Soybean plants [Glycine max (L.) Men., cv. Polanka], inoculated with the VAM fungus Glomus claroideum Schenck and Smith and Bradyrhizobium japonicum strain D344, were grown in pots and in the field. The VAM fungus positively influenced N2 fixation, nodulation and N, P, K, and Mg concentrations in the leaves. In pots, (at green pods formation) VAM inoculated plants produced a 24% greater biomass as compared with non-inoculated plants colonized by native VAM populations. Under field conditions characterized by a high level of P and N, the seed yield of VAM inoculated plants increased in comparison with non-and only rhizobia-inoculated soybean (+28% and 17%, respectively). Glomus claroideum was capable of competing with the native VAM populations both in the greenhouse and in the field experiment.

SUMMARYThe effect of magnesium sulphate on the colonization of maize roots by a vesicular-arbuscular mycorrhizal fungus was studied in hydroponic culture. Increased concentration of MgSO4 in the nutrient solution caused an increase in the percentage of root length infected. The highest infection levels were found when nutrient solutions contained 5-84-11-68 mmol 1"^ of MgSO^. Root colonization was stimulated by the increased concentration of magnesium but not calcium or potassium ions in the nutrient solution. No significant difference occurred in the percentage of root length infected when magnesium chloride was replaced by magnesium sulphate. A broad range of magnesium sulphate concentrations did not cause significant differences in plant biomass. The stimulation of root colonization by magnesium cannot be explained by changes in pH or osmotic pressure of the nutrient solution.

The influence of sugars and growth regulators on shoot and root growth of Dactylorhiza species was studied under in vitro conditions. The seedling development was stimulated with the application of glucose and sucrose at concentration of 10 g dm -3 each. The improvement of shoot growth rate and shoot length was enhanced by cytokinins N 6 -(2-isopentenyl)adenine or N 6 -benzyladenine and their combination with auxin indolebutyric acid (IBA). The root growth rate and root length of seedlings increased in the presence of IBA and α-naphthaleneacetic acid. Individual Dactylorhiza species showed statistically significant differences in shoot and root development depending on sugar and growth regulator combinations.

In Rhododendron L. cv. Azuro, Bohumil Kavka, Catharine van Toll, Grandiflorum, Mars, Nova Zembla, Ortrud, Ovation, Prof. Scholz, Purple Splendour, Rebe and Van Werden Poelman, the effect of growth regulators on organogenesis induction of shoot-tip meristems was tested. All cultivars significantly showed the highest shoot regeneration on MS medium containing 6 mg/dm³ isopentenyladenine (2iP). For most rhododendrons, the highest shoot multiplication was found on a medium with 8–10 mg/dm³ 2iP in combination with 1 mg/dm³ indoleacetic acid (IAA). Shoots rooted successfully in the substrate with high level of peat without growth regulators. However, the commercial preparation Racine significantly increased rooting in cv. Grandiflorum, Nova Zembla and Rebe compared with 0.03% indolebutyric acid (IBA).

The effect of two Bradyrhizobium japonicum strains (D344 and Urbana), on the frequency and intensity of infection by a VAM fungal Glomus sp. and the effect of VAM on biomass production by nodulating plants were tested in soybean growing in a soil containing low levels of accessible P and N. During the initial stage of vegetative growth, mycorrhiza frequency in roots inoculated with the two rhizobial strains did not differ. However, during flowering it was 178% higher in roots with the strain D344 than in the presence of the strain Ubrana. At final harvest (green pods) the VAM frequency did not differ in the presence of either strain. VAM positively affected biomass production, foliar concentrations of P, Zn and Cu, and number and dry matter yield of pods, but did not increase concentrations of total N and K. In nonmycorrhizal plants total nitrogenase activity (not nodule mass) and growth were higher with the rhizobial strain Urbana. The greatest nitrogenase activity, growth and yield occurred in the presence of the VAM fungus, and did not differ for plants with different strains of rhizobia.