Large Scale Cultivation of Bacillus velezensis CE 100 and Effect of Its Culture on Control of Citrus Melanose Caused by Diaporthe citri

Abstract

Diaporthe citri is an important fungal pathogen which causes melanose in various citrus growing regions of the world. In our study, control of D. citri was performed by using effective biocontrol agent, Bacillus velezensis CE 100. Mycelial growth of D. citri was highly restricted by strain CE 100 in dual culture plates. Our study demonstrates large-scale inoculation of strain CE 100 in non-sterilized PB medium. In addition, bacterial culture filtrate (BCF) of strain CE 100 from the large-scale culture showed better growth inhibition of D. citri than those from small-scale culture in the laboratory. Moreover, microscopic observation revealed that hyphal morphology of the pathogen was significantly affected by BCF, probably because of various cell-wall degrading enzymes and metabolites produced by strain CE 100. In addition, 50% BCF of strain CE 100 inhibited D. citri conidial germination by over 80%. Treatments, applied by foliar spray with fungicide and strain CE 100 culture, significantly lowered melanose disease incidence more than did control. The results of this study indicate that large-scale culture of strain CE 100 was effective for control of D. citri by means of adequate active metabolites and cells. Therefore, we demonstrate biocontrol applicability of B. velezensis CE 100 on control of citrus melanose by developing a low-cost PB medium using affordable large-scale fermenter. Effect of different treatments on melanose disease incidence on leaves of mandarin plants at 20 days after inoculation with D. citri. Statistical comparison between treatments was done by least significant difference (LSD) test at p < 0.05 level. Means with the same letter are not significantly different from each other. *Con- Control, CE 100- Treatment with B. velezensis CE 100 culture, F- Treatment with fungicide