بررسي توانايي بيوكنترلي و ديناميك جمعيت باكتري هاي آنتاگونيست عليه Sclerotinia sclerotiorum در كلزا

BIOCONTROL ABILITY AND POPULAnON DYNAMICS OF BACTERIAL ANTAGONISTS AGAINST SCLEROTINIA SCLEROTIORUM IN CANOLA

Sclerotinia stem rot of canola tBrossico napus L.) caused by Sciercninia sclerouorum is an important disease of canola crop in many major canol a growing regions of the world. Various control methods have been developed for this disease. but the safest are the biological control methods. Different bacterial populations were recovered from the rhizosphere and phyllospbere of canola and screened for their antagonistic ability by varions in vitro tests. One hundred and twenty strains of bacteria were isolated and purified of which 13 strains exhibited high antagonistic ability in dual culture assays. Of these,ll strains were gram positive and identified as Bacillus subtilis and two strains were gram negative and identified as Pseudomonas fluarescens. The results indicated that P.fluorescenuPf51 reduced the lesion size by 81.2% while increasing the fresh weight of canopy by 89%, The dry weight of canopy was increased by 92% in P. ftuorescens Pf5l when compared With positive control. The results indicated that P.jluorescens Pf51 increased the fresh weight of roots hy 87.710/1ʹ while increasing the dry weight of roots by 80% respectively. To determine the population dynamics of antagonist in greenhouse experiment;" mutants of double-antibiotic resistant were selected on nutrient agar containing rifampicin and nalidixic acid. The experiment was carried out in a factorial fashion in a complete randomized block design with 12 treatments and four replicates. The main factors Involved were the antagonist, pathogen and fungicide. The results indicated a significant difference (PsO.OI) among various treatments in root and foliar wet and dry weights, as well as lesion size. These results also showed that after an initial decline of the population of antagonists at the beginning of the experiment. the population increased once it was established and was able to maintain itself. The populauon of antagonist increaserJ \wolimes of Ihe beginning population, twenty days afler ino(:ulalion.In the presence of pathogen resulted in enhanced disease control. However, in the presence of fungicide the bacterial population declined.