THE OCCURRENCE OF ENTOMOPATHOGENIC FUNGI IN THE SOIL FROM THE PLANTATIONS OF BLACK CURRANT AND ARONIA

Anna Sapieha-Waszkiewicz¹, Barbara Marjańska-Cichoń², Zdzisław Piwowarczyk^1
1 Departmnet of Plant Protection, Podlasie University in Siedlce
² Laboratory of Pomology, Podlasie University in Siedlce

ABSTRACT

Using the method of bait insects, the studies established the species composition and the intensity of occurrence of entomopathogenic fungi in the soils from two black currant plantations: one very well-maintained and the other that had not been cultivated for a number of years, as well as in the soil under aronia cultivation. The following entomopathogenic fungi were isolated from the dead larvae of Galleria mellonella L.: Beauveria bassiana (Bals.) Vuill., Metarhizium anisopliae (Metsch.) Sorok and Paecilomyces fumosoroseus (Wize) Brown et Smith. Additionally, the occurrence of the species Metarhizium flavoviride Gams et Rozsypal was observed. The most larvae with symptoms of mycoses were isolated from the soil from the plantation of unprotected currant (72.5%), while the least from the soil from the protected plantation, where the symptoms of mycoses were shown by 32.5% of bait larvae. The larvae were most frequently infected by fungus B. bassiana, which dominated in the soil under the unprotected currant, and by M. anisopliae in the plough soil. The summer period was conducive to infection by B. bassiana, while autumn was favourable for P. fumosoroseus.

Key words: entomopathogenic fungi, protected and unprotected black currant, protected aronia, plough soil.

INTRODUCTION

The yielding of black currant and aronia is conditioned by a number of factors, one of the more important being the occurrence of diseases and pests, which considerably reduce the yielding of shrubs and cause a worse quality of the fruit. Big populations of harmful species and their remarkable reproductive potential with simultaneous generation of new pest breeds insensitive to insecticides enforces the use of highly toxic preparations. This also concerns the protection of plants from diseases and the weed control. However, chemical treatments carry the risk of infecting both plants and the soil environment, which is reflected in the impoverishment of the soil entomofauna [18].

Following the program of integrated plant protection, the chemical treatments on commodity plantations are limited to the necessary minimum and alternative ways of limiting the pest populations are sought. One of them is a possibility of entomopathogenic fungi making use of regulatory effects of pest populations which are in a temporary contact with the soil [3]. In favourable conditions entomopathogenic fungi can cause high mortality of insect pests, ranging from 24% even to 97.3% [4, 5, 8, 17, 21].

The effect of entomopathogenic fungi depends on a number of factors such as the manner of soil utilization and agricultural treatments, especially those related to plant protection. It follows from the studies conducted so far that the diversity and intensity of entomopathogenic fungi are greater in natural ecosystems as compared to the agriculturally cultivated areas [9, 11, 16, 20].

Orchards and berry patches in our country belong to the cultivations with high application of pesticides. Numerous papers point out that soil availability of entomopathogenic fungi decreases with increased numbers of chemical treatments using crop protection preparations [13, 16].

The purpose of the paper was to establish the species composition and intensity of the occurrence of entomopathogenic fungi in the soils from two plantations of black currant: one maintained in high culture and the other unprotected for a number of years, and in the soil from the cultivation of aronia.

MATERIAL AND METHODS

Two black currant plantations and one aronia plantation were chosen for the studies. The 12-year-old black currant plantation had not been treated for a number of years, whereas the 7-year-old black currant plantation and the 10-year-old aronia plantation applied protective treatments, including a full program of shrub protection from diseases and pests. The spraying of the plants on three examined plantations was performed 2-3 times during a season, depending on the intensity of the occurrence of pests and pathogens. Weeding was performed 1-2 times in a season, using the herbicides recommended to be applied in the plantations of fruiting berry patches. These were situated in the commune of Cegłów (unprotected currant) and Mrozy in the vicinity of Siedlce, on the IV class soil formed from poorly loamy sand.

Soil samples from the berry patches were taken by means of a sampling stick from the depth of 20 cm in summer (June) and autumn (November) of 2003. For comparative reasons, the studies took into consideration the soil taken from the field where potatoes were cultivated.

The fungi were isolated from the soil by the method of bait insects [23, 24]. The last but one larval stage of Galleria mellonella L. was used as the bait insect. 10 larvae of G. mellonella were placed in each of Petri dishes, which were then filled with soil. Each combination was prepared in 10 repetitions. The experiment was done at the temperature of 22°C. The first observation of the larvae´s mortality was performed after 7 days, and the following ones every 5 days. During each observation the dead larvae were cleaned and disinfected using natrium hypochlorite, and then they were washed twice in sterile distilled water. The larvae prepared in this way were placed in Petri dishes laid with a wet tissue paper and next put into moist chambers with the aim of obtaining the sporulation necessary for the fungi to be marked.

After the experiment was completed, the results obtained for the three most numerously represented fungi species were statistically analyzed. A detailed comparison of the mean values was made using Tukey´s test with the assumed significance level of α = 0.01.

RESULTS AND DISCUSSION

The experiment isolated the following species of entomopathogenic fungi: Beauveria bassina (Bals.(Vuill., Metarhizium anisopliae (Metsch.) Sorok. and Paecilomyces fumosoroseus (Wize) Brown et Smith. Additionally, the species Metarhizium flavoviride Gams et Rozsypal was sporadically recorded. It was observed only on 1% of the test larvae (0.5% under unprotected currant and 0.5% in the plough land). The common occurrence of B. bassiana, M. anisopliae and P. fumosoroseus in Polish conditions, independently of the manner of soil cultivation, is also pointed by Miętkiewski et al. [10, 15, 16], Miętkiewski and Miętkiewska [12], Marjańska-Cichoń et al. [6], Sapieha-Waszkiewicz et al. [9], while in the western and northern part of Europe it is observed by Zimmermann [23] and Vänninen et al. [22]. The fungus M. flavoviride occurs in the Polish soils only sporadically [7, 10, 15, 19].

The intensity of infection caused by entomopathogenic fungi depended on the studied habitat (fig. 1). The greatest number of larvae with the symptoms of mycosis was found in the soil from the black currant plantation that had not been treated for a number of years. In this case the number of the infected larvae was high, reaching nearly 73%. The studies conducted in field conditions by Machowicz-Stefaniak [5] confirm the results obtained by the authors of the present paper. According to these results, more larvae showed the symptoms of infection by fungi in the unprotected cultivations as compared to the protected ones. Those experiments concerned the reduction of the population of codling moth (Carpocapsa pomonella L.) in apple orchards by means of entomopathogenic fungi. Tkaczuk and Miętkiewski [21] as well as Miętkiewski et al. [9] also observed higher mortality of the larvae of ambush insects in the soils taken from the balk and in the forest soil as compared to the plough land.

The number of dead larvae in the soil under aronia and in the plough land was approximately the same (about 60%). The smallest infection of the test insects was observed in the soil from the plantation of protected currant, where the symptoms of mycosis were found only in 32.5% of the bait insects (fig. 1).

Independently of the cultivation, it was shown that larvae were the most frequently infected by fungus B. bassiana (fig. 2). The infection of the test insects by this species significantly exceeded (by 18% on average) the number of larvae infected by fungi M. anisopliae and P. fumosoroseus.

Fungus B. bassiana dominated in the soil where the unprotected currant grew, and it was in comparison to both the other cultivations and the other fungi (fig. 3). This species was the cause of mortality in the case of nearly 50% larvae. Similar results were obtained by Łabanowski [4], who stated that in the soil from the unprotected apple orchards the mortality of larvae and pupae of codling moth was in 62% caused by the species B. bassiana. Other authors observe that fungus B. bassiana dominates in the forest bedding and soil - the habitats where there was no toxic effect of pesticides [1, 9, 16]. It can be supposed that B. bassiana is a species sensitive to the effect of pesticides and hence it occurred with greater intensity in the cultivation of unprotected currant. Besides, its intensity could have been caused by a wider spectrum of the accessible hosts.

The number of larvae smaller by 15% died as a result of infection by M. anisopliae, which dominated in plough land where potatoes were cultivated (fig. 3). In this habitat, the infection by M. anisopliae also dominated in reference to the other fungi. The results are consistent with the observations by Kleespies et al. [2], Miętkiewski and Tkaczuk [14] and Marjańska-Cichoń et al. [7], who proved that lighter soils are dominated by fungus M. anisopliae.

The species P. fumosoroseus in the soil of all the studies cultivations occurred with the intensity similar to that of M. anisopliae, with the exception of plough land, where the number of larvae that died as a result of the effect of P. fumosoroseus was significantly lower as compared with the mortality caused by fungus M. anisopliae. Besides, significantly more rare infections by P. fumosoroseus were observed in the soil from the plantation of protected currant as compared to the unprotected plantation.

The studies showed that the season of the year differentiated the soil availability of entomopathogenic fungi (fig. 4).

The summer period favoured the increase of mortality (39%) of bait larvae caused by B. bassiana. In autumn the symptoms of mycoses caused by this species were significantly rarer as compared to the summer period. On the other hand, the number of larvae infected by P. fumosoroseus increased (fig. 4). Fungus M. anisopliae invaded the larvae with comparable frequency in both periods (fig. 4). The obtained results confirm the studies conducted by Miętkiewski et al. [11], who showed that soil samples taken in spring contained more B. bassiana, whereas those collected in autumn had more P. fumosoroseus. A similar standpoint is represented by Sapieha-Waszkiewicz et al. [19] and Marjańska-Cichoń et al. [7].

In addition to typical fungi entomopathogenic towards G. mellonella larvae the studies isolated accompanying species whose entomopathogenic effect was not well documented. The occurrence of fungi from the following genera was observed within this group: Aspergillus, Mucor and Penicillium (tab. 1). Besides, the studies found the presence of non-fruiting mycelium, which occurred abundantly in the group of fungi with unproved entomopathogenic qualities, causing high mortality of the test larvae, in some cases reaching nearly 48%. It can be supposed that those could have been entomopathogenic fungi where a lack of sporulation made it impossible to mark the species. Similar species were previously found in the Polish soils by Miętkiewski et al. [13, 16], Miętkiewski and Miętkiewska [12], Sapieha-Waszkiewicz et al. [19] and Marjańska-Cichoń et al. [7].

CONCLUSIONS

1. The following entomopathogenic fungi were isolated from the soil of berry plantations: B. bassiana, M. anisopliae and P. fumosoroseus. Additionally, the species M. flavoviride was sporadically observed.

2. The highest mortality of ambush larvae occurred in the soil from the black currant plantation that was not protected, while the lowest in the case on the soil where black currant maintained in high culture grew.

3. Independently of the species of the cultivated plant, the fungus B. bassiana caused the greatest mycoses of the test insects.

4. Infection of bait insects by the species B. bassiana dominated in the soil where the unprotected currant grew, while M. anisopliae infected the most in the plough land.

5. The summer period favoured the infections by B. bassiana, while autumn was conducive to P. fumosoroseus.

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