Contrasting growth and dry matter partitioning in winter and spring evening primrose crops (Oenothera spp.)

Evening primrose (Oenothera spp.) is a relatively new, high value oilseed crop for temperate regions. Despite a long growing season, seed yields are much lower than the average yields of the major arable seed crops and commercial spring crops can yield as much as winter ones. Biomass accumulation and partitioning and crop canopy development were compared between winter and spring crops of cv. Merlin in 2 years of field trials. A winter crop of cv. Peter was also studied in year 2, Although post-winter growth was slow to restart, the winter crops produced up to 1589 g biomass m(-2). The harvest index was low (<14%) because the crops grew tall and approximately half of the assimilate was partitioned into stem. Biomass production of the spring crops was lower, but the harvest index was higher (up to 17%) and in year 1, the winter and spring crops produced similar seed yields. The evening primrose leaf canopy was planophile and the peak green area index was in the region of 3-4, except in the year 2 winter crops where it was 7-8. Population density after crop establishment varied substantially between treatments but crops compensated for low plant populations by the production of larger, more branched plants bearing more capsules. Following the start of seed growth, the cultivar Merlin partitioned a greater proportion of new biomass into seed than did cv. Peter. The mean number of seeds per capsule was higher in cv. Merlin, but the seeds were smaller Machine harvesting resulted in the loss of 19 and 55% of the seed produced by the year 1 winter and spring crops. Improvements in harvest index in the winter crop, an earlier start to growth in the spring crop and an increase the proportion of seed recovered by combine harvesting would lead to substantial increases in the seed yield of evening primrose crops. (C) 2000 Elsevier Science B.V. All rights reserved.