Narrative
The present invention relates to a new and distinct trailing thornless blackberry cultivar named `Everthornless`. The `Everthornless` blackberry cultivar, and ex vitro somaclonal variant of the `Thornless Evergreen` cultivar of Rubus laciniatus willd., has good fruit yield, has a late ripening season and produces thornless, not thorny, shoots from its roots. The `Thornless Evergreen` is a periclinal chimera with a mutated thornless epidermal layer that encompasses internal cells which retain the genetic potential to produce thorns (technically, blackberry thorns are actually prickles that arise from epidermal tissue). As long as this periclinal arrangement is maintained, the plant stays thornless. However, any shoots arising from the internal tissue of a thorny genotype will be thorny and its gametes carry the thorny gene. Since blackberry roots develop from the thorny, internal parts of the stem, shoots coming from parental-type roots will always have thorns. Thorny canes interfere with cultural operations and harvest and may warrant abandonment of a planting. The `Thornless Evergreen` cultivar of Rubus laciniatus Willd., was introduced into shoot tip culture from virus-free plants. Shoot tips were proliferated and rooted in modified Murashige and Skoog plant tissue culture medium. These long-term cultures were used as research material for a project designed to identify an ex vitro nonchimeral thornless selection of `Thornless Evergreen`. Ex vitro plants of `Thornless Evergreen` were examined for trueness to the original type. Adventitious buds from root segments were used to screen for presence of the thornless mutation in internal tissues. First-test field trial plantings were established in Urbana and Dixon Springs, Ill. and growth, flowering, and fruit set were monitored. Vegetative propagules of selections from Illinois first-test field trials were sent to Oregon State University, North Williamette Experiment Station, Aurora, Oreg. for second-test field trials. From the second-test field trial, one somaclonal variant (a nonchimeral thornless plant) of `Thornless Evergreen` was selected based on its growth and fruitfulness. This selection is named `Everthornless`. The `Everthornless` produces thornless advantitious shoots from roots and is compact (primocanes which are less than 3 meters in length compared to `Thornless Evergreen` primocanes which are greater than 9 meters), which make it more suitable for the conventional trellising system of culture. Besides the shorter primocane length in the "Everthornless" cultivar, there are many other distinguishing features of the "Everthornless" cultivar relative to the parent "Thornless Evergreen" cultivar. Unlike the parent plant, the "Everthornless" cultivar produces thornless and not thorny shoots from its roots. In addition, the petioles of the "Everthornless" cultivar are quit different from the petioles of the parent "Thornless Evergreen". The petioles of the "Everthornless" cultivar are bent, a trait not found in the "Thornless Evergreen". Moreover, the "Thornless Evergreen" has clasping petioles that encircle the stem, while the petioles of the "Everthornless" have a swollen base, without the clasping petioles.