K.E. Hummer, P. Nathewet, T. Davis
The strawberry genus Fragaria L. (Rosaceae) has a base chromosome number of x = 7 with economically important diploid (F. vesca L.), hexaploid (F. moschata Weston), octoploid (F. ×ananassa Duchesne ex Rozier) cultivars, and artificially developed decaploids (F. ×vescana Rud. Bauer & A. Bauer). Since early in the 18th century, when American strawberries were first introduced into Europe, ploidy differences were recognized as a significant crossing barrier. During the past several decades, breeders have strategically expanded their parental reference material by incorporating selected wild species to reconstruct the cultivated F. ×ananassa gene pool. While typical ploidies have been reported for the recognized species, collections from the wild are revealing unexpected cytotypes. The occurrence of unreduced gametes in many Fragaria species is not infrequent. Considering evolutionary time, the opportunity for the hybridization of sympatric Fragaria species, despite widely disparate ploidy levels, is not trivial. This paper reviews previous reports of wild triploid, pentaploid, hexaploid and eneaploid cytotypes from California and a new account of decaploid cytotypes from Oregon, where sympatric diploid and octoploid Fragaria species occur. Breeders should be aware of unexpected ploidy levels in potential parental resources, use of which could reduce fecundity in subsequent selection generations. Researchers should consider the potential interbreeding between sympatric species, regardless of ploidy, prior to determining subspecific or forma designations. The identification of multiple wild decaploid sources could establish foundation germplasm for a new class of cultivated strawberries.
Hummer, K.E., Nathewet, P. and Davis, T. (2014). UNUSUAL POLYPLOIDY IN WILD STRAWBERRY SPECIES. Acta Hortic. 1049, 113-123
DOI: 10.17660/ActaHortic.2014.1049.9
Fragaria, genetic resources, germplasm, diploid, octoploid, decaploid

Acta Horticulturae