Scientific Study

BACKGROUND: walnut oil use is currently limited by its poor oxidative stability due to the high percentage of polyunsaturated fatty acids. Modifying the oil composition may be a goal in walnut breeding to increase interest in this crop. Exploring natural variability and identifying the main environmental factors affecting oil quality are necessary in crop selection. Therefore, 190 wild accessions were collected and evaluated during 2013 and 2014 for oil content and its fatty acids profile, and compared with five commercial cultivars as references. RESULTS: High variation in kernel oil content and fatty acid composition was found in the native walnut. Kernel oil content ranged from 54.2 to 72.2%. The major fatty acids were linoleic (range 46.9 - 68.6), oleic (10.0 - 25.1), linolenic (6.9 - 17.6), palmitic (3.9 - 11.4) and stearic acid (1.1 - 5.2). Some accessions had oil with a fatty acid ratio very different from the reference commercial cultivars, especially the oleic/polyunsaturated fatty acids (PUFAs) ratio. A significant linear relationship and positive correlation between the daily minimum temperature and oleic acid content was observed in the wild walnuts. CONCLUSIONS: The wide variation in fatty acid content and composition allows superior accessions to be selected for diffusion among growers. A suitable strategy would be to make a selection against PUFAs content rather than just for high oleic acid. In addition, the selected high oleic accessions, before being utilized per se or as donor parents in breeding programs, have to demonstrate they are not adversely affected by the environment.