Abstract
An outdoor pot experiment was conducted in 2016/2017 growing season at Giza Agricultural Research Station to evaluate reactions of 15 flax cultivars to powdery mildew (PM) in 6/4/2017 and 20/4/2017. The tested cultivars showed a wide range disease severity (DS) ranged from 8.84% on Ottowa 770B to 78.35% on Giza10 in the first evaluation date and from 11.94 on Brasium to 86.72%on Giza 10 in the second evaluation date. Gas-liquid chromatography analysis of the fatty acid composition of cultivar seeds revealed that the unsaturated fatty acids Oleic, linoleic, and linolenic were predominant in oils of all the tested cultivars. The mean percentages of the three fatty acids were 35.69, 14.32, and 30.12%, respectively. Pearson correlation coefficient was calculated to measure the degree of association between PM severity (X) and the percentage of each fatty acids (Y). None of the fatty acids, expect y(14), was significantly correlated with PM severity. This lack of correlation could be attributed to the fact that amounts of fatty acids are highly heritable characters, which indicates that they were mainly governed by genetic factors and therefore, slightly affected by biotic stress resulted from infection by PM. On the other hand, we do not have an immediate biological explanation for the positive and significant correlation between DS and the percentage of the fatty acid y(14). In spite of the significance of this correlation, it was not practically important due to the very low percentage of this fatty acid in the oil.