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Subject: Soil Science × Author: Devi, Yumnam Bijilaxmi × Start date: 2013 × Type: Thesis × Thesis Type: Ph.D ×
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    ThesisItemOpen Access
    CULTURABLE ENDOPHYTIC ACTINOBACTERIA: ISOLATION AND CHARACTERIZATION FROM RICE PLANTS
    (AAU, Jorhat, 2017-10) Devi, Yumnam Bijilaxmi; Nath, DhrubaJyoti
    In the present investigation, endophytic actinobacteria were isolated from six different varieties of rice namely Aghoni Bora, Badshabhog, Basundhara, Ranjit, Joha andSolpuna. Samples were collected from 33 sites located at Golaghat and Jorhat districts of Assam. The isolates were assessed for morphological characterization, biochemical characterization and physiological features with special reference to antimicrobial activities against pathogenic fungi as well as bacteria. Finally, eleven selected isolates were subjected to 16S rDNA sequence analysis for establishment of their genotypic position. Altogether 57 isolates were obtained from six varieties of rice in Starch Casein Agar (SCA) and Casein Yeast Extract Glucose Agar (CYGA) medium. Overall, occurrence of actinobacteria colonies were more prominent in roots compared to stems and leaves. Among the six different rice varieties, the frequency of morphologically well recognized actinobacteria colonies were found to be significantly highest in Solpuna in roots (131.00 g-1), stem (117.00 g-1) and leaves (106.00 g-1). Based on distinct colony morphology and prominent growth without contamination on SCA media, 24 isolates were selected for in-vitro plant growth promoting traits. The growth of all isolates was found to be optimum at pH 7.2 and at temperature 300C ranging from 4.78 to 7.94 log cfumL-1 and 5.00 to 8.67 log cfumL-1respectively. Most of the isolates showed positive result for intracellular and extracellular enzymatic activities. 50% of the isolates showed positive result for gelatin liquefaction. All the isolates except AL2 and SL3W could hydrolyze lipid. 70.83% showed positive result for nitrate reduction. All the isolates except AL2 and SR4 showed negative reaction for catalase activity. Except AS1, SL3W and WNPR1, all the isolates illustrated positive urease activity. All the isolates displayed negative result for H2S production except AS1. 62.5% isolates could produce siderophore and all the isolates could produce hydrogen cyanide. The ability of the isolates to solubilize P was recorded after 7 and 14 days of growth. After 7 days of growth, the value ranged from 0.067 to 0.500 µg mL-1 and 0.067 to 0.633 µg mL-1 after 14 days of growth. The isolates showed similar result in IMViC (Indole, Methyl red, VogesProskaur’s and Citrate utilisation), 66.7 % isolates giving positive result for methyl red test.Rare utilization of carbon sources utilization was observed in all the isolates.Twenty two isolates showed antimicrobial activity against at least three pathogenic fungi. Isolate AS1, AL1, ABR1, BRL2, BRL3, BSS1, BSL1, SS1, SS3, SS5, SL1, SL2, SL3W, SL3Y and SL4 showed inhibition against all the four pathogenic fungi viz.Fusarium oxysporum, Rhizoctoniasolani,Curvularialunataand Sclerotiniasclerotiorum. Overall, isolates BSL1 and SL3W showed high inhibition against all the four pathogenic fungi tested.Six isolates out of twelve selectedviz. ABR1, BRL2, BSL1, SL1, SL3W and SL4 showed high inhibition against pathogenic bacteria Xanthomonasoryzae and four isolates ABR1, BRL2, BSL1 and SL1 exhibited inhibition against Erwinia sp. The inhibition zone ranged from 17 to 24 mm against Xanthomonasoryzae and 19 to 30 mm against Erwinia sp. The isolates showing high antimicrobial properties showed antibiotic resistance against few common antibiotics. Taxonomic identity of selected 11 isolates belonged to Streptomyces longispororuber, Nocardiopsissp., Streptomyces rochei, Streptomyces finlayi, Nocardiopsisalba, Streptomyces sp., Streptomyces parvulus and Streptomyces coelicolor. Most common genus was found to be Streptomyces (81.8%).In conclusion, it was established that rice plants of Assam harbors potential endophytic actinobacteria possessing multiple plant growth promoting traits with antimicrobial activities. These isolatescould be potential candidates for inclusion in integrated nutrient management and organic farming as a means of growth promoter as well as plant disease suppressor.