Screening for Drought Resistance: Evaluation of Drought Susceptibility Index of Legume Plants under Natural Growth Conditions

Eighteen cultivars of legume species (field bean, soybean, field pea, lupine) were screened for drought tolerance in 3 year-long field experiments. The aim of the investigations was to evaluate the generic variation of drought susceptibility of the tested varieties. The experimental plots were equipped with an installation which enabled the limitation of the water content in soil and soil irrigation. The applied drought susceptibility index (DSI) considered the relations between seed yield of plants under drought conditions (Y_D) and that under conditions of good soil watering (Y_IR) as well as their dependence on the drought severity index (D_S). The use of the index divided the cultivars into two groups of different drought tolerances. The group of drought resistant cultivars characterized by mean values of the DSI index < 0.31 comprised field bean cultivars Bourdon, Gobo and Nadwislanski, soybean cultivars Aldana, Polan and Progres, field pea cultivars Miko and Solara and lupine cultivars Popiel and Bac. To the drought sensitive cultivars with DSI > 0.44 belonged Victor and Bronto of field bean species, Bareness and Mige of field pea species and Emir of lupine species. In general, the resistant cultivars when compared with the susceptible ones were characterized by lesser yield of seeds, which, however, was more stable both under conditions of drought and moistured plots. Any dependence of the degree of drought tolerance on the duration of the particular periods of plant growth was not observed in the experiments, however, both in’ drought susceptible and drought resistant cultivars there appeared the tendency to shorten the development phases under drought and to prolong them under artificial irrigation. In general, based on the results obtained, it can be concluded that legume plants belong to the species sensitive to water supply. The observed decrease of plant seed yield under moderate natural soil dryness in the year 1993 differed only a little from that found in experiments in the years 1994 and 1995, when soil dryness was much more severe.