Bacillus subtilis XF-1 is a gram-positive, plant-associated bacterium that stimulates plant growth and produces secondary metabolites that suppress soil-borne plant pathogens. In particular, it is especially highly efficient at controlling the clubroot disease of cruciferous crops. Its 4,061,186-bp genome contains an estimated 3853 protein-coding sequences and the 1155 genes of XF-1 are present in most genome-sequenced Bacillus strains: 3757 genes in B. subtilis 168, and 1164 in B. amyloliquefaciens FZB42. Analysis using the Cluster of Orthologous Groups database of proteins shows that 60 genes control bacterial mobility, 221 genes are related to cell wall and membrane biosynthesis, and more than 112 are genes associated with secondary metabolites. In addition, the genes contributed to the strain's plant colonization, bio-control and stimulation of plant growth. Sequencing of the genome is a fundamental step for developing a desired strain to serve as an efficient biological control agent and plant growth stimulator. Similar to other members of the taxon, XF-1 has a genome that contains giant gene clusters for the non-ribosomal synthesis of antifungal lipopeptides (surfactin and fengycin), the polyketides (macrolactin and bacillaene), the siderophore bacillibactin, and the dipeptide bacilysin. There are two synthesis pathways for volatile growth-promoting compounds. The expression of biosynthesized antibiotic peptides in XF-1 was revealed by matrix-assisted laser desorption/ionization-time of flight mass spectrometry.

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Since 2002 a severe root and stem disease of Dendrobium has occurred periodically each year in the plantations of Simao City, Yunnan Province, China. Symptoms included water-soaked and brown lesions, and rot of tissues. Based on the morphological characteristics and the internal transcribed spacer-1, 5.8S ribosomal RNA gene, and internal transcribed spacer 2 and b-tubulin gene sequences, the pathogen was identified as Pythium vexans de Bary. The pathogenicity of the fungus was confirmed by satisfying KochÕs postulates. This is the first world record of stem rot of Dendrobium caused by P. vexans.

Maize chlorotic mottle virus (MCMV) is one of the co‐infection pathogens that cause corn (maize) lethal necrosis, but the transmission mechanism of MCMV is not yet clear. In order to determine the ability of western flower thrips (Frankliniella occidentalis; WFT) to transmit MCMV, imported maize seeds from Thailand were germinated in an insect‐free greenhouse and the seedlings were tested for the transmission by WFT of chlorotic mottle virus disease. The thrips (WFT), starved for 48 h then allowed to feed for 30 min on maize plants infected with MCMV or asymptomatic maize plants, were transferred to healthy seedlings. After 35 days, the seedlings with WFT from diseased maize plants showed chlorotic mottle symptoms, whereas seedlings with WFT from asymptomatic maize plants remained healthy. A single band of 711 bp was amplified by RT‐PCR using primers MCMV‐F/MCMV‐R from the MCMV‐infected plants and WFT collected from the diseased plants. Sequencing of the amplified product and further sequence comparison indicated that the two viruses from both sources showed 99% similarity of nucleotides and they should be regarded as identical. In addition, isometric particles c. 30 nm in diameter, characteristic of MCMV, were found in the WFT samples from diseased maize plants. Thus, it is concluded that WFT transmits MCMV. Our findings suggest that corn lethal necrosis disease can be controlled or minimized by the eradication of WFT from the field or greenhouses.

A total of 13 Fusarium isolates were obtained from samples of malformed mango seedlings from Yunnan and Sichuan provinces in China, and five morphologically similar isolates were confirmed causing the disease by satisfying KochÕs postulates. One typical isolate (MG4) was selected for detailed morphological and molecular studies. Based on the following morphological characteristics, isolate MG4 was identified as Fusarium proliferatum: white aerial mycelium on PSA (potato sucrose agar: potato 200 g; sucrose 15 g; agar 18 g; distilled water 1000 ml) medium; hyaline reverse of colonies on PSA; production of pink pigment on rice medium and the production of conidia on branched conidiophore with monophialides bearing false heads of conidia. On carnation leaf agar medium, the microconidia were ovate to elongated ovoid, 0-1 septate, 3.1-10.2 · 1.5-2.2 lm; the macroconidia were fusiform, 3-5 septate, 18-38 · 1.8-2.4 lm, whereas chlamydospores and sexual structures were absent on all media used. The identity of the pathogen was confirmed by its high similarity (99.8-100%) in the sequence alignment of rDNA-ITS 1 and 4 with both isolates of F. proliferatum in the GenBank database.

Bacillus subtilis XF-1 has been used as a biocontrol agent of clubroot disease of crucifers infected by Plasmodiophora brassicae, an obligate pathogen. In order to maximize the growth inhibition of the pathogen, random mutagenesis using N-methyl-N'-nitro-N-nitrosoguanidine was applied to strain XF-1. The efficacy of 226 selected mutants was assessed against the growth of an indicator fungal pathogen: Fusarium solani using agar plate assay and the disruptive effects on the resting spores of P. brassicae. Four mutants exhibited inhibition activity significantly higher than the wild type. The cell extracts of these mutants and the XF-1 were subjected to matrix-assisted laser desorption ionization-time of flight mass spectra analysis, and three families of cyclic lipopeptides (CLPs) fengycin, surfactin and iturin were identified from the parental strain and the screened mutants. However, the relative contents and compound diversity changed after mutagenesis, and there was slight variation in the surfactin and fengycin. Notably, only 5 iturin components were discovered from the wild strain XF-1, but 13 were obtained from the mutant strains, and the relative CLPs contents of all mutant strains increased substantially. The results suggested that CLPs might be one of main biocontrol mechanisms of the clubroot disease by XF-1. The 4 mutants are far more effective than the parental strain, and they would be promising biocontrol candidates not only against P. brassicae but probably other plant diseases caused by fungi.