Regeneration and evaluation of first and second cycle somaclones of 'Thornless Evergreen' blackberry (Rubus laciniatus) Willd.)

A reliable in vitro regeneration system was developed for 'Thornless Evergreen' (TE) blackberry (Rubus laciniatus Willd.) using thidiazuron (TDZ) and naphthaleneacetic acid. TDZ was superior to benzylaminopurine (BA) in promoting adventitious shoot formation on in vitro-grown TE leaves. TDZ was active at lower concentrations than BA and stimulated adventitious shoot formation from petioles, while BA did not.After six months' growth in a greenhouse, ex vitro adventitious shoots were evaluated for somaclonal variation in growth habit; number and location of prickles; degree of reflexure of petioles; and degree of stem and petiole twisting. Dwarf plants had fewer prickles, which were confined to the leaf tips, and twisted stems and petioles. Normal plants had greater numbers of prickles, which were present on stems, petioles, and midribs of leaves. Stems and petioles were straight.Greenhouse-grown regenerants were transferred to a field planting. After one year, they were evaluated for growth habit; location and type of prickles on leaves and the base of their canes; and flowering and fruitfulness. Regenerants exhibited continuous variation for all characters measured. However, most plants could be classified as dwarf or normal. Greenhouse classifications accurately predicted field classifications. Normal and dwarf plants had similar numbers of flowers, but normal plants set more fruit, and their fruits were larger.Regenerants from chimeral TE leaves were predominantly dwarf, while those from normal, non-chimeral TE leaves were all normal. Two regenerants from dwarf, non-chimeral TE leaves had a normal growth habit. No regenerants from chimeral TE leaves were thorny. All regenerants from thorny TE leaves were thorny.We concluded that plants regenerating adventitiously from leaves of TE exhibit measurable somaclonal variation for growth habit, thorniness, and fruitfulness. Thornless regenerants are either stable, normal plants with moderately suppressed prickles; or unstable, dwarf plants with highly suppressed prickles. We speculate that the thornless gene is present in differing doses in the two classes of regenerants, possibly as a result of transposable element activity, and that as the prickle suppressing factor increases, it causes increasing malformation of stems and leaves.U of I OnlyETDs are only available to UIUC Users without author permissio