CAN LEAF LEVEL GAS EXCHANGE BE USED AS A PREDICTOR FOR DROUGHT TOLERANCE IN COMMON BEAN (PHASEOLUS VULGARIS)?

Abstract: This study aimed to examine drought tolerance among a variety of landraces of the species Phaseolus vulgaris to discover whether leaf level gas exchange can be used as a predictor for drought tolerance. Beans of different landraces from Rwanda were planted and when they had grown for four weeks a leaf-level gas exchange analysis was carried out, measuring one leaf from each plant both during the day and night. Half of the plants then stopped being watered. Once these plants had lost turgor pressure they were rehydrated. Chlorophyll fluorescence measurements were taken every day during the drought treatment and leaf area was measured. The results showed differences between the land races regarding the average wilting time and the average percentage of field capacity, the amount of water, left in the soil at wilting. Most types wilted between day five and seven although type 2 and 3 wilted somewhat sooner. Most types had an average field capacity of 21% at the time of rewatering. Type 20 had the highest field capacity. A strong correlation between leaf area and wilting time was found but no correlation between leaf area and percentage of field capacity. Between wilting time and leaf area times conductance a strong correlation was found. Based on the results, it was concluded that measuring chlorophyll fluorescence did not predict wilting, while leaf level gas exchange is a somewhat good predictor when it comes to predicting the rate of water loss, not, however, when it comes to how low of a percentage of field capacity the plants can withstand.