Submitted to: International Strawberry Symposium
Publication Type: Abstract Only
Publication Acceptance Date: August 31, 2011
Publication Date: N/A
Interpretive Summary: The strawberry has a base chromosome number of 7 with economically important species having 2-sets, 6-sets, 8-sets or artificially produced 10-sets of chromosomes. Since early in the 18th century, when American strawberries were first introduced into Europe, differences in the numbers of chromosomes were recognized as a problem for making crosses with strawberry species. During the past several decades, breeders have expanded the parents that they use for crosses by incorporating selected wild species into their crossing plans. While most of the world species has known numbers of chromosomes, collections from the wild are revealing unexpected numbers. Sometimes strawberries do not separated their chromosomes properly and a double dose of chromosomes may remain in an egg or pollen cell. This paper reviews reports of wild collected plants from California and Oregon, where this situation has occurred. Researchers should be aware of unexpected numbers of chromosomes in potential parents of their crosses. Otherwise some loss of viability in the offspring could result. The identification of wild sources of strawberries with ten sets of chromosomes could expand the parents for cultivation of strawberries with ten sets of chromosomes.
Technical Abstract: 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), or artificially developed decaploid (F. ×vescana Rud. Bauer & A. Bauer) cultivars. 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 ploidy has been reported for world 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 introgression of sympatric Fragaria species, despite widely disparate ploidy levels, is not trivial. This paper reviews reports of wild triploid, pentaploid, hexaploid, eneaploid, and decaploid cytotypes from California and Oregon, where sympatric Fragaria species occur. Researchers should be aware of unexpected ploidy levels in potential parental resources which could reduce fecundity in subsequent selection generations. The identification of multiple wild decaploid sources could establish foundation germplasm for a new class of cultivated strawberries.