Abstract: In soybean [Glycine max (L.) Merr.], drought is the greatest threat to profitability and too often a crop with great promise ends up with only fair or poor yields because of dry weather. Nitrogen fixation activity by soybean (Glycine max (L.) Merr.) nodules has been shown to be especially sensitive to soil dehydration.. The aim of this paper is to characterize water stress in inoculated soybean genotypes (with Nitrazon inoculant) using some physiological characteristics. In the two growing seasons of experiments with three genetic resources of soybean (Drina, Maverick, Nigra) was launched. Drought stress was secured by an irrigation interruption for a 9-day period in the mentioned growth stage. The influence of water stress was tested on some physiological parameters - stomatal closure, relative water content in leaf (RWC), free proline content and osmotic adjustment. Drought had a negative impact on the tested parameters. The objective of this research was to investigate possible genetic variation in the sensitivity of soybean cultivars for nitrogen fixation rates in response to soil drying. During the water stress was monitored the proline accumulation. Proline serves during the osmotic stress as a mediator of osmotic adjustment, a sink of energy and a stress signal. The higher content of free proline reached genotype Maverick with a level of 16.95 μmol.g-1Fresh Weight (according to the calculation on 100 % RWC) in dehydrated plants with the inoculant usage, what is related to the more notable RWC content decrease in the leaves. Among tested genotypes showed the higher capacity for osmotic adjustment during increasing drought conditions all genotypes with Nitrazon inoculation. The results indicate that physiological characteristics, such as relative water content, proline content and osmotic adjustment, are good indicators of water stress in soybean, proline content being a particularly reliable parameter corresponding to the actual water stress of plants.

drought, osmotic adjustment, soybean, proline

Presentation: oral