Studies on genetic variability and character association in wheat [Triticum aestivum L.]

Introduction

Wheat (Triticum aestivum L.) is a principal staple grain crop globally and a vital source of calories and protein, particularly in developing nations, so enhancing its yield is a priority for plant breeding initiatives. The efficacy of any wheat enhancement program primarily relies on the presence of adequate genetic diversity for yield and associated characteristics within the breeding stock (Gaur, 2019) [1] .

Background

Genetic diversity enables breeders to identify superior genotypes and to generate novel combinations of advantageous alleles for intricate quantitative variables, including grain production, harvest index, and stress tolerance. In bread wheat, characteristics such as plant height, days to heading and maturity, spike length, number of spikelets, grains per spike, and 1000-grain weight exhibit significant variability, hence allowing for successful selection (Meena et al., 2014) [4] .

Requirement for investigations into genetic variability "Quantitative traits are significantly affected by environmental factors; therefore, it is crucial to decompose the observed variance into genetic and environmental components utilizing metrics such as phenotypic and genotypic coefficients of variation, heritability, and genetic gain. The elevated heritability and significant genetic progress for traits like grain count per spike, efficient tillers, and 1000-grain weight signify the dominance of additive gene action, implying that straightforward selection might provide considerable enhancement.

Justification for the current research

Research on genetic variability and trait association in wheat seeks to find advantageous genotypes and essential yieldcontributing characteristics for use as selection criteria in breeding programs. Evaluating variability, heritability, genetic progress, and relationships among agronomic parameters offers a solid foundation for formulating effective selection techniques aimed at producing highyielding wheat cultivars suited to particular settings (Poonia et al., 2023) [7] .

Literature Review (Girma Seyoum & Sisay, 2021) [2] Wheat (Triticum aestivum L.) is a high-yield crop with extensive adaptability and serves as the primary food source globally and in Ethiopia. In Ethiopia, wheat productivity has, nonetheless, risen in recent years. Due to abiotic factors such as heat, drought, and frost, as well as biotic factors like rusts (stem, yellow, and leaf), Septoria, and Fusarium, production remains relatively low compared to other wheat-producing nations. The aims were to evaluate the variability of genotypic and phenotypic traits, as well as heritability and genetic advancement in bread wheat genotypes. Consequently, this study evaluated 30 bread wheat genotypes for yield and related parameters. A trial was conducted in Holetta, Ethiopia, during the 2018/19 agricultural season. The materials underwent testing with a three-replication alpha lattice design. The yield and related characteristics data were evaluated with SAS software version 9.3. The heritability estimates for 1000 kernel weight were determined to be exceptionally high, at 81.14 percent. The trait of 1000 kernel weight exhibited both strong heritability and a significant genetic advance as a percentage of the mean. It was determined that a kernel weight of 1000 may be established as the selection criterion for enhancing grain yield. Nevertheless, additional research must be undertaken. The future breeding efforts for bread wheat should concentrate on varietal development. (Mishra et al., 2019) [5] The study of thirty-six wheat genotypes found significant differences among them for all traits, indicating substantial variability in yield and its associated characteristics within the examined material. Among the genotypes evaluated, HI 1610 appears to be the most superior because to its high yield, early flowering, early maturation, large grain size, and dwarf stature. The GCV and PCV for days to heading, 1000 grain weight, and days to maturity were nearly equivalent, suggesting these traits are minimally affected by environmental factors. In contrast, grain yield and plant height demonstrated a significantly higher PCV compared to GCV, indicating that a substantial portion of the variation in these traits is attributable solely to environmental influences. Increased heritability was noted for days to heading, 1000 grain weight, and plant height. Significant heritability along with substantial genetic advancement observed for the traits of 1000 grain weight, plant height, days to heading, and grain yield indicates that these characteristics are influenced by additive gene effects; thus, directional selection for these traits would be more efficacious for achieving desired genetic enhancement. (Rathwa et al., 2018) [8] The experiment was conducted to evaluate genetic diversity about grain yield and its components for heat tolerance in durum wheat. The phenotypic coefficient of variation values under both sowing conditions were marginally greater than the genotypic coefficient of variation for all examined traits, suggesting a diminished influence of the environment on the expression of the analyzed characteristics. Under D0 conditions, the genetic gain at 5% selection intensity (k = 2.06) was significantly elevated for the number of grains per main spike, harvest index, and biological yield per plant. Under D0 conditions, moderate genetic advancement was noted for days to 50% flowering, plant height, grain filling duration, days to maturity, chlorophyll content at anthesis (CHLa), and grain yield per plant, but under D1 conditions, it was detected for the number of grains per main spike and harvest index. High heritability, along with significant genetic advancement expressed as a percentage of the mean, was noted for all traits except under D0 conditions for days to maturity, plant height, and length of the main spike. Under D1 conditions, this was observed for days to maturity, grain filling period, length of the main spike, and 100-grain weight. This phenomenon may be ascribed to the dominance of additive gene action, which exhibits substantial selective value, thereby indicating that selection pressure could be effectively applied to enhance these traits. (Singh et al., 2020) [9] Sixty advanced wheat lines were cultivated using a randomized complete block design (RCBD) with three replications. An analysis of genetic variability, heritability, and genetic progress for fifteen variables was conducted. The phenotypic coefficient of variation (PCV) exceeded the genotypic coefficient of variation (GCV) in magnitude for all examined traits. Peduncle length exhibited the largest phenotypic coefficient of variation (PCV) and genotypic coefficient of variation (GCV), measuring 29.34% and 27.33%, respectively. High broad-sense heritability was noted for 1000-grain weight (97.27%) and plant height (95.27%), while medium heredity was documented for wet gluten percentage (58.41%) and protein percentage (47.13%). The significant genetic gain as a percentage of the mean (at 5% selection intensity) observed for peduncle length is 52.46%. Significant heritability (bs) alongside a substantial genetic progress as a percentage of the mean (at 5% selection intensity) was noted for thousand grain weight (97.27%). This suggests that these characteristics may be governed by additive genetic diversity, which can be leveraged for subsequent breeding operations and crossing nurseries aimed at wheat enhancement. Key Features A comprehensive understanding of many quantitative and qualitative features is essential for the success of any crop development program. m The protein % and wet gluten percentage of each genotype were determined using the micro-Kjeldahl method and an automatic gluten washer, respectively. (Lone, 2017) [3] The morphological evaluation of the genotypes, conducted in accordance with DUS norms, indicated that over 50% of the genotypes exhibited a lack of coleoptile anthocyanin coloration, green leaves, awned structure, an intermediate growth habit, absence of waxiness, and medium pubescence. The genotypes were assessed for variability factors and relationships for seven quantitative characteristics. Marked genotypic differences were noted for all examined variables, demonstrating substantial diversity among genotypes for each characteristic. The estimations of genotypic coefficient of variation (GCV) and phenotypic coefficient of variation (PCV) were elevated for proline content and grain count per earhead, moderate for earhead length, peduncle length, effective tiller count per plant, and plant height. The heritability estimates were elevated for all examined traits. The anticipated genetic improvement as a percentage of means was substantial for proline content, grains per earhead, earhead length, peduncle length, effective tillers per plant, and plant height, whereas it was moderate for total phenols."

Methodology Experimental Material

"In the current study, eighteen genotypes of bread wheat (Triticum aestivum L.) were used to provide adequate variability in yield and the quantitative characteristics that are associated with yield. To determine the level of genetic variability and character association twelve agronomic characters such as phenological, morphological, and yieldcontributing characters were evaluated in these genotypes. The experimental layout and design was satisfactory, with petri-plates being used to perform the experiment. The experiment was setup in a Randomized Block Design (RBD) and replicated three times in order to reduce the variation in the environment and provide precision. All the genotypes were cultivated in the same agronomic conditions with the observance of the recommended cultural operations. Five plants of each genotype were randomly chosen in each replication and observations made on them, with the exception of days to 50 percent flowering which was made on a plot basis.

Data Collection

A total of twelve quantitative characteristics were measured, which were days to 50 percent flowering, height of plants, length of the peduncle, length of ear, number of tillers per plant, flag leaf length, flag leaf width, awn length, number of spikelets per ear, weight of the entire plant, 100-grain weight and weight of the grain per plant. The accurate and consistent results were obtained through standard measuring procedures.

Statistical Analysis

Statistical analysis of the recorded data was done to approximate the mean values and ranges. It was analysed using analysis of variance (ANOVA) to check the significance of differences among the genotypes based on standard procedures. Calculation of genotypic, phenotypic and environmental variances were done and coefficients of variation (GCV, PCV, ECV) were estimated. To ascertain the nature and degree of genetic control of traits that were being studied, broad-sense heritability and expected genetic advance were computed.

Statistical Analysis

The following statistical procedures were followed in the present investigation.

Mean

Test of Significance

The calculated F-values were compared with the table values. A calculated F-value higher than the table F-value at 0.05 probability level indicated significant differences among treatments. If the calculated F-value exceeded the table F-value at 0.01 probability level, the differences were considered highly significant.

Discussion

The results indicate that there is a considerable level of genetic variability of the genotypes of wheat on most of the quantitative traits, meaning that there is sufficient room to apply selection and genetic enhancement. The larger magnitude of the phenotypic coefficients of variations over the genotypic coefficients are indicative of environmental effect on the expression of the traits although the disparities were small in a number of characters. Plant height, peduncle length, ear length, and days to 50 percent flowering traits had a high heritability, which implies that they are mainly genetically determined. Yield-related traits were found to have moderate to low heritability due to their complexity. In general, the variability and genetic parameters noticed support the possibility of the traits to be useful as selection indices in wheat breeding programs.

Conclusion

The research conclusively proves that there is indeed high genetic variation within the considered wheat genotypes in terms of yield and related characteristics. The high heritability and the significant genetic progress of specific characters makes it probable that they will be influenced by additive action of genes which are susceptible to direct selection. Intermediate-heritability traits that contribute to yield are the determinants of indirect selection strategies. The findings give a sound genetic foundation into finding the best genotypes and prioritization of important features in breeding programs. Therefore, the research can be of great value in making effective selection strategies that would improve the productivity of wheat, and come up with better high yielding cultivars.

References

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3. Lone RA. Genetic variability and correlation studies in winter wheat (Triticum aestivum L.) germplasm for morphological and biochemical characters. International Journal of Pure & Applied Bioscience. 2017;5(1):82-91. doi:10.18782/2320-7051.2489.
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7. Poonia MK, Kumar A, Kumar V, Bhanu AN, Kumar S. Genetic variability and character association analysis for seed yield and its attributes in wheat (Triticum aestivum L.). International Journal of Plant & Soil Science. 2023;35(9):2912-2919. doi:10.9734/ijpss/2023/v35i92912.
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