Inheritance of spike color in einkorn wheat (Triticum monococcum L.)

specify the spike color inheritance in einkorn wheat ( Triticum monococcum L.


Introduction
Triticum monococcum L. is one of the first domesticated cereal crops whose cultivation has almost ceased until recently (Brandolini, Heun, 2019).In recent decades, interest in einkorn wheat has been revived among scientists, farmers, nutritionists, and ordinary consumers.This is explained by the fact that einkorn wheat has a higher content of gluten and protein (Geisslitz et al., 2019), antioxidants and vitamins (Pehlivan et al., 2021), microelements (Cakmak et al., 2000) than other wheat species which determines its value as a crop for healthy nutrition.Products of the einkorn wheat can be consumed by some categories of people with wheat gluten intolerance (Di Stasio et al., 2020;Rotondi Aufiero et al., 2022).
Comprehensive knowledge of the of wheat plant traits complex and the nature of their inheritance contributes to its purposeful improvement for cultivation.The color of the wheat spike determined by the color of the spike scales, has an adaptive value (Börner et al., 2005).This trait is widely used in taxonomy and for certification of wheat varieties and forms, and it is also a convenient model for genetic and molecular genetic studies (Khlestkina, 2013).Using spike color, agronomists calculate spikes number per unit area to predict yield (Zhao et al., 2014), and assess Fusarium wilt (Song et al., 2022).
It is known that the colored spike is dominant over the uncolored one (Khlestkina, 2013).In wheat and Aeglops, the genes determining the colored spike (red, brown, black, gray-smoky) are localized on the distal sections of the short arms of the first homeologous group chromosomes: Rg-A1, Rg-B1, Rg-D1, respectively, in chromosomes 1A, 1B, 1D (Khlestkina, 2013).In particular, the genes localized in the A genome derived from the einkorn wheat are of interest.Four alleles (a-d) are known for the Rg-A1 gene, located on the short arm of chromosome 1A.The Rg-A1b allele determines the red color of spikelet scales.
The Rg-A1c and Rg-A1d alleles control black color of the scales (http:www.shigen.nig.ac.jp/wheat/ komugi/genes/download.jspMacGene).Kozub et al. (2016) on T. spelta L. showed linkage of the Rg-A1 allele which determines black spike color with the Gli-A1j* allele which encodes the corresponding block of gliadin and can serve as a marker for the Rg-A1 allele.
To determine nature of traits inheritance in hybrids, the method of segregation analysis "Mixed major genes plus polygenes inheritance analysis" was developed (Gai et al., 2003), which can be used to determine the number of major genes and polygenes controlling quantitative traits.This method has been used to study a number of traits in tetra-and hexaploid wheats, such as productivity (Xie et al., 2020) and grain characteristics (Yang et al., 2013) in common wheat (Triticum aestivum L.), plant height in durum wheat (T.durum Desf.) (Gong et al., 2021).The aim of this study was to determine the nature of spike color inheritance when crossing forms of einkorn wheat with an alternative manifestation of this trait.

Object of study
The accessions from the National Plant Genetic Resources Bank of Ukraine were used to create reciprocal hybrids: UA0300282 var.nigricultum originating from Hungary, UA0300311 var.monococcum from Syria.The accession UA0300282 has a black spike, winter growth habit, the average spike length is of 6.25 cm, the 1000 kernels weight is of 25.0 g.The accession UA0300311 has a white spike, spring growth habit, the average spike length is of 6.95 cm, the 1000 kernels weight is of 22,8 g (Fig. 1).

Field tests
The research was conducted on the experimental field of the Plant Production Institute named after V.Ya.Yuryev of the National Academy of Agrarian Sciences of Ukraine.The soil type is chernozem.The F1 hybrids were created in 2019, the seeds were used to obtain F2.Re-crossing to obtain F1 was carried out in 2020 on the plots sown in the autumn of 2019.
All the generations (P1, P2, F1, F2) were grown at two sowing terms.Vegetation of autumn sowing plants began in October 2020 and ended in July 2021 (option E1).Spring sowing was carried out in March 2021, ripening occurred in July 2021 (option E2).

Statistical analysis
Segregation analysis was performed using R SEA v2.0 software developed by Wang et al. (2022a).Maximum likelihood indices and the Akaike information criterion of the genetic model were calculated.Three models were selected as candidates.The fit of the candidate model was checked using the χ 2 (U1 2 , U2 2 , U3 2 ), Smirnov (nW 2 ), and Kolmogorov (Dn) criteria.

Selection of a candidate model
The selection of the optimal genetic model was based on the AIC values obtained from the spike color data in the P1, P2, F1 and F2 generations.Models with the smallest AIC values were selected as candidates.The table 1 shows that in the combination UA0300311 × UA0300282 at autumn sowing, among the 24 calculated models, MX2-A-AD, 2MG-A and MX2-EA-AD have relatively low AIC values, which are 379, 383, 378, respectively.For spring sowing, three models were selected for testing: MX2-EA-AD, MX1-AD-AD, and MX2-CD-AD, with AIC values of 362, 392, and 346, respectively.In the reciprocal combination UA0300282 × UA0300311 for plants of autumn sowing, this condition is satisfied by the MX2-ADI-AD, MX2-CD-AD and 2MG-EAD models, the AIC values are 487, 492, and 500, respectively; for spring sowingmodels MX1-A-AD, MX1-NCD-AD and MX2-ADI-ADI with the corresponding AIC values: 522, 489 and 482.The values of the maximum likelihood function (MLV) are also presented in the table 1.

Test of spike color inheritance genetic models suitability
The suitability of the selected candidate models was tested according to the homogeneity (U1 2 , U2 2 , U3 2 ), Smirnov (nW 2 ) and Kolmogorov (Dn) criteria.The genetic model with the lowest AIC value and the minimum number of statistically significant indicators is considered optimal (Akaike, 1977).
It was concluded that for the combination UA0300311 × UA0300282 at autumn sowing, the most suitable inheritance model is MX2-EA-AD, which assumes the presence of two main genes with an equal additive effect plus a system of polygenes with an additive-dominant effect.In spring-sown plants, spike color is described by the MX2-CD-AD model which assumes the presence of two main genes with a full dominant effect plus polygenes with an additive-dominant effect.

Hao Fu
Серія «Біологія», вип.39, 2022 Series "Biology", issue 39, 2022 ISSN 2075-5457 (print), ISSN 2220-9697 (online) In the reciprocal combination -UA0300282 × UA0300311, the optimal model that best describes the dispersion of spike color in plants of autumn sowing is MX2-ADI-AD, which assumes the presence of two main genes with an additive-dominant-epistatic effect plus polygenes with an additive-dominant effect.The plant of spring sowing distribution by spike color is well described by the MX2-ADI-ADI model -two main genes with an additive-dominant-epistatic effect plus a system of polygenes with an additive-dominantepistatic effect.

Parameters of the optimal genetic model based on spike color
The genes manifest themselves differently in a trait depending on the weather conditions determined by the sowing timing.In the combination UA0300311 × UA0300282 at winter sowing, the additive effect of the first pair of main genes is positive and equal to 1.96.The additive effect of polygene ([d]) is negative and is represented by the number -1.41, the dominant effect of polygene ([h]) is 2.52.In the plants of spring sowing, the additive effect of the first and second pairs of main genes is negative and expressed weaker and at the same level, amounting to -0.08.The additive effect of polygenes is -2.35, and the dominant effect of polygenes is estimated at 2.69.In the reciprocal combination UA0300282 × UA0300311, the additive effect of the first pair is much greater than that of the second pair of main genes in terms of absolute value: respectively -2.98 and -0.01 for winter sowing, -3.25 and -0.25 for spring sowing.The dominant effect of the first pair of main genes is also much greater than that of the second pair: respectively, 1.86 and 0.04 for winter sowing, 1.75 and 0.25 for spring sowing.
In the plants of direct combination (UA0300311 × UA0300282) of autumn sowing, heritability determined by the main gene is 97%; and that determined by polygenes is estimated at 2.7%; in spring sowing, these values are equal to 67% and 32%, respectively.In the reverse combination (UA0300282 × UA0300311) from autumn sowing, the heritability is 99%, the polygenic system accounts for 1%; in plants from spring sowing, respectively, 72% and 28%.In the reverse combination (UA0300282 × UA0300311) of autumn sowing, the heritability is 99%, the polygenic system accounts for 1%; in plants of spring sowing, respectively, 72% and 28%.This means that the growing conditions and the environment strongly influence the spike color (Wei et al., 2017), it depends on the growing conditions, in particular on the light intensity (Zeven, 1983).
The results of the study on the plants quantitative traits inheritance obtained by the method of Mixed major genes plus polygenes inheritance analysis and the methods of molecular genetics, evaluate the genetic effect in various aspects.Studies show that the numbers predicted by these two methods and the QTL positioning results of major genes controlling plant quantitative traits are in agreement (Zhang et al., 2007;Wang et al., 2022b).

Conclusions
1.The difference in spike color between the black-spikeed and white-spikeed forms of einkorn wheat is under the control of two main genes and a polygene system.
2. The ratio of heritability components of spike color in einkorn wheat depends on the vegetation conditions: at autumn sowing, 97-99 % of the heritability is caused by the main genes and 1-3 % of the phenotypic variability is accounted by polygenes; at spring sowing, the heredity component due to the polygenic complex increases to 28-33 %.

Table 1 . Maximum likelihood functions and Akaike criteria
Note: E is sowing time, E1 is autumn sowing, E2 is spring sowing, MLV is maximum likelihood function, AIC is Akaike's criterion, 2MG is two major genes, MX is mixed model of major gene and polygene system, A is additive effect, ADadditive-dominant effect, ADI -additive-dominant-epistatic effect, EA -equal additive effect, CD -complete dominant effect.For example: MX2-A-AD means a mixed model of two major genes with an additive effect plus a polygene system with an additive-dominant effect.