Protección vegetal

 

Effectiveness of both synthetic compounds and biological extracts against powdery mildew (Blumeria graminis f. sp. tritici) on winter wheat

 

Efectividad de compuestos sintéticos y extractos biológicos contra el moho (Blumeria graminis f. sp. tritici ) en trigo de invierno

 

Lubomír Věchet^1* y Božena Šerá²

 

¹ Research Institute of Crop Production, Drnovská 507, 161 06 Prague, Czech Republic.

² Department of Biology, Faculty of Education, University of South Bohemia, Jeronýmova 10, 371 15 České Budějovice, Czech Republic. (bsera@pf.jcu.cz)

 

Received: February, 2014.
Approved: December, 2014.

 

Abstract

The objective of this study was to evaluate the effectiveness of foliar application of various synthetic compounds and biological extracts against powdery mildew on wheat. Seed coats of winter wheat were treated by synthetical compounds (benzothiadiazole, salicylic acid, and glycine betaine) or by the extracts from plants (oak, giant knotweed, curcuma, and ginger). Then the seeds were planted using small-field experiments with powdery mildew infection (repetitions over a two-year period; experimental field in Ruzyne, Prague). Leaf area infection was measured and the Cumulative Proportion of Leaf Area Diseased (CPLAD) was calculated. Data were analysed using ANOVA (Tukey test, p≤0.05). Effectiveness of preparations varied 30 % to 72 % in 2008, and 25 % to 65 % in 2009. The most effective synthetical compound was benzothiadiazole and the most effective biological extract was one from giant knotweed in both years (p≤0.05). Besides, plants treated with salicylic acid or glycine betaine had the least activity against powdery mildew (p≤0.05). Effectiveness in both years of cultivation was (p>0.05) similar, which indicates good stability of the biological extracts used. These findings suggest that these biological extracts may be a good preparation for using in organic farming.

Key words: biotechnology, curcuma, giant knotweed, ginger, infection, oak.

 

Resumen

El objetivo de este estudio fue evaluar la efectividad de la aplicación foliar de varios compuestos sintéticos y extractos biológicos contra el moho polvoriento del trigo. La testa de las semillas de trigo de invierno se trataron con compuestos sintéticos (benzotiadiazol, ácido salicílico, y glicina betaína) o con extractos de plantas (roble, knotweed gigante, cúrcuma y jengibre). Luego las semillas se plantaron en pequeños experimentos de campo con infección de moho polvoriento (repeticiones en un período de dos años campo experimental en Ruzyne, Prague). El área foliar de la infección se midió y se calculó la proporción acumulada de área foliar enferma (CPLAD). Los datos se analizaron con ANDEVA (Tukey, p≤0.05). La efectividad de las preparaciones varió de 30 % a 72 % en 2008 y de 25 % a el 65 % en 2009. El compuesto sintético más efectivo fue el benzotiadiazol y el extracto biológico más eficaz fue uno del knotweed gigante en ambos años (p≤0.05). Además, las plantas tratadas con ácido salicílico o glicina betaína tuvieron la menor actividad contra el moho polvoriento (p≤0.05). La efectividad en ambos años de cultivo fue similar (p>0.05), lo cual indica una buena estabilidad de los extractos biológicos. Estos hallazgos sugieren que estos extractos biológicos pueden ser una buena preparación para usarse en la agricultura ecológica.

Palabras clave: biotecnología, cúrcuma, knotweed gigante, jengibre, infección, roble.

 

INTRODUCTION

The 'European Crop Protection in 2030' book about crop protection in European agriculture was accepted by the European parliament and restrictions in the usage of pesticides were established (Labussiere et al., 2010). Plant resistance is an important component of modern, sustainable agriculture (Asadi et al., 2013). Understanding plant mechanisms that tolerate pathogens, insects, and abiotic stress are critical for understanding ways of increasing plant production and crop yields (Deepak et al., 2003; Khademi et al., 2012; Stenglein et al., 2012).

Induced resistance (IR) is a process of active resistance dependent on the host plant's physical or chemical barriers, triggered by biotic or abiotic agents (Kloepper et al., 1992). In its broadest sense IR means a control of pathogens and pests by prior activation of genetically programmed plant defence pathways. This enhanced state of resistance is effective for fungi, bacteria, viruses, nematodes, parasitic plants, and insect herbivores (Walling, 2000; Deepak et al., 2003; Walters et al., 2005).

Systemic acquired resistance (SAR) is a mechanism of induced plant defense to confer long-lasting protection against a broad spectrum of microorganisms (Durrant and Dong, 2004). SAR was characterized in plant mousear cress (Arabidopsis sp.) as the marked reduction in susceptibility to disease resulting from prior infection with an avirulent necrosing pathogen.

Benzothiadiazole (BTH) induces disease resistance to various plant pathogens (Qiu et al., 2004). Görlach et al. (1996) report successful control of powdery mildew, Septoria leaf spot (Septoria spp.), and leaf rust [Puccinia recóndita Roberge ex Desmaz. f. sp. tritici (Eriks and E. Henn.) D.M. Henderson] of wheat in field trials. BTH was also effective against downy mildew in maize [Peronosclerospora sorghi (W Weston and Uppal) C.G. Shaw] in the field when applied as a seed treatment (Morris et al., 1998). Stadnik and Buchenauer (1999a, b) report success in field experiments with single applications of BTH for controlling powdery mildew of wheat, but they had not clear results for Septoria leaf blotch (Septoria tritici Roberge in Desmaz). Salicylic acid and glycine betaine have an obvious effect like BTH (Vechet et al., 2009). Salicylic acid has a well-known ability to induce resistance and potentiates defense gene expression in tissue exhibiting acquired resistance (Mur et al., 1996). Glycine betaine is quaternary ammonium compound and has a role in plants during stress (Ashraf and Foolad, 2007).

In comparison to the synthetic compounds, influence of plant extract for reducing plant pathogen is not well known. According to Vechet et al. (2005, 2009), plant extract treatment shows a positive effect against plant pathogen; most of their experiments were carried out in laboratory and for field experiments they suggest using oak, giant knotweed, curcuma, and ginger.

Oak bark can be used in biological-dynamic agriculture because it supports disease resistance of plants (Dostálek and Hradil, 1998). Giant knotweed shows preventive and protective effects on powdery mildew in many plants and preparation Milsana®, based on giant knotweed, is commercially available (Wurms et al., 1999). Turmeric spice (curcuma) contains the flavonoid curcumin (diferuloylmethane), a low molecular weight polyphenol (Chainani-Wu, 2003), and curcumol. The major constituents of the ginger spice essential oil are sesquiterpenes zingiberene (35 %) and farnesene (10 %). monoterpenes (1,8-cineol, linalol, borneal, neral and geraniol) are also found, but in lower concentrations (Sakamura et al., 1986).

Therefore, the aim of this study was to test the effectiveness of individual resistance inducers of chemical and biological origin on the severity of powdery mildew in field conditions.

 

MATERIALS AND METHODS

Material

Three chemical substances and four plant extracts were used in the experiment. Chemical inducers benzothiadiazole (BTH, 1.2 mM; commercially produced as Bion^® and containing 50 % of BTH), salicylic acid (SA, 1 mM), and glycine betaine (GB, 0.3 M) were prepared as water solutions (Vechet et al., 2009).

Biological extracts were prepared from biomass (100 g) of: oak (Quercus robur L.), giant knotweed (Polygonum sachalinense Friedr. Schmidt), turmeric spice known as curcuma (Curcuma longa L.), and ginger (Zingiber officinale Roscoe). Dried crushed oak bark (QR), dried lcrushed leaves of giant knotweed (PS), turmeric spice (CL), and ginger spice (ZO) were extracted in 850 mL 20 % ethanol during 5 h with frequent shaking. The mixture was filtered through miracloth. Both chemical substances and biological extracts were used for wheat treatment.

Field experiment

Small-plot field experiments were carried out at the Crop Research Institute (Prague Ruzyne, 50° 5.1676' N, 14° 18.0464' E). Soil type is orthic luvisol, clay-loam, developed on dilluvial sediments mixed with loess, soil reaction is neutral (pH KCl is 6.8-7.1) in the profile (Simon, 2005). The winter wheat cultivar Kanzler (Triticum aestivum L. cv. Kanzler), which is regarded a standard for its susceptibility to powdery mildew, was used. Wheat was grown in a standard way and infection by powdery mildew was natural.

One small-plot with 1 m row length was used for one type of treatments (in two repetitions). The rows were isolated on both sides by five rows of plants of the same cultivar, which had not been treated. Each first neighbouring rows were treated using one type of preparations, whereas the next five rows did not receive any treatment. Seven individual preparations were applied using a manual sprayer, each separately, and 150 mL 1 m^-2 crop in one application. Foliar application was carried out three times in the early growth stage of wheat (December, March, and May) and evaluations were made on June.

Variables evaluated

Leaf area infection (LAIN) was evaluated for all live leaves on 15 plants (randomly chosen) in two replications as a percentage of leaf area covered by powdery mildew infection per one leaf. Based upon the infection, the cumulative proportion of leaf area diseased (CPLAD) was calculated, which expresses the disease severity for the whole plant (Vechet and Kocourek, 1987; Brière et al., 1994). All variables were evaluated in June (2008, 2009). Induced effectiveness (IE) was calculated in percentage of not-diseased leaf area per one plant. The plants without treatment were used as a control.

Variables were calculated as follows:

where M is number of treatment repetitions, N is number of leaves, A is leaf area disease, tr is treatment, and co is control.

The experiment was conducted in the 2008 and 2009 crop year.

Statistical analysis

STATISTICA program was used for all statistical analysis. Data were compared by one-way ANOVA followed by Tukey HSD multiple range comparison test (p≤0.05). The dependent variables LAIN, CPLAD, and IE were log-transformed (y=log x) in order to obtain the normal distribution before statistical analysis.

 

RESULTS AND DISCUSSION

Disease severity was high in the control in 2009 and low in 2008, but plant resistance after various treatments produced analogous results in mean infection (Table 1). Significant differences (p≤0.05) were found in CPLAD between inducers of BTH and RS in 2008, and between BTH, RS, and CU in 2009, as compared to control samples; these inducers caused a high reduction of LAIN and CPLAD (Table 1).

IE varied between 30 % and 72 % in 2008 and between 25 % and 65 % in 2009. IE of most inducers significantly differed from control samples in both years (Table 1). The best IE was found for RS (72.39 %) and BTH (70.51 %) in 2008, and for BTH (64.87 %) in 2009 (p≤0.05). GB (29.59 %) in 2008 and for SA (24.62 %) showed the smallest IE (p≤0.05).

Little is known about disease resistance inducers in wheat (Vechet etal., 2009; Randoux etal., 2010). In our experiments with resistance inducers under field conditions carried out on the Kanzler cultivar, the standard for susceptibility to this disease, a partial difference was observed in 2008 and 2009, which was probably influenced by weather conditions. These results are similar to those obtained with compounds of natural origin by Vechet etal. (2005). The higher disease severity registered in the control indicates that in wheat treated with resistance inducers, a protective reactions against powdery mildew was activated.

The efficiency of biological origin extracts is similar to those of chemical origin (Vechet et al., 2009). Benzothiadiazole and the extract from giant knotweed were very effective in reducing powdery mildew in both years (Table 1). Benzothiadiazole triggers plant defence responses without any direct antifungal activity (Kunz et al., 1997); besides, it is an inducer of SAR and activates gene expression and disease resistance in wheat (Gorlach et al., 1996). According to Qiu et al. (2004), SAR is an inducible defence response shown by a large range of plant species; for example, in papaya SAR was induced by exogenous application of silicic acid or related molecules like benzothiadiazole.

Milsana^® (made with plant extract of giant knotweed), which induces resistance to powdery mildew on cucumbers, reduced powdery mildew infection by 85 % on wheat (Randoux et al., 2006). There is a potential usage of this product in agriculture. The efficacy of Milsana^® against Leveillula taurica (Lev.) Arn. was tested on tomatoes and in four out of five trials the disease was reduced between 42 % and 65 % (Konstantinidou-Doltsinis et al., 2006) and only in one its efficacy was low (23 %). In contrast to fungicide preparations, Milsana^® was equally effective as wettable sulphur, thus indicating that its effect was preventive rather than curative. Giant knotweed contains many secondary metabolites (phenolic substances) with biological activities (Pavela et al., 2008; Vrchotová and Šerá, 2008). These compounds reduced powdery mildew in wheat in our study (Table 1).

Plants can be induced to develop enhanced resistance to pathogen infection by treatment with a variety of abiotic and biotic inducers. Resistance induced by these agents (resistance elicitors) is broad-spectral and long-lasting, but it rarely provides a complete control of infection. Many resistance elicitors provide between 20 % and 85 % disease control (Walters et al., 2005). Our experiments showed that the effectiveness of individual inducers, compared to an untreated control, ranged between 30 % for glycine betaine and 72 % for extracts from giant knotweed in 2008, whereas in 2009 the effectiveness varied from 25 % for salicylic acid to 65 % for benzothiadiazole (Table 1).

Effectiveness of the tested plant species and chemicals in field conditions was long-lasting, as the evaluation for disease severity after the first treatment was more than four months; besides, treatments were effective under natural conditions. The experiments showed the resistance inducer's effectiveness through the entire growing season, but the effectiveness of individual resistance inducers varied within individual treatment periods. Induced resistance is a plant's response to an attempted infection; therefore, expression of this response will be affected by several factors, including genotype and environment (Walters et al., 2005).

 

CONCLUSIONS

The seven preparations were tested as protection against powdery mildew (B. graminis f.sp. tritici) attack on winter wheat (T. aestivum L. cv. Kanzler). Benzothiadiazole and two plant extracts: giant knotweed (P. sachalinense) and turmeric spice (curcuma, C. longa), showed the best results.

 

ACKNOWLEDGEMENT

This research was supported by Ministry of Agriculture of the Czech Republic (project no. VZ VURV 0002700602) and by Department of Biology (Faculty of Education, University of South Bohemia in Ceske Budejovice). The authors would like to thank both reviewers for their comments, which helped to improve the manuscript.

 

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