USE OF SOME STREPTOMYCES ISOLATES AND THEIR MIXTURES AS BIOLOGICAL CONTROL AGENTS AGAINST POWDERY MILDEW OF FLAX CULTIVAR MARYLIN R3 IN AN OUTDOOR POT EXPERIMENT

Abstract

In this study, the effect of some isolates of Streptomyces and their mixtures was evaluated as a biological control agent against powdery mildew (PM) of flax cv. Marlin R3, its effect on disease incidence (DI), disease severity (DS), seed yield (SY) and straw yield (StY) R3 in an outdoor pot experiments of two seasons (2016 and 2017). Four Streptomyces isolates (SI) of SI-3, SI-5 and StI-11 with its mixture and 15 treatments. The individual isolates (SI-1), SI-3, and SI-5 were the most effective in the resistance of mildew disease with efficiency of 86.96, 69.57 and 86.96%, respectively. In contrast, individual isolates (SI-11) had no effect on the disease. On the other hand, there was a difference in the effect of the isolate’s mixture in the resistance of the PM, as demonstrated by the efficiency of the three mixtures (SI-1, SI-3, SI-5, SI-11) and SI-1 (SI-3) and SI-3, SI-5, SI-11), 86.96, 73.33 and 56.67%, respectively. The rest of the mixtures did not have any effect on the resistance of the PM disease. Linear correlation analysis showed a significant positive correlation between DI and disease intensity at a significant level (r = 0.985, p≤ 0.1) in 2016 and 2017 (r = 0.960, p ≤ 0.1). In 2016 there was a significant negative correlation between DI, DS, SY and StY. While in 2017 there was a negative correlation between the severity of the disease and the occurrence of the disease and SY only. Cluster analysis was only partially successful in the separation of the potent and ineffective strains of Streptomyces in the resistance to PM disease.