effects of nitrogen and pre-harvest desiccation on seed yield and oil quality of evening primrose (oenothera biennis l.)

disadvantages such as indeterminate inflorescence and high seed shattering during ripening are significant restrictions to introduce evening primrose as a commercial medicinal plant. following to the last works, a pot experiment was conducted to clarify the influence of defoliation before harvest on the seed yield, oil and gla (gamma-linolenic acid) percentage of evening primrose growing under nitrogen deficit. desiccation showed no significant influence on seed yield and yield components. however, the percentage of gla of the desiccated plants was significantly higher than that of non desiccated plants. nitrogen did not have significant influence on gla content, but the content of this fatty acid tending to increase with increase in the nitrogen concentration. based on the results, it can be concluded that desiccation as a harvest method increases the oil quality with increasing the gla percentage. evening primrose showed a positive response to n fertilizer. further investigation in this area seems to be necessary.