Citrus canker, caused by Xanthomonas citri subsp. citri (Xcc), is a quarantine disease that seriously affects citrus production worldwide. The use of microorganisms and their products for biological control has been proven to be effective in controlling Xanthomonas disease. In this study, a novel Xcc antagonistic strain was isolated and identified as Bacillus amyloliquefaciens F9 by morphological and molecular analysis. The lipopeptide extract of B. amyloliquefaciens F9 (F9LE) effectively inhibited the growth of Xcc in an agar diffusion assay and restrained the occurrence of canker lesions in a pathogenicity test under greenhouse conditions. Consistent with these findings, F9LE treatment significantly inhibited the production of extracellular enzymes in Xcc cells and induced cell wall damage, with leakage of bacterial contents revealed by scanning electron microscopy and transmission electron microscopy analyses. In addition, F9LE also showed strong antagonistic activity against a wide spectrum of plant pathogenic bacteria and fungi. Furthermore, using electrospray ionization mass spectrometry analysis, the main antimicrobial compounds of strain F9 were identified as three kinds of lipopeptides, including homologues of surfactin, fengycin, and iturin. Taken together, our results show that B. amyloliquefaciens F9 and its lipopeptide components have the potential to be used as biocontrol agents against Xcc, and other plant pathogenic bacteria and fungi.

Blast, caused by the ascomycete fungus Magnaporthe oryzae, is one of the most devastating diseases of rice due to the high variation of the pathogen. Breeding high-yielding rice cultivar with durable resistance to rice blast is a priority in Southern China and in places where rice cultivation is an important branch in farming. Effectiveness and accuracy of resistant cultivar breeding largely depend on the development of markers specific to the target gene. In silico prediction of the resistance (R) Pi39 gene content of the interval was made and hence a candidate gene was identified to develop a perfect insertionÀdeletion (InDel) based marker for Pi39 gene selection. The Pi39 gene was successfully introgressed in two elite cultivars using both foreground (the InDel) and background (genome-wide microsatellites) genotypic and phenotypic selection. Five selected BC 3 F 3 progeny lines were recovered and showed a high level of blast resistance. At least 97.5% of their genome was inherited from their recurrent parent. The agronomic performance of four lines (D94, D98, D112 and D113) was at least as good as that of their recurrent parent.