Abstract
Immature bulbs were used in two screening trials to identify daffodil genotypes resistant to basal rot disease caused by Fusarium oxysporum f. sp. narcissi. Progenies, having at least one parent with some resistance, were grown in compost infested with chlamydospores of the fungal pathogen, and survivors were recovered at final harvest. Survival rates were very low when one-year old bulbs were used; the greater survival of two-and three-year old bulbs indicates that resistance increased with bulb age. Selection pressure was influenced by inoculum concentration in the compost. Continuous variation of percentage bulb survival between progenies suggests a polygenic mode of inheritance; there was no evidence of maternal inheritance. Parental general combining ability (GCA) was highly significant and accounted for much of the difference in bulb survival between progenies, but non-additive parental effects were also apparent. GCA rankings in the two trials were similar and reflected the resistance of parental cultivars in the field. A three-dimensional graphing procedure was devised to depict ‘goodness of fit’ of progeny data to the additive model.
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