النظام الوراثى المتحکم فى المحصول والصفات المرتبطة فى عشائر ثلاث هجن من  قمح الخبز تحت الظروف الطبیعة والإجهاد المائى

أمجد محمد مرسى

قسم بحوث القمح- مرکز البحوث الزراعیة- الجیزة- مصر

أجریت هذه الدراسة خلال المواسم الشتویة لأعوام 2015 / 2016 و 2016 / 2017 و 2017 / 2018 بالمزرعة التجریبیة لمحطة البحوث الزراعیة بالاسماعیلیة محافظة الأسماعیلیة بإستخدام تحلیل العشائر الستة لثلاث هجن من قمح الخبز هى : (1) سخا 95 × Salah - 1 و سخا 95 × Amna 2 x Damara 6, Roma 2 x فى تصمیم قطاعات کاملة العشوائیة فى تجربتین، الأولى تم ریها بنظام الرى بالرش کل أسبوع خلال موسم النمو (ظروف الرى الطبیعى)، والثانیة تم ریها بنظام الرى بالرش کل ثلاث أسابیع خلال موسم النمو (ظروف الجفاف) وقد استهدفت الدراسة تقدیر النظام الوراثى وطبیعة الفعل الجینى المتحکم فى صفات عدد الایام حتی طرد السنابل والنضج وعدد السنابل /  نبات وعدد حبوب السنبلة ووزن الـــــ 100حبه ومحصول الحبوب للنبات تحت معاملتى الری الطبیعی و الاجهاد المائی. هذا وقد أظهرت النتائج أن تعرض هذه العشائر للجفاف قد أدى لحدوث نقص معنوى فى کل الصفات تحت الدراسة، أظهرت نتائج متوسط السلوک تفوق الجیل الاول على متوسط الأب الأفضل للمحصول وبعض الصفات المرتبطة به فى معظم الهجن تحت الدراسة تحت ظروف التجریب وقد کان تأثیر قوة الهجین فعالا ومعنویا فى معظم الحالات. وقد اختلف النظام الوراثى والتعبیر الجینى من ظروف الرى الطبیعى إلى معاملة الجفاف للصفات المدروسة فى معظم الحالات. و أظهرت نتائج إختیار المقیاس (A, B and C) تحت الظروف المثلى للرى بالرش ملاءمة المودیل الوراثى البسیط "المضیف – السیادى" فى تفسیر میکانیکیة وراثة وزن الـ 100 حبه فى الهجین الثانى بینما تحت ظروف الجفاف فقد کان المودیل الوراثى البسیط هو الملائم لتفسیر وراثة إرتفاع النبات فى الهجین الأول وعدد السنابل على النبات فى الهجین الثالث ووزن الـ 100 حبه فى الهجین الثانى وعلى الجانب الأخر کان المودیل الوراثى العقد هو الملائم لتفسیر وراثة محصول الحبوب للنبات عدد الایام حتی طرد السنابل و عدد الایام حتی نضج السنابل وعدد الحبوب للسنبله فى کل الهجین المدروسة تحت کلا النظامین الری الطبیعى و الاجهاد المائی وإرتفاع النبات وعدد السنابل على النبات فى الهجین الأول والثانى والثالث ووزن الـ100 حبه فى الهجین الأول والثالث تحت ظروف الرى الطبیعى. بینما کان المودیل الوراثى المعقد هو

المتحکم فى وراثة صفات إرتفاع النبات فى الهجین الثانى والثالث وعدد السنابل للنبات فى الهجین الأول والثانى ووزن الـ100حبه فى الهجین الأول والثالث تحت ظروف الاجهاد المائی. هذا وقد لعب الفعل الجینى المضیف دوراً معنویا فى وراثة عدد الایام حتی طرد السنابل و عدد الایام حتی نضج السنابل وإرتفاع النبات وعدد السنابل على النبات فى کل الهجن، وعدد حبوب السنبلة فى الهجین الثالث ومحصول الحبوب للنبات فى الهجین الأول ووزن الـ100حبه فى الهجین الثانى تحت ظروف الرى الطبیعى، وعدد الایام حتی طرد السنابل وعدد الایام حتی نضج السنابل فى الهجین الأول والثانى وارتفاع النبات فى الهجن الثلاثة وعدد السنابل فى الهجین الثالث وعدد حبوب السنبلة فى الهجین الثانى ومحصول الحبوب للنبات فى الهجین الأول والثانى تحت ظروف الاجهاد المائی. کان الفعل الجینى المضیف والسیادى والتفاعل مضیف × مضیف وسیادى × سیادى هو المتحکم فى وراثة عدد الایام حتی طرد السنابل فى الهجین الثالث وعدد الایام حتی نضج السنابل وإرتفاع النبات فى الهجین الثانى تحت ظروف الرى الطبیعى، وعدد الایام حتی طرد السنابل فى الهیجن الثانى تحت ظروف الاجهاد المائی. بینما کان الفعل الجینى المضیف والسیادى والتفاعلات مضیف × مضیف ومضیف × سیادى وسیادى × سیادى ذو اهمیة فى وراثة عدد الایام حتی طرد السنابل فى الهجین الثانى تحت ظروف الاجهاد المائی. کان التباین الوراثى المضیف هو المکون الأعظم المتحکم فى وراثة عدد السنابل / النبات فى الهجین الثالث ومحصول الحبوب للنبات فى الهجینین الأول والثانى تحت ظروف الرى الطبیعى، ووزن الـ 100 حبه فى کل الهجن الثلاثة تحت ظروف الاجهاد المائی. هذا وقد وجد أن التباین الوراثى السیادى کان هو المکون الأعظم المتحکم فى معظم الصفات تحت الدراسة فى الهجین الثلاثة فى کل من ظروف الری الطبیعى والاجهاد المائی. وقد تراوحت تقدیرات معامل التوریث فى المعنى الخاص من منخفض إلى متوسط لمعدل الحبوب للنبات والصفات المرتبطة به فى جمیع الهجین تحت ظروف کلا من الرى الطبیعى و الاجهاد المائی.

GENETIC ANALYSIS CONTROLLING THE YIELD AND ITS RELEVANT TRAITS IN THREE CROSS POPULATIONS OF BREAD WHEAT UNDER NORMAL AND WATER STRESS CONDITIONS

Amgad M. Morsy

Wheat Res. Dept., Agric. Res. Center., Giza, Egypt.

E-mail address: amgad. moursy@ gmail.com

Key Words: Bread wheat, drought stress, genetic system, heritability.

ABSTRACT

Six populations P₁, P₂, F₁, F₂, Bc₁ and Bc₂ of three bread wheat crosses. namely,1) Sakha 95 x Salah-1, 2) Sakha 95 x Rama- 2 and 3) Amna- 2 x Damara- 6, were raised in randomized complete block design during the three successive seasons of  2015 / 2016, 2016/2017 and 2017/2018 at Ismailia Agricultural Research station, El-Ismailia Governorate, Egypt. The six populations were evaluated in two adiacent expirments, one with irrigated by sprinkler system every week throught the season (normal condition) and the other was irrigated by sprinkler system every three weeks throughout the season (drought stress condition). The study aimed to determine the adeguacy of genetic model and gene action controlling days to heading, days to maturity, plant height, No. of spiks / plant, No. of grains/spike, 100-grain weight and grain yield/plant. Results indicated that, drought stress caused significant reductions in all studied traits. The heterotic effect was significant in most cases with a few exceptions. Genetic system and gene expression differed greatly from the normal and drought stress conditions in most cases. Scaling tests (A, B and C) provide evidence for the suitability of simple additive – dominance genetic model for explaining the inheritance of 100-grain weight in 2^nd cross under normal condition and plant height in the 1^st cross, No. of spikes / plant in the 3^rd cross as well as 100-grain weight in the 2^nd cross under drought condition. Otherwise, the complex genetic model was responsible for the inheritance of grain yield/plant, days to heading, days to maturity and No. of grains / spike in all studied crosses under both conditions, plant height and No. of spikes / plant in 1^st, 2^nd and 3^rd crosses under normal condition, also it responsible for plant height in the 2^nd  and 3^rd crosses and 100-grain weigh in the 1^st and 3^rd crosses under normal condition, plant height in 2^nd crosses as well as 100-grain weight in the 1^st and 3^rd ones under drought stress condition. Additive gene effect (d) was significant for days to heading, days to matunity plant height and No. of spikes / plant in all studied crosses and No of grains/spike in 3^rd cross, grain yield / plant in 1^st cross as well as 100-grain weigh in the 2^nd one under normal condition and days to heading and days to matunty in 1^st and 2^nd crosses / plant height in all crosses, No. of spike / plant in 3^rd crosses, No. of grains / spike in 2^nd cross as well as grain yield / plant in 1^st and 2^nd crosses under drought conditions. Both additive (d), dominance (h) and their interaction types, additive x additive (i) and dominance x domiuance (j) were involved in the genetics of days to heading in 3^rd cross and days to maturity and plant height in 2^nd cross under normal condition as well as days to heading in 1^nd cross under drought stress condition. Addilive (d), dominance (h), additive x additive (i), additive x dominance (i) and dominauce x dominance (I) were involved in controlling days to heading in 2^nd cross under drought stress conidian only. Additive (D) genetic variance was important in the genetics of No. of spikes / plant in 3^rd cross and grain yield / plant in 1^st and 2^nd cross under normal condition as well as 100-grain weight in all studied crosses under drought stress condition. The dominance (H) genetic variance was found to be the prevailent type controlling the most remaining crosses under both conditions. Heritability in narrow sense (Tn) was low to moderate percent for days to heading, days to maturity, No. of spikes/plant, No. of grains/spike, 100-grain weight and grain yield/plant in most cases under both conditions.

INTRODUCTION

Bread wheat (Tritium aestivum L.) is the first strategic crop grow during the winter season in Egypt due to its multiple uses and the cultivated area. Egypt suffer severe a wide range of environmental stresses. Among the environmental stresses water stress is the second contributor to yield reduction after disease losses (Farshadfar et al., 2008 a and Said, 2014). The Egyptian wheat breeding program are interesting in breeding for water stress tolerance to development of suitable cultivars for this purpose. This goal can be exploited in the rainfed areas of the Northern Coast and the newly reclaimed sandy soils in Toshka and Shark El-Owainat. The breeding process should focus on a reasonably high yield potential with specific plant characters, which could buffer yield against severe moisture stress (Blum 1983). So, it is important to know the genetic nature of earliness and yield and relevant traits (Misra et al 1994). The analysis of generation mean provide useful knowledge about the relative importance of average effects of the genes (additive effects), dominance deviations, and effects of non-allelic interactions, to assess the genotypic values and the mean genotypic values of individuals, families and generations (Viana 2000 and Elmassry and El-Nahas, 2018) .

The success of selection for water stress tolerance in segregating generations of wheat crosses depends needs the information of the pre-dominance of additive and additive x additive types of gene action. Additive gene action is evidently accounted for a large amount of variation for days to heading and maturity traits (Menshawy 2005 & 2007) and yield components (Subhani and Chowdhry 2000, Darwish 2003 and Riaz and Chowdhary 2003 a & b) under normal and water stress conditions. Epistasis was also reported for earliness traits (Tammam 2005 ; Abd El-Rahman and Hammad 2009) and for agronomic and yield traits  some studies (Dhanda and Sethi 1996, Hoshiyar et al 2003 and Morsy, 2014).

The efficiency of selection depends on the variation observed between the genotypes for the characters investigated and related to the magnitude of heritability and genetic advance (Johnson et al., 1955; Singh and Narayanan, 1993 and Farag et al., 2019). However, Heritability estimates along with genetic advance are important selection parameters and normally more helpful in predicting the gain under selection than heritability estimates alone. However, heritability estimates are influenced by the type of genetic material, sample size, method of sampling, type of experiment, method of estimation and effect of linkage. Genetic advance which refers to the improvement in the mean genotypic value of selected individuals over the parental population is influenced by the genetic variability, heritability and selection intensity (Sharma, 2003).

This study aimed to determine all types of gene action controlling inheritance of wheat agronomic traits in six generations (P₁, P₂, F₁, F₂, BC₁, and BC₂) in three cross populations under water stress and normal conditions.

MATERIALS AND METHODS

Crossing technique and experimental layout

The present study was conducted at Ismailia Agricultural Research station, Ismailia governorate, Egypt during the three successive growing seasons of 2015/2016, 2016/2017 and 2017/2018. Five diverse parental bread wheat genotypes i.e. Sakha 95, Salah -1, Rama 1, Amna 2 and Damara- 6 (Table 1) were selected according to diversity in their productivity as parental materials to build six populations of their wheat crosses: 1) Sakha 95 x Salah -1, 2) Sakha 95 x Rama- 2 and 3) Amna- 2 x Damara- 6. The origin and pedigree of these bread wheat genotypes are presented in Table (1).

Table (1). Pedigree and origin of the parents used in the four bread wheat crosses under study.

In 2015/2016 season, the parents were crossed to produce F₁ hybrid grains. In 2016/2017 season, the F₁ hybrid plants were backcrossed to their parents to produce BC₁ (F₁×P₁) and BC₂ (F₁×P₂) generations. In the mean time pair crosses were made to produce more F₁ grains, also the F₁ plants were selfed to produce F₂ grains.

In the third season 2011/2012 , the obtained grains of six populations (P₁, P₂, F₁, F₂, BC₁and BC₂) for each of the three crosses were evaluated using a randomized complete block design with three replications in two parallel experiments. The first experiment was irrigated by sprinkler system every week throughout the season (normal). The second experiment was irrigated by sprinkler system every three weeks throughout the season (severe drought stress by skipping two irrigations). Wheat grains were sown on the last week of November. Row was 2m long, row to row and plant to plant spacing were 20 and 5cm, respectively.

The recommended agricultural practices for wheat production under sandy soil conditions were performed. Date of days to heading was recorded at the time of full emergence of main spike. At full maturity data of days to maturity was recoded. At harvest, grain yield and its components were estimated from individual plants.

Biometrical assessment

A regular analysis of variance was firstly performed for the studied characters of the three durum wheat crosses.

Differences among means were tested using L. S. D. test at the 0.05 level according to Steel and Torrie (1980).

Heterosis and inbreeding depression

Heterosis was expressed as the deviation of F₁ generation from the mid-parents or better parent average values by Mather and Jinks (1982), as follows:

Heterosis over mid-parent %  =

Heterosis over the better-parent %  

To test the significance of the above estimate of heterosis, the variance of heterosis deviation was calculated as a linear function of three variances.  

Variances of heterosis over mid-parent deviation = VF1 + ¼ VP1 + ¼ VP2

Variances of heterosis over better-parent deviation = VF1 + VBP

            The inbreeding depression percentage was computed according to Mather and Jinks (1982) as follows:

is the first generation mean    and

is the second generation mean.

To test the significance of inbreeding depression, "t" test was calculated as follows

t. test of I.D   =

where

Standard error of mean =

= variance of F₁ mean

 = variance of F₂ mean

Testing the Genetic Models

The A, B and C scaling tests as outlined by Mather and Jinks (1982) were applied to test the presence of non- allelic interactions as follows;  and . Due to unknown biased effect of non- allelic interaction, the simple genetic model (m,d and h) was applied when epistasis was absent. Whereas, in the presence of non- allelic interactions, the analysis was proceeded to compute the interaction types involved using the six- parameters genetic model according to Jinks and Jones (1958). The significance of the genetic components were tested using the (t) test where:  

Components of the Genetic Variance

The components of genetic variance for each character in the studied crosses were partitioned into additive (D), dominance (H) genetic variance and environmental (E) one using Mather and Jinks (1982) formulae as follow:

E= (1/3) (VP₁ + VP₂+VF₁)

D= 4VF₂ – 2(VB₁ + VB₂) and

H= 4 (VF2 – ¹/₂VD – E)

The genetic components of variance were used further to compute average degree of dominance  and heritability in narrow sense (Tn) as Follow:

RESULTS AND DISCUSSION

Means performance, heterosis and inbreeding depression 

The six populations (P₁, P₂, F₁, F₂, BC₁, and BC₂) of the studied three crosses under normal and water stress conditions are illustrated in Table (2 and 3). Water stress caused significant reductions in all studied traits for all generations. Significant differences were observed between the two parents involved in each cross for all studied traits. Significant differences between parental means are a requirement for the six generations mean analysis.

The means of F₁ generation were in between P₁ and P₂ means for days to  heading in cross Sakha 95 x Salah - 1 under both conditions and cross Amna- 2 x Damara- 6 under control, maturity date in cross Amna- 2 x Damara- 6 under control, days to maturity plant height in cross Amna 2 x Damara- 6 under water stress, spikes/plant in crosses in crosses Sakha 95 x Salah - 1 and Sakha 95 x Rama- 2 under both conditions and cross Amna- 2 x Damara- 6 under water stress, grains /spike in crosses Sakha 95 x Salah- 1 and Sakha 95 x Rama -2 under both conditions and Amna- 2 x Damara- 6 under water stress, grain yield/plant in cross Saka 95 x Rama-2 under both conditions and Sakha 95 x Rama- 2 and Amna- 2 x Damara- 6 under control and 100- grain weight in cross Sakha 95 x Salah- 1 under both conditions, indicating partial or absence dominance. For thermoses, other cases indicated positive or negative overdominance.In this respect, LjubiČIĆ et al. (2017), Raza et al. (2019) and Abdallah et al. (2019), recorded the inheritance of days to heading and maturity revealed complex inheritance due to the involvement of non-allelic interactions.

Under both irrigation treatments, means of F₂ generation were lower than those of F₁ generation for days to heading in cross Sakha 95 x Rama- 2 under control and  Amna -2  ×Damara- 6 under water stress, days to maturity in cross Sakha 95 x Salah- 1 under water stress and crosses Sakha 95 x Rama- 2 and Amna- 2 x Damara- 6 under both conditions, plant height and grain weight in crosses Sakha 95 x Rama 2 and Amna 2 x Damara 6 under both conditions, and grain/yield in cross Sakha 95 x Rama 2 under water stressand Amna 2 x Damara 6 under control, indicating a positive inbreeding depression. On the contrary, F₂ generation means were higher or equal to the F₁ mean for other characters, indicating positive inbreeding effects, especially for spike/plant and kernel/spike under both irrigation treatments.

Table (2): Means and standard errors (SE) for days to heading, days to maturity and plant height of P₁, P₂, F₁, F₂, Bc₁ and Bc₂ populations in the studied crosses under normal and water stress conditions (2017/2018 season).

Table (3): Means and standard errors (SE) No. of spikes/plant, No. of grains/sjpile , 100 – grain weight  and grain yield/ plant of P₁, P₂, F₁, F₂, Bc₁ and Bc₂ populations in the studied crosses under normal and water stress conditions (2017/2018 season).

In general, means of the BC₁’s were close to those of their respective female parent (P₁) and means of the BC₂’s were close to their respective male parent (P₂) for most studied traits, which is logic from the breeding point of view, and supports the findings of Al-Naggar et al. (2010) and Al-Naggar and Shehab-Eldeen (2012).

Heterosis percent and inbreeding depression for all studied traits in the three cross populations under the two water treatments are presented in Table (4). The estimates of heterosis and inbreeding depression together provide information about type of gene action involved in the expression of various quantitative traits. The heterotic effect was significant in most cases except few of them. For earliness in days to maturity, the desirable heterosis towards earliness  were detected only in crosses Sakha 95 x Rama- 2 and Amna- 2 x Damara- 6 compared to the mid parents and cross Amna- 2 x Damara- 6 compared to the better parent under control. For days to heading, the heterosis compared to mid and better parent were undesirable in most cases condition. According to grain yield, the desirable heterosis were detected only in cross Sakha 95 x Salah- 1 compared to mid and better parent under water stress. The cross Sakha 95 x Salah- 1 had desirable mid and better heterosis for yield and its components in most cases. Absence of significant heterosis in other cases could be due to the internal cancellation of heterosis components.

Positive and significant values of inbreeding depression was detected for spikes/plant in the three crosses, grain yield and 100-grain weight in Sakha 95 x Salah -1 under both conditions, grain yield and grain weight in cross Amna- 2 x Damara- 6 and grain weight in cross Sakha 95 x Rama- 2 under water stress. Whereas, significantly negative value were observet for grain yield and grain weight in cross Amna- 2 x Damara- 6 under control (Moubarak and Morsy 2016).

Scaling test and gene effects

As shown in Table (5), performing the scaling test showed the significance of one at least of the scales A, B and C except for plant height and No of spikes/plant, indicating the presence of non-allelic interaction (epistasis) and the validity of using the six parameters model to estimate various genetic components. Estimates of gene effects calculated from the six-parameter model of the generation mean analysis for the studied traits under control and water stress conditions are presented in Table (5). Significant mean effects (m) were exhibited for all studied traits under both conditions, indicating that all the studied traits were quantitatively inherited.

Table 4: Heterosis relative to better parents (BP) and mid parents (MP) and inbreeding depression(ID%) for the studied traits in the three crosses under water stress and normal conditions.

*, ** Significant at 0.05 and 0.01 probability levels, respectively.

Positive and significant additive effects were observed for days to heading and maturity and grain yield in Sakha 95 x Salah- 1, plant height in all crosses, spike/plant in cross Amna- 2 x Damara- 6, No of grains /spike in Sakha 95 x Rama- 2 under both conditions and for No of grains/spike and 100-grain weight under control. This suggest the potential for obtaining further improvements of these traits by using phenotypic selection program. (Morsy, 2014 and Elmassry and El-Nahas, 2018).

Negative and significant additive effects were detected for plant height in the three crosses, days to heading and maturity in crosses Sakha 95 x Salah- 1 and Sakha 95 x Rama- 2, No of spikes/plant in cross Amna- 2 x Damara- 6, No of grains /spike in cross Sakha 95 x Rama- 2 and grain yield /plant in cross Sakha 95 x Salah- 1 under both conditions and No of grains/spike in cross Amna- 2 x Damara 6 and 100-grain weight in cross Sakha 95 x Rama- 2 under control.

Table 5: Scaling test (A, B, and C), mean estimates of the gene effects and some genetic parameters for studied traits in three crosses under control and water stress conditions.

Table 5: Cont.

*, ** Significant at 0.05 and 0.01 probability levels, respectively.

m, d, h, i, j, l, denote to, additive effect, dominance effect, additive x additive, additive x dominance, dominance x dominance interaction D, H, E, √H/D, T(n)%, GS and GS %, represents additive genetic variance, dominance genetic variance, environmental variance, degree of dominance, narrow sense heritability, genetic advance and genetic advance as percentage of F₂.

Negative and significant dominance effects were recorded for days to maturity and 100-grain  weight in cross Sakha 95 x Rama- 2 under both conditions, days to heading, and plant height in cross Amna 2 x Damara- 6 and grain yield /plant in crosses Sakha 95 x Salah-1 and Amna- 2 x Damara- 6 under control condition as well as days to maturity in cross Amna- 2 x Damara- 6, and plant height in cross Sakha 95 x Rama- 2 under water stress condition.

Positive and significant dominance effects were detected for days to heading and maturity in cross Sakha 95 x Rama -2 under water stress. This indicates an enhancing effect for these cases due to this type of gene action under corresponding environment. Some results reported by other investigators regarding the relative importance of either additive or dominance in the inheritance of earliness and yield traits in bread wheat are contradictory. Some researchers indicated that dominance was more important than additive effect in the inheritance of days to heading (Menshawy 2005) and grain yield (El- Danasory 2005 and Farhat, 2005). Differences in conclusions between this study and others with regard to the relative importance of either additive or dominance effects may be due to differences in genetic background of genetic materials used in these studies (Al-Naggar and Shehab-Eldeen, 2012 ; Morsy, 2014 and Elmassry and El-Nahass 2018).

In general, epistatic gene effects were generally important in the inheritance of studied traits.  In this respect, Hussein et al., (2009) indicated the existence of epistasis in wheat for earliness. Epistasis for agronomic and yield traits was also observed under irrigated and rainfed conditions (Dhanda and Sethi 1996 and Hoshiyar et al 2003).  Positive and significant additive x additive interaction were recorded for days to heading in Sakha 95 x Rama- 2 under water stress condition. Negative and significant additive x additive interaction were observed for days to maturity in cross Sakha 95 x Rama- 2 under both conditions, days to heading, plant height and No of spikes/plant in Amna- 2 x Damara- 6 and for No of spikes/plant and grain yield in cross Sakha 95 x Rama- 2 under control as well as days to maturity in cross Amna- 2 x Damara- 6 under water stress.

Negative and significant additive x dominance interaction were illustrated for days to maturity in cross Amna- 2 x Damara- 6 and for No of spikes/plant in cross Sakha 95 x Salah- 1 under control. Positive and significant additive x dominance interaction were documented for days to heading in cross Sakha 95 x Rama- 2 under both conditions, days to heading and maturity in cross Sakha 95 x Salah- 1, days to maturity in cross Sakha 95 x Rama -2 and No of spike/plant in cross Amna- 2 x Damara -6 under control and days to heading and plant height in cross Amna- 2 x Damara 6, grain yield / plant in cross Sakha 95 x Rama- 2 and for 100- grain weight in cross Sakha 95 x Salah- 1 under water stress.

Positive and significant dominance x dominance interaction were noted for days to heading, plant height and spike/plant in cross Amna- 2 x Damara- 6, days to maturity in cross Sakha 95 x Salah- 1, spikes/plant and grain yield in cross Sakha 95 x Rama- 2 under control and spikes/plant in cross Sakha 95 x Salah- 1 under water stress. Whereas, negative and significant dominance x dominance interaction were demonstrated for days to heading in cross Sakha 95 x Rama 2 under water stress.

Duplicate epistasis was prevailing for all the studied traits except for No of grains/spike in cross Sakha 95 x Salah- 1 under both conditions, days to maturity in cross Amna 2 x Damara 6, plant height and grain weight in cross Sakha 95 x Salah- 1 and No of grains/spike and grain yield in cross Sakha 95 x Rama- 2 under control and days to heading in cross Sakha 95 x Salah- 1, No of spikes/plant in crosses Sakha 95 x Rama- 2 and Amna- 2 x Damara- 6, grain yield/plant in cross Amna- 2 x Damara- 6 under water stress. This indicated that duplicate epistasis was greater and important when compared with complementary epistasis for previous cases. These results agreed with those obtained by Abd El-Aty et al. (2005) and Elmassry and El-Nahas (2018), reported that duplicate epistasis was observed for most studied characters.

Components of genetic variance and heritability

The results indicated that the genotypic variance for all the studied traits in all crosses was the major part of the phenotypic variance. Dominance genetic variances were greater than that of additive ones for all the studied traits except for No of grains/spike in cross Sakha 95 x Salah- 1 under both conditions, spike/plant and No of grains /spike in cross Sakha 95 x Rama- 2 under control and No of spike/plant in cross Sakha 95 x Salah- 1 and 100-grain weight in crosses Sakha 95 x Salah- 1, Sakha 95 x Rama- 2 and Amna- 2 x Damara- 6 under water stress condition. These results indicate the prevailing role of the dominance variance for most traits under study and the selection for these traits might be delayed to later generations for improving such traits in the three studied crosses.

The greater values of dominance variances resulted in (H/D)^1/2 ratio was more than unity, indicating the importance of over-dominance in the genetic mechanism controlling the abovementioned characters in these cases therefore the effectiveness of using hybrid breeding method when commercial seed production of wheat is feasible. While, the greater values of additive variances resulted in (H/D)^1/2 ratio was less than unity, suggesting the effectiveness of phenotypic selection for improving the foregone characters in these crosses. Similar results were found by Awaad (2002) and Morsy, (2014).

Narrow sense heritability values ranged from 9.08 % for days to heading in cross Sakha 95 x Rama- 2 under water stress to 60.43 % for 100-grain weight in cross Amna- 2 x Damara- 6 under normal irrigation . Heritability estimates in narrow sense were relatively high(<50%) only for No of grains/spike and grain yield /plant in cross Sakha 95 x Rama- 2 under control and grains/spike in cross Sakha 95 x Salah- 1,  under water stress allowing for considerable progress from selection. Similar results were stated by various investigators (El-Marakby et al. 2007; Magda and El-Rahman, 2013 ; Morsy, 2014 and Raza et al., 2019). The remaining traits had low to medium narrow sense heritabilities. These indicate that these traits greatly affected by non-additive and environmental effects. These results were coincident with those reported by Abd El-Aty (2002) and Abd El-Aty et al (2005). Said (2003), El-Sayed and El-Shaarawy (2006) and Hammad and Abd El-Aty (2007) Ahmadi and Bajelan (2008), Eid (2009) ; Morsy, (2014) and Elmassry and El-Nahas (2018) they reported that heritability in narrow sense was moderate to high. On the other hand, high values of narrow sense heritability were reported by Salem (2006), Said (2003) and El-Hawary (2010).

Genetic advance which refers to the improvement in the mean genotypic value of selected individuals over the parental population is influenced by the genetic variability, heritability and selection intensity (Sharma, 2003). The genetic advance % was high (more than 40%) for plant height in cross Sakha 95 x Salah -1 under water stress, while, it was moderate (14–40%), for No of spikes/plant and grain yield in all crosses under both conditions, plant height in cross Sakha 95 x Salah- 1 and No of grains /spike in cross Sakha 95 x Rama- 2 under control and No of grains/spike in cross Amna- 2 x Damara- 6, 100-grain weight in crosses Sakha 95 x Rama- 2 and Amna- 2 x Damara- 6 under water stress indicating the importance of direct selection for these characters. While, the remaining traits were with low genetic advance % (less than 14%), indicating the significance of indirect selection through correlated response with characters having high heritability and genetic advance (Farshadfar et al., 2008b).

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النظام الوراثى المتحکم فى المحصول والصفات المرتبطة فى عشائر ثلاث هجن من  قمح الخبز تحت الظروف الطبیعة والإجهاد المائى

أمجد محمد مرسى

قسم بحوث القمح- مرکز البحوث الزراعیة- الجیزة- مصر

أجریت هذه الدراسة خلال المواسم الشتویة لأعوام 2015 / 2016 و 2016 / 2017 و 2017 / 2018 بالمزرعة التجریبیة لمحطة البحوث الزراعیة بالاسماعیلیة محافظة الأسماعیلیة بإستخدام تحلیل العشائر الستة لثلاث هجن من قمح الخبز هى : (1) سخا 95 × Salah - 1 و سخا 95 × Amna 2 x Damara 6, Roma 2 x فى تصمیم قطاعات کاملة العشوائیة فى تجربتین، الأولى تم ریها بنظام الرى بالرش کل أسبوع خلال موسم النمو (ظروف الرى الطبیعى)، والثانیة تم ریها بنظام الرى بالرش کل ثلاث أسابیع خلال موسم النمو (ظروف الجفاف) وقد استهدفت الدراسة تقدیر النظام الوراثى وطبیعة الفعل الجینى المتحکم فى صفات عدد الایام حتی طرد السنابل والنضج وعدد السنابل /  نبات وعدد حبوب السنبلة ووزن الـــــ 100حبه ومحصول الحبوب للنبات تحت معاملتى الری الطبیعی و الاجهاد المائی. هذا وقد أظهرت النتائج أن تعرض هذه العشائر للجفاف قد أدى لحدوث نقص معنوى فى کل الصفات تحت الدراسة، أظهرت نتائج متوسط السلوک تفوق الجیل الاول على متوسط الأب الأفضل للمحصول وبعض الصفات المرتبطة به فى معظم الهجن تحت الدراسة تحت ظروف التجریب وقد کان تأثیر قوة الهجین فعالا ومعنویا فى معظم الحالات. وقد اختلف النظام الوراثى والتعبیر الجینى من ظروف الرى الطبیعى إلى معاملة الجفاف للصفات المدروسة فى معظم الحالات. و أظهرت نتائج إختیار المقیاس (A, B and C) تحت الظروف المثلى للرى بالرش ملاءمة المودیل الوراثى البسیط "المضیف – السیادى" فى تفسیر میکانیکیة وراثة وزن الـ 100 حبه فى الهجین الثانى بینما تحت ظروف الجفاف فقد کان المودیل الوراثى البسیط هو الملائم لتفسیر وراثة إرتفاع النبات فى الهجین الأول وعدد السنابل على النبات فى الهجین الثالث ووزن الـ 100 حبه فى الهجین الثانى وعلى الجانب الأخر کان المودیل الوراثى العقد هو الملائم لتفسیر وراثة محصول الحبوب للنبات عدد الایام حتی طرد السنابل و عدد الایام حتی نضج السنابل وعدد الحبوب للسنبله فى کل الهجین المدروسة تحت کلا النظامین الری الطبیعى و الاجهاد المائی وإرتفاع النبات وعدد السنابل على النبات فى الهجین الأول والثانى والثالث ووزن الـ100 حبه فى الهجین الأول والثالث تحت ظروف الرى الطبیعى. بینما کان المودیل الوراثى المعقد هو

المتحکم فى وراثة صفات إرتفاع النبات فى الهجین الثانى والثالث وعدد السنابل للنبات فى الهجین الأول والثانى ووزن الـ100حبه فى الهجین الأول والثالث تحت ظروف الاجهاد المائی. هذا وقد لعب الفعل الجینى المضیف دوراً معنویا فى وراثة عدد الایام حتی طرد السنابل و عدد الایام حتی نضج السنابل وإرتفاع النبات وعدد السنابل على النبات فى کل الهجن، وعدد حبوب السنبلة فى الهجین الثالث ومحصول الحبوب للنبات فى الهجین الأول ووزن الـ100حبه فى الهجین الثانى تحت ظروف الرى الطبیعى، وعدد الایام حتی طرد السنابل وعدد الایام حتی نضج السنابل فى الهجین الأول والثانى وارتفاع النبات فى الهجن الثلاثة وعدد السنابل فى الهجین الثالث وعدد حبوب السنبلة فى الهجین الثانى ومحصول الحبوب للنبات فى الهجین الأول والثانى تحت ظروف الاجهاد المائی. کان الفعل الجینى المضیف والسیادى والتفاعل مضیف × مضیف وسیادى × سیادى هو المتحکم فى وراثة عدد الایام حتی طرد السنابل فى الهجین الثالث وعدد الایام حتی نضج السنابل وإرتفاع النبات فى الهجین الثانى تحت ظروف الرى الطبیعى، وعدد الایام حتی طرد السنابل فى الهیجن الثانى تحت ظروف الاجهاد المائی. بینما کان الفعل الجینى المضیف والسیادى والتفاعلات مضیف × مضیف ومضیف × سیادى وسیادى × سیادى ذو اهمیة فى وراثة عدد الایام حتی طرد السنابل فى الهجین الثانى تحت ظروف الاجهاد المائی. کان التباین الوراثى المضیف هو المکون الأعظم المتحکم فى وراثة عدد السنابل / النبات فى الهجین الثالث ومحصول الحبوب للنبات فى الهجینین الأول والثانى تحت ظروف الرى الطبیعى، ووزن الـ 100 حبه فى کل الهجن الثلاثة تحت ظروف الاجهاد المائی. هذا وقد وجد أن التباین الوراثى السیادى کان هو المکون الأعظم المتحکم فى معظم الصفات تحت الدراسة فى الهجین الثلاثة فى کل من ظروف الری الطبیعى والاجهاد المائی. وقد تراوحت تقدیرات معامل التوریث فى المعنى الخاص من منخفض إلى متوسط لمعدل الحبوب للنبات والصفات المرتبطة به فى جمیع الهجین تحت ظروف کلا من الرى الطبیعى و الاجهاد المائی.