Thesis (Ph.D)-Cairo University, 2024.

Bibliography: pages 271-296.

Maximizing of maize productivity from land unit area in Egypt could be achieved via growing
tolerant hybrids to high plant density (HD) and low-N in combination with using the optimum
plant density and appropriate nitrogen fertilization rate. A set of inbred lines with obvious
diversity in their adaptive traits to HD and low-nitrogen (LN) were used in the present study as
parents of diallel crosses (without reciprocals) to study the inheritance of these traits, identify
tolerant genotypes to HD and LN stresses and determine adequate N-fertilization for
maximizing grain yield/fed (GYPF). The F crosses were made in 2019 and evaluation of
inbreds and hybrids was carried out in 2020 and 2021 seasons, at the Agricultural Experiment
and Research Station of the Faculty of Agriculture, Cairo University, Giza, Egypt. A split-split
plot design in randomized complete blocks arrangement with 3 replications was used, where
main plots were devoted to N levels (low; 40 kg N, medium; 120 kg N and high; 200 kg
N/fed), sub-plots to plant densities (20, 30 and 40 thousand plants/fed) and sub-sub plots to
maize genotypes. Some newly developed maize hybrids gave very high grain yield, reaching
54 ard/fed (ca. 20 t/fed) in the cross IL53×IL84, when were grown under high plant density
(40,000 plants/fed) and were given the highest N fertilization rate (200 kg/fed). Moreover,
some crosses (L17 × L54, IL53×IL84, L17×IL80, L28×IL84 and L17×L28) gave >44 ard/fed
under 40,000 plant density and using 120 kg N/fed. The inbreds L17, L21, L14 and L28
proved to be tolerant (T), while IL80, IL53, IL51 and IL84 were sensitive (S) to HD and/or
LN. T×T group of crosses exhibited better values in most studied traits than T×S and S×S
groups of crosses under both stresses. Both dominance and additive variances were significant,
but the estimates of dominance were much higher, in magnitude, than additive variance for all
studied traits under most environments, suggesting that heterosis breeding is the method of
choice for improving adaptability traits to both HD and LN stresses. The degree of dominance
was overdominance in most cases. For all studied traits under all environments, narrow-sense
heritability was generally of small magnitude (<15%), but reached ˃30% in LANG, PLE, PLB,
KPP, GYPP. Expected genetic advance from selection (based on 10% selection intensity) was
generally of small magnitude, but reached its maximum for grain nitrogen under E5 (48.42%).
The highest heritability along with the highest expected genetic gain from selection were
achieved by the traits LANG, SDL, SDU, PLE, PLB, ELA, leaf area produced 1g grain under
severe stress of both HD and LN together and plant height, rows/ear, kernels/row, 100-kernel
weight under stressed environment for high density.

تم استعمال مجموعة من سلالات الذرة الشامية ذات اختلاف واضح في صفاتها التأقلمية لاجهادي الكثافة النباتية العالية والنيتروجين المنخفض كآباء للهجن التبادلية لدراسة طبيعة توارث هذه الصفات، وتحديد التراكيب الوراثية المتحملة لكلا الاجهادين وكذلك الكثافة النباتية المثلى ومعدل التسميد المناسب لتعظيم محصول حبوب الفدان. بعض الهجن الجديدة أعطت محصول حبوب عالي جداً، عندما زرعت تحت كثافة نباتية عالية وأعطيت معدل التسميد النيتروجيني العالى. كان كلاً من تباين السيادة والتباين المضيف عالي المعنوية ، ولكن تقديرات تباين السيادة كانت اكبر كثيراً في المقدار من تقديرات التباين المضيف، في كل الصفات تحت الدراسة تحت كل البيئات. كفاءة التوريث بالمعنى الخاص كانت صغيرة في المقدار، ولكنها وصلت لاكثر من 30٪ لصفات زاوية الورقة ونفاذ الضوء حتى الكوز وحتى قاعدة النبات وعدد حبوب النبات ومحصول حبوب النبات.

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