FIELD EVALUATION OF SOME STREPTOMYCES ISOLATES TO SUPPRESS POWDERY MILDEW OF FLAX (SAKHA 1 CULTIVAR)

Abstract

Evaluation of 16 isolates of Streptomyces, as biological agents for controlling powdery
mildew (PM) of flax was carried out under field conditions in El-Gemmeiza and Sakha Agricultural
Research Stations in 2006 growing season. The isolates were used as foliar application. Disease
incidence (DI), disease severity (DS), seed yield, and straw yield were used as criteria to evaluate
the efficiency of the tested isolates. In El-Gemmeiza, Streptomyces isolates Qa-51, Sc-11, Qa-44,
S16, Sc-2, and Si-1 significantly decreased DI compared with the control and the efficiency of the
isolates were 31, 25.40, 19.74, 15.45, 14.77, and 12.61%, respectively. Isolates Sc-2, Sc-11, and Qa-
51 reduced DS by 25.54, 23.50, and 19.85% respectively. None of Streptomyces isolates
significantly affected both seed yield and straw yield. In Sakha, none of Streptomyces isolates
significantly affected DI. Isolates Sc-2, Si-1, Ma-13, and Qa-44 significantly reduced DS by 18.05
to 22.65%, and isolates Qa-51, Qa-53, Qa-84, and Da-3 reduced DS by 23.38 to 28.36%.
Streptomyces isolates Is-10, Da-3, and Qa-53 significantly increased seed yield by 2.35 to 3%. All
Streptomyces isolates were ineffective in increasing straw yield in Sakha. Correlation between
disease intensity variables (DI and DS) and yield (seed yield and straw yield) showed that DI
negatively correlated (r = - 0.735, P = 0.001) with seed yield and with straw yield ( r = - 0.630, P =
0.007), disease severity also negatively correlated (r = - 0.469, P = 0.05) with seed yield and straw
yield (r = - 0.736, P = 0.001) in El-Gemmeiza.