Narcissus and Daffodil

102 G.R. Hanks
using thiabendazole alone. Nematode levels in soils can be reduced by growing
Tagetes and other species. In experiments in soils inoculated with Pratylenchus penetrans
or Trichodorid nematodes, the population of P. penetrans was reduced by
planting Tagetes patula, and bulb yield in a subsequent narcissus crop was
increased (Conijn, 1994).
BREEDING AND PROPAGATION
Breeding Narcissus cultivars
Fernandes (1967) defined two sub-genera within Narcissus, Hermione with a base
haploid number of chromosomes of 5 (or 10 or 11), and Narcissus with 7 (or 13),
and crosses between the sub-genera result in a range of chromosome numbers.
Brandham (1986, 1992; see also Kington, 1998, p.12) and Brandham and Kirton
(1987) have made extensive studies of the cytogenetics of narcissus: diploid, triploid
and tetraploid cultivars are common, with high ploidy levels in some species
(e.g., N. bulbocodium is hexaploid). Brandham (1992) tabulated data for 731 cultivars.
Most narcissus cultivars, interpreted as the optimum level of horticultural
fitness, were tetraploids (2n = 28) (Brandham and West, 1993). Other cytogenetic
studies of narcissus include those of Kalihaloo (1987), Kalihaloo and Koul (1989)
and Gonzalez-Aguilera et al. (1988).
The bulk of narcissus breeding has been carried out by enthusiasts with the
show-bench in mind, for example, in Northern Ireland, the USA, New Zealand
and Australia. Commercial bulb growers identify new cultivars that may have the
right characteristics for commercial exploitation, such as high rates of bulb and
flower production. De Hertogh and Kamp (1986) and De Hertogh (1990) listed
the desirable characters for commercial cultivars, such as sturdy stems and leaves,
reliable bud opening, long-lasting flowers, fragrance, tolerance or resistance to
diseases, and critical weights for floral initiation such that a double-nosed bulb will
reliably produce two flowers. In some cases, breeding programs may have more
specific aims. In the UK, there have been breeding programs aimed at producing
yellow trumpet and large-cup flowers similar to ‘Golden Harvest’ or ‘Carlton’ but
with relative resistance to base rot derived from ‘St. Keverne’. One programme,
concentrating on the production of early field-grown flowers, has already resulted
in several cultivars being commercialised (Pollock, 1989). In another programme
investigating the genetic basis of resistance to base rot (Bowes, 1992), new cultivars
are presently under evaluation (Bowes et al., 1996). The latter programme exploits
the absolute resistance to base rot found in species such as Narcissus jonquilla
(Linfield, 1986a, 1990, 1992a,b), rather than the relative (or field) resistance of
commercial cultivars such as ‘St. Keverne’ (Tompsett, 1986). Breeding for resistance
to base rot is hampered by the difficulties in screening seedling bulbs because of
the development of adult plant resistance (Linfield and Price, 1986). Breeding for
resistance to base rot currently utilizes a lengthy screening method that requires
large numbers of clonal two-year-old bulbs (Bowes et al., 1992). An in vitro assay
using bulb scales is showing promise as a much faster alternative (J.H. Carder,
personal communication). Narcissus pollen can be stored long-term in liquid nitrogen
(Bowes, 1990).