Extracellular Chitinases of Fluorescent Pseudomonads Antifungal to Fusarium oxysporum f. sp. dianthi Causing Carnation Wilt |
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Authors: | Naosekpam Singh Ajit Rajni Verma V Shanmugam |
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Institution: | (1) Floriculture Division, Institute of Himalayan Bioresource Technology, Palampur, 176061, Himachal Pradesh, India |
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Abstract: | Vascular wilt of carnation caused by Fusarium oxysporum f. sp. dianthi (Prill. & Delacr.) W. C. Synder & H.N. Hans inflicts substantial yield and quality loss to the crop. Mycolytic enzymes such
as chitinases are antifungal and contribute significantly to the antagonistic activity of fluorescent pseudomonads belonging
to plant-growth-promoting rhizobacteria. Fluorescent pseudomonads antagonistic to the vascular wilt pathogen were studied
for their ability to grow and produce chitinases on different substrates. Bacterial cells grown on chitin-containing media
showed enhanced growth and enzyme production with increased anti-fungal activity against the pathogen. Furthermore, the cell-free
bacterial culture filtrate from chitin-containing media also significantly inhibited the mycelial growth. Both the strains
and their cell-free culture filtrate from chitin-amended media showed the formation of lytic zones on chitin agar, indicating
chitinolytic ability. Extracellular proteins of highly antagonistic bacterial strain were isolated from cell-free extracts
of media amended with chitin and fungal cell wall. These cell-free conditioned media contained one to seven polypeptides.
Western blot analysis revealed two isoforms of chitinase with molecular masses of 43 and 18.5 kDa. Further plate assay for
mycelial growth inhibition showed the 43-kDa protein to be antifungal. The foregoing studies clearly established the significance
of chitinases in the antagonism of fluorescent pseudomonads, showing avenues for possible exploitation in carnation wilt management. |
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