Carbon and nitrogen nutrition in relation to growth and sporulation of Fusarium oxysporum f.sp. elaeidis

Abstract

The carbon and nitrogen requirements of two isolates of F. oxysporum f.sp. elaeidis were investigated. Of the 13 carbon compounds tested, inulin was the best source of carbon while d ( + )xylose and lactose were comparatively poor sources of carbon for growth and sporulation of both isolates. The fungus made good growth and sporulation on filter-sterilized raffinose hydrate, soluble starch and inulin. Out of the 10 nitrogen compounds tested, good growth and sporulation were recorded on sodium, ammonium and potassium nitrates, peptone and dl -leucine. While moderate growth of the fungus was recorded on ammonium sulphate, calcium nitrate, l -asparagine and dl -aspartic acid, sporulation in these compounds was poor and ammonium sulphate induced chlamydospore formation. There was an increase in the total growth of the fungus as the carbon concentration (sucrose) increased, but no significant increase in growth was recorded with increase in the nitrogen (KNO3) of the medium. Maximum growth was recorded in the highest C/N ratio tested (120:1). Increasing the C/N ratio of the medium resulted in reduced macroconidial formation and increased chlamydospore production. The C/N ratio also influenced macroconidial morphology. It is suggested that the carbon concentration is a more important factor than the C/N ratio of medium in inducing these phenomena.