EFFECT OF MINERAL COMPONENTS OF THE MEDIUM USED TO GROW BIOCONTROL STRAIN UTPF61 OF PSEUDOMONAS FLUORESCENS ON ITS ANTAGONISTIC ACTIVITY AGAINST SCLEROTINIA WILT OF SUNFLOWER AND ITS SURVIVAL DURING AND AFTER THE FORMULATION PROCESS

Abstract

SUMMARY Mineral factors are important in optimizing growth media for production of high quality biocontrol agents. In this work we investigated the effect of some minerals and some combinations of them during fermentation of Pseudomonas fluorescens UTPF61 on its growth in flask and fermentor and its subsequent antagonistic activity in vitro and in planta. Its survival during the formulation process and shelf life over a period of 60 days was investigated. None of the mineral amendments had an effect on bacterial growth. In dual culture assays bacteria grown in a zinc-supplemented medium, showed the maximum inhibition (20 mm) of mycelial growth of Sclerotinia sclerotiorum. Medium including a combination of zinc, bromine and iron gave maximum inhibition of mycelial growth. In greenhouse studies, bacteria grown in medium with zinc showed high inhibition against S. scletoriorum. Cobalt, magnesium and copper had a negative effect on antagonistic activity. Bacteria obtained from medium including a combination of zinc and molybdenum showed high antagonistic activity and resulted in 55% healthy plants. A combination of Zn-FeMo improved resistance of the bacterial cells to the drying process. In all treatments (in both flask culture and fermentor studies) UTPF61 survived up to 60 days without any dramatic decline from the initial population.