The efficacy of selected biological control agents against citrus black spot (CBS) pathogen Phyllosticta citricarpa

Citrus black spot (CBS) caused by Phyllosticta citricarpa (McAlpine) Van der Aa (asexual state) synonym Guignardia citricarpa Kiely (sexual state) is one of the most devastating diseases of citrus which occurs in various citrus producing areas around the globe. Management is mainly based on monthly applications of copper fungicides and strobilurins under field conditions. In this study, bio-control agents were evaluated as alternative post-harvest treatments against citrus black spot disease. Two bio-control agents namely, Bacillus subtilis Cohn and Trichoderma harzianum Rifai were evaluated for their efficacy against P. citricarpa. Their efficacy was further compared with commercial fungicides Dithane 750 (Mancozeb, 750 g/kg). Results obtained showed that T. harzianum treatments were highly suppressive towards pathogen growth in vitro (85%) as compared to B. subtillis (4%) and Dithane 750 (12%). Treatment of artificially inoculated fruits with combined formulations of both biocontrol agents resulted in reduced CBS severity as compared to their single applications. These findings suggest that T. harzianum had highest suppression of pathogen growth as compared to B. subtilis. The results also suggest that their combined application can provide an effective disease management when compared to sole application of Dithane 750. Further studies are however, needed to determine their effectiveness under field conditions and also their efficacy can be sustained when applied with commercial fungicides.   Key words: Bacillus subtilis, biocontrol, dithane 750, Trichoderma harzianum.