FURTHER EXPERIMENTS ON THE FUSARIUM BULB ROT OF NARCISSUS

Abstract

Summary.1. Experiments on the inoculation of roots of Narcissus with Fusarium bulbigenum in the autumn show that, under suitable conditions of moisture and rather high temperature, the fungus is able to penetrate and destroy the roots of all varieties tested. Under similar suitable conditions it can penetrate bulbs of susceptible varieties via the parasitised roots. It is concluded that temperature conditions in England are seldom favourable to such penetration via the young roots during the autumn.2. Some evidence is given that penetration of the bulbs may take place via the old roots at the end of the growing season when soil temperature is likely to be more favourable to attack. Further work on this point is desirable.3. Gregory's statements that heavy losses from Fusarium may follow the standard hot‐water treatment against bulb eelworm, when carried out in the autumn, and that in such cases penetration usually takes place at the base of the bulb are confirmed and amplified.4. Experiments in which bulbs were hot‐water treated, with the addition of Fusarium spores to the water, at intervals during the storage period, indicate that bulbs pass through, a phase of minimum susceptibility in late August and early September, i.e. at the normal time of bathing.5. It has been shown that, where bulbs are hot‐water treated in the presence of Fusarium spores, the addition of formalin (0.1 per cent. or more) to the water materially reduces the resulting losses.6. A comprehensive series of experiments, with fourteen varieties, has been carried out during four seasons in order to test the effects of the addition of fungicide to the hot‐water bath. These experiments, for reasons which are discussed fully in the text, have not yielded any conclusive evidence on the effect of this treatment on the spread of the disease. It has been amply shown, however, that the incorporation of 0.1‐1.5 per cent. formalin in the bath has no harmful effects on foliage, date of flowering, quality and number of blooms or amount of increase in weight of bulbs during the growing season, but is often beneficial.7. Cold steeps in 0.1 per cent. mercuric chloride solution led to a retardation of the date of flowering.8. It is desirable that fungicidal treatment should take place before the normal date of hot‐water treatment, and experiments are in progress to test the efficacy of various cold steeps and dry dustings carried out in the early part of the storage season.In conclusion the writer wishes to express her thanks to Prof. W. Brown, who suggested this work, for much advice and assistance during its progress. Thanks are also due to Dr A. K. Ghamrawi who carried out some of the observations in the 1931 experiments.