The Outbreeding Enhancement and Correlation Studies in F1 Hybrids of Hexaploid Wheat (Triticum aestivum L.) Cultivars

The current study was conducted in the experimental field of the Department of Biotechnology and Genetic Engineering, Faculty of Life Science, University of Development Alternative, Dhaka, Bangladesh during the winter season 2017-2018. The study was performed to reduce the heterotic effect and phenotypic correlation among numerous yield characters for F1 hybrids of hexaploid wheat (Triticum aestivum L.). The experimental design has consisted of six parental variants (Sonalika, Balaka, Prodip, Kanchan, Agrahani and Protiva), which were crossed and nine possible cross combinations (F1 hybrids) (Prodip × Agrahani, Balaka × Agrahani, Prodip × Protiva, Protiva × Agrahani, Agrahani × Kanchan, Kanchan × Sonalika, Protiva × Prodip, Sonalika × Agrahani, and Prodip × Kanchan) were obtained. The experimental fields were selected and arranged in a randomized complete block design with four replicates, where eight characters were studied. The mean square of the analysis of variance showed that the hybrids differed significantly (p ≤ 0.01) for all studied characters except for maturity to 75% of days and height of the plant, while the parents only had no differences in grain yield. The mean square of the parent and the F1 hybrid indicated that considerable heterosis existed in the F1 hybrids. In general, correlation coefficients indicated that the maturity to 75% of days was significant but negatively correlated with most of the yield traits, suggesting that the genotypes which became mature early may have lower yields. Plant height was also negatively correlated with grain spike, How to cite this paper: Kumar, S., Khaldun, A.B.M., Rahman, M.M., Islam, M.M., Uddin, M.S. and Akanda, M.A.L. (2021) The Outbreeding Enhancement and Correlation Studies in F1 Hybrids of Hexaploid Wheat (Triticum aestivum L.) Cultivars. Agricultural Sciences, 12, 805-826. https://doi.org/10.4236/as.2021.128052 Received: March 30, 2021 Accepted: July 31, 2021 Published: August 3, 2021 Copyright © 2021 by author(s) and Scientific Research Publishing Inc. This work is licensed under the Creative Commons Attribution International License (CC BY 4.0). http://creativecommons.org/licenses/by/4.0/ Open Access


Introduction
Wheat (Triticum aestivum L.) is an important species of grass family grown throughout the world for human consumption [1]. The numbers of wheat species together are known as Triticum, the major widely grown wheat is known as bread wheat (Triticum aestivum). T. aestivum L. is a haxaploid (2n = 6x = 42) and the most grown wheat in the world [2]. Wheat is the most valuable grain crop and a staple food for increasing the human population around the world.
The genotypically and environmental elements play a positive and negative role in grain yield [3] [4]. Wheat is considered a 3 rd main source of calories in cereal crops [5]. The agriculture industry since the last 50 years has been growing up so fast and 50% of global food production depends on cereal crops [6]. Three main factors have been documented for rapid improvements in wheat yield: 1) genetically modified varieties using new breeding methods, especially the hybrid varieties are more important for yield; 2) Extension of the area under irrigation; 3) Prevailing use of fertilizers, especially phosphorus (P) and Nitrogen (N) [4].
Generally, access to the increasing area under irrigation and enhancing the use of fertilizers are getting limited. Therefore, the use of new breeding techniques is necessary for improving wheat yield [7] [8]. Improvement in wheat yield is very important for ensuring global food security as predicted by (FAO's) United Nations. There is increasing interest in new methods that extend yield production, especially for low-yielding conditions where wheat is broadly grown [9]. One of the most encouraging alternatives is to improve the yield production by heterosis (hybrid vigor) in a hybrid wheat variety. The heterosis is considered an important factor for improvement in wheat yield from 3.5% to 15% [10]. In the past, it was difficult to explore the heterosis in wheat varieties due to the complex nature of wheat inbreeding [11].
For the last 10 years, the hybrid wheat program is becoming more prominent for a modification if the total area under hybrid cultivation around the world. In the 1960s, the discovery of restoration processes and the sterility system in males for hybrid wheat increased the interest of public and private sectors for the development of hybrid varieties [12]. However, the exploration of the hybrid system was impractical and consequently difficult to adopt [13]. Nowadays, genetic engineering is being utilized to develop a range of new hybrids breeding innova-S. Kumar [14]. There are some important objectives that breeders keep in mind to achieve wheat cultivars with high yielding ability, develop resistance varieties against plant pathogens as well as insects and against environmental factors [15].
Yield is one of the most complex quantitative traits of most cultivars, and it is also hard for estimating which factors are responsible for low yielding [16].
Character-based selection helps wheat breeders to improve yield and its associated traits [17] [18].
Hybrid varieties frequently show more yield, increasing the stability of yield, and enhance resistance against abiotic and biotic factors due to hybrid vigor [19]. Thus, heterotic studies can be very useful for obtaining information about the increase/decrease percentage of hybrids (F 1 ) over their mid parents and superior parents. Breeding efforts have resulted in various varieties of hexaploid wheat, having improved yield and grain characters. Varieties and advanced lines with different morphological and economic characteristics are now available as breeding stock. For further progress, knowledge of breeding behavior, particularly of combining ability and type of gene action for the various traits, is necessary [20]. Heterobeltiosis is mainly associated with specific character combining the ability of the hybrids. Generally, positive heterosis is desired for yield improvement and selection of its components, whereas early maturity and short plant height are considered in negative heterosis [21]. The prevailing genetic theories related to the manifestation of hybrid vigor include actions of dominant, over-dominant and epistasis genes [22]. However, heterosis utilization is measured as the most important plant breeding attainment. Hybrid breeding in wheat through the utilization of heterosis is more informative than local techniques of plant breeding. Heterosis also provides informative knowledge relating the capability in breeding plans of parents as well as their practices [8] [23]. Assessment of heterosis over the improved parents (heterobeltiosis) could be helpful in classifying true heterotic cross groups. Heterosis is a quicker, cheaper and easier method of increasing crop production. With a sufficient level of heterosis, commercial production of hybrid varieties will be justified, and heterotic studies can provide the basis for the exploitation of valuable hybrid combinations in breeding programs. Hybrid wheat technology can play an effective role in enhancing grain production [24]. Genetic diversity is one of the key factors for the with tillers/plant were reported [28]. Thus, the present study was planned to determine the heterosis and correlation in hexaploid wheat varieties. The current research was aimed to analyze the ability of wheat varieties in hybrid combination to find out the heterosis (%) over-improved parent and mid parent and the correlation among various yield traits in the F 1 generation.

Materials and Methods
The six parents of seeds along with their nine F 1 hybrids were obtained from the Bangladesh Agricultural Research Institute, Joydebpur, Gazipur, Bangladesh.
The study was laid out in a randomized complete block design with four replica-  (Table 1).
The data of 10 plants and each genotype were collected from each replication selected at ten randomly selected plants at random was labeled for data recording in the laboratory and field. Length of spike: The length of the spike is divided in centimeters from the neck node to the highest spikelet (excluding the canopy) in centimeters.
Spikelets spike −1 : The Spikelets of the main spikes were counted at harvest time and the average was worked out.
Grains spike −1 : The total amount of main spike seeds was calculated and results were observed as grains spike −1 .
Seed index (1000 grains weight g): With the help of a laboratory digital balance, 1000 seeds were randomly calculated and weighed in grams.
Grain yield plant −1 (g): The harvested plants were threshed by hand, the grains were weighed on a digital electronic balance, and the production of plants was expressed in grams.
where F 1 = hybrid performance; MP = Mid-parent value (the mean of two parents) and BP = Better-parent value (the mean of better parents).

Statistical analysis
The results were compiled in excel software to form a database for analysis.
All the studied traits were analyzed statistically by (ANOVA) applied using Statistics 8.1. To differentiate the mean performance of genotypes, the statistical method of [29] was used. Whereas, the heterosis was calculated with the formula developed by [30] and correlated by [31].

Results and Discussion
The current study was laid-out to determine the heterotic effects and correlation studies in F 1 crosses of wheat. The experimental material has consisted of six parental varieties and their nine F 1 crosses. The field trial research was conducted in a randomized complete block design with four repetitions. The results achieved for several characters are shown hereunder: Agricultural Sciences

Analysis of variance
The results (

The Mean Percentage of F1 Hybrids and Parents
Data on the average percentage of parents indicated parental performance as shown in ( For the spike length, the parents on an average produced shorter spikes (11.46 cm) as compared to longer spikes of F 1 hybrids (12.10 cm). Among the parents, Agrahani produced the longest spikes (12.40 cm), and the minimum spike  On an average basis, the seed index of parents was 39.40 g, whereas the F 1 hybrids gave less seed index weighing 34.94 g. This large difference in parents and hybrids may be due to a greater number of grains in hybrids which ended up in less seed index. Among the parents, the highest seed index (45.21 g) was observed in Sonalika and lowest seed index (35.97 g) in Prodip. Regarding grain yield plant −1 , the parents on an average produced 17.69 g as compared to 31.47g of F 1 hybrids. Thus, F 1 hybrids showed a big increase in grain yield due to their heterotic effects. From parents, the maximum yield per plant was recorded in Kanchan (19.30 g) and minimum in Sonalika (15.75 g). Harvest index in parents, on an average, was recorded as 42.78% as compared to 46.34% of F 1 hybrids. The highest yield index among parents was given by Kanchan (45.97%) and the lowest harvest index was recorded in Protiva (42.63%). On average, total dry matter recorded for parents was 14.00 g, whereas F 1 hybrids produced considerably higher biomass (67.91 g) against the average of parents. These results suggested that due to heterotic effects the hybrids accumulated more total dry matter as compared to their parents. Among the parents, Agrahani weighed maximum total dry matter per plant (44.00 g), while less biomass was weighed by Sonalika (38.20 g).
The average percentage of F 1 hybrids is given in (

Heterotic Effects in F1 Hybrids
The hybrid vigor of various traits was calculated, and the potential of F 1 hybrids to improve various yields and their related traits were determined by using the hybrid vigor. The results of the hybrid heterotic effect of days to 75% in the F 1 hybrid are shown in (Table 4). Results showed that all F 1 hybrids showed negative comparative heterosis and hetero-beltiosis. The destructive comparative heterosis is between −2.65% and −9.11%, while the heterosis is between −6.21% and −9.97%. The highest negative relative heterosis was recorded in the cross Prodip × Sonalika (−9.11%) as compared to Prodip × Agrahani (−9.02%). The cross Prodip × Agrahani showed a greater hetero-beltiosis (−9.79%), followed by Prodip × Sonalika (−9.49%). All hybrids showing negative effects were considered to take 7 days to reach 75% maturity, as such hybrids produce premature hybrids.        Many hybrids showed excellent heterosis effects, but the Agrahani × Kanchan The effect of heterosis of F 1 hybrids in hexaploid wheat on the seed index of middle and superior parents is given in (   The results regarding relative heterosis and hetero-beltiosis are presented in (Table 12). The results showed that the relative heterosis in F 1 hybrids ranged from 21.53% to 100.24%. However, the maximum value of relative heterosis was recorded in cross Prodip × Kanchan (100.24%) followed by the cross Sonalika × Agrahani (92.21%). The minimum value for the relative heterosis was recorded in cross Balaka × Agrahani (21.53%) for total dry matter. As far as hetero-beltiosis is concerned, the maximum value was recorded for the cross Prodip × Kanchan (91.58%) and the minimum value was shown by the cross Balaka × Agrahani (18.63%).

Correlations
The correlation coefficients were worked-out among the grain yield and its mechanisms, so as to determine one or several traits highly correlated with yield and can be improved through indirect selection. The outcomes are presented in (Table 13).

Days to 75% maturity
Number of days to 75% maturity was significant but negative correlation with

Harvest index
There was a positive and significant correlation between the harvest index and spike length (r = 0.340**) and grain yield plant −1 (r = 0.323**), while this parameter was only negatively related to plant height (r = −0.257*).

Length of spike
The length of the spike was only positively correlated with spikelets spike −1 (r = 0.527**). It was positively correlated but non-significant with total dry matter (r = 0.140) and grain yield plant −1 (r = 0.206).
Total dry matter

Mean Performance of Parents and F1 Hybrids
Yield related characters, as well as other complex traits, are regulated by various genetics factors. Due to the genetic complexity of traits and interaction among genotypes and the environment, the selection of parents becomes difficult, which provides hybrids with a higher yield [32]. ANOVA analysis showed that the genotypes change significantly with all production characteristics analyzed in this study (p ≤ 0.01), for example, days to 75% maturity to, height of plant, spike length, spikelets spike −1 , grains spike −1 , seed index, grains yield plant −1 , harvest-index and total dry matter (  Table 2). Similarly, [20] revealed that parents comparatively showed higher plant length, shorter spikes, lesser spikelets spike −1 as well as grains spike −1 than F 1 hybrids.
On an average basis, the seed index of parents was 39.40 g, whereas the F 1 hy-  [33]. The total dry matter of parents stood at 14.00 g, whereas F 1 hybrids produced considerably higher biomass (67.91 g) against the average of parents. These results suggest that due to heterotic effects, the hybrids accumulated more total dry matter as compared to their parents (Table 3).

Heterotic Effects of F1 Hybrids
The heterotic effects in F 1 hybrids and parents for 75% days to maturity are pre-

Correlations
Correlation coefficients played a role among the nine yields and their related characteristics. Days to 75% maturity were significant and positively correlated with grains yield plant −1 . Plant height showed a positive correlation with grains yield plant −1 . Spikelets spike −1 was positively associated with grains yield plant −1 .
The results of the current study were confirmed by [3] and [43] who described that the grains yield plant −1 is critical, and the yield is divided by the tillers plant −1 , spikelets spike −1 and grain spike −1 . [37] also showed a significant positive correlation between grains yield plant −1 and its mechanisms (such as the production of tillers plant −1 , spike length, spikelets spike −1 , grain spike −1 and 1000 grains weight g). [44] observed genotype and phenotypic correlations between grain yield and other yield components, such as tillers plant −1 , number of spike per square meter, number of grains spike −1 , total biomass plant −1 , and harvest index and 1000 grains weight (g). [45] pointed out that plant height has a significant positive correlation with the spike length, spikelets spike −1 , grain spike −1 and grains yield spike −1 .
Generally, the correlation coefficient revealed that days to 75% maturity had negative associations with the majority of yield traits suggesting that the genotypes that mature earlier could be low yielding. Grains spike −1 increased by increasing the spike length, and harvest index; consequently, grains yield will increase, thus grains spike −1 presented the positive association with all of these yield characters. On the contrary, the increase in grains number will cause a re- As with 75% maturity and plant height present negative association to grains yield plant −1 and its components. Similar to our findings [27] demonstrated that grains yield plant −1 is positively correlated with grains number spike −1 , but is different from current results. They observed a positive correlation between grains yield and 75% of maturity days. Our results showed a negative correlation between grain yield and plant height, spike length, and 1000 grains weight (g).
Grain yield was significantly and positively correlated with all characteristics (plant height, spike length, spikelets spike −1 , grains spike −1 , and grains spikelets −1 ), which suggested that other positive correlations could be obtained through traits that increased grains yield and good selection criteria for wheat improvement.

Conclusion
The outbreeding enhancement and correlation were examined for various traits of economic importance, including days to 75% development, plant height, spike length, spikelets spike −1 , grains spike −1 , seed index, harvest index and total dry matter in hexaploid wheat genotypes. The six parents (Sonalika, Balaka, Prodip, Kanchan, Agrahani and Protiva) were crossed and nine possible cross combinations (F 1 hybrids) (Prodip × Agrahani, Balaka × Agrahani, Prodip × Protiva, Protiva × Agrahani, Agrahani × Kanchan, Kanchan × Sonalika, Protiva × Prodip, Sonalika × Agrahani, and Prodip × Kanchan) were obtained. The F 1 hybrids genotypes were varied expressively (p ≤ 0.01) statistically analyzed using analysis of variance (ANOVA) all studied characters. The average performance of parents and F 1 hybrids was presented, great importance that indicated considerable heterosis from F 1 hybrids. The experimental results effects for the characters days to 75% development, plant height, spike length, spikelets spike −1 , grains spike −1 , seed index, harvest index and total dry matter recorded. In view of the above hypothesis, the heterosis and correlation form this study are considered to be useful, to increase grain production and which can be used to selected plants with desirable traits and high yielding plants.