Use of Chlorophyll Fluorescence: A Tool to Determine Damage in Photosystems under Water-Stress Conditions in Legume Species.

The importance of legumes in agriculture is due mainly to their richness in high-quality protein for human food and animal feed.  In Mexico, one of the most limiting factors for legume production in rainfed areas is the random availability of water. The effect of water stress varies greatly not only among different species, but also among different varieties of the same species. The use of chlorophyll fluorescence is a simple and non-invasive procedure that yields information about the way plants tolerate environmental constraints such as water stress, and the extent the photosynthetic system is affected. Unfortunately, the use of this procedure is relatively new in Mexico, and little information about its efficiency has been reported. The objective of this study was 1) to determine damage in photosystems under water-stress conditions in soybean, common bean, and Tepary bean using chlorophyll fluorescence, and 2) to correlate the results with other photosynthetic parameters such as photosynthesis rate, stomatal conductance, CO₂ exchange, leaf area, dry weight, and yield. Four, three and two varieties from soybean, common bean, and Tepary bean, respectively were evaluated in Marin, Nuevo León, Mexico in summer and winter 2007. A complete randomized design (CRD) with five replications was used. At the beginning of flowering, water-stress was imposed.   The control plants were fully irrigated. Photosynthetic gas exchange was measured in irrigated and water-stressed plants using a Li-COR (Lincoln, NB, USA) 6400 portable photosynthesis system with a fluorometer attachment. Results indicated significant differences among species. The common bean varieties showed the most damage for water stress compared to soybean and Tepary bean. For Tepary bean, significant differences among irrigated and stressed plants were not observed. The chlorophyll fluorescence procedure correlated positively with other photosynthetic parameters so it could be used as a tool to determine water-stress induced changes at the photosynthetic level.