A. S. Lubaina1*, K. Murugan2
1Department of Botany, Christian College, Kattakada, Thiruvananthapuram, Kerala, India
2Plant Biochemistry and Molecular Biology Laboratory, Department of Botany, University College, Thiruvananthapuram, Kerala 695 034, India
*Address for Corresponding author
A. S. Lubaina
Department of Botany, Christian College, Kattakada, Thiruvananthapuram, Kerala, India
Objective: The perception of inductive signals from phytohormones coupled with developmental processes has received considerable attention in defence mechanism. Cytokinins are phytohormones that are involved in multiple physiological processes including plant immunity. Alternaria leaf spot is a major biotic pressure in Sesamum orientale leads to loss of yield. Plant extract based induction of defence is one of the challenged areas in plant disease management. An attempt was made to evaluate the efficacy of aqueous extract of Salvinia molesta against Alternaria sesami in sesame under in vitro condition. Materials and methods: Cytokinin isolated from the fronds of aquatic fern S. molesta and subjected to bioassay. The fractionation and quantification of isolated cytokinin by HPLC followed by light microscopic analysis of sesame pre-treated with 10% aqueous extract of S. molesta. The molecular mechanism of signalling pathway analysed by semi-quantitative RT-PCR and the pathogen related protein profile by SDS-PAGE Results: The isolated cytokinin showed positive results in the soybean callus bioassay and its fractionation resulted sixteen isoprenoid cytokinins including transCK, cisCK, dihyroCK and iP (isopentenyladenine) forms. Further, light microscopic analysis revealed delayed fungal penetration and spreading of hyphae in the leaf tissue pre-treated with water fern extract. This data further substantiated the results of reduction in disease incidence and severity in the sesame. Semi-quantitative RT-PCR analysis revealed the significant expression of MAPK-4 during the early periods of infection. Subsequently, the SDS-PAGE analysis showed the formation of new pathogen related protein bands and also over expression of other bands. Conclusion: The results suggests that cytokinin present in S. molesta extract up regulates plant immunity via MAPK-4 signalling which in turn induce the formation of pathogen resistant proteins related to resistance in sesame against Alternaria leaf spot disease.
Keywords: Alternaria, sesame, disease score, mitogen-activated protein kinase signalling, cytokinin