Alterations in Rhizosphere Microflora
Foliar application of various chemicals leads to alterations in the rhizosphere microflora by changing the pattern of root exudates. The pattern of the rhizosphere microflora i.e. numbers and species composition can be changed / altered by various factors, such as: (i) Soil amendments, (ii) Foliar application of fertilizers / nutrients, fungicides, insecticides and hormones and (iii) Bacterization / microbial seed inoculants.
A. Soil amendments:
Soil amendments with inorganic and organic fertilizers can alter the rhizosphere microflora and an understanding of the type of changes in the microflora can be useful in the indirect control of pathogens. Dwivedi and Chaube (1985) showed that amendment of soil with neem-cake can stimulate the activity of actinomycetes which results into the reduction of propagules of Macrophomina phaseolina. It is also known to control phytopathogenic nematodes in soil by stimulating nematode trapping fungi. Amendment of soil with castor and bean leaves stimulate the activity of Trichoderma viride and Penicillium in the rhizosphere leading to the control of Sclerotium rolfsii.
B. Foliar application of fertilizers and agrochemicals:
Translocation of photosynthete from leaves to roots takes place as a part of the normal metabolic activity in plants. Therefore, organic substances, including plant protection chemicals (fungicides, insecticides), growth regulators and plant nutrients applied to foliage / leaves get absorbed into the leaf tissue and further get translocated to roots along with photosynthates. Many workers have reported that foliar application with various chemicals cause marked alterations in the number and kind / qualities of microorganisms in the rhizosphere of several cereals and leguminous crop plants. Thus, such an approach can be used as a new tool in the biological control of root diseases, stimulation of activity of nitrogen-fixing bacteria and other beneficial microorganisms in the soil.
C. Seed treatment with bio inoculants:
Bio inoculants such as Azotobacter, Beijerinckia, Azospirillum, Rhizobium or P -solubilizing microorganisms (eg. Bcillus, plymyxa, Azotobacter croococcum, Aspergillus niger, Penicillium digitatum etc.) When applied to the seed / soil helps in the establishment of beneficial microorganisms in the rhizosphere region which will further benefit in plant growth, encourage inhibition of plant pathogenic organisms in the root vicinity and enrich the soil with added microbial bio-mass.