Taxonomic identification of rhizospheric actinobacteria isolated from Algerian semi-arid soil exhibiting antagonistic activities against plant fungal pathogens

Abstract

The rhizosphere is a rich source of actinobacteria and some members of this bacterial group present strong abilities in the biocontrol of plant diseases. In the present study, 72 strains of actinobacteria were isolated from different rhizospheric semi-arid soils collected in Algeria. Their in vitro antagonistic activity was assayed toward the following plant pathogenic fungi: Verticillium dahliae, Fusarium culmorum, Drechslera teres, Microdochium nivale, Bipolaris sorokiniana, Botrytis fabae and Fusarium oxysporum. All isolates showed chitinolytic activity and six isolates (Lac1, Lac3, Vic8, Pin10, Pru14 and Pru16), which inhibited the growth of five or more of the fungi tested, were selected for further study. According to morphological and physiological characteristics, as well as phylogenetic analysis of 16S rRNA gene sequences, isolates Lac1, Lac3, Pru14 and Pru16 were identified as members of the genus Streptomyces, namely S. griseus, S. rochei, S. anulatus and S. champavatii, respectively. Two isolates, Vic8 and Pin10, were associated with the Nocardiopsis genus and identified as N. dassonvillei subsp. dassonvillei and N. alba, respectively. While antagonism of Streptomyces has been demonstrated against a wide variety of plant pathogens, only a few studies have reported production of antifungal products by the genus Nocardiopsis.