Climatic conditions during seed growth significantly influence oil content and quality in winter and spring evening primrose crops (Oenothera spp.)

Evening primrose (Oenothera spp) seed is an important source of gamma-linolenic acid, a relatively rare fatty acid with value as a pharmaceutical and nutritional supplement. The influence on oil content and quality of climatic conditions during seed growth was investigated in three years of held trials comparing crops sown in the late summer and overwintered with crops spring-sown the following year. At the onset of oil accumulation, palmitic acid, linoleic acid and cr-linolenic acid were the predominant fatty acids in the seeds and gamma-linolenic acid was hardly present. At maturity, linoleic acid constituted 70-75% of the oil, gamma-linolenic acid content ranged from 8.0 to 9.9% and alpha-linolenic acid was almost undetectable. In all years, seeds from the overwintered plants of cv. Merlin contained more oil than did seeds from the equivalent spring-sown plants, but the gamma-linolenic acid content of the oil was lower. The rate of increase in seed oil content was faster in the overwintered crops but the duration of oil accumulation was shorter. Oil content at seed maturity in cv. Merlin was positively correlated with both mean daily temperature (r(2), 0.59) and mean daily incident solar radiation (r(2) 0.71) during the main period of seed filling. Strong negative correlations existed between the final gamma-linolenic acid content of the oil and both climatic variables during the final phase of oil accumulation (r(2), - 0.78 and - 0.83, respectively). Temperature was probably the primary determinant of the final gamma-linolenic acid content but it was unclear which variable most influenced final seed oil content. Differences in oil content and seed size also existed between seeds harvested from different parts of the same plant. (C) 2000 Elsevier Science B.V. All rights reserved.