NARCISSUS VARIETAL SUSCEPTIBILITY TO FUSARIUM OXYSPORUM (BASAL ROT)

In the UK, the predominance of the cultivars Golden Harvest and Carlton which are both susceptible to attack, together with the traditional practice of two-year-down production are factors increasing the problem.

Breeding of new cultivars began at Rosewarne Experimental Horticulture Station in 1963. The primary initial objectives were earliness and cut flower quality but an additional requirement was basal rot resistance.

Since 1978 a testing system has been applied to a range of Rosewarne raised clones and existing commercial cultivars. This consists of planting healthy bulbs of each stock adjacent to inoculator bulbs - the latter being Fusarium-rotted Golden Harvest bulbs. The test has been carried out annually in the field and data for bulb survival and weight increase recorded.

Average infection rates for Carlton and Golden Harvest were 85 and 83% respectively. The cultivar St Keverne has not been attacked in this test. Dutch Master with 31% infection has shown itself to be intermediate, as it is in commercial experience.

Many Rosewarne raised clones have shown a high level of disease resistance especially when bred from St Keverne, Rijnveld's Early Sensation, Dawley or Malvern City. The cultivar Dutch Master represents the upper limit of Fusarium susceptibility which we consider acceptable for a new cultivar release.

This paper does not attempt to define the nature of basal rot resistance in narcissus or explain the mechanisms involved.

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