SOMACLONAL VARIATION AMONG EX-VITRO THORNLESS EVERGREEN TRAILING BLACKBERRIES - THE MORPHOLOGICAL STATUS OF SELECTED CLONES AFTER 7 YEARS OF FIELD GROWTH

Chimeral 'Thornless Evergreen' (CTE), (Rubus laciniatus Willd.) somacl ones selected in 1983 and field planted in 1985 were reexamined in 199 2 for various vegetative and reproductive characteristics. Two major t ypes of thornless (prickle-free) plants, intermediate-sized ('UI 6-6' = 'Everthornless') and dwarf ('UI 6-4'), originally selected from a ch imeral thornless parent plant, were compared with thorny plants. The i ntermediate and dwarf somaclones have maintained their distinctive hab its over 7 years' growth in the field, indicating that their growth ha bits are stable and not a transient effect of tissue culture. Although the thornless somaclones remained thornless, the degree and type of p rickle-like structures varies considerably, indicating that the thornl ess gene (S-te) does not entirely suppress the production of prickles, but apparently alters their development. Increasing suppression was d irectly related to increasing dwarfism, suggesting a link between thor nlessness and internode length.