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- Author or Editor: A. G. Otterbacher x
Although strawberry species have existed for an estimated 50 million years (17), and their use by man has been dated to the bronze age (19), only after the 14th century A.D. were strawberry plants gathered from the wild and grown in gardens. These first cultivated strawberry plants were grown for both ornamental and medicinal purposes (11). The strawberries of the past were different from those of today. The fruit was small, plants were not productive, and in many respects were far inferior to the large fruited cultivars that are now grown in many parts of the world.
The discrepancy in seed set observed in reciprocal crosses of red (Rubus idaeus L.) and black (R. occidentals L.) raspberries verifies unilateral incompatibility. The strength of the incompatibility varies between cultivars; some red × black crosses yield a small percentage of seed set by simple cross-pollination, while others produce almost no seed. Although black cultivars have shorter pistils than red cultivars, the role of this factor in incompatibility is unknown. Bud pollination and heat treatments increased seed set in some normally incompatible red × black crosses.
To study the causes of low germinability in dried blackberry seeds, seeds harvested from fresh `Thornless Evergreen' (TE) blackberry (Rubus laciniatus Willd.) were either air-dried (12, 24, 36, 48, 60, 72, 96, or 120 hours) or explanted directly onto growth-regulator-free medium after bleach disinfestation. Seeds were either cut in half before explanting or kept intact. None of the intact seeds germinated. Fewer of the halved seeds dried 12 hours or more germinated than control (fresh moist) seeds (42.7% and 54.5%, respectively). Germination decreased to <12% following >48 hours of air-drying. In a separate study, fresh seeds of TE and `Navaho' were either dried as described or held in sealed petri dishes on moist filter paper (moist treatment) for up to 60 hours. After 60 hours, germination of dried seeds of both cultivars had decreased significantly; there was no significant change in germination percentage for moist seeds. Since moist halved seeds germinated well and dried halved seeds did not, the inability of dried blackberry seeds to germinate is due to more factors than just the hard seedcoat typical of the genus.