Regev™ – a broad-spectrum hybrid fungicide for plant disease control

Introduction

The global search for plant-protection solutions that are both environmentally safe and efficacious is driven by the need to supply food to the ever-growing population. The call for chemical load reduction is an important aspect of sustainable agriculture. Recently, documented issues of widespread environmental contamination, toxicity to non-target organisms and negative effects on human health by synthetic agrochemicals have led to a resurgence of interest in "natural" means of pest and pathogen controls, including an intensified search for new sources of biopesticides and botanical pesticides. The latest solutions are generally used in crop protection and contain secondary metabolites, which can be (but are not always) involved in plant defense. Among the latest solutions, essential oils are considered to be attractive for plant protection. 

Tea tree oil (TTO) is a valuable essential oil extracted by the steam distillation of Melaleuca alternifolia leaves (belonging to family Myrtaceae). It contains many components of terpenes, sesquiterpenes, and their respective alcohol. The oil has proven to be an effective antiseptic, fungicide and bactericide. In the recent decade, it was found to be effective against a broad range of plant-pathogenic fungi in numerous crops, including vegetables, herbs, coffee, rice, grapevines, bananas, and fruit trees. 

New effective alternatives that can provide different and multiple modes of action with a lower risk for fungicide resistance, and which place a smaller chemical load on the environment, concomitantly with consistent disease control, are required to increase options for controlling plant diseases. The newly developed Regev EC by the Israeli bio-tech company, STK Bio-Ag Technologies, is a hybrid formulation: it contains 200 g/L of the systemic triazole fungicide difenoconazole plus 400 g/L of TTO. This unique prepacked formulation provides various mechanisms of action against a broad spectrum of plant pathogens with improved efficacy. 

Hybrid solutions can be the "bridge" between conventional agrochemical farming and sustainable farming. That’s because it is a "pre-mix", so it is easy-to-use, in the exact same way as the grower’s current chemical pesticide. To the best of our knowledge, this is the first bio and chemical-based hybrid product.

Modes of action

As a Hybrid, Regev combines the modes of action of the botanical extract with a synthetic chemical molecule. The fungicidal and antimicrobial activities of TTO against fungal pathogens, as documented, are derived from its ability to inhibit respiration and disrupt the permeability barrier presented by the membrane structures of living organisms. Our recents studies showed that TTO is effective against spore germination and significantly inhibited lesion development and the sporulation of fungal pathogens. TTO was found to disrupt the fungal cell membrane and cell wall in plant tissues infected with pathogenic fungi [see Figure 1], which explains why it exhibited a strong curative activity against fungal pathogens, making it a unique product and enabling growers to use it even when the disease was already visible on the tissue. In addition, TTO was found to be an activator of defense mechanisms and systemically induce resistance in plants. 

Figure 1. A section of fungal hyphae in the intracellular space of the mesophyll tissue of TTO-treated leaves: (a) at low magnification (x20,000=a) and (b) at high magnification (x50,000). Note the destruction and breakdown of the cell wall, causing leakage of cell content.

The sterol biosynthesis inhibitors, including difenoconazole, affect the fungal cell membrane by inhibiting the C-14 demethylation of lanosterol or 24-methylenedihydrolanosterol, a biosynthesis step that occurs during the conversion of lanosterol to ergosterol, the final product of fungal cell membrane sterol synthesis.

The different modes of action of TTO and difenoconazole, i.e. a combination of a natural product with broad-spectrum activity (TTO) and a traditional site-specific chemical, make Regev an effective and unique tool for resistance management, which is suitable for Integrated Pest Management programs. This combination results in a reduced synthetic chemical load on the environment compared to other mixtures based on two traditional chemicals.

Field trials

Regev is currently used for controlling a broad range of diseases on arable crops, cereals, fruits and vegetables. Diseases effectively controlled by Regev include powdery mildews, apple scab (Venturia inaequalis), Black Sigatoka (Mycosphaerella fijiensis) in bananas, species of Alternaria, Cercospora, Botrytis, Rhizoctonia, Pyricularia, Helminthosporium, Sclerotium and more. Numerous trials have been conducted with various crops and in different countries. Here, we present an example of Regev's activity against apple scab caused by Venturia inaequalis.

A field trial was undertaken in Northern Israel in a major apple growing region and the efficacy of Regev was examined, compared to the systemic fungicide, difenoconazole. Untreated trees served as controls. Six foliar sprays of each fungicide were applied, starting from the green tip at 6-10-day intervals. Treatments were arranged in a randomized complete block design. The results given in Figs. 2 and 3 show that difenoconazole inhibited scab development on apple trees compared to untreated control trees. However, Regev (TTO + difenoconazole) was significantly more effective in controlling apple scab.

Figure 2. Efficacy of Regev (TT+Difenoconazole) and difenoconazole in controlling apple scab. Different letters on bars indicate a significant difference (P < 0.05).

Resistance management

Regev has a unique multiple functional activity and presents a very low probability for the development of resistance or cross-resistance in plant pathogens, so it could be an important tool in preventing the development of cross-resistance during the season. Its application can be rotated with products that exhibit differing modes of action and to which populations of fungal pathogens have shown a loss of sensitivity, so that the population of individuals less sensitive to chemical products can be reduced. Studies showed that Regev (TTO plus difenoconazole) improved the sensitivity of difenoconazole against fungal isolates, which exhibited a lower sensitivity to difenoconazole, and subsequently, delayed the emergence of resistance to this fungicide.

Registration 

Regev has already been registered in the USA, Israel, the Philippines, Serbia and various Latin American countries for various crops and diseases. It is currently in the process of being registered in Brazil and the EU.

Summary

The different modes of action of TTO and difenoconazole, created by the combination of a natural product (TTO) with broad-spectrum activity and a traditional site-specific chemical, make Regev an effective and unique tool for resistance management. It presents multiple modes of action (FRAC Groups F7 and G1) to help prevent the development of resistance. This combination results in a reduced chemical load on the environment compared to other mixtures based on two traditional chemicals, leading to reduced residual potential. 

The preventive and curative activity of Regev, related to its efficiency of contact, mesosystemic plus systemic activity by a single application, together with the indirect activity via the host plant by systemic resistance, leaving little residue and providing significant added value to growers, make Regev an important component in the control of plant diseases. Regev has an expanded spectrum over either component alone and has demonstrated activity over a wide range of plant diseases. It can therefore be an efficacious and easy-to-use "bridge" solution for controlling various diseases.

Please contact Julia.levy@stk-ag.com with any questions about this article or Regev hybrid fungicide.

This article was originally published in AgroPages' 2020 Biologicals Special. 

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