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Abstract Twenty five genotypes of wheat (T. aestivum) were screened under pots and field experiment at Sids Agriculture Research Station. Beni Sweif Governorate for some agronomic and morphological characters that are considered to be criteria for selecting drought tolerance genotypes. The selected six wheat genotypes from the screening experiments were used to study the genetic system controlling the investigated characters and its relations under different soil moisture levels. The selected genotypes for this study were mainly based on the data of grain yield and drought susceptibility index (5). This index was calculated from the obtained data using the formula presnted by John et al.(1984). These six selected lines (parents) from screening experiment were three tolerent which produce high grain yield per plant under moisture stress levels (01 = 225 mm) and (D2 = 175 mm) as compared with the control treatment (DO = 500 mm). The value of drought susceptibile index (5) was low than one. indicating that parents were drought tolerent. These parents are NS 732- PIMA, Veery ”s” and sakha 69. One moderate tolerent parent was selected. The parent PVN ”s” - MN70121 and two otheres i.e. (STP-YRx WALO (3)- ERA and Kavco. were highly susceptible to water stress.The aims of the second experiment were to study the genetic Ivariance components. phenotypic correlations and genotypic correlations between different characters under water stress conditions.The studied characters included, plant height. grain yield per plant. number of kernels per spike. 1000 kernel weight, number of stomata on adaxial surface of flag leaf, root length. root dry weight. harvest index, total DNA content and total RNA content. Most of the studied characters were affected by moisture stress treatments (D1) and (02) except number of stomata on upper flag leaf surface. The greatest decreased in the average of plant height, grain yield. number of kernels per spike. 1000 kernel weight. total DNA content and total RNA content were observed under (D2) treatment as compared with the control for al~ Fl hybrids and the parents. The line . : Veery ”s” was the most tolerent parent producing high grain yield, number of kernel per spike, root dry weight and longest root length under water stress treatments (01=225 mm) and (D2=175 mm). The most affected parents were STP-YR x WALD(3)-ERA and Kavco which gave ~ >’, ; the lowest grain yield. number of kernels per spike and 1000 kernel (,0 0’ weight. Both parents were considered susceptible ones. Additive gene effects were more important in the inheritance of 1000 kernel weight and of stomata on upper flag leaf surface. Both additive and non-additive gene effects showed an equal I importance in the inheritance of plant height, grain yield per ’;.: plant, number of kernel/spike, root length, root dry weight, harvest index. DNA and RNA content under (01) and (D2) treatments.The averag degree of dominance was found to be overdominance for all characters under different water lev~ls except, (106) for number of stomata on upper flag leaf surface which showed partial dominance. The negative and positive alleles were not equally distributed among the parental population for most studied atttibutes under all treatments. The dominant genes are in excess in the parents in case of grain yield per plant, number of kernels/spike, root length and harvest index under (DO and 01) treatments. Low estimates of narrow sense heritability for the~e characters could indicate that the traits were greatly influenced by the environmental factors. Parent (Veery ”5”) seems to possess most of the dominant genes for grain yield per plant. number of kernels per spike, root length. root dry weight. harvest index and total DNA content. KavcO ”s” posses an excess of recessive genes for grain yield per plant, number of kernels per spike. lOOOkernel weight, root length and total DNA content. Highly significant positive phenotypic correlation was found between plant height and each of grain yield per plant, number of whereas, a highly significant negative correlation was obtained kernels per spike ,root length, root dry weight and RNA content ,” between plant height and harvest index. Highly significant positive phenatypic correlation was estimated between grain yield per plant and each of number of kernels per spike. 1000 kernel weight. root length, root dry weight,harvest index. root length root dry weight. harvest index, total DNA content and total RNA content . Highly positive phenotypic correlation was found between number of kernels/spike and each of root length, root dry weight, harvest index and total RNA content. The same trend was found between 1000 kernel weight and root length under all treatments, root dry weight and harvest index. A highly significant positive phenotypic correlation was observed between number of stomata and each of root dry weight and total RNA content under all treatments. Highly positive phenotypic correlation was found between root length and each of root dry weight under all treatments, DNA DNA content, and RNA. The same trend was observed between root dry weight and each of total DNA content and total RNA content. Highly positive phenotypic correlation was obtained between total DNA and total RNA contents. A negative genotypic correlation was estimated between plant plant height and each of grain yield/plant, number of kernels per spike and total RNA content. Grain yield/plant showed positive’ genotypic correlation with each of root length, root dry weight. number of kernel per spike, 1000 kernel weight, total DNA content and total RNA content under all treatments. A negative genotypic correlation was found between number of kernels and 1000 kernel weight.Positive genotypic correlation was detected between total DNA content and total RNA content under all treatments. It seems to be that any morphological or physiological improvement that reduces transpiration or increase absorption of soil water could postpone water deficit and reduce the harmful effect of water stress. In wheat, rabid growth, extensive root system, low number of stomata ,1000 kernel weight and number of kernels per spike may be considered good selection criteria for drought tolerance genotypes. Further research is required to study the effect of water stress on chloroplasts (cp DNA) and mitacondria (mt DNA) and RNA as well. |