Application of microorganisms, alone or in combination, to control postbloom fruit drop in citrus

Isolates of Trichoderma spp. (ACB-14, ACB-33, ACB-37, and ACB-40) and Bacillus subtilis (ACB-66, ACB-69, ACB-77, and ACB-83) were tested separately or in mixtures for suppression of postbloom fruit drop in citrus, caused by Colletotrichum acutatum. This work aimed at: (i) determining the incubation time and temperature for production of cells of biocontrol agents; (ii) determining the effect of the isolates, separately or in mixture on the germination conidia of C. acutatum; (iii) evaluating the efficiency of antagonistic isolates on detached citrus flowers and under field conditions. The results of the interactions in vitro showed that there was little differentiation in cell production among the species, and the optimum temperature was 27 degrees C. The best time for multiplication of bacterial cells was 36 hours, whereas for Trichoderma, the production of conidia continued to increase up to 120 hours of incubation. The mixtures of the ACB-77 plus ACB-66, ACB-33, or ACB-37 inhibited pathogen germination from 84% to 89%. Studies with detached citrus flowers showed that ACB-69 alone gave 99% control. The use of mixture ACB-69 plus ACB-37 proved to be viable in the control of disease under field conditions, but the efficiency of the control was lowest than the obtained by applications of ACB-69 alone.