Development of root endophytic plant growth promoters as bio-inoculants for protray seedlings

Abstract

The study entitled “Development of root endophytic plant growth promoters as bio-inoculants for pro-tray seedlings” was conducted at College of Agriculture, Vellayani during the period 2013-15 with the objective to develop microbial root endophytic plant growth-promoters as bio-inoculants in pro-tray seedling production of major solanaceous vegetable crops chilli, tomato and brinjal. Microorganisms were isolated by triturating the roots of vigorously growing seedlings of tomato, brinjal and chilli after surface sanitization. Bacterial isolates were subjected to a preliminary screening on their respective hosts for plant growth promotion. Seedling vigour was assessed under green house condition in portrays using sterile planting medium. Endophytes with plant growth promoting ability selected through the preliminary screening were assessed under in vitro condition using dual culture plate assay for assessing the compatibility with Piriformospora indica (Pi). Piriformospora indica is a wide host root colonizing endophytic fungus which allows the plants to grow under extreme physical and nutrient stress condition. It belongs to the Sebacinales in Basidiomycota. Eight compatible bacterial endophytes (four from tomato, two from chilli and two from brinjal) were further evaluated for their growth promoting ability individually and in combination with P. indica. Bacterial inoculants were provided as seed treatment and the fungal inoculant as additive in the transplant medium. The bacteria were identified as Bacillus megaterium, Alcaligenes faecalis, Streptomyces leeuwenhoekii, Bacillus pumilus, Bacillus megaterium, Bacillus licheniformis, Bacillus thuringiensis thuringiensis based on 16s rRNA sequence homology. and BacillusThe plant growth promoting experiments in tomato indicated that the combination treatment of bacterial strain Streptomyces leeuwenhoekii with Pi was found to be statistically superior in shoot fresh weight, root fresh weight and root dry weight (1764.54 mg, 332.88 mg/plant and 26.45 mg/plant). Treatment Alcaligenes faecalis + Pi was found to be statistically superior in shoot length (15.23 cm) followed by the treatment Streptomyces leeuwenhoekii + Pi (14.45 cm). All the treatment were found to be superior over control. Root colonization by P. indica was not found to be influenced by the combined application with endophytic bacteria. By assessing the plant growth promotion in brinjal, significantly higher values with respect to shoot fresh weight, and root fresh weight ( 844.27 mg/plant, 83.03 mg/plant) were observed with the plant treated with endophytic bacterial isolate. Bacillus thuringiensis + P. indica showed superior mean height of 6.95 cm which was on par with Bacillus thuringiensis (6.74 cm). However the combination treatment of endophytic isolates with P. indica showed superior values compared to control. Analising the efficacy of the endophytic isolates in chilli for plant growth promotion indicated that treatment with the endophytic isolate Bacillus megaterium was found to be have significantly superior values in leaf number, shoot length, shoot fresh weight, and shoot dry weight (5.66, 11.93 cm, 855.20 mg/plant and 87.97 mg/plant). All the treatments including the combinations were found to be superior to control. P. indica has capability to induce resistance against biotic and abiotic stress, including drought, salinity resistance and bacterial, fungal and virus infection in plants. The current experiment suggest that native root endophytic bacteria can be used in combination with P. indica as far as plant growth is concerned. Further studies are required to assess the potential of such combinations in combating drought, salinity etc. plant diseases and helping the plant overcome