DROUGHT AND SALT STRESS MITIGATION BY SEED PRIMING WITH KNO3 AND UREA IN VARIOUS MAIZE HYBRIDS: AN EXPERIMENTAL APPROACH BASED ON ENHANCING ANTIOXIDANT RESPONSES

Priming offers an effective means for counteracting different stresses induced oxidative injury and raising seed performance in many crop species. The present study was carried out to investigate the ability of potassium nitrate (KNO3) and urea to promote the tolerance of different maize hybrids to drought and salt stresses to identify some biochemical parameters associated with KNO3 and urea induced resistance in maize seedlings. An experiment was conducted in a controlled environment of the laboratory at the college of agriculture, Shiraz University, Shiraz Iran, during 2010. The first factor was stress type and intensity at five levels; moderate drought, severe drought, moderate salt, severe salt, and control (without stress). Seed priming was the second factor; water as control, KNO3, and urea, and maize hybrids, including Maxima, SC704, Zola, and 304 were the third factor. Results indicated that the highest chlorophyll a (Ch a), chlorophyll b (Ch b), total chlorophyll (Ch T) contents, and carotenoids (Car) were found in no stress treatments and the most proline, protein contents, superoxide dismutase (SOD), peroxidase (POD), and catalase (CAT) activities in severe drought treatment. Also, results revealed that generally, drought and salinity stresses decreased the amount of Ch a and the lowest Ch a was recorded for severe salinity stress (4.29mg g(-1)). Stresses caused decrease in Ch b, but the effect of sever salinity level was higher than the others. Priming of KNO3 had significantly higher proline content than water and urea priming. The SC704 and 304 hybrids showed higher proline content than the other ones. Finally, the maize seed KNO3 and urea priming lead to high activities of antioxidant defensive enzymes and increase the tolerance level to abiotic stresses such as salt and drought.