MSc

Rhizobacteria that are beneficial to the plant growth and development are often referred to as plant growth promoting rhizobacteria (PGPR). Application of PGPR is often found to increase plant growth, development and yield. Now a days, use of PGPR is on an increasing trend in sustainable ecofriendly agriculture. Along with the micro organisms, the farming community is still applying plant protection chemicals and fertilizers in modern agriculture. Even though chemical application will help a lot to protect the crops from pest and diseases, their application may influence the PGPR also. Scientific data on the compatibility aspects of agricultural chemicals with PGPR is scanty. With this in view, the present study on ‘ Population dynamics of plant growth promoting Rhizobacteria under the influence of agricultural chemicals’ was taken up at College of Horticulture, Vellanikkara, during 2003-2007. Five numbers of fungicides, insecticides and herbicides were tested along with their combinations in vitro and in the field. The ultimate idea was to evolve a database for compatibility of chemicals and PGPR.

The studies revealed that the fungicide copper oxychloride was most deleterious to the growth of Azospirillum sp. and P. fluorescens, whereas, tridemorph inhibited the growth of B. subtilis under in vitro conditions. In the combination studies, it was found that the fungicide mancozeb when combined with all herbicides and all insecticides inhibited the growth of Azospirillum sp. The combinations of all fungicides with paraquat and the combination of copper oxychloride with carbaryl were found highly inhibitory to the growth of B. subtilis. The combination of the insecticide lindane with the herbicide paraquat was inhibitory to the growth of Azospirillum sp. In the case of B. subtilis, the combination of carbaryl with paraquat was deleterious.

Another result was that, the fungicide carbendazim, all insecticides except carbaryl and all herbicides except paraquat were least inhibitory to all the test organisms at their recommended doses under in vitro conditions. In the combination studies, carbendazim with all insecticides and herbicides were found least inhibitory to the growth of PGPR. Also the combination of lindane, lamda cyhalothrin and chlorpyriphos with the herbicide 2, 4 –D were found least inhibitory to the growth of these beneficial rhizobacteria.

In the field situation, the chemicals carbendazim, chlorpyriphos and 2, 4-D were evaluated against these beneficial rhizobacteria and it was found that these chemicals affected the bacterial population immediately after their application to soil. All the bacterial populations recorded a decreasing trend as the rice plants grow. This trend was also noticed in the treatments where these PGPR were applied alone. The treatments significantly influenced the growth parameters of the rice plants and the post harvest observations like shoot weight, root weight, root length and panicle weight. Increase in growth parameters like plant height, production of tillers and productive tillers were recorded in the treatments where these PGPR were applied in combination with chlorpyriphos. In the post harvest observations like shoot weight, root weight and root length, positive influence was maximum in the same treatments. But the panicle weight and nutrient content were maximum in the treatments where all the beneficial rhizobacteria applied alone.

Based on the overall results on the studies, compatibility charts of agricultural chemicals and PGPR were prepared which will be a base for future recommendations on the use of chemicals and PGPR together.