Studies on areca catechulinn with special ref to ganooerma lucidum : a fungal pathogen of area palm

Abstract

The fungus Ganoderma lucidum is one of the common pathogens of a number of tropical palms such as coconut, arecanut etc. Although the pathogenicity of the fungus on a wide range of hosts has been recorded, there are very few reports on the control of this disease and little is known about the biochemical aspect of the host plant as well as the pathogen; practically nothing is known regarding the role played by the extracellular enzymes such as pectolytic and cellulolytic enzymes, and phenol oxidases, which are known to play an important role in pathogenesis.

Two enzymes namely endopolygalacturonase and laccase which are suspected to play a major role in pathogenesis were chosen for studies. The first part (Chapters II and III) deals with the studies on the (a) effect of fungicides on the in vitro growth of G. lucidum and (b) the two enzymes, endopolygalacturonase and laccase, which are elaborated by the fungus into the culture fluid. Studies on the effect of various fungicides, antibiotics and phenolic compounds showed that the antibiotic cycloheximide and the fungicides Maneb and K.C. 1584 were potent inhibitors of the fungus growth. The arecanut tannin inhibited the growth only at 1.0% level. - 158 -

The optimum conditions such as time, pH, effect of different concentrations of carbon and nitrogen sources, vitamins, casein hydrolysate and yeast extract, necessary for the growth as well as for the elaboration of the enzyme endopolygalacturonase showed that maximum growth was obtained by 16th day at pH 4.5 but enzyme production was maximum on 20th day at pH 5.0–5.5. Although addition of vitamins and yeast extract enhanced the growth they had decreased the enzyme production.

The enzyme endopolygalacturonase has been purified 65 fold and its properties such as substrate specificity, time course of enzyme activity, optimum pH, temperature, and the effect of enzyme and substrate concentrations on enzyme activity have been studied. In addition, the effect of metal ions, inhibitors, fungicides have been carried out. The enzyme had two temperature optima (50°C and 70°C). Attempts to separate them were not successful. Among the fungicides, inhibition by Blitox 50 was more significant than other inhibitors tested. The metal ions copper, cobalt and mercury and calcium inhibited the enzyme activity.

Based on the results obtained it is concluded (a) this high concentration of tannin required to inhibit the growth and (b) the high concentration of iron content and low calcium content in the soil, may be partly responsible for the susceptibility of arecanut palm to this fungal infection