A two-year greenhouse and field study was conducted at Giza and
EI-Kanater Agricultural Research Stations to (1) estimate heritability of
powdery mildew resistance when disease incidence and disease severity
were used as criteria to evaluate resistance, (2) assess resistance to
powdery mildew of 19 flax genotypes, and (3) quantify the relationship
between disease intensity ratings and agronomic traits. Genotype component
of variance of disease incidence was highly significant (p ~ 0.01) in two tests,
while that of disease severity was highly Significant (P ~ 0.01) in one test and
significant (P ~ 0.05) in two tests. In addition, the highly significant and the
significant genotype components of variance of disease incidence and
disease severity were associated with high heritability and with high genetic
advance expected from selection. Significant differences in the disease level
occurred between the 19 genotypes; however, some of these differences
were inconsistent from one test to another, which may indicate the
occurrence of genotype x environment interaction. Most of the tested
genotypes did not have satisfactory levels of powdery mildew resistance.
Moreover, the powdery mildew resistance, which was expressed by few of
the genotypes, was environmentally sensitive. Most of the significant
correlation coefficients between disease intensity variables and agronomic
traits were negative, which implies that selection for powdery mildew
resistance would necessarily lead to an lmprovement in agronomic traits and
vice versa.