The founding genetic base of the commercial strawberry, Fragaria ×ananassa Duchesne in Lamarck, is limited. It originated ≈250 years ago when a few clones of South American F. chiloensis chiloensis (L.) Miller subsp. chiloensis forma chiloensis and North American F. virginiana Miller subsp. virginiana accidentally hybridized in European gardens (Darrow, 1966). The systematic breeding of strawberries was started in England in 1817 by Thomas A. Knight using only a small number of native and cultivated clones. North American genetic improvement was initiated in the mid-1800s with a restricted group of European F. ×ananassa cultivars, South American F. chiloensis, and North American F. virginiana genotypes. This germplasm base played the predominant role in public and private breeding programs for the next 100 years.
Although impressive breeding progress was made using this narrow germplasm base, other horticulturally useful genes are likely available in native populations of Fragaria, because both octoploid species have extensive geographical ranges that encompass a broad range of biotic and abiotic stresses (Hancock et al., 2004; Staudt, 1999). Contained within the wild germplasm is a wide range of interesting flavors and aromas, unusual resistance to heat, drought and salinity, almost a continuum of photoperiod sensitivities, and tolerance to a wide variety of diseases and pests (Hancock, 1999; Hancock et al., 1990; Luby et al., 1991).
To date, almost all the novel native genes that have been incorporated into cultivated material have come through back-crossing (Hancock, 1999; Hancock et al., 1993a). At least eight wild clones have been introgressed into F. ×ananassa since the 1920s (Sjulin and Dale, 1987) bringing in such traits as day-neutrality, red stele and strawberry aphid resistance, drought and salinity tolerance, and winter-hardiness (Barritt and Shanks, 1980; Bringhurst and Voth, 1984; Daubeny, 1990; Galletta et al., 1989).
Back-crossing from wild genotypes has allowed for the rapid incorporation of a few genes into the genetic background of F. ×ananassa. However, only a limited number of native clones have been used in this manner, leaving much genetic diversity untapped. Also, potentially useful diversity at non-selected genes has likely been lost when back-crossing and tightly linked deleterious genes can be carried into late generations. These two disadvantages are compounded when only a single non-selected native clone is used rather than a group of elite selections from a broad screen of native material.
An alternate strategy for germplasm enhancement would be to pre-select native clones of F. virginiana and F. chiloensis for a wide range of horticulturally important characteristics and then reconstruct F. ×ananassa by hybridizing superior clones of each. Hancock et al. (1993a) suggested a multiple stage process of reconstruction (Fig. 1): 1) select elite clones of F. chiloensis and F. virginiana from published reports and personal experience; 2) intercross the elite selections within species and select the superior progeny; 3) intercross these elite selections again within species and select the most promising genotypes; 4) reconstruct F. ×ananassa by making interspecies crosses among the elites of F. virginiana and F. chiloensis; and 5) select superior genotypes of reconstructed F. ×ananassa that can be used in further breeding and/or varietal release.
There are several advantages to using the reconstruction approach. The most obvious is that genetic diversity will be greatly expanded within the F. ×ananassa gene pool. This will not only afford breeders with an expanded germplasm base, but unique epistatic interactions might appear that are of horticultural use. If sufficiently large populations of native material are screened, a breeder should be able to select for a wide group of positive characteristics with the minimum level of deleterious combinations. This method may also produce higher levels of genetic heterozygosity than conventional back-crossing methods, because the starting material will be more diverse than the typical breeding populations.
Of course, there are several potential disadvantages to the “reconstruction” approach. When a high number of traits are being selected simultaneously, numerous linked genes with negative impacts are often carried in the breeding population (Galletta et al., 1989). In back-crossing strategies, deleterious associations are less of a problem, simply because fewer genes are being selected. However, F. chiloensis and F. virginiana have been interbred on numerous occasions without any reports of chromosomal, physiological, or morphological abnormalities (Darrow, 1966, Luby et al., 2008). The existence of separate sexes in the wild species (dioecy) might also present a problem, although sex can be controlled through the selection of hermaphroditic parents or by incorporating the trait in later stages when existing hermaphroditic F. ×ananassa are used. The genetics of sex in the octoploid strawberries is regulated by a single locus or closely linked ones in which female is dominant to hermaphrodite, which is dominant to male (Ahmadi and Bringhurst, 1991; Spigler et al., 2008).
We recently undertook a study to test how well native clones of F. chiloensis and F. virginiana combine genetically. We intercrossed 15 genotypes of the two species that had high vigor, good yields, and resistance to common foliar diseases as well as large, attractive fruit that were unusually firm for wild clones (Luby et al., 2008). The progeny were planted in Minnesota and Ontario and evaluated for disease resistance, winter-hardiness, spring bloom date, fruit set, seed set, fruit size, and photoperiod sensitivity. We found that substantial breeding progress could be made by reconstructing F. ×ananassa if care is taken to select elite, complimentary genotypes of F. virginiana and F. chiloensis.
We report on another reconstruction effort that differed from the previous effort in two major ways: 1) we used a broader germplasm base that included elite clones of Chilean germplasm that were horticulturally superior to the F. chiloensis previously studied; and 2) we performed a round of improvement within species before making the interspecific crosses to maximize levels of genetic diversity. We did not sib the best performing interspecies F1 hybrids as previously suggested in Hancock et al. (1993a), because we felt few deleterious genes would actually segregate out in a single generation of inbreeding an octoploid. This approach yielded superior reconstructed F. ×ananassa with very broad adaptations, high yields, excellent fruit quality, and near commercial-sized fruit.
Barritt, B.H. & Shanks C.H. Jr 1980 Breeding strawberries for resistance to the aphids Chaetosiphon fragaefolii and C. thomasi HortScience 15 287 288
Bringhurst, R.S. & Voth, V. 1978 Origin and evolutionary potentiality of the day-neutral trait in octoploid Fragaria Genetics 90 510
Cameron, J.S. , Sjulin, T.M. , Shanks, C.H. & Muñoz, C.E. 1991 Collection of Fragaria chiloensis in central and southern Chile 108 118 Dale A. & Luby J. The strawberry into the 21st century Timber Press, Inc Portland, OR
Carrasco, B. , Hancock, J.F. , Beaudry, R.M. & Retamales, J.B. 2005 Chemical composition and inheritance patterns of aroma in Fragaria ×ananassa and F. virginiana progenies HortScience 40 1649 1650
Crock, J.E. , Shanks, C.H. & Barritt, B.H. 1982 Resistance in Fragaria chiloensis and F. ×ananassa to the aphids Chaetosiphon fragaefolii and C. thomasi HortScience 17 959 960
Doss, R.P. & Shanks, C.H. 1987 The influence of leaf pubescence on the resistance of selected clones of beach strawberry [Fragaria chiloensis (L.) Duchesne] to adult black vine weevils (Otiorhynchus sulcatus F.) Sci. Hort. 34 47 54
Galletta, G.J. , Draper, A.D. & Maas, J.L. 1989 Combining disease resistance, plant adaptation and fruit quality in breeding short day and day-neutral strawberries Acta Hort. 265 43 51
Gambardella, M. , Cadavid, A. , Díaz, V. & Pertuzé, R. 2005 Molecular and morphological characterization of wild and cultivated native Fragaria in southern Chile HortScience 40 1640 1641
Hancock, J.F. & Bringhurst, R.S. 1979 Ecological differentiation in perennial, octoploid species of Fragaria Amer. J. Bot. 66 367 375
Hancock, J.F. & Bringhurst, R.S. 1989 Yield component interactions in wild populations of California Fragaria HortScience 23 889 891
Hancock, J.F. , Callow, P.W. , Dale, A. , Luby, J.J. , Finn, C.E. , Hokanson, S.C. & Hummer, K.E. 2001a From the Andes to the Rockies: Native strawberry collection and utilization HortScience 36 221 225
Hancock, J.F. , Callow, P.W. , Serçe, S. & Schilder, A.M.C. 2001b Relative performance of strawberry cultivars and native hybrids on fumigated and nonfumigated soil in Michigan HortScience 36 136 138
Hancock, J.F. , Finn, C.E. , Hokanson, S.C. , Luby, J.J. , Goulart, B.L. , Demchak, K. , Callow, P.W. , Serçe, S. , Schilder, A.M.C. & Hummer, K.E. 2001c A multistate comparison of native octoploid strawberries from North and South America J. Amer. Soc. Hort. Sci. 126 579 586
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Hancock, J.F. Finn, C.E. Hokanson, S.C. Luby, J.J. Goulart, B.L. Demchak, K. Callow, P.W. Serçe, S. Schilder, A.M.C. Hummer, K.E. 2001c A multistate comparison of native octoploid strawberries from North and South AmericaJ. Amer. Soc. Hort. Sci. 126 579 586
Hancock, J.F. , Callow, P.W. , Serçe, S. & Son, P.Q. 2003 Variation in the horticultural characteristics of native Fragaria virginiana and F. chiloensis from North and South America J. Amer. Soc. Hort. Sci. 128 201 208
Hancock, J.F. , Harrison, R.E. , Luby, J.J. & Hancock, J.F. 1993b Morphological variation in Fragaria virginiana from the Rocky Mountains Acta Hort. 348 94 101
Hancock, J.F. , Maas, J.L. , Shanks, C.H. , Breen, P.J. & Luby, J.J. 1990 Strawberries 489 546 Moore J.N. & Ballington J.R. Genetic resources in temperate fruit and nut crop Internat. Soc. Hort. Sci Wageningen, The Netherlands
Hancock, J.F. , Serçe, S. , Portman, C.M. , Callow, P.W. & Luby, J.J. 2004 Taxonomic variation among North and South American subspecies of Fragaria virginiana Miller and F. chiloensis (L) Miller Can. J. Bot. 82 1632 1644
Hokanson, K.E. , Harrison, R.E. , Luby, J.J. & Hancock, J.F. 1993 Morphological variation in Fragaria virginiana from the Rocky Mountains Acta Hort. 348 63 68
Lavín, A. 1997. Caracterización botánica, fisiológica y agronómica de ecotipos chilenos de Fragaria chiloensis (L.) Duch., recolectados en las X and XI regiones de Chile. Informe final. Proyecto Fondecyt 1940083 (1996). Centro Experimental Cauquenes (INIA).
Lavín, A. , Barrera, C. , Retamales, J.B. & Maureira, M. 2005 Morphological and phenological characterization of 52 accessions of Fragaria chiloensis (L.) Duch HortScience 40 1637 1639
Lewers, K.S. , Turechek, W.W. , Hokanson, S.C. , Maas, J.L. , Hancock, J.F. , Serçe, S. & Smith, B.J. 2007 Evaluation of elite native strawberry germplasm for resistance to anthracnose crown rot disease caused by Colletotrichum species J. Amer. Soc. Hort. Sci. 132 842 849
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Lewers, K.S. Turechek, W.W. Hokanson, S.C. Maas, J.L. Hancock, J.F. Serçe, S. Smith, B.J. 2007 Evaluation of elite native strawberry germplasm for resistance to anthracnose crown rot disease caused byJ. Amer. Soc. Hort. Sci. Colletotrichumspecies 132 842 849
Luby, J.J. , Dale, A. , Hancock, J.F. & Serçe, S. 2008 Reconstructing Fragaria ×ananassa utilizing wild F. virginiana and F. chiloensis: Inheritance of winter injury, photoperiod sensitivity, fruit size, gender, female fertility and disease resistance in hybrid progenies Euphytica 163 57 65
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Luby, J.J. Dale, A. Hancock, J.F. Serçe, S. 2008 ReconstructingEuphytica Fragaria× ananassautilizing wild F. virginianaand F. chiloensis: Inheritance of winter injury, photoperiod sensitivity, fruit size, gender, female fertility and disease resistance in hybrid progenies 163 57 65
Luby, J.J. , Hancock, J.F. & Ballington, J.R. 1992 Collection of native strawberry (Fragaria ssp.) germplasm in the Pacific Northwest and Northern Rocky Mountains of the USA HortScience 27 12 17
Luby, J.J. , Hancock, J.F. & Cameron, S. 1991 Expansion of the strawberry germplasm base in North America 66 75 Dale A. & Luby J.J. The strawberry into the 21st century Timber Press Portland, OR
Nishizawa, T. , Nagasawa, S. , Mori, Y. , Kondo, Y. , Sasaki, Y. , Retamales, J.B. & Lavín, A. 2005 Characteristics of soluble sugar accumulation in commercially grown Fragaria chiloensis HortScience 40 1647 1648
Pinkerton, J. & Finn, C.E. 2005 Responses of strawberry species and cultivars to the root- lesion and northern root-knot nematodes HortScience 40 33 38
Sakin, M. , Hancock, J.F. & Luby, J.J. 1997 Identifying new sources of genes that determine cyclic flowering in Rocky Mountain populations of Fragaria virginiana ssp. glauca Staudt J. Amer. Soc. Hort. Sci. 122 205 210
Scott, D.H. 1959 Size, firmness and time of ripening of fruit of seedlings of Fragaria virginiana Duch. crossed with cultivated strawberry varieties Proc. Amer. Soc. Hort. Sci. 74 388 393
Scott, D.H. & Lawrence, F.J. 1975 Strawberries 71 97 Janick J. & Moore J.N. Advances in fruit breeding Purdue University Press West Lafayette, IN
Serçe, S. & Hancock, J.F. 2005a The temperature and photoperiod regulation of flowering in Fragaria chiloensis, F virginiana, and F ×ananassa genotypes Sci. Hort. 103 167 177
Serçe, S. & Hancock, J.F. 2005b Inheritance of day-neutrality in octoploid species of Fragaria J. Amer. Soc. Hort. Sci. 130 580 584
Serçe, S. , Callow, P.W. , Ho, J.J. & Hancock, J.F. 2002 High temperature effects on CO2 assimilation rate in genotypes of Fragaria ×ananassa, F chiloensis and F virginiana J. Amer. Pomol. Soc. 56 57 62
Shanks, C.H. & Moore, P.P. 1995 Resistance to two-spotted spider mite and strawberry aphid in Fragaria chiloensis, F. virginiana, and F. ×ananassa clones HortScience 30 596 599
Shanks, C.H. , Chandler, C.K. , Show, E.D. & Moore, P.P. 1995 Fragaria resistance to spider mites at three locations in the United States HortScience 30 1068 1069
Shanks C.H. Jr , Chase, D.L. & Chamberlain, J.D. 1984 Resistance of clones of wild strawberry, Fragaria chiloensis, to adult Otiorhynchus sulcatus and O. ovatus (Coleoptera: Curculionidae) Environ. Entomol. 13 1042 1045
Spigler, R.B. , Lewers, K.S. , Main, D.S. & Ashman, T.-L. 2008 Genetic mapping of sex determination in a wild strawberry, Fragaria virginiana reveals earliest form of sex chromosome Heredity 101 507 517
Stahler, M.M. , Ascher, P.D. , Luby, J.J. & Roelfs, A.P. 1995 Sexual composition of populations of Fragaria virginiana (Rosaceae) collected in Minnesota and western Wisconsin Can. J. Bot. 73 1457 1463
Staudt, G. 1999 Systematics and geographic distribution of the American strawberry species: Taxonomic studies in the genus Fragaria (Rosaceae: Potentilleae) University of California Press Berkeley, CA