Biocontrol of tomato leaf curl virus (ToLCV) in tomato with chitosan supplemented formulations of Pseudomonas sp. under field conditions

Abstract

Of all the disease reported in tomato, the tomato leaf curl virus (ToLCV) disease is cited to be the most devastating both in terms of quantitative and qualitative yield losses. Often, the loss reaches to the extent of 100% during summer throughout India. Several majors have been taken to control the vector Whitefly. However, it has not been very effective in preventing epidemics and yield losses due to these viruses. There has been several researches done in this regard but so far, no economically viable management practices are available to manage ToLCV in tomato crop. Hence, the present investigation was carried out to evaluate previously proven potent rhizobacterial isolates against ToLCV. The investigations were carried out with potent rhizobacterial isolates alone and, along with elicitor molecules such as chitosan to determine its ability to control ToLCV in tomato. Different formulations of PGPR and chitosan were evaluated for controlling ToLCV and growth promotion of tomato under field conditions. A field experiment was laid out using a randomized block design (RBD) conducted in July, 2011, to study the efficacy of potential rhizobacterial strains along with chitosan in plant growth promotion and against ToLCV at a field in Dharwad, Karnatka, India. It was found that the application of Pseudomonas sp. in combination with chitosan reduces the severity of the ToLCV disease by 80.33-90.33 per cent. Application of chitosan or the bacterial inoculant alone was not effective to control the severity of ToLCV disease. However, the plants inoculated with the chitosan based formulation of Pseudomonas sp.(206(4) +B-15+ JK-16) recorded the highest activity of ISR molecules and recorded maximum plant height, total biomass, chlorophyll content, fruit number and yield over the diseased control. The quantification of viral load was done by semi quantitative PCR analysis which revealed the lowest viral load in plants inoculated with both chitosan and Pseudomonas sp. 206(4) + B-15+ JK-16. After application of chitosan, substantially higher number of bacterial cells on the roots was observed through scanning electron microscopy without any morphological and other qualitative differences. The results, thus, indicate that addition of chitosan has enhanced the biocontrol efficacy of Pseudomonas sp.against ToLCV.