Biocontrol potential of endophytic Pseudomonas stutzeri isolated from watermelon (Citrullus lanatus Thunb) against Colletotrichum orbiculare causing anthracnose disease in watermelon

The biocontrol potential of bacterial endophytes isolated from watermelon leaf was evaluated against the pathogen causing anthracnose disease in watermelon. Totally ten Colletotrichum isolates were isolated using tissue segment method and confirmed as Colletotrichum sp. based on the cultural and morphological characteristics. The virulence of the pathogenic isolates was confirmed through pathogenicity test. Among the 10 isolates, WEC 2 was identified as a highly virulent isolate. Eighteen bacterial endophytes were isolated from healthy watermelon plants and identified as Bacillus spp. (10 isolates) and Pseudomonas spp. (8 isolates) based on the cultural characters. The effect of 18 bacterial endophytes was tested against the highly virulent Colletotrichum isolate WEC 2 using dual culture technique. Among the 18 bacterial endophytes, isolate WE 8 was found to be highly potential in inhibiting the pathogenic isolate WEC 2. The next best isolate was WEC 17, which exhibited 57.78% inhibition of pathogen over control. The least mycelial reduction was depicted by the isolate WE 16. The pathogenic isolate (WEC 2) was further confirmed at molecular level using the universal primers ITS 1 and ITS 4 as Colletotrichum orbiculare (WEC 2) and the potential bacterial endophytic isolate WE 8 as Pseudomonas stutzeri (WE 8) using ITS 27 F and ITS 1492 R primers.