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Title: N2-FIXATION RESPONSE TO DROUGHT IN COMMON BEAN (PHASEOLUS VULGARIS L.)

Author
item SERRAJ, R. - SEMLALIA, MOROCCO
item Sinclair, Thomas

Submitted to: Annals of Botany
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 4/30/1998
Publication Date: N/A
Citation: N/A

Interpretive Summary: Common bean is an important crop in many regions of the world. With an increasing emphasis on sustainable agriculture, the ability of grain legumes such as common bean to assimilate atmospheric nitrogen via symbiotic nitrogen fixation makes them important in many crop production schemes. Previous research has suggested, however, that the nitrogen fixation of some grain legumes is very sensitive to drought stress. Because common bean is frequently grown in drier regions, this study was undertaken by a USDA-ARS scientist at Gainesville, FL to evaluate the drought sensitivity of nitrogen fixation in common bean. It was found that, in fact, nitrogen fixation in both tested cultivars of common bean is highly drought tolerant. It appears that this tolerance is a result of the nature of the nitrogen compounds that are exported from the sites of nitrogen fixation to the rest of the plant. Common bean appears to be a good candidate for grain legume production in dryland areas.

Technical Abstract: Nitrogen fixation activity in common bean is generally thought to be low and sensitive to soil drying, and consequently, drought can have important negative effects on N accumulation and yield potential. The objectives of this research were to examine the response of N2 fixation to drought stress in common bean, and to determine if there is any link between the drought sensitivity and the ureide levels in the plants. Two greenhouse experiments were conducted to compare the responses of leaf transpiration and acetylene reduction activity (ARA) to soil water contents. ARA decrease during soil dehydration was found to lag behind transpiration. This indicates that ARA is relatively less sensitive to soil dehydration, compared to leaf gas exchange. The ureide concentrations measured in common bean plants were relatively low, ranging from 0.1 to 1.0 mmol L-1 in xylem sap exudates. A negative correlation was found between sap ureide and ARA response to drought. It was concluded that in common bean the lower sensitivity of N2 fixation to drought compared to leaf gas exchange could be related to low ureide concentrations in petioles and xylem sap.