Screening and identification of antagonistic bacteria with potential for biological control of Penicillium italicum of citrus fruits

A total of 81 bacterial isolates from the surface of mandarines, apples, lemons and kumquats were screened for antagonism against Penicillium italicum wehmer and used to control postharvest blue mold. Bacterial YS-1 was isolated from the surface of kumquat fruit and identified as Paenibacillus brasilensis by the Biolog microbial identification system combined with 16S rDNA sequence analysis, biochemical and physiologic characteristics and rpoB sequence analysis. YS-1 showed obvious antifungal activity to four different fruit pathogens. Effect of different treatments with strain YS-1 against disease caused by P. italicum on inoculated Nanfeng oranges was also investigated. Results showed that citrus blue mold incidence of fruits treated by cell culture, cell-free filtrate and cell suspension of strain YS-1 were all less than 45% and the lesion diameter were all below 10 mm. Also the treatment of cell suspension showed significant comparing with other two treatments. Lesion diameter and disease incidence treated at 5 °C were higher than those at 25 °C. In this article, strain YS-1 is reported for the first time as a biocontrol agent against blue mold of citrus. The research will provide a theoretical basis for research of postharvest antagonistic bacteria in citrus.