Changes in Bacterial and Actinomycetes Diversity of Groundnut Phyllosphere with reference to Plant age, Kind of leaves and Season Adopting Culture Dependent Methods
S Namasivayam, K Sahayaraj
diversity, groundnut, phyllosphere
S Namasivayam, K Sahayaraj. Changes in Bacterial and Actinomycetes Diversity of Groundnut Phyllosphere with reference to Plant age, Kind of leaves and Season Adopting Culture Dependent Methods. The Internet Journal of Microbiology. 2008 Volume 6 Number 1.
Phyllosphere or plant leaf surface is a habitat for many microorganisms 1 (Raimen, 1961). The leaf surface microbes are important in several ways. Some of them are known to fix atmospheric nitrogen 2,3 (Murty, 1983; Favilli and Messini, 1990), produce plant growth regulators 4 (Buckley and Pugh, 1971) and can control plant parasites either by stimulating plants to synthesize phytoalexins 5 (Last and Warren, 1972) or by producing antibacterial (Mc Cormack
Materials & Methods
12 different Groundnut fields in an around Shencottai Taluk (77 0 25 1 E LONG, 8 0 97 1 N ALT), Tirunelvli district, Tamil Nadu, India were selected in this study. Sampling was done at the age of 20, 40, 60 and 80 DASE (Days After Seedlings Emergence) in both summer (February to May) and khariff (June to August). The leaves of healthy, pest infested aphids and lepidopteron) and diseased leaves were collected in sterile polythene bags kept in icebox, brought to the laboratory and identification of the leaves was done immediately. Pests' infestation and diseased leaves (Leaf spot) were identified by the criteria suggested by Wightman and Rao (1993) 11 and Sokhi (1983) respectively. 12
Five gram of (each kind) leaves were suspended separately in 100 ml of sterile distilled water with 0.01% Tween 80 and shaken in rotatory shaker at 100 rpm for 30 minutes. The suspension was serially diluted and 0.1 ml of aliquote was spread plated on standard plate count agar (Hi media,India ). and starch casein agar(Hi media,India) The seeded plates were incubated at 37 0 C for 48 hours and 37 0 C for 14 days (actinomycetes) Developed colonies were counted and then randomly chosen and purified for identification. The purified colonies were stored on respective agar slants at 4 0 C in refrigerator. All the bacterial including actionmycetes by Bergey's manual of systemic bacteriology (Buchanon and Gibbons, 1979; 13 Kirieg and Holt 1984) 14
The microbial populations were correlated with the season and kind of leaves using STATISTICA statistical package. Similar statistical package has also been used for the comparison of health leaves to infested and infected leaves. The significant was expressed at 5% level.
Enumeration of total heterotrophic bacterial and actinomycetes population
The total heterotrophic bacterial (THBP) and actinomycetes population varied according to the season and the kind of leaves investigated. A strong positive correlation (r = 1.0) was observed between the population and the season, as well as kind of leaves. During summer season, bacterial population was found to be maximum in all kind of leaves, except diseased leaves. In the case of healthy leaves the bacterial population increased from 20 days old plant (17.6 x 10 5 CFU/g) to 80 days old plant (13.2 x 10 7 CFU/g) (r = 0.9812). But during khariff season, the bacterial population recorded at the age of 20, 40, 60 and 80 days were 9.3 x 10 3 , 17.7 x 10 3 , 23.1 x 10 3 and 27.6 x 10 3 CFU/g respectively (r = -0.5134) (Table 1). As observed for healthy leaves THBP was same or more or less similar at all ages as well as both seasons in lepidopteron-infested leaves. Irrespective of season, the aphids infested leaves recorded highest bacterial population and this was statistically significant (P < 0.05). In aphid-infested leaves, the bacterial population increased from 23.7 x 10 7 CFU/g to 71.7 x 10 8 CFU/g as the plant advanced from 20 to 80 days of age respectively in summer season. Similar trend was also observed during khariff season. But the diseased leaves consist of least bacterial population in both seasons as well as in all ages than the other kind of leaves recorded (Table 1).
Actinomycetes population fluctuated according to the season. The actinomycetes population at the age of 20, 40, 60 and 80 days recorded in healthy leaves during summer season were 6.4 x 10 2 , 27.4 x 10 3 , 16.4 x 10 3 and 29.0 x 10 2 CFU/g respectively but during khariff season actinomycetes population was not recorded at 20 and 40 DASE. Aphids infested leaves did not showed any effect on actinomycetes population as in bacteria. The diseased leaves of 40 DASE consist of 17.5 x 10 1 CFU/g in summer and the actinomycetes count was absent during khariff.
Table 1. shows bacterial and actinomycetes population from groundnut phyllosphere
367 bacterial isolates belonging to different species were isolated from the phyllosphere of groundnut with different kinds of leaves. The bacterial composition has showed variation with respect to age, kind of leaves and season.
The aphids infested leaves had shown more bacterial species than the other leaves during both seasons. During summer,
Table 2 shows generic composition of bacterial species iso.lated from groundnut phyllosphere
127 actinomycetes were isolated which belonging to three genera such as
Table 3 shows generic composition of actinomycetes isolated from groundnut phyllosphere
The microbial communities of leaves are diverse and include many different genera of bacteria, actinomycetes, filamentous fungi, yeast and less frequently protozoa and nematodes (Brighna et al, 1997). 15 The total heterotrophic microbial population varied according to the age of the crop, season and kind of leaves. Andrews
In the present study, 367 bacterial isolates belonging to 9 bacterial species were isolated from different kinds of groundnut leaves during both summer and khariff.
Raujimakers et al (1995) 26 reported that effective colonization and high population size of the introduced bacterial biological control agents on plant surfaces have been considered to be important factor in the successful control of plant diseases. Ji and Wilson (2003) 27 also studied the enhancement of population size of a biological control agent and their bio-efficacy in the control of bacterial speck of tomato through salicylate and ammonium surface amendments. In future, trials will be carried out to control leaf spot diseases using
The present study simply explained the bacterial and actinomycetes composition of the phyllosphere of groundnut by culture dependent methods. In contrast, Ching Hung Yang