Biocontrol agent for apple Fusarium rot: optimization of production by Streptomyces hygroscopicus
Postharvest Fusarium rot of apple fruit, caused by a fungal pathogen Fusarium avenaceum, has become a problem in apple storage in Serbia. Considering that chemical protection has a negative effect on human health and the environment, this research was done to find potential eco-ways of controlling Fusarium infection of apple fruit. The aim of this study was to examine the potential of Streptomyces hygroscopicus for control of two F. avenaceum isolates obtained from apple fruit exhibiting rot
... t exhibiting rot symptoms. As a first step, optimization of three the most important medium nutrients: glycerol (C 3 H 8 O 3 ), ammonium sulphate (NH 4 ) 2 SO 4 ) and dipotassium phosphate (K 2 HPO 4 ), was performed in order to obtain their optimal concentrations. At the optimal medium composition, nine bioprocesses were performed in a laboratory bioreactor with a working volume of 2 dm 3 at different agitation speeds and aeration rates in order to determine, at which process conditions the highest production of the target antagonist occurs. Results of medium optimization showed that the optimal concentration of glycerol, ammonium sulphate and dipotassium phosphate are 19.59, 0.25 and 1.35 g dm -3 , respectively. Investigating the effect of agitation and aeration on the antagonistic agent production in nine bioprocessing conditions showed that antifungal activity of S. hygroscopicus supernatant obtained in the bioprocess with an agitation speed of 100 rpm and aeration rate of 1.5 vvm is statistically significantly higher compared to that in other bioprocesses. Under these conditions, the highest production of antagonist agents was achieved after 96 hours of cultivation, forming the inhibition zone diameters of F. avenaceum KA12 and KA13 isolates of 59.33 and 55.67 mm, respectively. The activity was also confirmed in planta.