In vitro antagonism of rhizobacteria isolated from coffea arabica l. Against emerging fungal coffee pathogens

Abstract

In vitro antagonistic effects of rhizobacteria associated with Coffea arabica L. against some fungal coffee pathogens were studied. The aims were to screen indigenous coffee-associated isolates for their inherent antagonistic potential against major coffee wilt diseases induced by Fusarium spp. Antagonistic effects, siderophore, HCN and lytic enzyme production were determined on standard solid media. Chemical methods were employed to categorize the major types of siderophores. From a total of 212 rhizobacterial isolates tested, over 10 % (all Pseudomonas and Bacillus spp.) exhibited remarkable inhibition against Fusarium spp. One isolate AUPB24 (P. chlororaphis) showed maximum inhibition of mycelial growth against all fungal pathogens tested, whereas other isolates were mostly inhibitory to F. stilboides and F. oxysporum. The isolate AUBB20 (B. subtilis) was most antagonistic to F. xylarioides. Of the rhizobacterial isolates tested, 67 % produced siderophores and 35 % produced HCN. Many strains (all Pseudomonas spp.) produced siderophores of the hydroxamate type and only a small proportion produced those of the catecholate type. Few antagonists showed chitinase activity. The production of siderophores and HCN by Pseudomonas spp., lipase and protease by all antagonists and b-1,3-glucanase by several Bacillus spp. could be considered the major mechanisms involved in the inhibition of fungal growth. The in vitro results provide the first evidence of an antagonistic effect of coffeeassociated rhizobacteria against the emerging fungal coffee pathogens F. stilboides and F. xylarioides and indicate the potential of both bacterial groups for biological control of coffee wilt diseases. Keywords: Fungal coffee pathogens, Rhizobacteria, Siderophores Received: June 19, 2007; revised: September 6, 2007; accepted: September 7, 2007 DOI: 10.1002/elsc.200700004