Introduction Apical abortion in calabrese (Brassica oleracea var. Demand from retailers for fresh produce early in the year italica), a highly destructive disorder which occurs in has led to the practice among growers of Brassica oleracea overwintered transplants, has been investigated using groups such as calabrese, kohlrabi, brussels sprouts, and a model system in which blindness (abortion of the cauliflower, of raising autumn-sown seedlings under glass apical meristem) can be reproducibly

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... predictably for transplanting outside in late winter. In certain years induced. An initial experiment examined the suscepticonsiderable financial loss has been suffered as a result bility of 12 cultivars to apical abortion when grown of a failure of the apical meristem; a condition referred throughout a winter period under commercial condito as 'blindness' ( Wurr et al., 1994). This is thought to tions. Three of those varieties showed very high levels be associated with either apical abortion involving cessaof blindness (100%). Subsequently, plants of the sustion of leaf production by the vegetative apical meristem, ceptible cultivar PETO 7204 were subjected to an or with its failure to change to a reproductive apex. inductive period of low light intensity (30 mmol m−2 Previous investigations of this phenomenon (Mounseys−1) and low temperature (4°C). Apical meristematic Wood, 1957) suggested that short periods of frost led to cells of all plants ceased mitotic activity within 3 d of blindness in cauliflower transplants, while Nieuwhof being transferred to a regime comprising higher light (1969) concluded that periods of low temperature (above intensity (100 mmol m−2 s−1) and temperature (15°C). freezing) caused this phenomenon. In a recent investi-Using this system the structures of normal apices were gation of blindness in calabrese, Wurr et al. (1996) compared with those which became blind. Blindness examined the effects of sowing date, freezing, light level, was characterized by a cessation of leaf primordium and temperature and concluded that the amount of production by the vegetative apex, the last formed blindness (between 0 and 80% of plants) was affected by primordium growing on in some cases to form a mature sowing date. normal leaf, or in others, a deformed structure known A major problem facing workers investigating the as a whip-tail. The inactive apical bud became embeddevelopment of blindness in these plants has always been ded in the tissues of this last-formed structure. The the uncertainty of inducing this syndrome. This is because, cells of the inactivated apical bud remained alive, hitherto, the factors responsible for the induction of but lost their meristematic capability, becoming blindness were unknown, and the condition could not be enlarged, highly vacuolated parenchyma cells with induced reliably and predictably. One aim of the work amyloplasts. described in this paper was therefore to develop a model system comprising a susceptible cultivar and a set of inductive conditions, which could be used for systematic Key words: Apical abortion, apical meristem, blindness, studies of the phenomenon. calabrese. The term 'apical abortion' is often applied to the condition of blindness and has connotations of death.