Effects of temperature and photoperiod on days to flowering, yield and yield components of Lupinus albus (L.) under field conditions

A better understanding of the agronomic importance of planting date and the influence of cold temperatures and photoperiod during germination and plant growth may lead to better management strategies for cultivation of the sweet white lupin (Lupinus albus). The effects of planting date (temperature and photoperiod) were determined on the number of days to flowering, yield and yield components of four early to medium and one late sweet white lupin genotype in a field trial at Potchefstroom, South Africa, planted during February 1996 to January 1997, Moisture stress was avoided through regular irrigation. Duration of the developmental phases planting date to emergence, emergence to floral initiation, initiation to first flower, duration of flower and days to physiological and harvest maturity was related to field measurements of temperature and photoperiod. Differences in the main determinants of yield, i.e. seeds per pod, pods per plant, single seed mass (SSM), plant and pod height and yield, were measured. Results showed that both temperature and photoperiod influence the growth and development of the Lupinus albus genotypes 'Esta', 'Hantie', 'Tifwhite', 'Kiev' and 'LAL 186'. Temperature influences include the effect of vernalization at seedling emergence. Minimum grass temperatures wider 5 degrees C at emergence are effective for vernalization. However, after grass temperatures at emergence increased again from June to December, together with an increase in the photoperiod length,'Tifwhite' as well as the other genotypes still flowered earlier, confirming that these cultivars are long-day plants, which is in accordance with controlled-environment data. Cool vernalizing temperatures thus not only influence obligate vernalization requiring genotypes such as 'Tifwhite', but also influence the non-obligate genotypes studied. Planting date had a significant influence on pods per plant, single seed mass (SSM) and seed yield. In all trials later planting, from June to November, decreased SSM and seed yield. The highest seed yield of 1.5 t ha(-1) was obtained for the 10 June planting date and the lowest average yield of 0.450 t ha(-1) for the 5 November planting date.