In a previous study, we screened the combination of the three bacterial strains—Bacillus subtilis AR12, Bacillus subtilis SM21, and Chryseobacterium sp. R89—(BBC), which can control mixed diseases, including Ralstonia wilt, Phytophthora blight, and Meloidogyne root-knot on bell pepper with high biocontrol efficacy and yield increase under greenhouse and field conditions. In this study, to achieve the best biocontrol agents for separately controlling Ralstonia wilt, Phytophthora blight and Meloidogyne root-knot by BBC, the biocontrol efficacy by BBC-related BCAs (AR12, SM21, R89, AR12 + SM21, AR12 + R89, SM21 + R89 and AR12 + SM21 + R89) were compared regarding all three single diseases and the mixed diseases, respectively. BBC achieved the highest biocontrol efficacy against all three single diseases and the mixed diseases (biocontrol efficacies of 92.46 %, 81.81 %, 86.49 % and 87.31 % against Ralstonia wilt, Phytophthora blight, Meloidogyne root-knot and the mixed diseases, respectively), which were significantly more than that attained by the three single strains and the two-strain combinations AR12 + SM21, AR12 + R89 and SM21 + R89. Although a biomass increase of 4.86–21.14 % was attained by BBC-related BCAs without BBC, BBC achieved a maximum biomass increase of 64.67 %.

Ustilaginoidea virens is a ubiquitous plant pathogen that causes rice false smut disease, one of the most destructive diseases of rice (Oryza sativa L.) production. However, data concerning the effect of inoculation on disease development and the infection process of this pathogen are not comprehensive. In this study, the developmental processes of U. virens in rice panicles were characterized using an enhanced green fluorescent protein (EGFP) labelled strain. A mixture of hyphae and conidia of U. virens was used to inoculate rice panicles by leaf sheath injection during the booting stage of rice plants grown in a greenhouse. The panicles were assessed to determine the relationship between artificial inoculation and disease occurrence. Increasing volumes of inocula (0.2, 0.5, 1, and 2 ml of a mixture of hyphae-fragment and 2 × 106 conidia/ml suspension) caused more severe infections, and small differences were also observed for the different inoculation sites at the base, apex and mid-point of rice panicles. The optimum inoculation condition was 1–2 ml inoculum injected into the mid-point of rice panicles. Spikelet samples were collected as the disease progressed and observed by confocal laser scanning microscopy and scanning electron microscopy. The images collected showed that the primary site of U. virens colonization was at the base of the filaments with the inner spikelets becoming infected by hyphae at 24 h post inoculation (hpi). The accumulation of hyphae reached its highest level at 168 hpi, before the rice heading stage, as the infection extended upward from basal filaments to the anther apex, and then enclosed all the floral organs to produce a velvety smut ball.

•2-Allylphenol is an effective fungicide against a number of plant pathogens.•Major metabolites derived from 2-allylphenol were synthesized and analyzed.•Activity of the metabolites against fungal plant pathogens was evaluated in vitro.•Metabolite 2-(2-hydroxypropyl) phenol was the most active in pathogen suppression.2-Allylphenol (2-AP) is an effective fungicide against a number of plant pathogens, which can be metabolized and bio-transformed to four chemical compounds by Rhizoctonia cerealis. To determine if its degradation affects antifungal activity, two major metabolites derived from 2-AP including 2-(2-hydroxypropyl) phenol and 2-(3-hydroxypropyl) phenol were synthesized. Inhibition of mycelial growth of several plant pathogens by the metabolites was evaluated, and structures of two metabolites were determined by hydrogen nuclear magnetic resonance (1H NMR). Among these metabolites, only 2-(2-hydroxypropyl) phenol inhibited test pathogens effectively. EC50 values of 2-(2-hydroxypropyl) phenol for inhibition of mycelial growth of R. cerealis, Pythium aphanidermatum, Valsa mali and Botrytis cinerea ranged from 1.0 to 23.5 μg/ml, which were lower than the parental fungicide 2-AP that ranged from 8.2 to 48.8 μg/ml. Hyphae of R. cerealis and P. aphanidermatum treated with 2-(2-hydroxypropyl) phenol were twisted. Newly developed hyphae were slender, twisted and swollen on the tip, while old hyphae were hollow and ruptured. This is the first report indicating the formation of 2-(2-hydroxypropyl) phenol may have contributed to toxicity of 2-allylphenol in control of plant pathogens.Download high-res image (70KB)Download full-size image