Elżbieta Patkowska
Biodiversity of microorganisms colonizing soybean, Glycine max (L.) Merrill, and susceptibility of different varieties of plants to infection by fungi with special regard to Phomopsis sojae Lehman
Introduction. Soybean is one of the most valued cultivated plants in the world. In recent years, interest in the cultivation of soybean has increased in Poland, which is due to the biological and nutritious value of its seeds. Different infection factors, especially fungi, which are the major cause of this plant’s diseases, affect the size and quality of the yield.
Purpose of studies. The purpose of the present paper was to find out the dynamics of the population of soil and phyllosphere microorganisms colonizing Glycine max and to determine plants’ susceptibility of different soybean cultivars to infection by fungi. The appearance of Phomopsis sojae, which has not been observed in Poland yet, among the fungi isolated from soybean plants inspired studies on this species. Hence, the paper also took into consideration the studies concerning genetic differentiation, pathogenicity as well as the possibility of using different methods in limiting the occurrence of Phomopsis sojae, which is the pathogen causing the necrosis of the pods, stems and seeds. This is an economically important disease occurring in all areas of this plant’s cultivation. 

Material and methods. Three many years’ field experiments were conducted which determined biodiversity of phyllosphere and soil bacteria and fungi colonizing 8 Polish soybean cultivars. Besides, the studies examined susceptibility of 10 cultivars (Polish and Canadian) grown in three different areas of the Lublin region to infection by fungi, especially by P. sojae. Besides, the effectiveness of chosen biotechnical preparations in the protection of 10 soybean cultivars in field conditions was established. Laboratory and growth chamber experiments studied the effect of microorganisms to P. sojae and other species of fungi pathogenic to this plant, genetic differentiation of P. sojae isolates using the RAPD-PCR method, P. sojae pathogencity towards the seeds, leaves, stems and seedlings of soybean as well as the effect of Biochikol 020 PC, Biosept 33 SL, Polyversum, Vitavax 200 FS and Bravo 500 SC on the growth of P. sojae in in vitro conditions.

Results and discussion. The quantitative and qualitative composition of soil and phyllosphere microorganisms depended on the examined soybean cultivar. The stock, healthiness and yielding of soybean cultivated in a monoculture were weaker than when this plant was grown in the correct crop rotation. Plants of ‘Polan’, ‘Progres’, ‘Optimus’ and ‘OAC Vision’ cultivars were especially susceptible to infection by different fungi species, including P. sojae. Plants of’Mazowia’ and ‘Aldana’ cultivars were least susceptibility. In in vitro conditions, bacteria Pseudomonas spp. and Bacillus spp. had an inhibiting effect on the growth and development of P. sojae. Trichoderma spp., Gliocladium spp., Fusarium culmorum, F. oxysporum, F. solani, Rhizoctonia solani and Sclerotinia sclerotiorum were also characterized by an inhibiting effect towards P. sojae.Molecular studies made it possible to use a relatively small number of starters to determine genetic similarity in a given population of P. sojae. The studies found no clear relation between the place of origin of P. sojae isolates, the organs from which they were obtained and their DNA profile. Effects of artificial inoculation confirmed P. sojae pathogenicity towards the seeds, leaves, stems and roots of the studied soybean cultivars. In in vitro conditions, the effect of Biosept 33 SL and Biochikol 020 PC in inhibiting the growth of P. sojae was a little smaller than the effect of Vitavax 200 FS and Bravo 500 SC. Polyversum preparation was the weakest in inhibiting the growth of P. sojae in all applied concentrations. The use of biotechnical preparations and fungicides in pre-sowing dressing of the seeds and in spraying older plants of the studied cultivars of soybean grown in field conditions had a positive effect on the emergence, number, healthiness and yielding of the species under discussion.
Conclusions. Plants of ‘Polan’, ‘Progres’, ‘Optimus’ and ‘OAC Vision’ cultivars were especially susceptible to infection by P. sojae. Plants of’Mazowia’ and ‘Aldana’ cultivars were least susceptibility. RAPD-PCR methods proved helpful in establishing genetic differentiation of P. sojae isolates. The studied isolates were rather homogeneous, which can probably testify to little differentiation of P. sojae population occurring in Poland and makes it possible to suppose that this species does not propagate genetically in our country. The studies found out considerable usefulness of the method of cultivating P. sojae on a weak PDA medium with an addition of clove leaves with the aim of stimulating this fungi to fast and abundant sporulation. P. sojae should be considered an especially dangerous pathogen of soybean as it is able to colonize plants without any symptoms. This poses the danger of an epidemic development of the disease when the conditions conducive to the development of this fungi occur. It should be expected that Biochikol 020 PC and Biosept 33 SL preparations will be useful in integrated protection of soybean and in the future they will be taken into consideration in the program of the protection of this species.