SUMMARY A study was made of the growth of the storage root of sugar beet as a sugar accumulating organ. The storage root grew by simultaneous cell multiplication and expansion from a series of peripheral secondary meristems laid down during the early stages of development. The weight of water and of non‐sugar dry matter per cell increased in proportion to the increase in cell volume. The amount of sugar per cell was proportional to cell volume only during the initial stage of cell expansion up to volumes of about 15 times 10‐8 cm3; thereafter it was less proportional. Thus, average cell size is a major determinant of the sugar concentration of the storage root. The implications of this are discussed.

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The distributions of glucosinolates and sulphur were measured in the vegetative and reproductive tissues in a series of single-and double-low cultivars of oilseed rape (Bienvenu, Ariana, Cobra and Capricorn) grown on a sulphur-sufficient soil at Rothamsted in 1987/88, and in crops of the cv. Libravo grown with none or 40 kg/ha of sulphur on a sulphur-deficient soil at Woburn in 1990/91.The glucosinolate measurements demonstrated large differences in the abilities of single-and double-low cultivars to synthesise glucosinolates, and showed that the biosynthetic differences were associated more with the developing pods than the vegetative tissues. It indicated that potential contribution of intact glucosinolates from vegetative tissues to the seed was likely to be small, but did not preclude the possibility that the vegetative tissues were a source of glucosinolate precursors. The sulphur measurements showed that the glucosinolates contained only a small proportion of the crop's total sulphur and that they were unlikely to be a major source of recyclable sulphur, even under conditions of severe sulphur deficiency.

SUMMARYA new model is presented that relates the numbers of bolters in sugar-beet crops to an intensity of vernalization calculated as the accumulated number of hours between sowing and the end of June that temperatures were between 0 and 13°C, with each temperature within this range differentially weighted for its vernalizing effect. The model allows varieties to be characterized in terms of a threshold number of vernalizing hours needed to induce bolting (the vernalization requirement) and the increase in the proportion of bolted plants with each additional 10 vernalizing hours accumulated above this vernalizing threshold (the bolting sensitivity). When parameterized for variety, the model allows the level of bolting to be predicted for crops sown on specific dates in particular locations.Data from variety-assessment trials done at a wide range of locations throughout the main UK sugar-beet growing areas between 1973 and 2006, and from early sown bolting trials done at a few sites between 2000 and 2008, were used to define specific aspects of the model. These included the range and weightings of vernalizing temperatures, the period during which vernalization occurs, and the temperatures likely to cause plants to become devernalized.The vernalization-intensity bolting model was parameterized and validated using separate subsets of the UK variety-assessment trial data. It was shown to be more discriminating and robust than an existing ‘cool-day’ model, which relates bolting to the number of days from sowing in which the maximum air temperature was below 12°C. Examples are given of the use of the new model to assess the bolting risk associated with early sowing in different regions of the UK, to interpret recent patterns of bolting (especially the large numbers of bolters seen in some commercial crops in 2008), and its potential use as an advisory tool.

SUMMARY The influence of season, and certain agronomic treatments (irrigation, nitrogen fertiliser, density of planting and sowing date) on leaf number were analysed in a series of sugar‐beet crops grown during the five seasons 1978‐82. Leaf appearance was a linear function of thermal time (accumulated temperature above 1°C) and could be described by four variables: a) the thermal duration of the seedling establishment phase, d′s; b) the thermal time interval between appearance of each of the early leaves, θe; c) the thermal duration of the early phase of leaf appearance, d'a, and d) the thermal time interval between the appearance of each of the later leaves, θ1. The progression of leaf death could also be described by a thermal time interval, θd. There were only small differences in the number of leaves produced by the eleven crops grown during the five seasons. Such differences as appeared, were largely attributable to changes in d'a and θ1, which were interpreted as responses to increasing competition for mineral nutrients and assimilate at the shoot apex. θe was similar in all crops; 30°Cdays were needed between the appearance of each of the early leaves. Only the early leaves died. Each one was retained by the plant longer than its predecessor. Increasing soil moisture deficit under an unirrigated crop shortened θd and depriving crops of nitrogen lengthened it. It is concluded that small differences in the rates of leaf appearance did not greatly influence the rates at which leaf canopies expanded early in the season, but that the rates of leaf death influenced both the time at which the canopies reached their maximum sizes and the rates at which leaf areas subsequently declined.

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It is now well established that considerable variation occurs between locations and seasons in seed glucosinolate concentrations even in the newer double-low varieties entering the national lists. Agronomic trials have demonstrated that little of the variation is attributable to the practices used to grow the crop. Our research has shown that concentrations of glucosinolates increase during seed growth, and that the final concentrations tend to be proportional to seed size and to be lower in crops in which the ratio of sulphur to seed number is small. It is known that drought at particular stages of growth increases glucosinolate concentrations and that the duration of seed growth depends on environmental conditions and varies between years. However, the underlying physiological mechanisms are not fully understood and variations in seed glucosinolates cannot confidently be predicted.