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BACTERIAL AND STREPTOMYCES FLORA OF SOME JORDAN VALLEY SOILS I. SAADOUN and F. AL-MOMANI Dept. Biological Sciences, Jordan University of Science and Technology, P.O. Box 3030, Irbid, Jordan 22110
Code Number:AC96014
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ABSTRACT. A microbial survey carried out in seven fields of three grapevine nurseries in the Jordan Valley showed significant differences in the viable count of total bacteria between the fields within the same nursery and between fields of different nurseries. Average Streptomyces counts however were not significantly different. Viable counts for both total bacteria and streptomycetes were mostly higher in spring and lower in autumn. No significant correlation (P< 0.05) was observed between viable bacterial and Streptomyces counts and environmental conditions (temperature, pH, soil moisture, total nitrogen content, phosphorus, potassium and soil texture). Plant type, plant exudate, plant age and microbial interaction may have accounted for the observed fluctuations. Since the discovery of antibiotics, in the search for novel substances various attempts have been made to isolate actinomycetes from various habitats (Hussein et al., 1980). Studies on the biological control of phytopathogens in soil by streptomycetes (Turhan, 1981) are also of interest in regard to their antagonistic effects on soil borne pathogens.
By comparison with total bacteria, actinomycete numbers in temperate climates range from 10^6 to 10^8 per gram of dry soil. Streptomycetes account for about 1-20% of the total bacterial count, but in some soils they may dominate (Flaig & Kutzner, 1960). Keast et al. (1984) studied the effects of various environmental factors, including geographic area and nature of the plant rhizosphere, on actinomycete populations in soils of Western Australia. The effect of pH and humidity on bacterial and actinomycete counts in cerrado soil in Brazil was studied by Coelho and Drozdowicz (1979). The occurrence of actinomycetes in soils from different geographic locations of Iraqi was reported by Hamdi and Al-Tai (1977).
The present paper deals with the effects of environmental conditions on the total bacterial and streptomycete counts in three nurseries of the Jordan Valley, where crown gall disease have been observed in fruit trees and particularly in grapevines.
MATERIALS and METHODS
Location. Samples were collected in seven fields of three governmental nurseries:
- Rayyan Nursery. Rg: Vineyard; Rc: Untilled control. - Dair Alla Nursery. D1: Vineyard, soil fumigated with methyl bromide before planting; D2: Vineyard, soil not fumigated; Dc: Untilled control, soil not fumigated.
Soil characteristics. Organic matter was determined by burning 10 gm of oven dry soil at 500 C (6 hrs), and similarly the moisture content at 105 C (24 hrs) and the pH on a soil solutions in water (1:2.5, w/v) with a pH meter. Other analyses (total nitrogen, phosphorus, potassium, and soil texture) were carried out by the Department of Projects, National Centre for Agriculture Research and Technology Transfer, in Amman.
Sampling. Monthly collections started in April after grapevine plantation and continued until March of the following year. After removing approximately 5 cm of the soil surface, samples were collected to a depth of 20cm with an auger from each of six different sites within each field. Equal samples of soil (two auger holdings) were collected from each site, mixed thoroughly and sieved (2mm mesh). Samples were placed in polyethylene bags, closed tightly and stored in a refrigerator. Bags were opened from time to time to allow air exchange. At the end of each season, three monthly samples were combined and mixed thoroughly to give the seasonal sample.
Viable counts. Samples were suspended in sterile distilled water on a reciprocal shaker (190 rpm, 30 min), serially diluted (up to 10^-6 ) and 0.1 ml of the appropriate dilution was spread over the surface of agar plates with sterile L-shaped glass rods. Triplicate plates of Standard Plate Count agar (Merck) and glycerol nitrate casein agar (Kster and Williams, 1964) were used for total bacterial and streptomycete counts respectively. Plates were incubated at 27 C and the number of colonies was counted after 48 hrs (bacteria) and 10 dd (streptomycetes).
RESULTS and DISCUSSION
The highest bacterial counts, as shown in Table 1, were recorded in spring and ranged between 10^7 to 10^10/gm dry soil and were significantly different (P<0.05) for most locations with reference to other seasons. The larger supply of organic matter deriving from root decomposition and root exudates, in addition to optimal temperature and soil moisture, may explain the results.
The lowest bacterial counts in most fields were detected in autumn and were similarly significant (P<0.05). Values observed in this season may possibly be due to a decrease in root exudate or to plant age (De Boer, 1982). Total bacterial counts in spring were the highest in cultivated fields at Baqura and Rayyan nurseries (Table 1), however the lowest ones in autumn were found in the control soils (Bc, Rc and Dc). Table 1. Number of total bacteria and streptomycetes and seasonal characteristics of the sampling sites [a - i: data non significant (P<0.05) between corresponding pairs; bacterial counts at D1 were not significantly different; Bact.: bacterial counts; Stm.: streptomycete counts; Tem.: temperature; RH: relative humidity; Mst.: moisture; Org.Mat.: organic matter].
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BAQURA NURSERY
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Environmental characteristics
Bact. Stm. -----------------------------------------
Season Site x x Tem Air Soil Org. pH Tot
10^7 10^4 C RH Mst. Mat. N(%)
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Spring Bg 1146.13 49.13 24.7 58.0 4.2 2.3 8.1 1.15
Bc 5.61b 64.76 3.8 2.0 8.1 1.00
Summer Bg 0.93a 44.71 29.9 59.0 4.0 2.0 8.0 1.00
Bc 4.21b 40.23 2.4 1.8 8.0 0.90
Autumn Bg 1.12a 29.05 20.7 62.2 4.8 2.1 8.0 1.05
Bc 0.25 10.3 6.0 1.7 8.2 0.85
Winter Bg 2.30 48.80 15.0 64.3 6.3 2.2 8.0 1.00
Bc 1.68b 32.70 7.0 1.8 8.0 1.00 -
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BAQURA NURSERY (continued)
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Environmental characteristics
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Season Site P K Silt
ppm ppm (%) (%)
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Spring Bg 16 560 21.5 59.2
Bc 16 640 18.8 55.3
Summer Bg 6 560 20.4 58.7
Bc 20 550 22.1 59.1
Autumn Bg 20 495 23.0 55.7
Bc 24 550 29.2 55.3
Winter Bg 18 485 22.7 56.3
Bc 26 540 22.3 56.7
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RAYYAN NURSERY
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Environmental characteristics
Bact. Stm. -----------------------------------------
Season Site x x Tem Air Soil Org. pH Tot
10^7 10^4 C RH Mst. Mat. N(%)
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Spring Rg 587.66c 36.32 25.0 58.3 4.9 1.6 8.1 0.80
Rc 865.07 310.54 4.7 1.1 8.1 0.55
Summer Rg 26.08c 100.03 30.3 62.0 5.6 1.7 8.2 0.85
Rc 6.98 12.44 3.6 1.2 8.2 0.60
Autumn Rg 2.44d 45.64 19.8 68.0 6.0 1.6 8.1 0.80
Rc 0.66e 13.32 5.7 1.1 8.0 0.55
Winter Rg 2.74d 14.17 14.7 69.0 6.7 1.6 8.2 0.80
Rc 2.70e 155.53 6.6 1.1 8.2 0.55
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RAYYAN NURSERY (continued)
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Environmental characteristics
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Season Site P K Silt
ppm ppm (%) (%)
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Spring Rg 48 565 25.3 56.4
Rc 4 565 29.3 58.2
Summer Rg 50 735 28.6 58.6
Rc 2 550 32.2 63.2
Autumn Rg 50 735 27.2 61.4
Rc 7 565 27.8 64.1
Winter Rg 50 730 29.2 57.7
Rc 8 565 31.2 59.3
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DAIR ALLA NURSERY
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Environmental characteristics
Bact. Stm. -----------------------------------------
Season Site x x Tem Air Soil Org. pH Tot
10^7 10^4 C RH Mst. Mat. N(%)
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Spring D1 8.75 88.61 25.9 44.7 5.0 1.5 8.0 0.75
D2 102.01 190.50 5.0 1.5 8.1 0.75
Dc 3.24h,i 85.91 4.0 1.6 8.0 0.80
Summer D1 7.12 76.34 31.1 41.3 4.8 1.5 8.0 0.80
D2 0.97f,g 58.35 4.9 1.4 7.8 0.70
Dc 1.93i 75.90 3.8 1.8 8.0 0.90
Autumn D1 2.06 8.48 21.8 44.7 8.7 1.5 7.9 0.75
D2 0.42 61.64 9.0 1.5 8.0 0.75
Dc 0.31g 23.45 6.5 2.0 7.9 1.00
Winter D1 2.60 47.23 17.0 51.3 6.6 1.5 8.0 0.75
D2 2.22f 46.75 4.4 1.5 8.1 0.75
Dc 1.31h 41.59 6.6 2.1 8.0 0.75
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DAIR ALLA NURSERY (continued)
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Environmental characteristics
-----------------------------------------
Season Site P K Silt
ppm ppm (%) (%)
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Spring D1 9 665 25.1 45.6
D2 12 655 34.5 45.4
Dc 6 695 31.3 47.3
Summer D1 8 695 29.5 41.0
D2 9 695 29.6 46.6
Dc 8 710 24.6 54.3
Autumn D1 13 670 25.6 49.0
D2 4 695 25.7 55.3
Dc 7 740 29.0 54.7
Winter D1 7 640 33.2 40.6
D2 10 655 28.1 46.2
Dc 6 730 27.6 52.3
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In any case no significant correlation was observed between bacterial (and streptomycete) counts and environmental conditions (temperature, pH, soil moisture, total nitrogen content, phosphorus, potassium and soil texture).
On the other hand Streptomyces counts varied from 10^5 to 10^6 and were not significantly different (P< 0.05) for either cultivated or untilled soils. Similarly seasonal counts were not significantly different for all fields and between nurseries.
The availability of nutrients and soil mechanical properties (i.e., soil texture and pore size) might have slowed down fluctuation and development of Streptomyces flora. The seasonal variation regarding total bacterial counts is shown in Table 2. Table 2. Seasonal percentages (total bacteria = 100) of streptomycete counts in the fields investigated
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SEASON FIELD
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Bg Bc Rg Rc D1 D2 Dc
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Spring 0.004 1.15 0.006 0.035 1.00 0.18 2.65
Summer 4.80 0.46 0.12 0.18 1.00 6.00 3.93
Autumn 2.60 4.14 1.42 2.00 0.41 7.56 14.67
Winter 2.10 1.95 1.20 7.00 1.80 2.10 3.17
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In general terms percentages are within the range (1-20%) reported by Flaig and Kutzner (1960). However, the percentage of Streptomyces in cultivated fields was much lower than that in untilled controls. This might be due by the aerobic metabolism of most common soil actinomycetes and to the consequent inability to develop and spread when free oxygen is limited in irrigated soils. In addition, as an effect of irrigation actinomycete spores might have been moved to depths below the volume of soil sampled.
REFERENCES Coelho, R.R & A.Drozdowicz (1979). The occurrence of actinomycetes in cerrado soil in Brazil. Rev. Eco. Biol., 15: 459-474
De Boer, S.H. (1982). Survival of phytopathogenic bacteria in soil. In: M.S.Mount & G.H.Lacy (eds.) Phytopathogenic Prokaryotes. Academic Press, New York. Vol. 1, pp. 285-305
Flaig, W. & H.J.Kutzner (1960). Beitrag zur ™kologie der Gattung Streptomyces Waksman et Henrici. Arch. Mikrobiol., 35: 105-138
Hamdi, Y.A & A.Al-Tai (1977). Occurrence of actinomycetes in Iraqi soils. SLR. Tech. Bull. 33 Hussein, A.M., A.M.Ragab, A.A.Elgammal, F.A.Mansour, E.Sami, M.Helmy & N.E.Shehata (1980). Taxonomy of gray pigmented Streptomyces spp. isolated from Egyptian soils. Egypt. J. Bot., 23: 9-16
Keast, D., P.Rowe, B.Bowra, L.Sanfelien, E.D.Staplay & H.B.Woodruff (1984). Studies an the ecology of West Australian actinomycetes. Factors which influence the diversity and actinomycetes in Australian soils. Microbiol. Ecol., 10: 123-136
Kuster, E. & S.T.Williams (1964). Selection of media for isolation of streptomycetes. Nature, 202: 928-929
Turhan, G. (1981). A new race of Streptomyces ochraceiscleroticus in the biological control of soil-borne plant pathogens: 2. In vivo studies on the possibilities of using c/2-9 isolate against some important diseases. Z. Pflanzenkr.Pflanzenschutz., 88: 422-434. Copyright 1996 C.E.T.A., The International Centre for Theoretical and Applied Ecology, Gorizia |
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