Eight isolates from sugarcane (S1-S8) and seven isolates from ryegrass (R1-R7) were obtained from endorhizosphere of both the crops. The growth of cultures S3, S4 (sugarcane) and R1, R2 (rye grass) on respective media was recorded to be circular and transparent in colour. Morphologically, the cells appeared to be gram negative, motile vibroids. Sugarcane (S1) and rye grass isolate (R6) exhibited formation of yellow colored irregular colonies and cells were motile, gram negative rods as observed under microscope. Lindberg and Granhall (1984) reported similar morphological characteristics in dinitrogen fixing bacteria from rhizosphere of temperate cereals and forage grasses.

Another kind of cultural characters were also observed for (S2) sugarcane and (R7) ryegrass isolates that appeared to have greyish white irregular colonies and morphologically were gram positive motile coccobacilli. (Table 1) These findings are similar to morphological characteristics of Bacillus sp. isolated from coconut palm (Prabhu et al 2000)

Figure 1

Table1 Morphological characterization of bacterial isolates from sugarcane and rye grass

Acid production: Amongst sugarcane and rye grass isolates S3, S4, S5, S8, R4 and R7 exhibited acidic reaction on Norris media (Table2) However S1, S2, S6, S7 amongst sugarcane isolates and R1, R2, R3, R5, R6 amongst ryegrass isolates exhibited negative reaction for acid production. Standard Azospirillum strain showed acid production, which was also recorded in S3 and S4 (Azospirillum).

Catalase production: Out of eight sugarcane isolates only five (S2, S3, S4, S5 and S8) whereas six rye grass isolates (R1, R2, R4, R5, R6, R7) exhibited catalase positive reaction i.e. showed bubble formation on addition of hydrogen peroxide (Table 2). These results corroborate to findings of Lindberg and Granhall (1984) who reported catalase production in Azospirillum and E. coli isolated from temperate cereals and forage grasses. In similar report, Pseudomonas was found negative for catalase activity which shares similarity with sugarcane isolate S1 (Pseudomonas). Muthukumarasamy et al (2002) reported catalase production in an endophytic bacteria Gluconacetobacter sp. isolated from sugarcane endorhizosphere.

Three sugarcane isolates S4, S7 and S8 and four ryegrass isolates R1, R2, R6 and R7 showed acid production in sugar fermentation broth supplemented with mannitol which indicates mannitol utilization as carbon source (Table2). Isolate S3 (sugarcane) and isolates R1, R2, R3, R4 (ryegrass) were able to utilize lactose. Galactose was utilized by sugarcane isolates (S5, S6) and ryegrass isolates (R1, R2, R3). Two ryegrass isolates i.e. R1 and R2 and two sugarcane isolates S2 and S3 were able to utilize xylose, which is a ketopentose. Majority of isolates among sugarcane isolates (S1, S2, S3, S5, S7) and ryegrass (R1, R3, R5, R6, R7) were able to utilize glucose indicating glucose to be a preferred carbon source. Lindberg and Granhall (1984) reported that E. coli was found to produce gas in fermentation broth in the presence of glucose and these findings were similar to our isolates i.e.S5, S7, R3 and R5 (E. coli). Muthukumarasamy et al (2002) reported that Gluconacetobacter sp. isolated from sugarcane were able to utilize galactose, xylose and mannitol.

Figure 2

Table1. Biochemical characterization of bacterial isolates

All sugarcane isolates were sensitive to gentamycin, amikacin and streptomycin. Isolate S5 (Bacillus) was observed to be sensitive to all antibiotics used and a similar antibiotic resistance pattern was exhibited by isolate S3 and S4 (Azospirillum). All ryegrass isolates were sensitive to gentamycin and R6 isolate (Pseudomonas) was observed to be sensitive to all antibiotics used. R3 along with R5 exhibited same pattern of antibiotic resistance i.e. sensitivity to chloramphenicol, gentamycin, amikacin and resistance to pencillin G, ampicillin and oxytetracycline (Table 3).

Figure 3

Table3. Antibiotic resistance spectra of bacterial cultures

Out of all fifteen isolates only sugarcane isolate S6 (E. coli) was observed to solubilize phosphate. The amount of phosphate solubilized by S6 isolate was observed to be 21 mg P. Mikanova and Kubat (1994) reported high phosphate solubilizing activity (25-26 mg P) from strains of Rhizobium trifolii

The range of nitrogenase ativity in case of sugarcane isolates was 217.3 -1221.0 nM C₂H₄h ^-1 g ^-1 protein with maximum value recorded by isolate S3 (Azospirillum) i.e. 1221.0 nM C₂H₄h ^-1 g ^-1 protein. The ryegrass isolates exhibited nitrogenase activity in range of 121.3- 1168.3 nMC₂H₄h ^-1 g ^-1 protein with R1 (Azospirillum) recording highest value i.e. 1168.3 nMC₂H₄h ^-1 g ^-1 protein (Table4).

All the isolates produced siderophore in range of 0.7-3.0 mg l ^-1 . Out of eight isolates of sugarcane only six were observed to produce siderophore. S6 isolate (E. coli) produced the maximum amount (2.4 mg l ^-1 ) whereas isolate S2 and S8 were found to be negative for siderophore production. Six ryegrass isolates (R1, R2, R3, R5, R6, R7) were found to be positive for siderophore production (Table4). Amongst ryegrass, isolate R6 (Pseudomonas) produced maximum amount (3.0 mg l ^-1 ) of siderophore.

Figure 4

Table 4. Functional potentiality of bacterial isolates

All the isolates were observed to produce the phytohormone IAA, which ranged from 4-19.3 g ml ^-1 among sugarcane isolates. Isolate S5 (Bacillus) produced maximum IAA i.e. 19.3 g ml ^-1 .The IAA production varied from 4.5-20 g ml ^-1 for rye grass isolates. The maximum amount of IAA (i.e. 20 g ml ^-1 ) was recorded for R7 (Bacillus) ryegrass isolate (Table 4). Hassan et al (1998) isolated Azospirillum from inoculated rice roots, which exhibited production of significant level of IAA (2.0-21.6 gml).