**10. Discussion**

Ahmadi and Bringhurst [16] reported having received only hermaphroditic descendants (24 plants) from the selfing of the hermaphroditic cultivar 'Capron' (*F. moschata*), while the cross between the female 'Perfumata' hermaphroditic 'Capron' resulted in 12 females and 10 males and no hermaphroditic. This 1: 1 ratio was confirmed in the 9-ploid hybrids, 74 females and 72 males. The female *F. moschata* (Jokioinen) hermaphroditic *F. viridis* cross (**Table 3**) also fits the heterogametic nature of female plants.

The hermaphroditism seems to lower yield in octoploid strawberry species compared with dioecious female clones [46, 47]. With three endemics American octoploid strawberries, also the sex of the plant was found to significantly affect the microbiomes on the flowers [48]. In environments, where both female and male clones of *F. moschata* are frequent enough for cross pollination, the fitness of female clones may be higher than that of hermaphrodites. In the margins of the sparse distribution of *F. moschata* with only one sex attainable on the place, this species relays on vegetative spread. The vegetative spread has also been promoted by human activities. The hermaphroditic *F. moschata* (syn. *F. elatior*) variety 'La Grange' could have sterile flowers from 7 to 90%, with an average of 52% of fertile flowers as written by Longworth in 1846 [49 cited in 46]. The recently arisen hermaphroditic mutant 'Kotka' of musk strawberry resembles the properties of 'La Grange' having variably perfect male fertility.

In most octoploid *Fragaria* taxa, a 13 kb sequence that occurred in all females and never in males was called sex-determining region (SDR). The SDR cassettes revealed a history of repeated translocation [50]. This also raises the hypothesis that the sex mutation from female to hermaphroditic ('Kotka') could be caused by a transposition. The probability for an occurrence of a transposon in the Kotka female clone is high, because transposable element sequences make up about 36% of the total genome assembly in the octoploid strawberry [51], and variation in the location of the sexdetermining genes within the homoeologous chromosome group VI was shown in the North-American octoploid *F. virginiana* [52].

Thinly variegating leaves (**Figure 6**) occurred in five descendants of the openpollinated *F. moschata* in Kotka, where the female clone was evidently back-crossed by its male-fertile hermaphroditic mutant. The variegation can be an expression of an unstable gene and could be caused by the movement of a transposing element, which may have been activated by an environmental mutagen. Already in 1955, Darrow [53] concluded that "The evidence is that variegation is due to a frequently mutating or unstable gene and that the tendency to mutate is inherited as recessive" and "A similar variegation has been obtained when seeds have been irradiated". The Kotka site was subjected to high doses of radioactive airborne fallout from the fire of the Chernobyl nuclear power plant in the Soviet Union in April–May of 1986. In Kotka, on June 6, 1986, a hot or high-activity particle apparently caused dysfunction in a monitor of radioactivity [54]. About five months after the beginning of the Chernobyl fallout, on October 1, 1986, in the Kotka area, the external dose rate was up to 0.159 μSv/h and

the estimated 137Cs surface activity up to 45 kBq/m2 [55]. The mutating rate was high in parts of Finland after airborne fallout radioactivity from Chernobyl since the 1986 April, because one could make autoradiograms on Kodak X-OMAT AR films with fresh grass [54], and because of the occurrences of the hot particles [56]. On some sites, tens of such hot particles occurred on a 1-dm<sup>2</sup> area of land [54]. In a highly radioactively polluted area 32 km NW of the site of the 'Kotka'strawberry [55], three mutants occurred in less than 200 wheat plants grown for other research purposes in the field soil in the 1986 season, and were detected in subsequent seasons and generations [57]. On a tested site, radioactivity dose rate (mR/h) was 50 higher on the soil surfaces than at the 1-m level still on May 28, 1986 [54].

The 1986 radioactive airborne fallout from Chernobyl may have induced genetic changes in vegetative, on land surface lying strawberry stolon tissue, later somatically segregating into the phenotype like the hermaphroditism or, after inbreeding, occurring in seedlings like the variegation. Somatic segregation of polyploidy from stolon was shown in the polyploidization technique derived for strawberries ([40], figure 1d). There under the action of colchicine on cell division, polyploidized cells and cell-groups are numerous. Instead, a radiation-induced mutation on a given gene per cell is extremely rare, and it takes years that a viable mutated cell-line forms a mutant-carrying strawberry stolon, if ever. A recessive mutant needs a meiotic division to manifest, like the variegation gene (**Figure 6**).

The hybrids between *F*. *moschata* and *F*. *bifera*, *F*. *vesca* or *F*. *viridis* provide a wide variety of berry flavors and sweetness. They could be added as flavors mixed to other berries and berry products. The musk strawberries 'Capron Royal' and 'Profumata di Tortona' were among the highest aromatic 17 cultivars, 15 of which were modern *F*. *ananassa* cultivars [58]. Studying the aroma of two sources of musk strawberries, Ferreira et al. [59] detected more than 100 distinctive volatile compounds by GC–MS.

During some seasons, berries of musk strawberry may be infected with the fungus *Spherotheca macularis* f. sp. *fragariae*. Environmental factors like drought, high proportion of sunshine and amount of UV may control the occurrence of the infection. There may be hope to recombine resistance towards the fungus from *F*. *viridis* or *F. vesca* strains.

*F*. *viridis* is self-incompatible [60] and needs another genotype of incompatibility to pollinate. The self-incompatibility apparently increases chance of *F*. *viridis* to be pollinated with *F*. *vesca* where *F*. *viridis* is marginal and rare. The self-incompatibility is not inherited to the *F*. *moschata F*. *viridis* hybrids. The self-incompatibility also gives up in the autotetraploid form of *F*. *viridis* studied with the polyploidization technique [40] which permits to test the single genotype on diploid and tetraploid level (unpublished).
