Effect of soil amendment with Eucalyptus rostrata leaves on activity of hydrolytic enzymes, total phenol content and onion-white-rot disease incidence

Abstract

Summary The application of Eucalyptus leaf amendments to soil was not only efficient in controlling the white rot disease of onion caused by Sclerotium cepivorum, but also in production of significantly higher crop yield after 5 months growth. The pectolytic activities of healthy untreated bulbs transplanted in unamended or amended soils fluctuated between 46–51 and 43–58% reduction in viscosity of pectin, respectively. A tremendous increase in enzyme activities ranging from 88–100% was evident when bulbs became infected. The cellulolytic activities in both healthy and diseased tissues were lower than the pectolytic activities. Eucalyptus amendment was promotive to cellulases in healthy onion bulbs, but the infected ones showed a clear depression. Contrary to the high phenolics in infected tissues, the relatively low level of such compounds in bulbs of healthy uninfected onion plants most probably indicates that the soil itself was the area of struggle and inhibition of the pathogen. On the other hand, the healthy bulbs previously planted in Eucalyptus-amended soil showed higher phenolic content than their corresponding untreated ones.