Inheritance of traits in F 1 hybrids of diploid einkorn wheat of the spring crop

Diploid einkorn wheat (2n = 14) is an ancient crop that people cultivate for 10 thousand years. The grain of this wheat is a valuable product for a healthy diet, which determines the increasing interest in einkorn wheat by scientists and agricultural producers. Meanwhile, the wide use of this crop is hindered by several shortcomings that complicate the usage of modern technologies: low yield, ear fragility, a t endency to lodging, and difficult grain threshing. Nevertheless, there are some preconditions for improving the agronomic properties of this crop. We carried out crosses in seven combinations with the use of three wheat species ( T. boeoticum , T. monococcum , T. sinskajae ) to improve the diploid einkorn wheat in terms of productivity and threshing. In total, the hybrid seed set in the crosses varies from 6.3 % to 79.7 %. In the combination of cultivated wheat T. sinskajae with wild T. boeoticum , differences in the results of reciprocal crosses are observed specifically in the hybrid seed set (in the forward cross it equals 6.3 %; in the reverse one, 48.9 %). Hybrids from reciprocal crosses of T. monococcum var. sofianum UA0300649 and T. sinskajae f. aristata were equivalent in seed set (72 and 82 %) and inheritance patterns and had similar quantitative traits. In other combinations, the seed set varied from 12.5 to 45.6 %. Hybrid depression was the most frequent (22 cases out of 49) inheritance type of the F 1 quantitative traits in einkorns; dominance of the parent form with a large trait manifestation was registered in 11 cases, and heterosis in four cases. In hybrids, the inheritance of spike length is correlated with the inheritance type of the ear number ( r = 0.92) and the grain number ( r = 0.78) per spike. The dominance degrees after these two traits are also highly correlated ( r = 0.89). The combination UA0300400 T. boeoticum var. thaoudar ARM / UA0300224 T. sinskajae var. sinskajae RUS, which manifested heterosis for kernel number per spike ( Hp = 1.2), the weight of spike ( Hp = 11.8) and weight of kernels per spike ( Hp = 5.4) is of particular interest. The combination UA0300222 T. monococcum var. hohensteinii / UA0300224 T. sinskajae var. sinskajae is promising for creating easily threshed material.


Introduction
Diploid einkorn wheat (2n = 14) is an ancient crop that mankind has been cultivating for 10 thousand years (Heun et al., 1997). The grain of this wheat is a valuable product for a healthy diet (Hidalgo, Brandolini, 2014). It may also be beneficial for people with wheat gluten sensitivity (Di Stasio et al., 2020). All this determines the increasing interest in einkorn wheat of scientists and agricultural producers. Meanwhile, the wide use of this crop is hindered by a number of shortcomings that make it difficult to use modern technologies: low yield, tendency to lodging, fragility of ear, difficult grain threshing. Nevertheless, there are preconditions for improving the technological qualities of this crop. For example, threshing can be facilitated by using for hybridization a species Triticum sinskajae A. Filat. et Kurk. with easy threshing although not highly productive (Filatenko, Kurkiev, 1975). It is possible to predict the effectiveness of hybridization for the genetic improvement of einkorn wheat by manifestation of traits in F1 hybrids (Kostylev, Nekrasova, 2015), which is also important for the development of commercial heterotic hybrids.
The purpose of the research is to find out the trait inheritance modes in F1 hybrids of einkorn wheat accessions and to identify promising hybrid combinations for a prospective increase of subsequent generations' productivity.

Materials and methods
Seven hybrid combinations involving representatives of three einkorn wheat species were used as the material for the study. Among them, there were two reciprocal combinations (1/2 and 5/6, Table 1). The studies were carried out in the experimental field of the Plant Production Institute named after V.Ya. Yuryev of the National Academy of Agrarian Sciences of Ukraine (eastern forest-steppe). The soil of the experimental field is chernozem (black soil). During the growing season in 2021 from March to July, the average temperature was +14℃ and the total precipitation was 188 mm whereas the long-term temperature is of +13℃ and the total precipitation is 219 mm. Thus, the year is characterized as dry.
The "single cross" method was used to create the hybrids. At least 10 spikes were pollinated in each combination, at least 200 flowers in total. The F1 hybrid seeds were sown manually in blocks according to the scheme: mother-hybrid-father. The row length was 1 m, and the row spacing was 15 cm. The number of rows depended on the number of available seeds in each hybrid combination. The evaluation of hybrids by biological and economic characteristics was carried out according to the guidelines (Merezhko et al., 1999).
Hullness (H) is calculated by the formula: where WS -weight of spike, WKS -weight of kernels per spike.
Crossability (C) is determined by the formula: where PFN -pollinated florets number, SS -seed setting.
The degree of dominance (Hp) of the trait in F1 hybrids was determined by the Griffing formula (Griffing, 1956): Where F1 -arithmetic mean value of a trait in a hybrid F1, Mp -arithmetic mean value of a trait in a parental form, Pmax -the best parental form for the trait under study. At Hp > 1, the expressiveness of the trait is designated as heterosis i.e. overdominance of the parent with a higher value of the trait. Hp value < -1 is designated as hybrid depression or overdominance of the parent with a lower value of the trait. The value -1 < Hp < 1 indicated intermediate dominance, i.e., incomplete dominance. The value Hp = 1 indicates the complete dominance of the parent with a higher value of the trait, Hp = -1 indicates the complete dominance of the parent with a lower value of the trait.

Results
Crossability. In plant breeding, crossability serves as a guideline for the selection of parental pairs. This indicator in hybrid combinations of einkorns varies from 3 to 88 % (Table 1). When T. sinskajae is taken as the maternal form and wild wheat T. boeoticum is taken as the paternal form (combination 5), the lowest crossability is obtained -an average of 6 %. In the reciprocal cross (combination 6), the setting percentage was 49 %. Both reciprocal combinations T. monococcum var. sofianum UA0300649 / T. sinskajae f. aristata showed high seed setting (72-82%) (1 and 2 in Table 1). In other combinations, the crossability was at the level of 13-46 %, which is a good result for the dry conditions of spring 2020. Degree of dominance. Of the 49 indicators (Table 2), in four cases there is a overdomination of the parent with higher trait index: in the combination 3 it is shown for proportion of husks, in the combination 6 -for grain number per spike, for weight of spike, for grain weight per spike. In 22 cases there is overdomination of the parent with lower trait index, in five -no dominance (Hp is close to zero) is observed, in 11 -dominance of the parent with higher trait index, in seven -dominated the parent with lower trait index. In the combination 7, overdomination of the parent with lower trait index is observed for all traits. It should be noted that in reciprocal combinations 1 and 2, the inheritance patterns of all traits are similar. In contrast, in reciprocal combinations 5 and 6, the inheritance patterns for five of the seven traits are not the same, and only two -the spikelet number in spike and the mass of 1000 grains -are near. This result is consistent with crossability in these combinations and points to the role of crossing direction.
The analysis shows a correlation between the dominance degrees of the traits. It is established ( Table 3) that dominance for the spike length is near to the dominance for spikelet number (r = 0.92) and for kernel number per spike (r = 0.78). The degrees of dominance in the latter two traits are also closely correlated (r = 0.89).

Discussion
The inheritance of quantitative traits in bread and durum wheat including their hybrids is well studied whereas for einkorns such studies are rare (Kuspira et al.,1989). In F1 hybrids of spring polyploid wheat, overdomination of the best parent is often observed for productivity elements, (Ljubičić et al., 2014;Valekzhanin, Korobeynikov, 2016;Mukhordova, 2018). In our experiments with diploid wheat, this type of inheritance was observed in only one combination. This phenomenon requires more thorough analysis in special experiments.
From a practical point of view, combination 6 is of interest because it is more likely than other combinations to select relatively more productive forms in subsequent generations.

Conclusions
1. In the combination of cultivated T. sinskajae / wild T. boeoticum, differences in hybrid grain setting are observed: in direct cross it equals 6 %, in reciprocal cross it equals 49 %. In other combinations, the index varied from 13 % to 46 %. Both reciprocal crosses between T. monococcum var. sofianum UA0300649 and T. sinskajae f. aristata showed high seed setting (72-82 %) (1 and 2 in Table 1).
2. In F1 hybrids of einkorn wheat, the inheritance pattern of the spike length is similar to the inheritance patterns of the spikelet number per spike and kernel number per spike (the correlation coefficients are 0.92 and 0.78, respectively). Also closely correlated are the dominance degrees in the last two traits (r = 0.89).
3. The combination UA0300400 T. boeoticum var. thaoudar ARM / UA0300224 T. sinskajae var. sinskajae RUS is of interest for breeding as showing heterosis for kernel number per spike (Hp = 1.2), for spike weight (Hp = 11.8) and for kernel weight per spike (Hp = 5.4); the combination UA0300222 T. monococcum / UA0300224 T. sinskajae is valuable for developing easily threshing material.