Identification of Heterosis and Nature of Gene Action in Bread Wheat Under Normal and Drought Stress Conditions

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Published on International Journal of Agriculture & Agribusiness
Publication Date: April 19, 2019

El-Sherbeny, G. A. R., Khaled, G. A. A. & Haitham, M. A. Elsayed
Dept. of Genetics, Fac. Agric., Sohag University
Sohag, Egypt

Journal Full Text PDF: Identification of Heterosis and Nature of Gene Action in Bread Wheat Under Normal and Drought Stress Conditions.

Abstract
The effects of drought stress on heterosis and the component of genetic variances were investigated using half diallel mating design among eight bread wheat cultivars. The results demonstrated that, the majority of cross combinations were earlier, tallest, and high yielding than their mid and better parents under each environment and their combined data, indicating the prevalence of heterotic effects and non-additive gene effects. Non-additive gene action (σ2D) was found to play the major role in the inheritance of studied traits under each environment and their combined data. Whereas, the interaction of (σ2D x E) were larger than those of (σ2A x E) for all studied traits, reflecting that the non-additive genetic effects tended to interact with environments than additive effects. The parents P2 and P8 were a good general combiners for earliness, while the parents P5, P6, P7 and P8 were the best general combiner for plant height and grain yield/plant under the two environments and combined data. The crosses (P1xP2), (P2xP3) and (P2xP5) were the highest desirable specific combining ability effects for days to 50% flowering, plant height and grain yield/plant under normal conditions. In addition, the crosses (P4xP7), (P6xP7) and (P2xP5) were the highest specific combining ability effects under drought stress. The estimates of narrow sense heritability were lower than those of broad sense heritability for days to 50% flowering, plant height and grain yield/plant under normal, drought and combined data, respectively. The drought susceptibility index based on grain yield/plant exhibited that, the cross combinations which have parents P1, P2, P3 and P8 were relatively tolerant to drought.

Keywords: Wheat, half diallel analysis, drought stress, heterosis, combining ability, gene action and drought susceptibility index.

1. INTRODUCTION
Wheat (Triticum aestivum L.) is one of the most important cereal crop overall the world and Egypt. Abiotic environmental factors are considered to be the main source of yields reductions (Boyer, 1982). Drought is one of the most common environmental stress that affects growth and plant development through alterations in metabolism and gene expression (Leopold, 1990). Drought stress may occur early in the season or terminally at grain filling and development.
Nowadays, Egypt facing a huge problem with the shortage in the water resources and applicable land for wheat production (Abd El-Mohsen et al, 2015). Therefore, improvement productivity of wheat cultivars under drought conditions becomes one of the important objectives in wheat breeding program in arid and semi-arid regions of Egypt. Most of the Egyptian newly reclaimed lands (West and East of the Delta and West of the Nile Valley in Upper Egypt) suffer from drought and salinity stresses. Moghadam and Hadi-Zadeh (2002) found that, drought susceptibility index was more useful for selecting favourable cultivars under stress and non-stress conditions.
Exploitation of heterosis is considered to be one of the outstanding achievements of wheat breeding. In this trend (Samir and Ismail, 2015; Saied et al. 2017) assessed four different genotypes of bread wheat using half-diallel design. They reported that the crosses showing the best mid and better parents could be recommended to improve the days to 50% flowering, plant height and grain yield/plant.
Diallel cross technique provides useful information on the genetic identity of genotypes especially on dominance-recessive relations and some other genetic interaction to determinate the inheritance of traits among a set of genotypes and to identify superior parents for hybrid. Combining ability analysis of Griffing (1956) partitioned total genetic variance into the variance of general combining ability GCA, as a measure of additive gene action and specific combining ability SCA, as a measure of non-additive gene action. The significant and the important role of GCA and SCA for most studied traits were studied by Kohan and Heidari, (2014); Kumar and Kerkhi, (2015); Kandil et al. (2016); Saied et al. (2017); Emad et al. (2018). The predominance of non-additive gene effects in the inheritance of grain yield/plant was reported by Ahmad et al. (2011). On the other hand, additive gene action controlled the inheritance of plant height and grain yield/plant (Farook et al, 2011; Shehzad et al, 2015).
Therefore, the objectives of the present investigation were directed to study the performance of eight different genotypes of bread wheat and their half diallel crosses under normal and drought stress conditions for days to 50% flowering, plant height and grain yield/plant. Moreover, nature of gene action controlling the inheritance of the three traits was also studied.

2. MATERIALS AND METHODS
2.1 Genetic materials and experimental design:
The genetic materials used in this study were consisted of eight bread wheat genotypes, Misr-1 (P1), Sids-12 (P2), Sahel-1 (P3), Katela (P4), Sakha-94 (P5), Deibera (P6), Weiber (P7) and Canada-462 (P8), which represent a wide range variability in their several agronomic traits. The present study was carried out at El-Kawther Experimental Research Farm of Faculty of Agriculture, Sohag University, Sohag, Egypt during the two successive wheat seasons 2016/2017 and 2017/2018.
In the winter season 2016/2017, eight parental genotypes were planted and crossed according to half diallel mating design to produce 28 F1 hybrids. In the winter season 2017/2018, seeds of eight parents and their 28 F1 hybrids were sown under normal and drought environmental conditions in a randomized complete block design (RCBD) with three replications. Each plot consisted of 3 rows 3 m. long and 30 cm. wide. Plants were spaced by 10 cm. within row. The soil at the experimental site was sandy to loamy sand. All recommended cultural practise were applied under normal conditions (irrigation every 10 days) and drought stress (irrigation every 20 days). Data were recorded on ten plants/genotype chosen at the middle portion of each plot for days to 50% flowering, plant height and grain yield/plant.

2.2 Biometrical analysis:
In each environment, data were subjected to the analysis of variance to test the significance of the differences among the tested genotypes according to Cochran and Cox (1957). Combined data over the two environments were also subjected to the combined analysis of variance to test the interaction of genotypes with environments.

Estimates of heterosis over mid and better parents were determined for each cross as follow:
H (M.P) % = x 100
H (B.P) % = x 100
Where;
F1 is the mean of F1 hybrids.
MP and BP: means of the mid parents and better parent, respectively.
The heterotic values were tested for significance to establish the differences of the F1 hybrid means from their respective mid and better parents using the least significant difference value (L.S.D.) at 5% and 1% levels of significances, according to the equations suggested by Steel and Torrie (1985).
General combining ability GCA and specific combining ability SCA variances were partitioned from total genotypic variance in each environment according to (Griffing, 1956) method 2, model 1. In addition, the combined analysis over the two environments was calculated to partition the men squares of genotypes and the interaction of genotypes with environments into sources of variations due to GCA, SCA, and their interaction with the environments (GCA x E and SCA x E).
With the assumption that there is no epistasis, the genetic components could be obtained from the estimates of GCA variance (σ2g), SCA variance (σ2s), GCA x E variance (σ2g x E) and SCA x E variance (σ2s x E) according to Matzinger and Kempthorne (1956); Singh, (1979). Estimates of heritability in broad (h2b.s. %) and narrow sense (h2n.s. %) were also calculated.
Drought susceptibility index “S” estimated according to Fischer and Maurer (1978) equation as follows:
DSI= [(1-YD/YW) / (1-YMD/YMT)]
Where;
YD: Is the yield under drought stress.
YW: Is the yield under normal condition.
YMD: Is mean yield for all genotypes under drought.
YMT: Is mean yield for all genotypes under normal condition.
Genotypes with average susceptibility or resistance to drought have an “S” value of 1.0. Values of less than 1.0. Indicate less susceptibility and greater resistance to drought. While, a value of S=0 indicates maximum possible drought resistance (no effect of drought on yield) Fischer and Maurer (1978).

3. RESULTS AND DISCUSSION
3.1 Genotypic variations:
The analysis of variance (Table 3) showed highly significant between environments for days to 50% flowering, plant height and grain yield/plant with the overall means of normal conditions higher than those of drought stress conditions. Mean squares of genotypes were found to be highly significant for all studied traits under the two environments and their combined data, providing evidence for presence of large amount of genetic variability, which considered adequate for further biometrical analysis. Moreover, mean squares due to G x E interaction were highly significant for all studied traits, revealing that these genotypes were inconsistent from environment to another. These results are in harmony with those of Samir and Ismail (2015); Saied et al. (2017); Semcheddinne et al. (2017); Jyoti Yadav, (2017); Sundeep et al. (2018); Emad et al. (2018).

3.2 Performance of parents and their crosses:
The results presented in Table 4 indicated that, the performance of the eight parents and their 28 F1 hybrids were variable. The parental average decrease from 94 to 77 days for days to 50% flowering, 102.4 to 78.33 cm. for plant height and 44.53 to 13.6 gm for grain yield/plant under normal conditions and drought stress, respectively. Drought stress caused reduction about 3.72%, 13.07% and 39.87% for days to 50% flowering, plant height and grain yield/plant, respectively. It could be noticed that, the best parents for earliness were P2 and P8 under normal, drought stress and combined data. While, the tallest were P7 and P6 under each environment and combined data. For grain yield/plant P2, P3, P5 and P6 were the best under normal, drought stress and combined data, respectively.
The F1 hybrids average reduced from 84.67 to 83.17 days for day to 50% flowering, 103.62 to 91.46 cm. for plant height and 31.33 to 21.69 gm for grain yield/plant in the normal and drought stress, respectively. The stress conditions caused about 1.77%, 11.74% and 30.77% reduction in the average of F1 hybrids for days to 50% flowering, plant height and grain yield/plant, respectively. The cross combinations (P1xP8), (P3xP5), (P5xP8) and (P7xP8) were the earliest hybrids under each environment and combined data. The tallest cross was (P6xP7) under normal, drought stress and combined data, respectively. While, the crosses (P1xP3), (P1xP5), (P1xP6), (P2xP5), (P4xP5), (P4xP6), (P4xP8), (P5xP6), (P5xP7), (P6xP8) and (P7xP8) were the highest for grain yield/plant under each environment and combined data.

3.3 Drought susceptibility index “S”:
The estimated values of drought susceptibility index “S” based on grain yield/plant for the eight parents and their 28 F1 hybrids are shown in Table 4. It could be observed that the parental genotypes P1, P2, P3 and P8 showed S values less than one, revealing relative drought resistance through drought escape. While, the crosses (P1xP2), (P2xP3), (P3xP5), (P3xP7) and (P3xP8) were relatively tolerant to drought stress. These results indicated that the tolerant parents P1, P2, P3 and P8 transmitted their genes controlling drought tolerance to their hybrids. Consequently, these crosses could be considered promising populations for isolating useful segregates to be cultivated under drought stress. Similar results found by Khan and Naqvi, (2011); Li et al. (2012); Khaled et al. (2015); Yuxiu et al. (2017); Stanisław et al. (2018).