Volume 18, Issue 2 (4-2026)
J Crop Breed 2026, 18(2): 16-23 |
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Moghaddam A, Mofidian S M A. (2026). Estimation of Narrow-sense Heritability and Selection Gain using Poly-cross Progenies Test in Iranian Alfalfa (Medicago sativa L.) Ecotypes. J Crop Breed. 18(2), 16-23. doi:10.61882/jcb.2026.1612
URL: http://jcb.sanru.ac.ir/article-1-1612-en.html
URL: http://jcb.sanru.ac.ir/article-1-1612-en.html
1- Seed and Plant Improvement Institute, Agricultural Research, Education and Extension Organization (AREEO), Karaj, Iran
Abstract: (476 Views)
Extended Abstract
Background: Iran is recognized as one of the regions of alfalfa origin in the world, possessing a wide genetic diversity related to this crop. In general, alfalfa yield improvement is the main goal of all alfalfa breeding programs. To start a breeding program for one or more traits in a crop, such as alfalfa, it is essential to have information about the heritability of traits, especially the narrow-sense heritability (h2n). By definition, the narrow-sense heritability is the ratio of additive genetic variance to phenotypic variance in a population or set of genotypes. In general, information about the narrow-sense heritability of the interested traits helps the breeder to have a good understanding of the potential of trait improvement through selection. Therefore, an important application of the narrow-sense heritability estimation is to predict the genetic gain from selection among the studied genetic material. One of the most widely used methods in forage crops, such as alfalfa, to estimate additive genetic variance and narrow-sense heritability is the poly-cross test, which is especially used in the production of synthetic cultivars. This study aimed to estimate the narrow-sense heritability and predict the genetic yield of selection among Iranian alfalfa cultivar/ecotypes to produce and release one or more synthetic varieties.
Methods: An experiment was conducted with 10 half-sib families (progenies from poly-cross) derived from poly-crosses between 10 genotypes. These genotypes included two Bami and Yazdi alfalfa ecotypes, two released cultivars (Ahang and Mandegar), and ecotypes from cold and temperate regions, including KFA3, KFA15, KFA13, KFA11, KFA4, and KFA16. The experiment was executed in a randomized complete block design with three replications in Karaj during the years 2020-2022. The experiment was conducted in the research fields of the Seed and Plant Improvement Institute, Karaj, in September 2020, and the traits were recorded in 2021 and 2022. The studied traits included plant height (cm), number of stems per square meter, regrowth rate (cm), fall dormancy score, and annual yields of dry and fresh forage (t ha⁻¹) over 2 years. Combined variance analysis of the data related to the measured traits was performed based on a split-plot experiment in time. Genotype and year were considered fixed factors, and replication was taken as a random factor. To calculate additive variance, the genetic variance among half-sib families was first estimated using the expectation of the mean squares. The genetic variance among half-sib families is equal to the covariance within half-sib families and represents additive variance. For autotetraploid plants such as alfalfa, the genetic variance among half-sib families equals one-fourth of the additive variance and one-thirty-sixth of dominance variance. The narrow-sense heritability was estimated based on the 2-year phenotypic mean of half-sib families, followed by predicting genetic gain from selection among the families. Additionally, phenotypic and genotypic coefficients of variation were calculated for various traits.
Results: Statistical analysis results revealed significant differences among half-sib families for the regrowth rate (α ≤ 0.01), fall dormancy score (α ≤ 0.01), and dry forage yield (α ≤ 0.05). Two half-sib families, Poly-Yazdi and Poly-KFA3, with 8.7 and 8.6 scores, and two half-sib families, Poly-KFA11 and Poly-KFA15, with 5.07 and 5.13 scores, gained the maximum and minimum fall dormancy scores, respectively. Poly-KFA3 and Poly-KFA15 exhibited the highest (22.91 t ha⁻¹) and lowest (19.48 t ha⁻¹) dry forage yields, respectively. Narrow-sense heritability estimates for traits, such as plant height, the number of stems per square meter, regrowth rate, fall dormancy score, fresh forage yield, and dry forage yield, were 0.24, 0.25, 0.94, 0.87, 0.42, and 0.61, respectively. The highest genotypic coefficient of variation was observed for fall dormancy score (19.65%), regrowth rate (10.46%), and dry and fresh forage yields (3.80% and 3.02%, respectively). Conversely, the lowest variation was noticed for plant height (1.08%) and the number of stems per square meter (1.63%). Regarding the phenotypic coefficient of variation, the highest values were associated with the fall dormancy score (21.07%), regrowth rate (10.80%), and dry and fresh forage yields (4.85% and 4.65%, respectively), while the lowest values were observed for plant height (2.23%) and the number of stems per square meter (3.29%).
Conclusion: According to the results of this study, the expected genetic gain from selection, using a 50% selection intensity and a parental control factor of 2, was estimated for the traits. These included fresh forage yield (1.52 tons per hectare), dry forage yield (0.62 tons per hectare), plant height (0.4 cm), number of stems per square meter (4.21 stems), regrowth rate 14 days post-harvest (3.68 cm), and fall dormancy score (1.17). Finally, five populations, Bami, Yazdi, KFA3, KFA13, and KFA16, were selected for mean comparison results, narrow-sense heritability estimations, and genetic gain from selection to create a new synthetic population after crossing in an isolated field and multi-location forage yield trial.
Background: Iran is recognized as one of the regions of alfalfa origin in the world, possessing a wide genetic diversity related to this crop. In general, alfalfa yield improvement is the main goal of all alfalfa breeding programs. To start a breeding program for one or more traits in a crop, such as alfalfa, it is essential to have information about the heritability of traits, especially the narrow-sense heritability (h2n). By definition, the narrow-sense heritability is the ratio of additive genetic variance to phenotypic variance in a population or set of genotypes. In general, information about the narrow-sense heritability of the interested traits helps the breeder to have a good understanding of the potential of trait improvement through selection. Therefore, an important application of the narrow-sense heritability estimation is to predict the genetic gain from selection among the studied genetic material. One of the most widely used methods in forage crops, such as alfalfa, to estimate additive genetic variance and narrow-sense heritability is the poly-cross test, which is especially used in the production of synthetic cultivars. This study aimed to estimate the narrow-sense heritability and predict the genetic yield of selection among Iranian alfalfa cultivar/ecotypes to produce and release one or more synthetic varieties.
Methods: An experiment was conducted with 10 half-sib families (progenies from poly-cross) derived from poly-crosses between 10 genotypes. These genotypes included two Bami and Yazdi alfalfa ecotypes, two released cultivars (Ahang and Mandegar), and ecotypes from cold and temperate regions, including KFA3, KFA15, KFA13, KFA11, KFA4, and KFA16. The experiment was executed in a randomized complete block design with three replications in Karaj during the years 2020-2022. The experiment was conducted in the research fields of the Seed and Plant Improvement Institute, Karaj, in September 2020, and the traits were recorded in 2021 and 2022. The studied traits included plant height (cm), number of stems per square meter, regrowth rate (cm), fall dormancy score, and annual yields of dry and fresh forage (t ha⁻¹) over 2 years. Combined variance analysis of the data related to the measured traits was performed based on a split-plot experiment in time. Genotype and year were considered fixed factors, and replication was taken as a random factor. To calculate additive variance, the genetic variance among half-sib families was first estimated using the expectation of the mean squares. The genetic variance among half-sib families is equal to the covariance within half-sib families and represents additive variance. For autotetraploid plants such as alfalfa, the genetic variance among half-sib families equals one-fourth of the additive variance and one-thirty-sixth of dominance variance. The narrow-sense heritability was estimated based on the 2-year phenotypic mean of half-sib families, followed by predicting genetic gain from selection among the families. Additionally, phenotypic and genotypic coefficients of variation were calculated for various traits.
Results: Statistical analysis results revealed significant differences among half-sib families for the regrowth rate (α ≤ 0.01), fall dormancy score (α ≤ 0.01), and dry forage yield (α ≤ 0.05). Two half-sib families, Poly-Yazdi and Poly-KFA3, with 8.7 and 8.6 scores, and two half-sib families, Poly-KFA11 and Poly-KFA15, with 5.07 and 5.13 scores, gained the maximum and minimum fall dormancy scores, respectively. Poly-KFA3 and Poly-KFA15 exhibited the highest (22.91 t ha⁻¹) and lowest (19.48 t ha⁻¹) dry forage yields, respectively. Narrow-sense heritability estimates for traits, such as plant height, the number of stems per square meter, regrowth rate, fall dormancy score, fresh forage yield, and dry forage yield, were 0.24, 0.25, 0.94, 0.87, 0.42, and 0.61, respectively. The highest genotypic coefficient of variation was observed for fall dormancy score (19.65%), regrowth rate (10.46%), and dry and fresh forage yields (3.80% and 3.02%, respectively). Conversely, the lowest variation was noticed for plant height (1.08%) and the number of stems per square meter (1.63%). Regarding the phenotypic coefficient of variation, the highest values were associated with the fall dormancy score (21.07%), regrowth rate (10.80%), and dry and fresh forage yields (4.85% and 4.65%, respectively), while the lowest values were observed for plant height (2.23%) and the number of stems per square meter (3.29%).
Conclusion: According to the results of this study, the expected genetic gain from selection, using a 50% selection intensity and a parental control factor of 2, was estimated for the traits. These included fresh forage yield (1.52 tons per hectare), dry forage yield (0.62 tons per hectare), plant height (0.4 cm), number of stems per square meter (4.21 stems), regrowth rate 14 days post-harvest (3.68 cm), and fall dormancy score (1.17). Finally, five populations, Bami, Yazdi, KFA3, KFA13, and KFA16, were selected for mean comparison results, narrow-sense heritability estimations, and genetic gain from selection to create a new synthetic population after crossing in an isolated field and multi-location forage yield trial.
Keywords: Yield comparison, Poly-cross progenies, Ecotype, Narrow-sense heritability, Selection gain
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