Effect of Cadmium Salts on Some Growth and Metabolic Activities of Selected Fungi from the Rhizosphere of Glycine max and Zea mays PDF

Keywords

mycelial, cadmium, fungi

Abstract

Six fungi, isolated from the rhizosphere of Glycine max and Zea mays, were selected for their variable resistance to soil application of cadmium nitrate and cadmium sulphate, at the range of 100-1000 ppm concentration. These were (a) Aspergillus terreus and Rhizopus oryzae: (b) Paecilomyces divaricata, Curvularia tetramera; (c) Fusarium oxysporum and (d) Cladosporium herbarum Fifty ppm cadmium salts exerted no effect on spore germination of R. oryzae, F. oxysporum or C. tetramera, stimulated A. terreus and P. divaricata and suppressed C. herbarum. 100 ppm dose exerted variable effects dependent on the organism and/or accompanying anion. 1000 ppm cadmium arrested spore germination of all the tested fungi except F. oxysporum where marked suppression were observed. Cadmium arrested growth of C. herbarum and P. divaricata at 50 ppm, initiated that of A. terreus, C. tetramera and F. oxysporum but seemed without effect on R. oryzae. Larger doses seemed to be inhibitory to all organisms, R. oryzae being least affected. Seven-day old mycelial felts of the last mentioned four fungi were produced from 5 mm diameter mycelial discs grown on media containing 0, 50, 100, or 500 ppm cadmium nitrate or cadmium sulphate. These, as well as the media, were analysed for their nitrogen and phosphorous components. The results show that nitrogen secretion was not a function of tolerance of the fungi to cadmium applied to the soil but was largely controlled by the effect of cadmium on the permeability of the cells of each individual fungus. Cadmium seemed to stimulate nitrogen metabolism of Aspergillus and Fusarium, had little to no effect on that of Rhizopus but suppressed that of Curvularia. Most accumulated nitrogen was in the form of amino and other soluble nitrogen. Cadmium inhibited the incorporation of absorbed phosphorus into energy-rich compounds. this was concomitant with the failure of amino acid incorporation into proteins