BIOLOGICAL CONTROL OF FUSARIUM WILT OF CUCUMBER (Cucumis sativus) BY ANTAGONISTIC LACTIC ACID BACTERIA ISOLATED FROM RHIZOSPHERE OF FIVE MEDICINAL PLANTS

Abstract

Fusarium wilt is one of the important diseases of cucumber and causes economic loss to farmers. The present study was undertaken to evaluate the potential of rhizosphere lactic acid bacteria as biocontrol agents of Fusarium wilt of cucumber. Lactic acid bacteria (LAB) were isolated and identified from the rhizosphere of five medicinal plants. The in-vitro antagonistic activity of LAB strains on F. oxysporum f.sp. cucumerinum was evaluated by dual culture method. The screen house experiment was then conducted to assess the effect of antagonistic LAB isolates on Fusarium wilt disease incidence in cucumber plants. The antagonistic LAB strains were further characterized using 16S rRNA gene sequencing technique. The total LAB counts of rhizospheric soil samples ranged from 7.0×10⁵ cfu/g to 15.0×10⁵ cfu/g. The LAB isolates were identified as strains of Lactobacillus acidophilus (21.4%), L. plantarum (35.7%), L. fermentum (28.6%), L. alimentarius (7.1%) and L. brevis (7.1%). Treatment of cucumber seeds with antagonistic LAB strains significantly reduced Fusarium wilt of cucumber incidence from 95% to 48%. Lactobacillus fermentum isolated from the rhizosphere of A. indica exhibited strong disease suppression (49.5%). The study therefore revealed that the rhizospheric-LAB could be applied to reduce the manifestation of Fusarium wilt in cucumber.