Membrane Thermal Stability as a Selection Criteria for Combined Heat and Drought Tolerance in Landraces of Corn in Northeastern Mexico.

Drought and high temperature are two abiotic stresses that can each significantly affect plant growth, development, and physiological processes.  However, when plants are exposed to both drought and high temperature simultaneously, even greater negative effects can occur.  The objective of this research was to study the interaction of combined drought and high temperature stress on physiological characteristics in two landraces of corn from Northeastern Mexico classified based on their membrane thermal stability (electrolyte leakage) characteristics (C-3014-heat-tolerant vs C-3014-heat-susceptible).  Plants were grown from seed under controlled greenhouse conditions in polyethylene bags containing 5 Kg of dry soil.  Treatments included two levels of water availability and two temperature regimes in a factorial experiment with five replicates.  Well watered plants were maintained in soil kept at a minimum of 80% of field capacity throughout the experiment while for water stressed plants, water was withheld when the plants reached the fourth ligulate leaf stage.  The two temperature regimes tested were 28/20 C and 44/28 C day/night ambient temperatures.  Our results showed that when water stress and high temperature occurred simultaneously, total and osmotic water potential values were reduced more significantly than when these stresses occurred alone.  Transpiration, stomatal conductance, and carbon fixation rates decreased slowly in response to water stress under high temperature treatment.  For all physiological variables tested, the heat-resistant genotype was less susceptible when both water and high temperature stress were combined.  Carbon fixation was reduced to almost zero in the heat-susceptible genotype by 8 days after initiating combined high temperature and water stress but this was not observed in the heat-tolerant genotype.  We conclude that the technique of membrane thermal stability (electrolyte leakage) can serve as a useful selection criteria for classifying corn genotypes tolerant to high temperature when exposed to water stress.