Effects of Plant Extracts, Salicylic acid and Fungicide in Biocontrol of Fungal Diseases of Maize (Zea mays L.) and Wheat (Triticum aestivum L.)

Abstract

Agricultural production can be improved through the use of environmental friendly, cost effective and biodegradable treatments to reduce crop losses due to pathogen infection. Present attempt is a comparative study of plant extracts, chemical fungicides and hormonal inducers/elicitors i.e. salicylic acid to modulate the defense system of host plants (maize and wheat) against the most destructive fungal diseases (stalk rot, leaf spot blotch and leaf rust). Seven selected plants viz; Calotropis procera (Asclepidaceae), Cassia fistula (Caesalpiniaceae), Citrullus colocynthis (Cucurbitaceae), Jacaranda mimosifolia (Bignoniaceae), Lantana camara (Verbenaceae), Ricinus communis (Euphorbiaceae) and Thevetia peruviana (Apocynaeceae) were screened on the basis of their secondary metabolites and in vitro antifungal potential. The efficient plant extracts were used to prepare bioformulations with salicylic acid and chemical fungicide for the control of stalk rot in maize, leaf blotch/spot blotch and leaf rust in wheat. The activities of defense related enzymes and endogenous phytohormone content were quantified in maize and wheat under non-infected and infected conditions. Pathogenesis-related proteins were identified through proteome analyses (1DE, 2DE and mass spectrometry). The transcript levels of defense related genes were also investigated by qRT-PCR. In the first experiment, in vitro antifungal potential of seven selected plant species were determined against Fusarium moniliforme and Helminthosporium sativum. Both the methanolic and aqueous leaves extracts of J. mimosifolia (1.2%) showed significant inhibition ranging from 93–97% in the mycelial growth of F. moniliforme and H. sativum. Methanolic and aqueous leaf extracts of T. peruviana and C. procera also exhibited significant inhibition but of lower magnitude than that of J. mimosifolia. In the second experiment the efficacy of plant extracts was tested alone and in combination with fungicide and salicylic acid against stalk rot in maize, both under axenic conditions in potted plants and under natural conditions of field. The half-dose formulation of J. mimosifolia with fungicide significantly reduced stalk rot disease both in pot and field experiments. The chlorophyll content, soluble proteins, leaf phenolic content, PPO activity and yield attributes were significantly enhanced by the full-dose formulation of J. mimosifolia. While the half-dose formulation of J. mimosifolia with fungicide significantly increased the enzyme activities like SOD, peroxidase, polyphenol oxidase, proteases, acid invertases, phenylalanine ammonia lyases, chitinase and endogenous level of phytohormones (ABA, SA) and macronutrients (Ca, K, Mg, Na). In the third experiment, foliar spray of all formulations to wheat plants decreased the disease incidence of leaf spot blotch in wheat. But foliar application of J. mimosifolia in combination with fungicide and in combination with SA exhibited significant decrease against spot blotch disease in both pot and field experiments. The percent decrease in disease severity was higher in the pot experiment. The effects of full and half-dose formulations of plant extracts were similar to that of stalk rot in maize. In fourth experiment, the effect of aqueous leaf extracts were studied on defense related enzymes and on mechanism of action of plant extracts to control leaf rust of wheat. The leaf extracts of J. mimosifolia, T. peruviana and C. procera—were found to reduce P. triticana spore germination in vitro. The disease incidence was significantly lower than in infected controls. Formulations containing leaf extracts and fungicide were significantly more effective in reducing disease incidence than fungicide alone. Activities of peroxidase, chitinase and phenylalanine ammonia lyase (PAL) were significantly higher in intercellular washing fluid (IWF) samples from plants treated with the leaf extracts of J. mimosifolia in combination with fungicide. The combined formulation of C. procera with fungicide significantly enhanced β-1,3- glucanase activity compared to full-dose formulation of fungicide. One-dimensional and Two-dimensional electrophoresis of IWF proteins followed by identification with mass spectrometry revealed increases in abundance of various defense-related gene products as a result of plant treatment with specific leaf extract formulations. Leaf extract formulations with fungicide significantly up-regulated the expression of defense-related genes encoding chitinase, glucanase, peroxidase and PR-proteins in the apoplast of wheat leaf infected with rust. It is inferred that the combined formulations of Jacaranda mimosifolia, Thevetia peruviana and Calotropis procera with very low concentration of chemical fungicide presents a new approach for the management of stalk rot in maize, leaf spot blotch and leaf rust in wheat.