The potential protein kinase A (Pka) phosphorylation site is required for the function of FgSge1 in Fusarium graminearum.

The new transcription factor Sge1 has garnered much attention in filamentous fungi recently, which highlights its role in pathogenicity, conidiation, and the production of secondary metabolites. In this study, we demonstrated that FgSge1 is localized in the nucleus in Fusarium graminearum using fluorescent protein GFP. Mutants containing a T67A mutation within the potential protein kinase A (Pka) phosphorylation site of FgSge1 exhibited a significant decrease in conidiation and dramatically impaired virulence on both wheat head and non-host tomato. These results indicated that the Pka phosphorylation site is required for the function of FgSge1 in F. graminearum. In addition, we characterized the FgSGE1 deletion mutants and found that the mutants showed increased sensitivity to osmotic stress mediated by NaCl or KCl, and to cell wall damaging agent congo red (CR). Real-time PCR assays revealed increased transcription levels of FgSGE1 with the treatment of NaCl or CR, and decreased FgSGE1 transcription in the FgOS-2 deletion mutant ΔFgOs-2. Based on the transcription levels, it can be concluded that FgSge1 is a downstream target of the mitogen-activated protein kinase FgOs-2.

Genetic diversity of Ralstonia solanacearum strains from China assessed by PCR-based fingerprints to unravel host plant- and site-dependent distribution patterns.

Bacterial wilt caused by Ralstonia solanacearum is a serious threat to crop production in China. A collection of 319 R. solanacearum strains isolated from 14 different diseased host plants collected in 15 Chinese provinces was investigated by BOX fingerprints in order to test the influence of the site and the host plant on their genetic diversity. Phylotype, fliC-RFLP patterns and biovar were determined for all strains and the sequevar for 39 representative strains. The majority of strains belonged to the Asian phylotype I, shared identical fliC-RFLP patterns and were assigned to four biovars (bv3:123; bv4:162; bv5:3; and bv6:11). Twenty strains were phylotype II, assigned to biovar 2, and had distinct fliC-RFLP patterns. BOX-PCR fingerprints generated from the genomic DNA of each strain revealed a high diversity of the phylotype I strains, where 28 types of BOX fingerprints could be distinguished. While many BOX clusters comprised isolates from different provinces and several host plants, some groups contained isolates that were plant or site specific. All phylotype II isolates originating from 10 provinces belonged to sequevar 1 and displayed identical BOX patterns as the potato brown rot strains from various regions of the world.

Biological control of aflatoxin contamination of crops.

Aflatoxins produced primarily by two closely related fungi, Aspergillus flavus and Aspergillus parasiticus, are mutagenic and carcinogenic in animals and humans. Of many approaches investigated to manage aflatoxin contamination, biological control method has shown great promise. Numerous organisms, including bacteria, yeasts and nontoxigenic fungal strains of A. flavus and A. parasiticus, have been tested for their ability in controlling aflatoxin contamination. Great successes in reducing aflatoxin contamination have been achieved by application of nontoxigenic strains of A. flavus and A. parasiticus in fields of cotton, peanut, maize and pistachio. The nontoxigenic strains applied to soil occupy the same niches as the natural occurring toxigenic strains. They, therefore, are capable of competing and displacing toxigenic strains. In this paper, we review recent development in biological control of aflatoxin contamination.

Repeat domain diversity of avrBs3-like genes in Ralstonia solanacearum strains and association with host preferences in the field.

Genes homologous to avrBs3 of Xanthomonas were detected in 309 strains of Ralstonia solanacearum biovars 3, 4, and 5 but not biovar 1 or 2. A statistically significant association between the originating plant species and internal repeats of the gene was found. Sequences of repeats and variation between nearly clonal strains revealed evidence of frequent recombination.

Curtobacterium flaccumfaciens pv. beticola, A New Pathovar of Pathogens in Sugar Beet.

Bacterial leaf spot of sugar beet was first discovered in 1995 in Inner Mongolia of China. The pathogen was shown to be a bacterium with properties of gram-positive bacteria: small irregular rods, lateral flagella, aerobic, and catalase-positive. The colonies of sugar beet strains produced a pale-yellow pigment. The optimum temperature for the bacteria to grow was 24 to 27°C. The bacteria could utilize a wide range of organic compounds, including hydrolyzed casein, starch, esculin and Tween 80, and released H2S from cysteine, cystine, and Na2S2O3·5H2O, but could not produce urease, oxidase, or indole. The cell wall peptidoglycan was based on ornithine (type B2ß). The predominant menaquinone was MK-9. Polar lipids contained several glycosyldiacyl-glycerols. The DNA G+C content of a type strain of the new pathovar, T30T, was 67.5%. DNA-DNA homology between T30T and Curtobacterium flaccumfaciens pv. flaccumfaciens (International Collection of Micro-Organisms from Plants, New Zealand [ICMP] 2584) was 70.1%. The new pathovar and C. flaccumfaciens pv. flaccumfaciens had 99.9% identity in DNA sequence of 16S rRNA. Close genetic relatedness was observed for the representatives of the species Curtobacterium flaccumfaciens, but a low level of similarity between the different pathovars was found. Based on these physiological, biochemical, chemotaxonomic, phylogenetic, and genetic characteristics, we demonstrate that the pathogen represents a new pathovar of C. flaccumfaciens, for which we propose the name Curtobacterium flaccumfaciens pv. beticola pv. nov. The type strain is T30T (=ATCC BAA-144T).

[RAPD analysis of plant pathogenic coryneform bacteria].

RAPD analysis was used for the taxonomy of plant pathogenic coryneform bacteria, especially for the classification of two new pathogens (Curtobacterium flaccumfaciens pv. basellae pv. nov. and Curtobacterium flaccumfaciens pv. beticola pv. nov.). 20 random primers were screened from 50 ones to detect polymorphism among the total strains used. 80.4% were polymorphic bands among the 225 ones produced. The results of pairwise similarity and UPGMA cluster analysis suggest that the two new pathovars of sugar beet (Beta vulgaris var. saccharifera) and malabar spinach (Basella rubra) are genetically close related with Curtobacterium flacumfaciens, and the minimal similarity coefficient is 0.6511. According to the RAPD analysis and previous research, some newly made taxonomic changes of the plant pathogenic coryneform bacteria are discussed.