Asian Journal of Plant Sciences

Year: 2021 | Volume: 20 | Issue: 2 | Page No.: 313-323
DOI: 10.3923/ajps.2021.313.323

Induced Mutations in Wheat (Triticum aestivum L.) and Improved Grain Yield by Modifying Spike Length

A.S. Anter

Abstract: Background and Objective: Wheat bread is classified as the main food crop in Egypt. However, Egypt is the largest importer of wheat globally. The objectives of this study were to increase genetic variation of bread wheat and to identify among mutant lines those with high-yielding under marginal lands conditions. Materials and Methods: Grains of five bread wheat varieties were irradiation by three doses of gamma rays (100,200 and 300 Gy). Fifteen M₀ combination seeds along with the mother varieties arranged in randomize complete blocks design with three replicates at Agricultural Production and Research Station of National Research Centre, Egypt, during four winter seasons (2016-2019). The phenotype selection was applied to the M₃ generation based on a longer spike length, as a result, twenty-three mutant lines have been created, which considered as putative mutants. To confirm these mutant lines, five distinct mutant lines out 23 mutant lines were reevaluated based on grains yield components in M₄ generation. Results: Analysis of variance showed significant variation (p<0.05) among resource mutant lines for quantitative phenotypic traits in mutated generations. Compared to the mother varieties, five mutant lines presented highly outstanding quantitative phenotypic traits. All characters recorded high heritability accompanied with moderate genetic advance, therefore, the possibility of improving wheat grain yield through phenotypic selection. All characters, except plant height, evidenced to be priority traits in selection for higher grain yield due to their powerful direct association with grain yield. Conclusion: These mutant lines provide exciting new valuable resources to investigate and improvement of complex traits in bread wheat.

Keywords: new mutation resources, spike length, sustainability development, genetic diversity and Bread wheat

INTRODUCTION

Bread wheat (Triticum aestivum L.) is the primary crop in Egypt. The rising Egyptians population have resulted an increasing demand for bread wheat in the following years. Wheat grain is used as food for humans and the straw is used as fodder for animals¹. However, Egypt is the largest wheat importer in the world due to the limited amount of cultivated land and there is little use of modern farming technology². Therefore, increasing local production through improving grain yield per unit area becomes a matter of importance.

Plant breeding techniques, mutagenesis, biotechnology genetic engineering and molecular breeding have played a pivotal role in exploiting available germplasm resources to create variability and develop improved cultivars³. In this regard, mutagenesis shows as an easy and effective mean of inducing genetic variation. Several researchers have used mutation breeding to improve grains yield of bread wheat^4-6. The main idea of mutation breeding is to identify individuals with a target mutation, which involves two prime steps: mutant screening and mutant confirmation⁷. Mutant screening is a selection of individuals from a huge population that meet specific selection criteria, such as height, earliness, shape, weight compared to the their parents. Wheat spike is key components for improving grain yield because it is positively correlated with grain yield components such as grains per spike and weight per spike^8,9. Most studies have attributed the increased grain yield is due to in increases in grains per spike¹⁰, 1000 grain weight or both¹¹. In addition, the spike, non-foliar organ, can be considered as the photosynthetic organ to grain production^12,13. Thus, improving grain yield can be achieved by indirect selection for spike length, it has the number of spikelet’s, the number of fertile spikelets and the grains per spike¹⁴.

The expected response to selection for studied traits can be estimated by some parameters like phenotypic (PCV) and genotypic (GCV) coefficient of variability, heritability and genetic advance. The GCV measures extent of genetic variability shown by studied trait but it is not possible to determine quantity of variation that is heritable. Estimation of heritability is basically for selection process as it determines the transmissibility of a studied trait in the next generation but does not give a true picture of the expected gain in the next generation. Heritability and genetic advance are two guidelines for determining the genetic control of studied traits and estimate its expected gain from selection in the next generation¹⁵. Correlation coefficients are prerequisites to improve any crop¹⁶. Knowledge of the correlation between yield and its components is essential in establishing plant selection guidelines for plant selection¹⁵. Therefore, the major focus in this study was on selection for a long spike length, non-foliar organ, because it can be detected easily in the field to supply quantitative character data related to grain yield. The objectives of this study were to increase genetic variation of bread wheat and to identify among mutant lines those with high- yielding under marginal lands conditions.

MATERIALS AND METHODS

Plant material and mutagens: The basic strategy for breeding mutations is based on modifying one or more traits of distinct varieties¹⁷. Grains of five bread wheat varieties, Sakha 93 (P₁), Sids 13(P₂), Giza 168 (P₃), Gemmeiza 9 (P₄) and Maryout 5 (P₅) obtained of Agriculture Research Centre, Ministry of Agriculture and Land Reclamation, Egypt. The characteristic of the mother varieties are shown in Table 1.

They were irradiated by three doses of 100, 200 and 300 Gy of gamma rays (Cobalt-60) at the Egyptian Atomic Energy Authority.

M₁, M₂, M₃ and M₄ generations: After the irradiation, the experiment was set up using 15 M₀ combination seeds along with the mother varieties (as control) in order to obtain M₁ plants. The generations (M₁ to M₄) was grown at the Agricultural Production and Research Station of National Research Centre, El-Nubaria, Al-Buhayrah Governorate, Egypt. The experiment was carried out in a randomized complete block design with 3 replicates during growth seasons (2016-2019). The sowing was done in November, 2016 by hand at the rate of 350 seeds m^–2 into the 1.2 m length×0.6 m wide, with 3 rows 0.2 m on row distance (plot size = 2.16 m²). Sprinkler irrigation was applied. Out crossing with other varieties was avoided. Weeds were removed by hand throughout the growing seasons. The standard agricultural practice was applied. The soil characteristics presented in Table 2.

At harvest, spikes from main tillers were taken from survival seeds about ~70% as a subvitals mutation. The seeds obtained from the harvested plants in M₁ generation were sown to rise M₂ generation in 2017. Seeds collected of each combination were sown to rise M₃ generation. In 2018, each combination was grown in three replicate six-row plots, 1.2 m long and 0.60 m wide with 20 cm between rows (plot size = 4.3 m²). At harvest, thirty spikes from each combination were selected based on Spike Length (SL),10 cm <, measured from the base of the rachis to the end of the terminal spikelet, Grains per Spike (GS), Grain Yield per Spike (GYS) and 1000 Grain Weight (TGW).

Selection was delayed to M₃ generation due to studied traits produced a huge phenotypic effect that is recognizable on individual plant and called a macromutation. It is known that a macromutations are polygenic in nature¹⁸. Twenty-three mutant lines (as putative lines) were resulted as follows: lines numbered from 1-5 resulted from the 200-Gy radiation dose, lines numbered from 6-10 resulted from the 300-Gy radiation dose and lines numbered from 11-23 resulted from the 100-Gy radiation dose. Line number, mother varieties and doses are presented in Table 3.

In M₄ generation, five out of 23 mutant lines were sown as previous generations and reevaluated based on previous traits plus to Plant Height (PH), number of spikes/m² (NH) and Grains Yield ha^–1 (GYH).

Statistical analysis of quantitative traits: Data of each trait were subjected to a regular analysis of variance of RCBD according to John¹⁹. The p-value<0.05 was considered statistically significant. ±: Standard deviations. Phenotypic (PCV) and genotypic (GCV) coefficients of variation for lines were calculated according to method of Singh and Choudhary²⁰ as follows:

where, V_p, V_g and X are the phenotypic variance, genotypic variance and grand mean of lines, respectively for studied characters. Broad sense heritability (h_b2%) estimated as the ratio of the genotypic variance (v_g) to the phenotypic variance (V_p) as described by Allard²¹. According to Johnson and Wichern²², the heritability value of a trait when reaches 80% considered as high, moderate when it ranged from 40-80% and low when it less 40%. The expected genetic advance under selection (GA) as well as GA as percentage of the genotype mean assuming selection of the superior 5% of the genotypes were estimated in accordance with the formula illustrated by Allard ²¹ as follows:

where, k is the selection differential at 5% intensity = 2.06, σ2ph: Phenotypic standard deviation, h_b2%: Broad sense heritability.

Deshmukh et al.²³ categorized genetic advance from selection as percent of mean as low (<10%), moderate (10-20%) and high (>20%). Correlation coefficients were calculated between all the studied traits according to Kashiani and Saleh²⁴.

RESULTS

Genetic variation among mutant lines: Twenty-three mutant lines have resulted from treatment of five wheat varieties seeds by doses of gamma rays (100,200 and 300 Gy). Analysis of variance showed a very highly significant difference (p< 0.05) among the mutant lines for all the studied traits in M₃ and M₄ generations (Table 4).

The mean square for mutant lines vs. their mother varieties was significant (p<0.05) for all studied traits. Spike length was recorded the maximum coefficient of variation (8.3%), while 1000 grain weight recorded the least coefficient of variation (3.7%) in M₃ generation. In M₄ generation, grains yield per spike showed the highest value of CV% (11.2), while grains yield ha^–1 scored the lowest value (5.5%).

Quantitative traits in M₃ generation: The mean performance, grand mean and range of genotypes for the studied traits were showed in Table 5 to illustrate the differences between lines and their parents. Five mutant lines (1, 2, 3, 12 and 14) exhibited the higher mean performance for spike length (18 cm <) compared to the mother varieties. Mean performance of mutant lines for spike length ranged from 11.6 cm for line-7 to 18.5 cm for line-14 followed by line-1 (18.2 cm) while mother varieties ranged from 13.2 cm for P₃ to 17.6 cm for P₅. Grand mean of mutant lines for spike length was 15.9 cm while grand mean of mother varieties was 15.3 cm. In support of these results, Fig. 1 clearly showed that three mutant lines numbered 1 to 3 were longer spike length compare to mother varieties as shown in Fig. 2. Also, Fig. 3 showed that line -14 excelled in spike length compared to its parent and this was evidenced in Fig. 4.

Concerning with grains per spike, five mutant lines (1, 3,4,12 and 17) showed higher grains per spike (75<) compared to their parents (70.2>). Mean performance of mutant lines for grains per spike ranged from 30.0 for line-23 to 87.0 for line-12 followed by line-4 (82.0) while mother varieties ranged from 55.2 for P₁ to 70.2 for P₄. But, parents achieved the higher grand mean (66.4) compared to grand mean of mutant lines (55.3). In this study, mean performance and grand mean of parents for grains yield per spike was higher than mutant lines. But, mutant lines recorded wide range for this trait ranged from 1.2 g for line -23 to 3.6 g for line -12. Five out of twenty-three mutant lines (6,15,20,21 and 23 ) recorded higher mean performance for 1000 grain weight (45 g <) compared to their parents (44.1g>).

Two lines, 20 and 23, recorded the highest 1000 grains weight (46 g) while P₄, the highest parent, recorded 44.1 g. Mutant lines showed wide range for 1000 grain weight ranged from 25.0 g for line-16 to 46.0 g for line-20 with grand mean 38.3 while mother varieties ranged from 41.1 g for P₂ to 44.1 g for P₄ with grand mean 41.7 g. From of M₃ generation, five mutant lines (1, 2, 3, 12 and 14) identified based studied traits and consider as putative mutants. To confirm that these mutant lines are true, they reevaluated in M₄ generation plus to plant height, number of spikes m^–2 and grains yield ha^–1 (Table 5).

With regard to plant height, mean performance of mutant lines for plant height ranged from 80.1 cm for line-14 to 103.2 cm for line-3 with grand mean 88.6 cm (Table 6). While mother varieties ranged from 77.4 cm for P₄ to 105.5 cm for P₃ with grand mean 89.3 cm. The grand mean of mother varieties and mutant lines are equal. Regarding spike length, mean performance of mutant lines ranged from 15.7 cm for line-14 to 18.4 cm for line-2 with grand mean 17.0 cm. In contrast, mother varieties ranged from 12.2 cm for P₃ to 18.3 cm for P₂ with grand mean 15.5 cm. The difference between the line-2 and its parent for the spike length was evidenced in the Fig. 5.

For grains per spike, the line 2 had the highest mean performance (90.4) compared to P₄, its parent, (80.0) and other parents (85.1>). And grand mean of mutant lines (83.8) was superior to mother varieties (76.7). Regarding grains yield per spike, line 2 showed the highest mean performance (4.8 g) while P₄ recorded 3.7 g. Also, grand mean of mutant lines (4.1g) was higher than mother varieties (3.6 g). Furthermore, line 2 was superior in 1000 grain weight (52.0 g) compared to P₄ (41.2) and grand mean of mutant lines for 1000 grain weight (45.9 g ) was higher than mother varieties (42.3 g). Mutant lines ranged from 41.2 g for line-14 to 52.0 g for line-2. With respect to number of heads m^–2 and grains yield ha^–1, line-2 achieved the highest mean performance (159.3 and 7441.3 kg) compared to P₄ (111.2 and 3344.5 kg) and other parents and mutant lines.

Traits selection value: The total variability was expressed in terms of the PCV and GCV. The values of PCV in all the traits were higher than the values on corresponding GCV in M₃ and M₄ generations (Table 7). In M₃ generation, the highest value of GCV (20% <) was recorded for grains per spike (25.9%) followed by grains yield per spike (16.7%). Nevertheless, the smallest GCV was for 1000 grain weight (13.5).

The low differences between values of PCV and GCV values found for studied traits (1.1>). The highest value of heritability found for grains per spike (98.1%). In general, all traits recorded high value of heritability (80.0% <). In the same direction, all traits which recorded a high value of heritability (80%<) were associated with high genetic advance (48.2%>) as % of lines mean, except for spike length was moderate (14.7%).

In M₄ generation, the highest value of GCV was recorded for grain yield ha^–1 (26.3%) followed by 1000 grain weight (11.2%) while grains per spike recorded the smallest value (10.1%). Phenotypic (PCV) and genotypic (GCV) coefficients of variability were low for all studied traits expect grain yield ha^–1 compared to M₃ generation. However, the differences between the two parameters were less (1.1>). High estimate of heritability (99.0%) accompanied with high genetic advance (53.0 %) as % of lines mean was recorded for grain yield ha^–1. The rest of traits recorded a high value of heritability (81.8% <) accompanied with moderate genetic advance (20.0% >) as % of lines mean. From these results, the genetic variability was presented for studied traits which provide ample opportunity for further selection.

Relationship among studied traits: In this study, data in Table 8 showed correlation coefficients among studied traits illustrated that grain yield ha^–1 recorded a positive significant correlation with spike length (0.901) grains per spike (0.875), grains yield per spike (0.801 ),1000 grain weight (0.820) and number of spikes/m² (0.830). Spike length recorded a positive significant correlation with grains per spike (0.840) and 1000 grain weight (0.849).

DISCUSSION

In this study, gamma irradiation was used as a strategy for a broad genetic base within bread wheat to improve the efficiency of the breeding programs because the human selection contributed to a long time in the loss of important allelic variance²⁵. Data in the Table 4 showed that presence variation among mutant lines in M₃ and M₄ generations, indicating that mutant lines did not perform uniformly across different gamma rays. Traits showed that the CV% was less than 20%, indicating that experimental data were not dispersed and traits were not severely affected environment⁵. Often the mutations are recessive and of low frequency. Thus, the major focus in this study was on phenotypic selection for a long spike length because it can be detected easily in the field to supply quantitative character data related to grain yield. In the M₃ generation, some putative mutant lines (1, 2, 3, 12 and 14) were identified by a longer spike length (18 cm <) compared to their parents. To confirm these mutant lines are true, they were screened for the spike length in the M₄ generation and found that line 2 recorded the longest spike length (18.4 cm) compared to their parents (18.1 cm)^5,6. Wheat spike comprises spikelets, each with several florets. Consequently, an increase in the spike length can be selected concurrently with increased grains per spike²⁶. In this study, plant height trait was estimated in M₄ generation which was equal with mother varieties. In the current study, five mutant lines (1,3,4,12 and 17) recorded higher grains per spike (75.0<) compared to their mother varieties (70.2<). Mutant line-12 showed the highest grains per spike (87.0) in M₃ generation. While in M₄ generation the P₅ superior to mutant lines for grains per spike^5,26. This finding showed that the increase in the spike length of line 2 had a positive effect on the grain per spike compared to other mutant lines. For grains yield of each spike, mean performance of parents was higher than mutant line in M₃ generation, but in M₄ generation, the situation changed in desired direction. Because, the mutant line 2 achieved the highest mean performance of grains yield per spike compared to mother varieties and other lines^6,8. Regards to 1000 grain weight, six mutant lines (6, 9, 15, 20, 21 and 23) were heavier 1000 grain weight than mother varieties in M₃ generation^6,8,27. However, these lines had a short spike length (16 cm >) and low grains per spike (45>). In M₄ generation, mutant line-2 recorded the highest 1000 grain weight (52.0 g) compared to mother varieties. Grain yield improvement has been significantly connected with increased 1000 grain weight²⁸. In contrast, Xiao et al.²⁹ found that grain yield negatively correlated with1000 grain weight. For both number of spikes m^-2 and grain yield ha^–1, mean performance of mutant lines and mother varieties are equal for number of spikes m^-2 in M₄ generation. Mean performance of mutant line 2 for grains yield ha^–1 was higher than mother varieties and other mutant lines^4-6,27. The reason for superior mutant lines vs. mother varieties for spike length, grains per spike, grains yield per spike,1000 grain weight and grain yield ha^–1 may be due to generate of new mutated alleles responsible for increasing these traits. Hence, specific merit of mutation induction is the possibility of winning unselected genetic variation, improvement of one or a few characters of an excellent cultivar is to be modified³⁰. Therefore, the maximize grain yield in bread wheat obtained by manipulating and predicting spike morphology traits such as spike length, grains per spike, grain yield per spike and 1000 grain weight. It noted that grand mean of mutant lines for grains per spike, grains yield per spike and 1000 grain weight in M₃ generation were lower than M₄ generation. The ranges gained in the M₃ generation were higher than M₄ generation for studied traits (Table 5 and 6). Due to the variability dive gradually from M₂ to M₄ generations¹⁷.This study identified line 2 as a promising line. Because, it achieved the highest level of performance for studied traits. It was cleared that the use of the spike length character had a positive effect for identifying the distinct mutant among a large number of plants, especially in early generations. The sum variability was showed in terms of the PCV and GCV. In this context, the values of PCV were higher than their corresponding GCV for all studied traits in two mutated generations, which environmental impact was comparatively low on the expression of studied traits. In this study, a narrow gap was found between the PCV and GCV values of studied traits in two mutated generations, indicating that the environmental factors had lower influence on the expression of these characters than the genetic factors. Grains yield ha^–1 recorded a high value of PCV and GCV, suggesting that this trait is under the influence of genetic control. This indicated that this trait could be improved through hybridization and selection for better yield performance. Heritability and genetic advance give generic behavior of traits which increases the efficiency of selection. High heritability (80% <) was coupled with high genetic (20% <) advance as percent of mean lines observed for studied traits except for spike length was moderate (14.7%) in M₃ generation. In M₄ generation, grains yield ha^–1 recorded high heritability coupled with high genetic advance. This indicated that mutation take place in more than one locus¹⁷. This indicated that the additive gene action controlled in grains yield ha^–1 and can easily be selected through phenotypic selection⁵. All traits, except plant height, recorded a positive and significant correlation with grain yield ha^–1 indicates that the important role of these traits in determining grain yield, consequently, these traits have priority in selection for higher grain yield. Spike length was positively correlated with grains per spike and grains weight^14,31. This indicated that spike length has a great role in improving grain yield ha^–1 of bread wheat in sandy soil. This finding suggests that crossing between proper mutant lines possessing longer spike length (18 cm<), higher grains per spike (80<) and heavier 1000 grain weight (46 g <) and crossing with commercial cultivars would be given positive results. Another use of these lines is further evaluation under biotic and abiotic stresses with evaluation in many locations for many years. Consequently, broaden genetic variation of bread wheat in Egypt by add a novel genes and give a chance for grain yield improvement. The introduction of a new adaptive allele in the diverse genetic backgrounds may assist to promote grain yield of old or newly developed varieties of bread wheat to balance supply and demand in Egypt.

CONCLUSION

Five varieties of bread wheat were irradiated by three doses of gamma rays to increase genetic variability and to improve grain yield. Twenty -three mutant lines were generated based on spike length in M₃ generation. Five out 23 mutant lines were reevaluated based on grain yield components. Mutant lines showed significant variation in the studied traits that were established through phenotypic and genotype coefficients of variation. Several mutant lines were superior to their mother varieties for most studied characters in M₃ and M₄ generations. High values of heritability associated with moderate genetic gain observed in all studied characters. This indicated these characters were controlled by additive gene effects and selection may be effective for these characters to grain yield improve. All traits, except plant height, recorded a positive and significant correlation with grain yield ha^–1 indicates that the important role of these traits in determining grain yield. These mutant lines provide exciting new valuable resources to investigate and improvement of complex traits in bread wheat.

SIGNIFICANCE STATEMENT

This study discovered the direct selection for spike length has a positive effect of grain yield of bread wheat that can be beneficial for wheat breeders. This study will help the wheat breeder to use new valuable resources to investigate and improvement of complex traits to uncover the critical areas of grain yield improvement that many researchers were not able to explore.

REFERENCES