Studies on root excretion and the rhizosphere microflora in peas (Pisum sativum)

Abstract

It has been recognised that soil microflora is complex and it is responsible for the numerous reactions in the soil, which in turn, influence the plant growth. The decay of dead plant and animal residues, solubility and availability of nutrients, plant diseases and the beneficial association of plants and organisms are some of the established facts, which are directly the results of the heterogeneous microflora. But many processes, which are attributed to particular microflora, isolated from the soil and subsequently grown on enriched media could not be proved successfully under field conditions, due to different environmental conditions in the latter and the influence of other organisms, which exist in soil. Therefore, the evaluation of the role of micro-organisms in soil science, has become difficult, even though most of the soil fertility processes are directly connected with soil microflora. Recently, a new approach for the study of microflora has been made in the hope that this method may help in elucidating some problems, which relate to the association of pants and organisms. This approach is based on broadly classifying the microflora and studying their nutritional requirements and physiological characteristics. Especially so in Rhizosphere, which is a zone of enrichment due to root excretions and decay of roots. In the Rhizosphere, the soil microflora is stimulated more, and the nature of it largely furnishes the information of its beneficial or adverse effect on the plant. At the same time, furnishes a fund of information about the physiological aspect of plants, which is responsible for promoting a particular type of microflora which may be beneficial or injurious to plant itself. It has been established by the Canadian investigators and other workers that the rhizosphere microflora in some disease resistant and susceptible varieties of crops differ quantitatively and qualitatively and is numerically larger and physiologically more active in the susceptible varieties than the resistant one. This difference is attributed to the metabolic substances exuded by the plants. These metabolic products inhibit the growth of organisms in the resistant variety and stimulate them in the susceptible varieties. The excess multiplication of soil flora in the root zone of the susceptible variety, probably, provides a clue for the physiology of the plant, as well as for the possible disease infection, due to the lack of vigour in plant growth on account of severe competition for food by the organisms. It is known that Fusarium lini causes wilt disease in peas. The primary object of the present study is to differentiate the microflora of Rhizosphere in resistant and susceptible varieties of peas, quantitatively and qualitatively, in order to see whether the results of pea varieties also follow the same trend as noted by the Canadian investigators in the case of flax and tobacco. If so, the aim is to correlate the differences in microflora with the physiological characteristics of pea varieties through their root excretion studies.