High plant populations caused a reduction in pod set and consequently in seed yield. Removal of axillary branches reduced the average weight of seed and percentage seed oil on primary racemes, indicating transport of photosynthate from branch leaves to storage sites in pods on primary racemes. Debranching at low densities was also associated with premature senescence of leaves and desiccation of immature pods, suggesting that branch removal need not have an exclusively simple nutritional basis. High canopy density reduced oil content, and seeds borne on primary racemes had lower oil levels than those on axillary branches.Reports on several crops indicate that spacing affects the percentage of oil in harvested seed (Dillman and Brinsmade, 1938;Hinson and Hanson, 1962;Donovan et al., 1963). In preliminary experiments forming part of the present study it was also observed that seed borne on secondary racemes could develop a higher oil content than those on the primaries, though the increased oil levels were generally found only when plants were grown in dense stands. Furthermore it has been established (McGibbon, 1978) that a reduction in light intensity reduced seed oil content. The present experiments were planned to study further the relation between plant population, canopy density and pod shading on yield of seed and on oil content. MATERIALS AND METHODSThe work was conducted at the experimental field unit of the Plant Science Laboratories, University of Reading. Experiments 1 and 2 were established in field plots, Expt 3 was conducted on pot-grown plants in the open and Expt 4 on pot-grown plants in an unheated glasshouse. The material was grown and recorded during the 1976 and 1977 growing seasons. The techniques used for determining oil content in seeds have already been described by McGibbon (1978). Experiment 1. Three populations were sown at 6, 25 and 100 seeds per m 2 according to a randomized block design in the field. Plots at the highest densities were divided on day 45, after anthesis of the first flower on the primary raceme, into two sub-plots in which plants (a) were allowed to develop normally to maturity, or (b) had the axillary branches held away from the plant 28.

SUMMARYThe effects of temperature, light intensity and nitrogen supply on the amount and fatty acid composition of the seed oil in Lupinus albus has been investigated. The percentage seed oil was reduced and its degree of saturation increased at higher temperatures. High temperatures during the dark period caused a reduction in percentage oil only when combined with day temperature of 20 °C, indicating a highly specific interaction between day and night temperatures. Shading reduced oil content, an effect which may determine response to population density and the optimal phenotype for high-oil cultivars.

The accumulation of lipid in embryos of lupin was found to be most rapid between 30 and 40 days after anthesis, coinciding with the stage of maximal dry weight increase of the developing seed. The percentage composition of oleic acid increased and that of linoleic acid decreased as the seed matured. Factors which cause premature cessation of embryo development are likely to affect adversely the oleate: linoleate ratio in the seed as well as the percentage oil content.

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