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Single-node cuttings of potato cultivars 'Jemseg', 'Katahdin', 'Russet Burbank' and 'Superior' were cultured on a multiplication medium containing MS salts and no growth regulators. Cultures were exposed to 8 h (SD) and 16 h (LD) photoperiodic regimes. The subsequent plantlets were excised and single node cuttings from each photoperiodic regime were placed under SD or LD on a second medium containing growth regulators which promoted tuberization. Production of microtubers was strongly influenced by genotype and by photoperiodic treatments. 'Superior' produced stunted plantlets and some microtubers under SD conditions in the multiplication medium. The number of microtubers formed by 'Jemseg' was not influenced by photoperiod. However, 'Katahdin' and 'Russet Burbank' formed fewer microtubers under LD-LD conditions compared to LD-SD, SD-SD and SD-LD regimes. Compared with the other regimes, LD-SD photoperiod generally promoted microtuber formation with larger diameters and significantly (p < 0.05) greater fresh weight. The intensity of the tuberization stimulus was affected by daylength, and this was characterized by microtubers with secondary tubers, the growth of more than one axillary microtuber, and microtubers subtended by stolons. The maturity group of the potato cultivars and photoperiodic regime in vitro strongly influenced the production of microtubers. These results can be employed to adapt light regimes for multiplication and tuberization to the specific requirements for cultivars from different maturity groups, and thus increase the efficiency of potato multiplication protocols.

A new technique is reported here for the rapid propagation of Narcissus cultivars involving the induction of shoot and root apices from small pieces of leaf base tissue, inverted scape sections, and from ovaries, in axenic culture. Shoot and root apices were obtained on the above explants of all nine Narcissus cultivars tested. The optimal medium contained modified Murashige and Skoog (1962) inorganic salts, the organic constituents recommended by Ziv et al. (1970), and higher-than-normal growth regulator levels. Proliferating shoot apices were induced on a medium containing 4.4 × 10−5 M (10 mg/litre) 6-benzylaminopurine (BAP) and 5.3 × 10−6 M (1 mg/litre) naphthaleneacetic acid (NAA). Plantlets grew optimally if transferred to a medium containing 9.0 × 10−6 M (2 mg/litre) BAP and 2.0 × 10−7 M (2 mg/litre) NAA. The induction of roots on plantlets grown in vitro required a half-strength salt and sucrose solution without growth regulators.In 5 months, 2620 plantlets were produced from two leaf base explants. This technique is considerably more efficient than any known conventional methods of propagating Narcissus.Root apices were optimally produced on a medium containing 2.0 × 10−6 (0.5 mg/litre) to 2.0 × 10−5 M (4 mg/litre) BAP and 1.0 × 10−4 (20 mg/litre) to 2.0 × 10−5 (4 mg/litre) NAA. Callus was induced on leaf base explants, inverted scape sections, and on ovaries; the ovary expiants required the highest levels of auxin for the induction of callus and were most responsive. Thus, the levels of growth regulators required to induce a response in vitro are higher than so far reported for plants that have been propagated by tissue culture.Although the levels of various growth regulators used were found to be important in obtaining apices, the relative ratio of cytokinin to auxin was also found to be critical. Although considerable differences in clonal responsiveness were noted, cultures were obtained from all nine Narcissus cultivars tested.The induction of adventitious meristems of leaf base explants is a particularly promising method for the propagation of virus-free material and for the rapid propagation of valuable horticultural material.

A protocol is presented for the rapid induction of microtubers on micropropagated, layered potato shoots of 'Kennebec', 'Russet Burbank' and 'Superior' in medium devoid of growth regulators. Layered shoots microtuberized more rapidly and produced significantly larger microtubers compared with nodal cuttings. The addition of coumarin or (2-chloroethyl)-tfimethylammonium chloride and benzyladenine to microtuberization medium, either had no effect or significantly reduced microtuber weight per shoots compared with medium containing only 80 g x 1-1 sucrose and minimally affected the number of microtubers per shoot. Increasing the incubation period from 28 to 56 days did not affect the number but significantly increased the weight of microtubers per shoot and substantially increased the proportion, up to 20%, of microtubers heavier than 1 gram.Abbreviations: Ba -benzyladenine, ccc -(2-chloroethyl) trimethylammonium chloride, coumarin -2h-1-benzopyran-2-one, ga3 -gibberellic acid