Thesis (Ph.D.) - Cairo University - Faculty of Agriculture - Department of Agronomy

Exposing maize plants to drought and/or low nitrogen (N) stresses results in a huge reduction in grain yields. Current breeding programs should pay great attention to develop hybrid corn of high tolerance to these stresses. The objectives of the present study were to assess the genetic diversity of 19 maize hybrid cultivars and populations for tolerance to these stresses and stability across combinations of two irrigation and three N levels, to estimate heritability under both stresses and to identify the selection criteria for tolerance to such stresses. A two-year field experiment was conducted using a split-split-plot design with three replications. Main plots were allotted to two irrigation regimes; sub-plots to three nitrogen fertilizer rates and sub-sub-plots to nineteen maize genotypes. Twenty-two traits were recorded. Combined analysis of variance showed that variances due to genotype, irrigation and N level and their interactions were significant (P{u2264} 0.05 or 0.01) for most studied traits. Water stress, low N stress and water stress along with low N stress caused a significant reduction (P{u2264} 0.05 or 0.01) in grain yield/plant (GYPP) by 28.56 %, 31.63 % and 51.42%, respectively. The highest yielding and highest nitrogen use efficiency (NUE) and the most drought and/or low N tolerant genotype was the single cross SC-101 followed by SC-30K8, SC-131 and SC-10, in descending order. Significant (P {u2264} 0.01) superiority of tolerant (T) over sensitive (S) genotypes in GYPP under low N (109.5 %), under drought (39.6 %), and under both severe stresses (141.9 %) was associated with significant (P{u2264} 0.01) superiority expressed in all yield attributes, shorter anthesis silking interval (ASI), higher nitrogen utilization efficiency (NUTE), higher NUE

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