Induction of resistance against cowpea aphid-borne mosaic virus in vigna unguiculata var. sesquipedalis (l) verdcourt

Abstract

Studies were conducted to induce resistance in cowpea against CABMV using abiotic and biotic factors. Various abiotic and biotic factors were screened to find out their efficiency in local lesion host of the virus, Chenopodium amaranticolor and cowpea. Different chemicals and plant extracts were found to inhibit local lesions produced by CABMV. Salicylic acid and ethrel inhibited the formation of local lesions in C. amaranticolor. Pre inoculation spray of indigeneous materials viz. panchagavya and neem seed oil emulsion reduced the number of local lesions. But they were not as much effective as chemicals. Among the chemicals having antiviral properties, betadiene and manganese chloride showed better inhibition over control. Ten plant extracts were tested to induce resistance in cowpea plants. Phyllanthus niruri and Boerhavia diffusa recorded 100 percent inhibition of local lesions in C. amaranticolor. Pre inoculation spay of P. fluorescens, the biotic agent were found very much effective against CABMV. Biotic and abiotic factors that showed high inhibition percentage in local lesion host also reduced the symptom development in cowpea. Among the abiotic factors, chemicals like salicylic acid (250 ppm), ethrel (250 ppm), betadiene (0.1 percent) and plant extracts viz., Phyllanthus niruri (10 percent) and Boerhavia diffusa (10 percent) were used for evaluation. Pseudomonas fluorescens (TNAU culture, 108cfu ml-1), the biotic agent was also selected for the assay. AVPs were found very much effective in reducing the symptoms produced by CABMV in cowpea. Biochemical changes indicated a significant difference in protein in treated plants. P. niruri recorded maximum protein content. Among the treatments tested AVPs viz. B. diffusa and P. niruri recorded the maximum total sugar content in pre, post and simultaneous inoculation. P. niruri treated cowpea plants recorded increased reducing sugar content. Application of selected biotic and abiotic factors on cowpea cv. Sharika challenged with CABMV induced higher accumulation of phenolics. AVPs and chemicals inducing resistance showed accumulation of phenol when compared to healthy plants. Studies on the mode of action of AVPs and chemicals against CABMV revealed that they induced defence mechanism in plants challenged with CABMV. AVPs and chemicals treated and challenged with CABMV increased the accumulation of phenyl alanine ammonialyase, polyphenol oxidase and peroxidase, than healthy and virus inoculated control. Many defence proteins and PR-proteins were induced in response to various treatments. The induction of PR-proteins was more in leaves which were treated with biotic agent and also with plant extracts. This induction of PR-protein was more prominent during early stages of treatments and gradually decreased in due courses.