Industrial Crops and Products 12 2000 137 – 147
Climatic conditions during seed growth significantly influence oil content and quality in winter and spring
evening primrose crops Oenothera spp.
Andrew F. Fieldsend
a,
, James I.L. Morison
b
a
Scotia Pharmaceuticals Ltd, Plant Technology Centre, Writtle College, Chelmsford CM
1 3
RR, UK
b
Department of Biological Sciences, Uni6ersity of Essex, Wi6enhoe Park, Colchester CO
4 3
SQ, UK Accepted 31 March 2000
Abstract
Evening primrose Oenothera spp seed is an important source of g-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 field 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 a-linolenic acid were the predominant fatty acids in the seeds and g-linolenic acid was hardly present. At maturity, linoleic acid constituted 70 – 75 of the oil, g-linolenic acid content ranged from 8.0 to 9.9 and a-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 g-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 g-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 g
-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. © 2000 Elsevier
Science B.V. All rights reserved.
Keywords
:
Evening primrose; Oenothera spp.; Seed oil content; g-linolenic acid; Solar radiation; Temperature www.elsevier.comlocateindcrop
1. Introduction
In common with most major commercial oil- seeds, the seeds of evening primrose Oenothera
spp contain significant amounts of 9c,12c-linoleic acid C18:2 in the oil. Linoleic acid is the main
Corresponding author. Present address: Semundo Ltd., Abbots Ripton, Huntingdon, PE28 2PH, UK. Tel.: + 44-
1487-773595; fax: + 44-1487-773532. E-mail
address
:
andrew.fieldsendswseed.se A.F.
Fieldsend 0926-669000 - see front matter © 2000 Elsevier Science B.V. All rights reserved.
PII: S 0 9 2 6 - 6 6 9 0 0 0 0 0 0 4 9 - 2
dietary essential fatty acid for humans where, to be fully utilised by the body, it must be converted
into 6c,9c,12c-linolenic acid C18:3v6, g-linolenic acid, a reaction catalysed by the enzyme delta-6-
desaturase. Although healthy adults will obtain sufficient g-linolenic acid in this way, the conver-
sion of linoleic acid to g-linolenic acid can be very slow in individuals suffering from a number of
common diseases Horrobin, 1990. Substantial clinical improvements can be produced in patients
suffering from diseases such as atopic eczema or breast pain by administering a regular exogenous
supply of g-linolenic acid. Whereas in many oil- seeds the desaturation of linoleic acid gives rise to
9c,12c,15c-linoleic
acid C18:3v3,
a -linolenic
acid, in evening primrose the product of linoleic acid desaturation is g-linolenic acid. Although
there are other sources of g-linolenic acid, both plant and fungal, evening primrose oil appears to
be clinically the most effective Horrobin, 1990. Hence, evening primrose oil has become commer-
cially significant in recent years, being officially recognised as a prescription pharmaceutical in
several countries and sold as a dietary supplement in many more.
Compared to mainstream oilseed crops, the oil content of evening primrose seed is relatively low
approximately 25 and an increase in oil con- tent can lead to significant reductions in extrac-
tion costs. A g-linolenic acid content of 9 has become the minimum acceptable standard for the
nutritional supplements industry. Seed containing less than 9 g-linolenic acid in the oil can be of
considerably reduced value, or even unmarketable in years of oversupply. Hence, both the total oil
and g-linolenic acid contents of evening primrose seed are of considerable economic importance.
A plant breeding programme at Writtle Col- lege, Chelmsford UK, has produced several culti-
vars which yield improved oil and g-linolenic acid contents, including cv. Peter and cv. Merlin.
However, in addition to genotype, the oil content of oilseeds is known to be affected by a number of
environmental factors, including water stress, temperature, disease and nitrogen nutrition Har-
ris et al., 1978. Several studies on evening prim- rose e.g. Lotti et al., 1978; Reiner and Marquard,
1988; Court et al., 1993 suggest that a positive correlation exists between seed oil content and
temperature during seed filling, although in some instances the results are not conclusive. On the
other hand, it has long been known that in many oilseed crops e.g. oilseed rape, sunflower and
flax the extent of desaturation in the fatty acid composition of the seed oil is inversely related to
temperatures prevailing during seed maturation Canvin, 1965. This seems to be the case with
evening primrose, too e.g. Levy et al., 1993 and crops grown at warmer latitudes tend to produce
oil with lower g-linolenic acid content Simpson and Fieldsend, 1993.
In the UK, evening primrose crops ripen during a period of reducing daylengths, light levels and
temperatures and, at a given location, climatic conditions can influence oil and g-linolenic acid
content in two ways. Firstly, conditions will differ between years. Secondly, owing to a difference in
maturity date of several weeks, crops which are sown in late summer and overwintered and crops
sown in the spring will experience different condi- tions during ripening. Through three seasons of
field studies, this paper investigates the effect of climatic conditions in eastern England, a major
evening primrose growing area, on oil and g-lino- lenic acid accumulation during seed growth. Dif-
ferences in oil and g-linolenic acid content were found to occur both between seeds from different
parts of plants and between overwintered and spring-sown crops harvested at the optimal
growth stage. Final oil content and oil quality were shown to be determined at different stages
during seed growth.
2. Materials and methods
