Physiological response of selected eragrostis species to water-deficit stress
Plant water-deficit stress is considered to be one of the greatest threats to world agriculture. In an effort to identify a better performing crop variety of Eragrostis tef under this stress, the responses of two varieties, white (W) and brown (B) seeded, were compared with those of the resurrection grass Eragrostis nindensis during a dehydration/rehydration cycle. After 6 days of dehydration, relative water content (RWC) dropped to 33%, 43% and 39% in En, Et(B) and Et(W) plants, respectively. This water loss was accompanied by a decline in transpiration and increased electrolyte leakage in the Et varieties. Et(W) did not recover from this level of drying when watered. Et(B) on the other hand recovered fully from 43% RWC, but lost viability after 9 days dehydration, RWC < 30%. En showed full metabolic recovery from drying to 10% RWC. Loss of viability in the Et varieties was accompanied by an increase in electrolyte leakage and irreversible decline in photosynthesis and transpiration. Ultrastructural study also indicated a drying-induced damage to membranes and organelles of Et tissues dehydrated for 6 days which was reversed in Et(B), 43% RWC, on rehydration. However, after 9 days of dehydration, (< 30% RWC), severe irreversible damage occurred to the entire subcellular organization of both Et varieties and was accompanied by loss of viability. This study shows that En is a true resurrection plant and both Et varieties are desiccation sensitive but drought tolerant to varying degrees. Et(B) is more drought tolerant and hence a better choice crop in drought prone areas. Comparative study of closely related plant species might be a better approach in finding adaptive characters in crop plants with respect to environmental stresses.
Key words: Eragrostis tef, eragrostis nindensis, dehydration, desiccation, gas exchange, leakage, ultrastructure.