**4. Expanding the use of the genetic pool**

As a corollary of the information gathered from the available literature on the subject under discussion, it was evident that genetic improvement in strawberries was fundamentally aimed at increasing productivity, the sensory quality of strawberries, and adaptation to various environments [9], and in certain countries, there were also relevant experiences in the formation of varieties with resistance to root diseases [71, 135], foliar diseases [11] and to viral complexes [74]. Among the wide genetic diversity existing in the 26 species, only a part of the reservoir has been used, basically from *Fragaria* x *ananassa* [11], infrequently, from other octoploid species [74, 136], and exceptionally, with a lower of ploidy level [128].

Several avant-garde approaches have been besought and applied to use the genetic richness of wild species, to expand the genetic base of cultivated strawberries. One is the use of synthetic octoploids to take advantage of the genes of different levels of ploidy and bring them to the octoploid level [137], another is to perform the synthesis of *Fragaria* x *ananassa* again, but using a select group of progenitors of both, *F. chiloensis* as well as *F. virginiana*, which have been chosen for many characters such as: yield, quality and resistance to adverse factors [4, 6, 105, 138], and one more, is to form synthetic decaploids to introduce the complete genome of both, octoploid and diploid species [128, 139]. The introgression of genes of octoploid species towards the cultivated one [74] has been practiced successfully and with economically impressive results, but its contribution to broadening the genetic base is minimal. The first three day-neutral cultivars released, contributed only 6.25% of *F. virginiana* ssp. g*lauca* genes.

The collected germplasm of *F. chiloensis* [117, 140–143] and *F. virginiana* [142, 144, 145], are available in the gene banks of certain countries [140], they have been characterized for certain attributes of cyclic flowering [4, 146], horticultural [5], resistance to diseases [89], resistance to pests [111, 112, 147], and at the molecular level [148–150]. However, it is important to characterize them to deal with global problems like pests, diseases, adaptation, and tolerance to abiotic factors, as well as for their nutraceutical properties. Among the global problems that the strawberry industry is facing, the best cultivars are susceptible to the most important pests and diseases, and regarding genetics, it stands out that there is little information on the sources of resistance to pests. The same situation occurs, towards resistance to low temperatures and there is also a great deficit of information on the richness of nutraceuticals in wild species.

Researchers from Michigan University [4] evaluated 2500 *F. virginiana* clones and 6000 *F. chiloensis* clones collected in California, the Pacific coast of North America and Chile. Among them, 38 elite parents were identified, and used to synthesized populations of *F.* x *ananassa*. If this germplasm were available, it could be characterized and used to deal with the global problems mentioned. If no sources of resistance are found for all the problems mentioned, the collection of octoploid species should be expanded. The populations of *F. chiloensis* from Alaska, whose genotypes

*The Genetic Diversity of Strawberry Species, the Underutilized Gene Pool and the Need… DOI: http://dx.doi.org/10.5772/intechopen.102962*

withstand temperatures of −10°C and whose usefulness for that purpose was mentioned last century [11].

Little documented is the gene pool in species other than the octoploid level. There are likely valuable genes of economic importance that do not exist in octoploid species, that are currently underutilized, and that could contribute to solve emerging problems in the strawberry industry. As an example, the immunity reported to *Xanthomonas fragariae*, in *F. moschata* [102], and also, about the resistance in *F. pentaphylla* [101], and *F. vesca* [102], for the probable tolerance to *Drosophila suzukii* in *F. vesca* [17], to name just a few cases already published.

Under the above-mentioned needs, it is important to continue with the germplasm collections of Asian species [108, 151] since, to date, it is the region with the highest number of reported species, where all levels of ploidy are found, except the hexa and, octoploids. Due to the contrasting environments where they are found, and the molecular genetic diversity existing in regions such as Tibet [152]; the presence of genes for resistance to low temperatures is potentially suspected, and certain indications reinforce this hypothesis. Luo et al. [153] demonstrated the possibility of transferring resistance at low temperatures from a wild pentaploid parent from China. It is also possible that, in Chinese species, there is resistance to moisture deficits and excesses, and resistance to foliar diseases [102, 108]. Tetraploid species are particularly interesting and hypothetically important, since if there were genes for outstanding traits absent in the octoploids [154], their transfer to these in some evolutionarily related species would be relatively less genetically complicated [138]. There is a lack of knowledge of the degree of genetic affinity between the five tetraploid and octoploid species, for the use of the possible genetic richness of the tetraploids at the octoploid level. Classic breeding methods for crosses between species of the same and different ploidy levels have been widely described [11, 74, 75, 137, 139], and they should be surely complemented with recently developed biotechnological techniques [155].
