of Fungicides to Suppress Phytophthora cactorum at Diverse Life Stages, and Variability in Resistance Found among Isolates

“…The resistance of P. cactorum against metalaxyl was first reported in 1988 by Utkhede and Gupta in an in vitro environment [ 25 ], while the resistance of P. cactorum isolates to mefenoxam in strawberry fields in the USA was reported for the first time by Jeffers et al in 2004 [ 26 ]. Recently, Marin and Peres [ 27 ] reported that the fungicides cymoxanil, fluopicolide, mandipropamid and oxathiapiprolin completely inhibited the mycelial growth of P. cactorum isolates from Florida at a concentration of 1 µg/mL, but significant differences in the resistance to some chemical fungicides have already been found between P. cactorum isolates or their genetic lineages [ 28 , 29 , 30 , 31 , 32 , 33 , 34 ].…”