Studies of the effects of fungicides on the rhizosphere of Pisum Sativum L. Var victory freeze: A thesis submitted in partial fulfilment of the requirements for the Degree of Bachelor of Horticultural Science with Honours in the University of Canterbury

Abstract

The concept of 'rhizosphere' gradually took shape in the late 19th century as a direct result of the long recognized intimate association between the plant roots and the soil micro-organisms. Following Hellreigel and Wilfarth's discovery of the symbiotic relationship between nodule-bacteria and leguminous plants in 1888 (Clark, 1949), there has been immense interest in the studies of the plant rhizosphere, but it was not until 1929-1931 when Starkey observed that microbial number and activities were differentially stimulated by plant roots and that the rhizosphere population was affected by factors such as plant type, plant age, conditions of plant growth etc., that the scope of plant rhizosphere studies widened. Subsequently, the region where plant roots are in close contact with the surrounding soils has been shown to be a region of great microbial activity, and therefore any beneficial or toxic effect the microorganisms may have on the plants is most revealed here. This is true of course in the reverse sense and the term "rhizosphere effect" has been designated to the effect of plant roots on the micro-organisms. Environmental factors such as soil conditions, light intensity, relative humidity etc., are also reported by many workers to have profound influence on the rhizosphere micro-organisms but more often this influence is indirect in the sense that the plants are affected and they in turn, through their root exudates, tip the balance of a rhizosphere microflora which was previously in equilibrium. The studies of plant rhizosphere have now broadened to include several important issues such as the role of the rhizosphere microflora in the formation of a stable soil structure; the importance of the rhizosphere microflora in the differential susceptibility and resistance of plant roots to disease; the residual effects of rhizosphere microflora in successive cropping and the possible manipulation of the rhizosphere composition for a more desirable plant growth.