Grain Protein, Oil and Starch Contents and Yields of Maize (Zea mays L.) as Affected by Deficit Irrigation, Genotype and Their Interaction

The main objective of this investigation was to study the effects of deficit irrigation (I) at flowering stage, genotype (G) and G × I interaction on maize grain quality and yield traits of 6 inbred lines and their 15 diallel crosses. The parents and F1's were evaluated in two seasons. A split plot design was used, where main plots were allotted to two irrigation treatments, i.e. well watering by giving all recommended irrigations and water stress by withholding the 4th and 5th irrigations, while sub plots were allotted to genotypes. Water stress caused a significant decrease in protein yield/ha by 25.5 and 13.8%, oil yield/ha by 29.9 and 20.2%, starch yield/ha by 25.0 and 17.03%, grain yield/plant by 32.88 and 19.47% and grain yield/ha by 27.76 and 17.47% for parents and F1's, respectively, but slightly increased grain protein content of F1's by 4.19% and grain starch content of parents by 0.63%. On average, means across F1 crosses were higher than those across inbreds for all studied traits, except for grain protein content, where the opposite was true, under both water stress and non-stress conditions. The rank of inbreds and crosses for studied traits under water stress was changed from that under well watering conditions. Grain yield/ha of drought tolerant (T) was greater than that of sensitive (S) inbreds and crosses by 220.6 and 75.70%, respectively under water stress conditions. This superiority in grain yield/ha was associated with superiority in grain yield/plant, protein yield/ha, oil yield/ha and starch yield/ha. Although there was a negative correlation between grain yield/plant and each of grain protein content and grain oil content in inbreds, it was possible to identify some inbreds and hybrids characterized by high yield and high grain protein or oil content simultaneously under water stress conditions.