Antagonism of walnut endophytic bacteria against six crop pathogenic fungi and its diversity

Abstract

Plant endophytes are great resources and potential capital in versatile application, including plant diseases biocontrol. We aimed to evaluate the antagonism of English walnut endophytic bacteria against different crop pathogenic fungi, to provide more alternatives for future disease biocontrol agents. The biocontrol capacity of thirty-six walnut endophytic bacterial isolates against the anthracnose fungus, Gnomonia leptostyla was evaluated. Fifteen isolates were tested against other five pathogenic fungi such as the cauliflower black spot pathogen, Alternaria brassicicola; the tobacco brown spot pathogen, A. alternata; the corn leaf spot pathogen Curvularia lunata; wheat Fusarium head blight pathogen, Fusarium graminearum and the cucumber anthracnose pathogen Colletotrichum orbiculare. From our results, it was observed that all the assayed strains suppressed the growth of six fungal pathogens at least 20% in petri dish. Among the endophytes, the highest inhibition rates were observed in endophytes XWR6 and XWL14 against A. brassicicola with values of 68.8 and 61.6% respectively; and the endophyte XWS7 against walnut anthracnose pathogen has the inhibition value of 60.5%. Particularly, endophytes XWS7 and XWS4 isolated from walnut stem, showed an inhibition rate above 40% in all the tested pathogens. Biochemical, physiological and phylogenetic analysis based on 16S-rDNA and gyrB sequences, allowed the identification of the fifteen endophytes at Bacillus spp. However, physiological differences and sequence diversity was observed among the isolates. These findings reveals English walnut endophytic bacteria have strong antagonism activities against crop pathogenic fungi, and show diversity in biochemical, physiological, 16S-rDNA and gyrB sequences.

Keywords: Walnut, endophyte, walnut anthracnose, antagonism, Bacillus spp.