The seed yields and maturity dates of an indeterminate cultivar (Lunoble) and a determinate line (CH304/70) of Lupinus albus L. were measured at three locations in France (Lusignan, Dijon and Gotheron) and at Rothamsted, UK, in 1989/90 and 1990/91. Different combinations of sowing dates, plant densities and irrigation treatments were tested at some sites.
Averaged over all sites, CH304/70 yielded more than Lunoble (3·26 v. 2·98 t/ha) but there were significant genotype × location interactions for yield and date of maturity. Both genotypes gave similar yields at the three locations in France (3·13 and 3·06 t/ha, respectively). But under the cool and wet conditions at Rothamsted, CH304/70 yielded 4·26 t/ha compared with only 202 t/ha for Lunoble. Yields of CH304/70 were more stable than those of Lunoble across locations and years; the coefficients of variation about the overall means were 14 and 22%, respectively. CH304/70 ripened up to 16 days sooner than Lunoble in France, and 6 weeks earlier than Lunoble in the cooler conditions of the UK.
In wet growing conditions (Lusignan 1989/90, Rothamsted 1990/91) Lunoble had increased vegetative growth which decreased the proportion of yield produced by mainstem pods and correspondingly increased the proportion borne on second-order branches. This continued branching also delayed harvest, especially in the UK where the crop was not harvestable until early November. In these conditions, CH304/70 outyielded Lunoble at Lusignan (3·4 v. 2·7 t/ha) and at Rothamsted (4·3 v. 2·0 t/ha) and was harvested acceptably early in mid-September. However, under warm, dry conditions, Lunoble produced only one order of branches at Gotheron and two orders at Lusignan in 1990/91. At Gotheron, both genotypes matured at the same time but CH304/70 yielded slightly better (3·1 v. 2·8 t/ha) because it produced a higher proportion of its yield on the mainstem, whereas at Lusignan, Lunoble yielded better than CH304/70 (4·1 v. 3·4 t/ha) because of extra yield from pods on second-order branches.
CH304/70 produced seeds of larger mean size and had greater stability of seed size across years and locations than Lunoble did. This was apparently the result of CH304/70's determinate structure, in which c. 75–100% of the yield was from pods on the mainstem and first-order branches, whose seeds were larger and less variable in size than those from pods on higher-order branches of indeterminates.
The development of autumn-sown genotypes with a determinate structure that combine adequate yield and early harvest under cool conditions offers the prospect of extending the geographical range of lupins, grown for grain, both to the cool regions of northern Europe and to hotter and drier regions in southern Europe where summer drought limits the yield of conventional indeterminate types.