Submitted to: HortScience
Publication Type: Abstract Only
Publication Acceptance Date: March 1, 2008
Publication Date: July 21, 2008
Citation: Hummer, K.E., Bassil, N.V. 2008. Unexpected Polyploidy in Wild Asian Strawberries [abstract]. HortScience. 43(4):1187. Interpretive Summary: Wild species of the strawberry have multiple chromosome sets. Some species have the normal double set, some have four, five, six, or 8 sets. Plants can be artificially crossed to have 5, 8, or 10 sets. High numbers of chromosomes probably arose through a unification of gametes. Scientists have seen large pollen grains in the Alpine and hybrid cultivar species. Strawberry species can sometimes cross with other species that grow in their same native habitat. East Asia has been suggested as the origin for some strawberry species, and of a hypothetical ancestor that may have given rise to the North American species. To date, only one species with 8 sets of chromosomes has been reported in Asia. Species with two sets of chromosomes have been reported on Hokkaido, Sakhalin, and the Kurile Islands. In recent USDA sponsored plant exploration trips to continental Siberia, Hokkaido, and the Kurile Islands, plants that seemed to have higher numbers of chromosmes were collected. The objective of this study was to determine if these plants had higher numbers of chromosome sets. Standards of wild specimens and the unknowns were analyzed by machine. Some specimens from eastern Iturup and Southern Sakhalin had unexpectedly high amounts of chromosomes. These may be escapes of the hybrid cultivated strawberry. A seedling from eastern Hokkaido also had 8 sets of chromosomes, but the plant seems wild and not cultivated. Samples of the Asian species with 8 sets, collected on the flank of Asunupuri Volcano on Iturup Island had a higher than the expected amount of DNA. Further analysis will be performed by microscopic counts to confirm these results.
Technical Abstract: The strawberry genus, Fragaria, has a haploid chromosome number of x = 7 and multiple ploidy levels in wild species, which include diploid (2x = 2n = 14), tetraploid (2x = 4n =28), pentaploid (2x = 5n = 35), hexaploid (2x = 6n = 42), and octoploid (2x = 8n = 56) plants. Artificial pentaploids, octoploids and decaploids (2x = 10n =70) have been reported. Polyploidy probably arose through unification of 2n gametes. Unreduced gametes, observed as large pollen grains, are reported in F. vesca, L. and F. x ananassa, nothosubsp. ananassa. Introgression of conspecific species has been noted on several continents. East Asia has been suggested as a center of origin for diploid species, and of a hypothetical octoploid ancestor, which gave rise to the North American octoploids. To date, while tetraploids occur in China and continental Eastern Russia (Siberia), one octoploid species, F. iturupensis, Staudt, has been reported in Asia. Diploid species F. iinumae, Makino and F. nipponica Makino have been reported on Hokkaido, Sakhalin, and the Kurile Islands. In recent USDA sponsored plant exploration trips to continental Siberia, Hokkaido, and the Kurile Islands, plants with morphologies that suggest polyploidy were collected. To determine ploidy levels, leaves of species standards, and of wild specimens were analyzed with flow cytometry. DNA ratios of standards of diploid, tetraploid, hexaploid, octoploid and decaploid species were obtained. Octoploid ratios were observed on undetermined species from eastern Iturup and Southern Sakhalin. These may be escapes of the hybrid cultivated strawberry. A seedling from eastern Hokkaido also tested octoploid but resembles species material. Samples of F. iturupensis, collected on the flank of Asunupuri Volcano had higher amounts of DNA than the expected octoploid. This species might have larger than usual chromosomes. Further analysis will be performed by chromosome counts to confirm these results.