MSc

A study on “Potentiality of endophytic micro-organisms in the management of leaf blight disease of amaranth” was carried out in the Department of Plant Pathology, College of Horticulture, Vellanikkara, during the year 2006-2007.

The pathogen causing the leaf blight of amaranth was isolated from both red and green amaranth types from different locations and all the isolates were found to be same and identified as Rhizoctonia solani Kuhn based on the cultural and morphological characters. Endophytic micro-organisms were isolated from red, green and wild amaranth types, which yielded more of endophytic bacteria than fungi. Based on the nature of growth, 46 bacterial and 17 fungal endophytes were selected for further work. These selected endophytes were tested for their antagonistic effect on the growth of R.solani by dual culture studies under in vitro condition. For comparing the efficiency of endophytes, two standard cultures each of fungal bioagents viz. Trichoderma harzianum (IISR) and T.viride (KAU) and bacterial bioagents viz. P.fluorescens (KAU) and P.fluorescens (TNAU) were also used.

Among the 46 endophytic bacteria, six viz. EB-4, EB-20, EB-22, EB-38, EB-43 and EB-45 showed antagonism towards R.solani with per cent inhibition ranging from 44.55 to 57.73. Out of the 17 endophytic fungi tested, only one fungus EF-2 recorded cent per cent inhibition of R.solani. The standard bioagents T. harzianum (IISR), T.viride (KAU), P.fluorescens (TNAU) and P.fluorescens (KAU) also showed antagonism towards R.solani with per cent inhibition of 91.1, 84.4, 57.27 and 57.73 respectively. Thus from the in vitro evaluation, six endophytic bacteria and one endophytic fungus were selected.

The cultural, morphological and biochemical characters of selected endophytic bacteria were studied. All isolates were observed as short rods and among them four isolates viz. EB-4, EB-20, EB-38 and EB-43 were found as Gram positive and endospore forming and were identified as Bacillus spp. The other two endophytes viz. EB-22 and EB-45 responded negatively to Gram staining and identified as Pseudomonas spp. Based on the cultural and morphological characters the endophytic fungus EF-2 was identified as Trichoderma harzianum Rifai.

A pot culture experiment was conducted to evaluate the efficiency of selected endophytes in managing leaf blight disease, promoting plant growth characters and inducing systemic resistance in amaranth. Their effects were compared with standard cultures of fungal and bacterial bioagents and fungicide, mancozeb. The results revealed that the endophytic bacteria isolated from red amaranth EB-22 and EB-43 were found to be efficient in reducing leaf blight disease severity in amaranth whereas EB-20 , EB-22 and EB-43 showed the ability to promote plant growth characters .

The isolates EB-20 and EB-22 recorded maximum peroxidase and polyphenol oxidase activity where as the standard cultures of bioagents viz. T. harzianum (IISR), P.fluorescens (KAU) and P.fluorescens (TNAU) showed high phenylalanine ammonia lyase activity. The uninoculated healthy plants recorded higher peroxidase activity but lower PPO and PAL activity than control.