The two main foci of the present study were:
a) Biological control of soil born plant pathogens, and
b) Role of fungi as indicator of anthropogenic air pollution.
Over a seven year study period extensive experiments were planned and a variety of assays were designed in pursuance of the goal. The outcome of the surveys and experimental work was fruitful and exciting.
Focus I: Biological control of root borne plant pathogens has been first of the two major objectives of the present study First chapter describes the details relevant to this objective. The goal of biological control was successfully achieved by:
Using arbuscular mycorrhiza separately and in combination with beneficial antagonistic fungi. It is concluded from the results that diseases can be controlled biologically by employing arbuscular mycorrhiza. Mycorrhizal plants showed a significantly better response when exposed to pathogens as compared to those which did not had a prior inoculum of arbuscular mycorrhiza. Plants when inoculated with beneficial antagonistic fungi like Trichoderma along with arbuscular mycorrhiza, the response was further enhanced.
Use of antagonistic soil fungi in various combinations have also proved useful in achieving the objective of bioprotection. The fungi like Trichoderma viride and Aspergillus flavus used in combination or inoculated separately provided a comprehensive control of disease biologically. The specific soil moisture contents however being critical for best performance.
Soil is a medium of growth for microbes and plant roots. By altering soil and other conditions while manipulating the use of AM and other beneficial antagonistic fungi, significant results have been obtained in the present study. Soil texture has been found to be an important factor affecting the efficacy of arbuscular mycorrhizal fungi. The results have shown that the soil mix, which could retain lesser moisture, provides conducive conditions for mycorrhizal fungi and therefore better control of plant diseases.
In yet another segment to further manipulate the role of AM and beneficial antagonistic fungi, pretreatment of seeds/fungal cultures with IAA, NAA and humic acid was employed in possible strategy for bioprotection. Lower concentrations like 100 and 150 ppm were promising. The results of this part have very strongly emphasized the effective use of growth stimulants in plant microbe relationships. The resistance levels of plants getting seed presoaking treatment in specific concentrations of auxins and humic acid have also improved.
Focus II: In this part of the study some open-top chamber experiments were designed for three economically important plants. Better growth and performance was noticed in all three plants supplied with filtered air in open-top chambers. Significant reductions were recorded in unfiltered (dust free) and ambient air.
In a first ever investigation, an attempt was made to relate the impact of pollution to diversity and density of arbuscular mycorrhizal association. The results presented in this segment have shown that the anthropogenic air pollutants like O3, NO2 and dust particles (to some extent) affect mycorrhizal plants but the effects were severe on plants without arbuscular mycorrhiza. Furthermore, some of the species of arbuscular mycorrhizal fungi and other soil mycoflora exhibited better tolerance to air pollution in comparison to the rest of the associated microbes.