Volume 3
Issue 2
Horticulture
JOURNAL OF
POLISH
AGRICULTURAL
UNIVERSITIES
Available Online: http://www.ejpau.media.pl/volume3/issue2/horticulture/art-01.html
BACTERIA AND FUNGI COMMUNITIES OCCURRING IN THE SOIL AFTER THE CULTIVATION OF CEREALS AND POTATO
Danuta Pięta, Alina Pastucha, Elżbieta Patkowska
The studies conducted in the years 1997-1999 concerned the soil after cultivation of rye, winter wheat, triticale and potato. The purpose of the studies was to determine the composition of bacteria and fungi communities in the soil after the cultivation of these plant species.
Key words:
antagonism, Bacillus spp., Pseudomonas spp., Trichoderma spp., Gliocladium spp., winter wheat, triticale, rye, potato..
INTRODUCTION
The basic plant species cultivated in Poland include winter wheat, triticale, rye and potato. It follows from abundant information in literature that each of these plants exerts a remarkable influence on the quantitative and qualitative composition of fungi and bacteria in the soil environment [Huber, Watson, 1970; Księżak, Kobus, 1993]. Organic residue of particular plants plays a significant role in the formation of microorganisms [Huber, Watson, 1970]. On the other hand, in the vegetative period a special effect on the composition and numbers of bacteria and fungi populations is also exerted by root exudates, which are a rich source of free aminoacids and sugars [Funck-Jensen, Hockenhull, 1984; Pięta, 1981; Smith, Peterson, 1966; Rovira, 1965; 1969]. The chemical composition of organic residue and root exudates can have a stimulating or inhibiting effect on the growth and development of particular populations of microorganisms [Funck-Jensen, Hockenhull, 1984; Martyniuk et al., 1991; Pięt a et al., 1999; Rovira, 1965; Schoruvitz, Zeigler, 1989; Sundin et al., 1990]. According to Solarska [1996], ploughing over the green mass of rye caused an increase of bacteria population by 50%, and this especially concerned the number of fluorescent Pseudomonas spp. characterised by antagonistic effect towards pathogenic fungi. Ploughing over post-harvest residue of barley caused an increase of the number of antagonistic isolates of Bacillus subtilis [Weinhold, Browman, 1968].
Determination of the composition of microorganisms populations formed in the soil under the effect of the cultivation of winter wheat, triticale, rye and potato was the purpose of the presented studies.
MATERIALS AND METHODS
The studies were carried out in the years 1997-1999 on an experimental field in Czesławice near Nałęczów. The plot was sown with winter wheat (Kobra cv.), triticale (Malno cv.), rye (Amilo cv.) and with cultivation of potato (Bronka cv.). The soil after the harvest of these plants was the subject of the studies. Soil sampling and then the manner of conducting the microbiological analysis in order to determine the population of microorganisms were true to the method described by Martyniuk et al. [1991]. Soil samples from particular plots were taken from the depth of 5 to 10 cm to sterile Petri dishes. Next, in the laboratory sterile conditions a soil solution was prepared in the dilutions ranging from 10-1 to 10-7.
The total number of bacteria in 1 g of dry weight of the examined soil was determined on the medium ”Nutrient agar” using soil solutions in the dilutions of 10-5, 10-6, 10-7. In the case of Bacillus spp. ”Tryptic soy agar” medium and dilution of 10-4, 10-5, 10-6 were used, while for Pseudomonas spp. the studies made use of ”Pseudomonas agar F” medium and dilutions of 10-2, 10-3, 10-4. The total number of fungi in 1g of dry weight of the same soil samples was determined on Martin’s medium [1950], using the dilutions of 10-2, 10-3, and 10-4.
The results concerning the number of bacteria and fungi were statistically analysed, and the significance of differences was determined on the basis of Tukey’s confidence intervals.
In each year of the studies the obtained isolates (100 isolates of Bacillus spp. and 100 of Pseudomonas spp.) and all the isolates of saprophytic fungi of Gliocladium spp. and Trichoderma spp. were used to determine their antagonistic effect towards such pathogenic fungi as Fusarium culmorum, F. oxysporum, F. solani, Pythium irregulare and Rhizoctonia solani. In order to determine the antagonistic effect of the studied bacteria towards pathogenic fungi a 5-degree scale described by Martyniuk et al. [1991] and degrees of inhibition of the growth of pathogens provided by Pięta [1999] were used. An estimation of the effect of saprophytic fungi on the examined pathogenic fungi was performed by means of biotic rows [Mańka, 1974; Mańka, Mańka, 1992], while an individual antagonistic effect was determined on the basis of the scale provided by Mańka and Kowalski (1968).
RESULTS A microbiological analysis of the soil after the cultivation of winter wheat, triticale, rye and potato found out differences in the number of particular populations of microorganisms (tab. 1). In particular years, the total number of bacteria in 1 g of dry weight of the examined soil samples ranged from 2.98×106 colonies (in 1999 after rye cultivation) to 5.01×106 colonies (in 1999 after potato cultivation). The lowest number of bacteria, i.e. 3.08×106 colonies, was found in the soil after rye cultivation, while the highest (5.01×106) after potato cultivation (tab. 1). The other two examined soil samples, that is after triticale cultivation and winter wheat cultivation, differed with the total number of bacteria. In each year there were significantly more bacteria colonies in 1 g of dry weight after winter wheat cultivation (4.89×106 on average) than in the soil after triticale cultivation (3
.99×106 on average).
Type Total number of bacteria (mln/1g d. w. of soil) Number of bacteria Number of bacteria Total number of fungi (thous./1g d. w. of soil) 1997 1998 1999 mean 1997 1998 1999 mean 1997 1998 1999 mean 1997 1998 1999 mean rye 2.99a* 3.27a 2.98a 3.08a 0.71a 0.89a 0.98a 0.86a 2.01c 2.12c 2.08c 2.07b 26.12b 28.61a 30.08a 28.27a triticale 3.75b 4.02b 4.20b 3.99b 0.89ab 0.99a 1.03a 0.97ab 1.56b 1.68b 1.65b 1.63ab 34.03c 39.97b 42.22b 38.74b winter wheat 4.68c 4.93c 5.05c 4.89c 1.17b 1.39b 1.55b 1.37b 1.86bc 1.99bc 2.18c 2.01b 21.98a 28.72a 27.87a 26.19a potato 4.96c 4.99c 5.08c 5.01c 1.08b 1.19ab 1.24b 1.17ab 0.89a 1.08a 1.12a 1.03a 39.73c 44.53b 45.07b 43.11b *means in columns differ significantly (P In the case of Bacillus spp. bacteria the number of colonies in 1 g of dry weight of soil ranged from 0.71×106 (in 1997 after rye cultivation) to 1.55×106 (in 1999 after winter wheat cultivation). In each year the greatest number of Bacillus spp. colonies was found in the soil after winter wheat cultivation (1.37×106 colonies on average), while the smallest one in the soil after rye cultivation (0.86×106 colonies on average) (tab. 1). The mean number of Bacillus spp. bacteria occurring in soil samples after triticale cultivation (0.97×106 colonies) and potato cultivation (1.17×106 colonies) varied, but the differences were statistically insignificant.
Results of the microbiological analysis showed that in each year of the studies the highest number of Pseudomonas spp. colonies was found in the soil samples after rye cultivation (2.07×106 colonies on average) and after winter wheat cultivation (2.02×106 colonies in 1 g of soil dry weight on average). The lowest number of colonies of this bacteria genus was found after potato cultivation (1.03×106 colonies in 1 g of soil dry weight on average), tab. 1.
The mycological analysis of the examined soil samples pointed at considerable differentiation in the number of fungi (tab. 1). The smallest number of fungi colonies was found in the soil after rye cultivation (28.27×103 colonies on average) and winter wheat (26.19×103 colonies on average), while the greatest after potato cultivation (4.113 colonies in 1 g of soil dry weight). A high number of fungi, namely 38.74×103 colonies, was found in 1 g of soil dry weight after triticale cultivation (tab. 1).
The mycological analysis of soil samples after the cultivation of particular plants isolated both pathogenic and saprophytic fungi. The proportion of those fungi differed with the species of the cultivated plant. The greatest number of pathogenic fungi, especially of Fusarium spp. and Rhizoctonia solani was found in the soil after potato cultivation, and the smallest number after the cultivation of rye and winter wheat (fig. 1). The isolated fungi of Fusarium spp. included F. culmorum, F. solani and F. oxysporum.
Within the saprophytic fungi the dominating species were of Pseudomonas spp. and Trichoderma spp., especially in the soil after the cultivation of winter wheat and rye. Penicillium spp. was represented by P. brevi-compactum, P. decumbens, P. fellutanum, P. frequentans, P. funiculosum, P. janthinellum, P. lividum, P. meleagrinum, P. nigricans, P .paxilli, P. purpurescens, P. purpurogenum, P. roseo-purpureum, P. velutinum, P. verrucosum var. cyclopium, P. verrucosum var. verrusocum, while Trichoderma spp.was represented by T. hamatum, T. harzianum, T. koningii, T. viride. Those fungi were a little less numerous in the soil after triticale cultivation, and the least numerous in the soil after potato cultivation (fig. 1). The saprophytic fungi marked as ‘others’ in the chart included the species from the genera of Acremonium, Chaetomium, Cladosporium, Gliocladium, Mucor and Rhizopus. The pr
oportion of isolates of those fungi in particular soil samples ranged from 10.01% to 17.03% of the total number of fungi colonies (fig. 1).
Among the bacteria Bacillus spp., Pseudomonas spp. and the fungi Gliocladium spp. and Trichoderma spp., laboratory studies in vitro separated the isolates characterised by antagonistic effect towards pathogenic fungi. The frequency of the occurrence of antagonistic microorganisms in particular soil samples varied (tab. 2). In the case of Trichoderma spp. all the isolates separated from the analysed soils turned out to be antagonistic. On the other hand, 70% isolates within Gliocladium spp. were distinguished by these properties, while antagonistic bacteria of Bacillus spp. constituted 23% on average, and those of Pseudomonas spp. made up 27% of all the obtained isolates. The highest number of antagonistic bacteria and fungi (388 isolates) was found in the soil after winter wheat cultivation, and the lowest in the soil after potato cultivation (105 isolates). In the other soils, that is those after rye and t
riticale cultivation, there were 327 and 286 isolates of antagonistic microorganisms, respectively (tab. 2).
Bacteria and fungi Number of isolates rye triticale winter wheat potato Bacillus 31 37 51 13 Pseudomonas 117 86 105 18 Gliocladium catenulatum 12 17 32 7 Gliocladium roseum 3 1 3 1 Trichoderma hamatum 36 27 36 8 Trichoderma harzianum 43 39 56 - Trichoderma koningii 29 31 43 26 Trichoderma viride 56 48 62 32 Total 327 286 388 105 DISCUSSION Results of the studies pointed at varied composition of bacteria and fungi communities formed under the effect of cultivation of particular plant species. The soil after potato cultivation contained the greatest total number of bacteria and fungi colonies. On the other hand, the soil after winter wheat cultivation was characterised by the smallest number of fungi colonies. Small numbers of fungi colonies were also found in the soil after rye cultivation, and a big number of fungi was present in the soil after triticale cultivation. The quantitative and qualitative composition of microorganisms could have been affected by root exudates and post-harvest residue of the cultivated plants [Huber, Watson, 1970; Rovira, 1965; 1969; Schroth, Hildebrand, 1964]. According to Funck-Jensen and Hockenhull [1984], the chemical composition of root exudates and plant residue significantly affects the changes in the numbers within the populations of bacteria and fungi. Chemical compounds exudated by roots t
o the soil or those occurring in post-harvest residue can stimulate or inhibit the growth and development of soil-borne microorganisms.
Results of the mycological analysis showed that the soil after rye and winter wheat cultivation contained twice a smaller number of pathogenic fungi than the soil after potato cultivation, while the soil after triticale cultivation contained 50% fewer pathogenic fungi as compared to the soil after potato cultivation, but 35% more of them in comparison with the soil after rye and winter wheat cultivation. A high number of isolates of pathogenic fungi in the soil after potato cultivation can be explained by the smallest proportion of bacteria and saprophytic fungi populations with an antagonistic effect. On the other hand, the smallest proportion of pathogenic fungi isolates was found in the soil after rye and winter wheat cultivation, which can be related to numerous occurrence of antagonistic bacteria of Bacillus spp. and especially Pseudomonas spp., and such antagonistic fungi as Gliocladium spp. and Trichoderma spp.
According to Keel [1992] and Weller [1988], bacteria of Pseudomonas spp. are capable of active colonisation of plant roots, owing to which they can effectively compete with pathogens for nutritive elements found in root exudates and thus become a factor of biological plant control. The species from the genera of Gliocladium and Trichoderma, which are found in big numbers in the soil after the cultivation of the studied cereals (rye, winter wheat, triticale) can significantly reduce the numbers of populations of soil-borne pathogens (Łacicowa, Pięta, 1985a; 1985b; 1989; Papavizas, 1985]
REFERENCES
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Responses to this article, comments are invited and should be submitted within three months of the publication of the article. If accepted for publication, they will be published in the chapter headed ‘Discussions’ in each series and hyperlinked to the article.
Table 1. Number of bacteria and fungi occurring in the soil after cultivation of particular plants
of soil
of Bacillus spp.
(mln/1g d. w. of soil)
of Pseudomonas spp. (mln/1g d. w. of soil)
0.05), if they are not marked with the same letter
Fig.1. Participation of fungi in soil after cultivation of particular plants: 1 – total pathogenic fungi, 2 – Fusarium spp., 3 – Rhizoctonia solani 4 – total saprophitic fungi, 5 – Penicillium spp., 6 – Trichoderma spp., 7 – other saprophitic fungi
Table 2. Antagonistic bacteria and fungi isolated from the soil after cultivation of particular plants (sum of isolates 1997-1999)
Submited:
Danuta Pięta, Alina Pastucha, Elżbieta Patkowska
Department of Phytopathology
Agricultural University of Lublin
7 Leszczyńskiego, 20-069 Lublin, Poland
tel. (+48 81) 532 30 47
e-mail: dpieta@consus.ar.lublin.pl