Narcissus and Daffodil

106 G.R. Hanks
and cross-cutting, standard techniques used with hyacinth bulbs, gave poor results
with narcissus (Stone, 1973; Stone et al., 1975), and leaf cuttings were unsuccessful
(Alkema, 1971b). Twin-scaling and chipping were, however, successfully adapted
to narcissus from methods used with other Amaryllidaceae in which the bulb is cut
into a number of segments and the segments divided into single or paired scale
pieces each with a piece of the base plate attached (Luyten, 1935; Traub, 1935;
Everett, 1954). Only a small percentage of single scale pieces, but over 80% of
paired scales, produced bulblets (Alkema, 1970, 1971a, 1975; Broertjes and
Alkema, 1971). These bulb division methods rely on the destruction of the apical
dominance of the existing buds, resulting in adventitious bud formation on the
proximal part of the bulb scale adjacent to the base plate (Hussey, 1975; Grootaarts
et al., 1981).
In ‘twin-scaling’, flowering-size bulbs are cut into a number of longitudinal
segments (often 8 or 16), each with a wedge-shaped piece of base plate; these
segments are further divided by cutting off the scales in pairs, each with a conjoining
piece of base plate, and 60 to 100 twin-scales can be cut from one large bulb.
These pieces are incubated in a moist medium (usually damp vermiculite) for 3
months at 20 °C, when bulblets develop, usually one per ‘twin-scale’ (Alkema,
1970, 1975; Alkema and van Leeuwen, 1977). Typically, 80–90% of twin-scales
from bulblets, and a small percentage rots. When grown-on, the bulblets flower in
their third or fourth year (Mowat, 1980b). This method was used to multiply VT
narcissus stocks in Scotland (Sutton and Wilson, 1987). Testing a wide range of
cultivars, Fry (1978) found that one bulb could be multiplied to between seven and
41 flowering-size bulbs in 4 years, compared with six by natural increase. Practical
accounts of twin-scaling include those of Flint and Hanks (1982) and Hanks and
Phillips (1982).
While twin-scaling is a simple technique, it is time-consuming and the
propagules are small and delicate. More robust propagules can be obtained by
only partly dividing the original bulb segments, giving pieces with a few scales
each (Everett, 1954; Stone, 1973), or by leaving the original 8–16 segments intact,
the method known as ‘chipping’ (Flint, 1982) (Figure 4.10). Several practical
accounts of chipping are available (e.g., Flint, 1984; Vreeburg, 1984a, 1986;
ADAS, 1985c; Hanks, 1989). As well as being used for on-farm multiplication of
select stocks and cultivars, chipping produces attractive round bulbs ideal for sale
in ‘pre-packs’ and with potential for improving predictability, uniformity and
mechanised handling (Vreeburg and van der Weijden, 1987a; Hanks, 1989). The
method has been used extensively with the popular dwarf cultivar ‘Tête-à-Tête’
(Vreeburg and van der Weijden, 1987a), where 14 to 71% of bulblets flowered in
their second year, and it is also successful with several Narcissus species (Hanks,
1987). Although earlier projections of multiplication rates now appear unduly
optimistic, multiplication rates of 3- or 4-fold per annum (6.5 or 5 years from one
to 1000 bulbs) seem realistic (Hanks and Rees, 1979; Hanks, 1993).
The factors affecting the productivity of twin-scaling and chipping have been
reviewed by Hanks and Rees (1979) and Hanks (1993). In the following account,
only the more important effects will be mentioned. It is generally recommended
that bulbs for chipping should receive HWT about a week before cutting, which
improves results and controls bulb scale mites (Vreeburg and van der Weijden,
1987a), but HWT immediately before chipping is harmful. Although twin-scales