Isolation and Characterization of Mesorhizobium Sp. Bacterial isolates were recovered from chick pea root nodules collected from different sites of Dehradun. All isolates showed colonies similar in appearance with large mucoid (LM) and large watery (LW) with diameter of 2-4.5 mm, round, white colored till 3-4 days of growth and turning yellowish in color after 4 days. All isolates were gram negative rods (Table 1) Selected isolates were catalase positive as confirmed by the liberation of oxygen around the bacterial colonies. Positive results for oxidase and urease were also observed by different isolates. None of the strain showed growth on medium containing methylene blue (0.1%), gentian violet (0.1%), glucose peptone agar and citrate agar. All isolates showed growth on lactose peptone agar. Positive results were obtained from starch hydrolysis assay, when the inoculated plates were subjected to iodine test, which was indicated by a clear zone around the colonies. All the isolates were gelatinase negative as there was no clearing zone formed around the colonies . On the basis of these tests forty isolates were designated as BCR1-BCR14, ECR1-ECR4, TCR1-TCR5, SCR1-SCR8, DCR1-DCR5, MCR1-MCR2 and HCR1-HCR2.(Table 2.0).
Effects of Salt and Ph on Different Mesorhizobium Isolates
Tolerance of rhizobial isolates to NaCl concentration showed variation among strains. All isolates showed growth at YEMA containing 2%, 3% and 4%,of NaCl. isolate. At higher concentrations, number of tolerant strains decreased rapidly and only eight isolates i.e. BCR2, ECR2, SCR3, SCR5, SCR6, DCR3, DCR4, & DCR5 tolerated NaCl concentrations of 5%, 6%, 7%, & 8% (Figure 1) Differences in pH tolerance are shown in Figure2. All isolates except SCR5 grew at pH 4.0 to 8.5. All were found to resist at pH 9.0.
Antibiotic Resistance Pattern of Recovered Isolates
All isolates were sensitive to Meropenem, Netillin, Amikacine, and Ceftriaxone. Resistance to Ampicillin, Streptomycin, Amoxycilline, Clindamycin, Polymyxin-B, and Cefalexin was recorded for only 45%, 5%, 57.5%, 25%, 10% and 12.5% of the isolates, respectively. Isolates BCR13, BCR14, SCR4, SCR5, SCR6, SCR7, DCR3, DCR4, MCR1, and HCR1 were found to be tolerant to almost all antibiotics. Maximum resistance were observed with Amoxycilline and Ampicillin, the most potent antibiotics that allow the growth of only few isolates (Figure3).
Carbohydrate Utilization Pattern of Mesorhizobium Isolates
Almost all of the isolates were able to catabolize a large variety of carbon substrates (Tables 4.7). All tested strains grew on Mannitol, Lactose, Sucrose, Sorbitol, Arabinose, Galactose, Mannose, Maltose, and Raffinose except Dextrose. Only 47.5% isolates utilized Dextrose. All isolates utilized Sorbitol except TCR2 & DCR7 and only DCR7 was also unable to utilized Mannose. 97.5% of the isolates utilized Raffinose and Mannitol (Figure4).
Effects of Different Concentration of Fungicides on Mesorhizobium Isolates
The results presented in Figures 5-8 shown the effect of four fungicides namely Mancozeb, Zineb, Thiram & Carbendazim .All parameters depends on the tested fungicide and applied concentrations. Almost 98% isolates were found to be sensitive against Mancozeb, Thiram and Zineb. SCR4, SCR2, and MCR1 were found to be resistant at 25, 50, 75, concentrations, respectively against Mancozeb. DCR5 and MCR1 were resistant to all concentrations of Zineb. At lower concentration (25mg/l) BCR11, TCR5, SCR1, SCR6, SCR8 were showed no zones against Thiram.Most of the isolates showed resistance behavior while using Carbendazim.. Twenty three isolates ie. BCR1, BCR2, BCR7, BCR9, BCR12, BCR13, BCR14, ECR1, TCR1, TCR2, TCR3, TCR5, SCR1, SCR2, SCR3, SCR4, SCR6, SCR7, SCR8, DCR3, DCR4, HCR1 and HCR2 showed resistance to all tested concentrations used in present study.