Narcissus and Daffodil

Production of Narcissus bulbs 63
diseases – stem nematode, bulb rots, foliar diseases and viruses. Bulb stocks should
be obtained in good time to carry out HWT prior to prompt planting, and bulbs
should be properly stored until planting.
In the EU, a ‘Plant Passport’ scheme is in operation for bulb sales within the
‘Single Market’. In the UK, for example, bulb stocks are entered by the grower
with the Plant Health and Seeds Inspectorate (PHSI) of MAFF. Stocks are then
inspected for stem nematode, the only EU quarantine pest of narcissus, in a growing
season inspection (GSI), and a dry bulb inspection (DBI) is carried out after
cleaning and grading bulbs to ensure freedom from soil. Bulbs are eligible for the
grower to issue a plant passport if both inspections are passed; if they are not, it
may be permitted for the bulbs to be sold for retail sales or landscape use only.
Similar arrangements exist in other EU countries. For exporting bulbs to ‘third
countries’ (i.e., outside the EU), plant health inspections and their criteria depend
on the requirements of the importing country: for example, for export to the USA
and Canada, the requirements also include strict freedom from soil on the bulbs,
that bulbs are grown on certified PCN-free land, and that they undergo field
inspections for freedom from other pests and diseases as well as pre-export inspections.
When narcissus bulbs are bought in from a different climate, they may take
some time to become synchronised with local stocks. Abbiss and Craze (1948)
showed that Dutch stocks took at least three years to synchronise with local stocks
in south-west England.
Most ordinary narcissus stocks have widespread virus infection (Stone, 1973;
Brunt, 1980), and VT propagation schemes offer the best opportunity for improving
stocks (Hollings and Stone, 1979). Limited quantities of ‘virus-free’ narcissus
stocks, more properly called virus-tested (VT) or virus-indexed stocks, are available
from nuclear stocks produced from meristem-tip culture or from indexed plants
(Brunt, 1985; Asjes, 1990; Lawson, 1990). VT stocks of narcissus should be grown
in 50 m isolation from ordinary stocks (Broadbent et al., 1962) or in sterilised substrate
in vector-proof fine mesh tunnels (Moore et al., 1979). VT stocks offer the
general advantages of improved vigour. VT bulbs may have lower critical weights
for flowering, and more, larger and brighter flowers (Stone, 1973). VT stocks may
show increased bulb yields of 10–20%, compared with ordinary stocks, as well as
earlier growth (Sutton et al., 1986, 1988). In some trials there was a consistent yield
advantage for VT stocks over ordinary stocks in Cornwall, but not in Lincolnshire,
suggesting that VT stocks were able to take advantage of the different conditions in
Cornwall (Hanks, 1992a). Much greater advantages of VT stocks were reported in
New Zealand by Allen and McIntosh (1994). When growing VT stocks, cultural
practices may have to be adjusted to take account of their greater vigour, e.g., using
lower planting densities. VT stocks of some cultivars are re-infected only slowly by
viruses if grown in isolation (Hanks, 1997).
In the UK, there are three grades of VT certification for narcissus under the
voluntary Plant Health Propagation Scheme: (1) Virus-Tested Mother Stocks are
the highest grade, strictly maintained in vector-proof conditions with zero tolerance
for pests, diseases and off-types; (2) Foundation, field-grown stocks grown
in isolation with low tolerance for pests and diseases (e.g., 0.05% for severe virus
symptoms and 0.5% for mild virus symptoms); and (3) Élite, for which isolation
and tolerances are less exacting (e.g., 2% for severe virus symptoms) (MAFF
Plant Health Division, 1999). Methods for selecting, producing and certifying