Abstract
The balance between beneficial and harmful microorganisms in the rhizosphere has an important bearing on crop productivity. The manipulation of this relationship in favour of the beneficial species is now a realistic possibility. Many rhizosphere bacteria release volatile HCN from the degradation of certain plant root exudates. For example, linseed (Linum usitatissimum) exudes an average of 6.9 nmol of cyanogenic glucosides per plant per week which are rapidly hydrolysed in non-sterile soil. Sensitive assays have been developed which reveal cyanide concentrations in excess of 12 nmol.g -1 soil under bracken (Pteridium aquilinum) and 5.5 nmol.g-1 soil under wheat. Cyanogenic bacteria have the potential to be both plant growth inhibitory and to restrict the growth of fungal phytopathogens. Laboratory and greenhouse experiments using cyanogenic Pseudomonas fluorescens species as root inocula are described. Phospholytic rhizosphere microorganisms are capable of solubilizing phosphate. The changing activities and composition of various phosphatases during the growth of various plants-and following infection with VA mycorrhizae is described. Acid and alkaline phosphatases have been immobilized in various ways and tested for their stability in soil and capacity to release orthophosphate from organic P. The potential of these preparations will be evaluated. Finally, microbes and enzymes are being examined to discover if they can be used to restrict the growth of root pathogens such as Pythium species, to stimulate the degradation of agricultural waste, and to accelerate pesticide degradation. © 1989 Vlastimil Van?ra, FrantiÅ¡ek Kunc.