Evaluation of fungicides enestroburin and SYP1620 on their inhibitory activities to fungi and oomycetes and systemic translocation in plants

Highlights

• The newly developed Enestroburin and SYP1620 showed strong inhibitory activities on hypha growth and spore germination.

• Enestroburin and SYP1620 penetrated and spread in wheat leaves at levels lower than that of azoxystrobin.

• Enestroburin, SYP1620 and azoxystrobin were all rapidly taken up by wheat roots and transported upwards.

• Enestroburin and SYP1620 are systemic fungicides that inhibit a broad spectrum of fungi and oomycetes.

Abstract

Enestroburin and SYP1620 are newly developed strobilurin chemicals carrying fungicidal activity and need to be fully characterized in activities of anti-oomycete or anti-fungi, disease prevention and systemic translocation in planta. Their inhibitory activities were examined by amending the chemical in agar media, on which selected plant pathogens were grown and mycelial growth were measured. Effective concentrations for 50% inhibition (EC₅₀) of mycelial growth were calculated to determine the level of fungicide sensitivity of the pathogen. Azoxystrobin was used as control. To examine the prevention and systemic translocation in plants, the fungicides were either sprayed on wheat leaves or dipped on wheat roots, which then were detected using high performance liquid chromatography. All the three fungicides inhibited mycelial growth of Sphacelotheca reiliana, Phytophthora infestans, Peronophythora litchi, and Magnaporthe oryzae, with EC₅₀ values ranging from 0.02 to 2.84 μg/ml; EC₅₀ of SYP1620 was significantly lower than that of azoxystrobin and enestroburin on Valsa mali, Gaeumannomyces graminis, Alternaria solani, and Colletotrichun orbiculare. The three QoI fungicides showed strong inhibitory activities on spore germination against the 13 pathogens tested and were highly effective on biotrophic pathogens tested. Enestroburin and SYP1620 penetrated and spread in wheat leaves, but the penetration and translocation levels were lower compared to azoxystrobin. The three fungicides were all rapidly taken up by wheat roots and transported upwards, with greater fungicide concentrations in roots than in stems and leaves. The results indicate that enestroburin and SYP1620 are systemic fungicides that inhibit a broad spectrum of fungi and oomycetes.

Introduction

Quinone outer inhibitors (QoI) are a class of fungicides that are derivatives of strobilurin [1]. QoI fungicides include azoxystrobin and enestroburin, and newly developed compounds, such as pyrimidine moieties or chalcones [2], [3]. These fungicides inhibit respiration of plant pathogens by binding to the quinol outer site of the cytochrome bc₁ enzyme complex III [2]. QoI fungicides have inhibitory activity on a broad spectrum of plant pathogens including fungi and oomycetes [4]. Furthermore, some of these fungicides are systemically transported in plants, such as azoxystrobin, kresoxim-methyl, trifloxystrobin picoxystrobin, and metominostrobin [5], [6].

Enestroburin is registered for the control of cucumber downy mildew (Pseudoperonospora cubensis), grape downy mildew (Plasmopara uiticola), apple alternaria leaf spot (Alternaria mali), and wheat scab (Fusarium graminearum) [7]. SYP1620 is registered for the control of powdery mildew of cucumber (Sphaerotheca fuliginea), powdery mildew of wheat (Blumeria graminis f. sp. tritici), rice blast (Magnaporthe oryzae), rice sheath blight (Rhizoctonia solani), and wheat stem rust (Puccinia graminis f. sp. tritici) [7]. Although substantial inhibitory activity has been documented for most of the commercialized QoI fungicides [8], [9], [10], [11], not all of them offer complete disease control, and their efficacies vary depending on plant pathogens. Although inhibitory activities of enestroburin and SYP1620 to some pathogens have been reported [12], [13], [14], [15], they are still in the early stage of application in field. To date, no information on their antifungal spectrum has been available. Therefore, more pathogens need to be studied with these fungicides.

Systemic translocation in plants can enhance the effectiveness of inhibition activity of fungicides. Understanding how a fungicide is distributed inside a plant after its application will help the management of fungicide application. For example, 2-allylphenol can be transported from roots to leaves [16], or from leaf to root [17]. Bartlett et al. [1] reported that azoxystrobin and picoxystrobin possess strong systemic activities, such as translaminar movement, xylem-systemic activity, uptake into leaves, and systemic movement to areas of new growth. Since enestroburin and SYP1620 are in the group of QoI, they are expected to be systemic for distribution in plant. However, this has not been quantitatively investigated.

In this study, enestroburin and SYP1620 were examined and compared with azoxystrobin, a well-known QoI fungicide. The objectives of this study were as follows: (1) to clarify their antifungal spectrum of enestroburin and SYP1620 by determining the inhibitory activity against 25 plant pathogens in vitro; (2) to investigate their preventive activity through a planta assay; (3) to carry out an evaluation on their systemic translocation in wheat leaf and plant using bioassay and HPLC methods.