A field trial was conducted in 2002/2003 and 2003/2004 growing seasons at
Giza Agricultural Research Station to evaluate the reactions of ten flax cultivars to
powdery mildew (PM) disease. In general, the tested cultivars could be divided into
four distinct groups, i.e. highly resistant (Ottowa 770B, Dakota and Bombay), resistant
(Cass, Wilden, and Clay), susceptible (Koto and Manshall), and highly susceptible
(Cortland and C.1.2008). The cultivars showed considerable variation in disease
severity (OS) ratings ranged from 3.69 on Bombay to 100% on C.1.2008. GLC
analysis of fatty acid composition of cultivar seeds revealed the presence of the
following fatty acids: Myristic, palmitic, palmitoleic, stearic, oleic, linoleic, linolenic and
arachidic. However, the unsaturated fatty acids oleic, linoleic and linolenic were
predominant in linseed oil. The total percentage of the three fatty acids ranged from
88 in Cortland to 92.9% in Ottowa 770B. PM severity was positively correlated with
each of palmitoleic (r=0.776, p < 0.01) and stearic (r=0.704, p < 0.05). On the other
hand, none of the other fatty acids was significantly correlated with PM severity. Data
for PM ratings and amounts of fatty acids were entered into computerized stepwise
multiple regression analysis. Using the predictors supplied by stepwise regression, a
two-factor model was constructed to predict PM severity. This model showed that PM
severity differences were due to largely to the fatty acids palmitoleic and myristic,
which accounted for 80.16% of the total variation in PM severity. These results
indicate that fatty acid composition of linseed oil may provide a supplementary assay
of greenhouse and field tests to distinguish quantitatively between PM resistant and
susceptible genotypes.