Somaclonal variation among Ex vitro Thornless Evergreen trailing blackberries

'Thornless Evergreen' (TE) blackberry (Rubus laciniatus Willd.) is a periclinal chimera in which the epidermis has mutated to thornlessness (designated 't'), while the internal portions of the plant remain genetically thorny (tTT). Over 300 ex vitro plants (from shoot tip cultures of TE) were established in the field and observed over two fruiting seasons for various vegetative traits and fruiting characteristics. Both parental types and variants were included in the field plantings. Plants were evaluated for growth habit, vigor, flowering, and fruiting traits. Continuous variation for growth habit, vigor, flower number, and fertility was observed. Some of the variation could be explained in terms of chimeral segregation (pure thornless vs. chimeral types). Tissue culture-induced (somaclonal) variation was assumed to be the source of most of the other variation.