The possible involvement of cytokinins in the pathogenicity of Helminthosporium maydis

Green islands/infection sites recorded higher cytokinin activity than surrounding tissue as well as non-inoculated tissue. This activity in infected areas increased with time of incubation while in tissue surrounding the green islands and non-inoculated tissue, cytokinin activity decreased with time of incubation. The culture filtrate extracts of H. maydis had cytokinin activity which increased with growth of the fungus. Cytokinin activity of thin-layer Chromatographic fractions from tissue and culture filtrate extracts revealed that a major portion of the activity was confined to Rf zone 0.6 to 0.8 which co-chromatographed with zeatin and zeatin riboside. Presence of zeatin and zeatin riboside in tissue and culture filtrates was confirmed by high performance liquid chromatography. Cytokinin substances, such as zeatin and zeatin riboside, increase at infection sites with growth of the pathogen suggesting they may be involved in the pathogenicity of H. maydis on maize.     

Pathogenesis of barley leaves by Helminthosporium teres I: Green island formation and the possible involvement of cytokinins

Infection sites/green islands were formed in host leaf tissue infected with drops of H. teres. They exhibited higher cytokinin-like activity, sugar and starch than their surrounding tissue and tissue under water drops. The cytokinin-like activity at the infection sites increased from 24 to 72 h of incubation. However, the cytokinin-like activity of the tissue surrounding the infection drops and the tissue under water drops fell from 24 to 72 h incubation. The culture filtrate extracts of the fungus also produced cytokinin-like activity which increased from 1 to 10 days incubation. Application of this culture filtrate extract evoked green island formation. Application of kinetin to host leaves duplicated the green island effect. Thin-layer chromatographic fractions of the tissue extracts and the culture filtrate extracts revealed that a major portion of cytokinin-like activity corresponded to zeatin and zeatin riboside. The presence of zeatin and zeatin riboside (both in tissue and culture filtrate extracts) was confirmed by high performance liquid chromatography. Increases in the amounts of cytokinin-like substances, particularly zeatin and zeatin riboside, attributed to pathogen influence are suggested to be involved in infection and pathogenicity of H. teres.     

Genetic variation in Drechslera teres populations as indicated by RAPD markers

Random amplified polymorphic DNA (RAPD) was used to assess genetic variation among 48 isolates of Drechslera teres originating from different sites in Finland. RAPD profiles were generated with five arbitrary 10-mer primers and revealed polymorphisms suitable for screening differentiation in this fungal population. Using UPGMA clustering analysis, a similarity coefficient of approximately 63% was observed between all D. teres isolates studied. The variation was, however, distributed on a small scale as different genotypes were found from the same plant. The isolates could not be grouped according to geographic origin, aggressiveness, growth rate or morphological features, indicating that the primers used in this study were neutral markers for these characters. The primers were, however, able to differentiate between isolates of Helminthosporium species (D. teres, Drechslera graminea and Bipolaris sorokiniana).     

Biotransformation of organic sulfides. Part 9. Formation of (S) para-substituted phenyl methyl sulfoxides by biotransformation usingHelminthosporium species NRRL 4671

Phenyl methyl sulfides substituted in thepara position with methyl, fluoro, chloro, bromo, cyano, nitro, amino, acyl, methoxy, thiomethyl and methylsulfinyl groups have been converted to (S) sulfoxides by biotransformation usingHelminthosporium species NRRL 4671. The highest yields and enantiomeric excesses were obtained with bromo, cyano, methoxy, thiomethyl and methylsulfinyl substituents and in two cases (para-Br and -CN) the products could be crystallized to give (S) sulfoxide of ≥ 96% ee.     

Biodegradation of rice stumps by soil mycoflora

Summary Cellulose and lignin contents in left-overs of rice stump decreased due to decay caused by soil mycoflora. The loss of cellulose and lignin was considerable in presence of Curvularia and Fusarium respectively. Other tested mycoflora could also destroy cellulose and lignin to some extent. The amount of loss of cellulose and lignin increased with time of incubation of the tested mycoflora.     

粟长孺孢菌的异核现象

本文报道了粟长孺孢的菌(Hetminthosporium setariae)的异核现象。用γ-射线和甲基磺酸乙酯诱变获得的颜色、形态和营养突变株(H8、Hw)可在基本培养基上形成异核体(8W)。其以上各种特性不同于亲本。 8W分离之后的突变株可稳定地传代,混合后仍能形成异核体。从而证实了该菌的异核性。观察并测定了亲本株和异核体的生长率、致病性及产孢能力。粟长孺孢菌(H8)和玉蜀黍长孺孢菌(866·R-8)可形成种间异核体。     

The discovery of the virulence gene ToxA in the wheat and barley pathogen Bipolaris sorokiniana

Bipolaris sorokiniana is the causal agent of multiple diseases on wheat and barley and is the primary constraint to cereal production throughout South Asia. Despite its significance, the molecular basis of disease is poorly understood. To address this, the genomes of three Australian isolates of B. sorokiniana were sequenced and screened for known pathogenicity genes. Sequence analysis revealed that the isolate BRIP10943 harboured the ToxA gene, which has been associated previously with disease in the wheat pathogens Parastagonospora nodorum and Pyrenophora tritici‐repentis. Analysis of the regions flanking ToxA within B. sorokiniana revealed that it was embedded within a 12‐kb genomic element nearly identical to the corresponding regions in P. nodorum and P. tritici‐repentis. A screen of 35 Australian B. sorokiniana isolates confirmed that ToxA was present in 12 isolates. Sequencing of the ToxA genes within these isolates revealed two haplotypes, which differed by a single non‐synonymous nucleotide substitution. Pathogenicity assays showed that a B. sorokiniana isolate harbouring ToxA was more virulent on wheat lines that contained the sensitivity gene when compared with a non‐ToxA isolate. This work demonstrates that proteins that confer host‐specific virulence can be horizontally acquired across multiple species. This acquisition can dramatically increase the virulence of pathogenic strains on susceptible cultivars, which, in an agricultural setting, can have devastating economic and social impacts.     

Mitochondrial DNA variation in maize plants regenerated during tissue culture selection

Summary Plants resistant to Helminthosporium maydis race T were obtained following selection for H. maydis pathotoxin resistance in tissue cultures of susceptible, Texas male-sterile (T) cytoplasm maize. The selected lines transmitted H. maydis resistance to their sexual progeny as an extranuclear trait. Of 167 resistant, regenerated plants, 97 were male fertile and 70 were classified male sterile for reasons that included abnormal plant, tassel, anther or pollen development. No progeny were obtained from these male-sterile, resistant plants. Male fertility and resistance to the Phyllosticta maydis pathotoxin that specifically affects T cytoplasm maize were co-transmitted with H. maydis resistance to progeny of male-fertile, resistant plants. These three traits previously were associated only with the normal (N) male-fertile cytoplasm condition in maize. Three generations of progeny testing provided no indication that the cytoplasmic association of male sterility and toxin susceptibility had been broken by this selection and regeneration procedure. Restriction endonuclease analysis of mitochondrial DNA (mtDNA) revealed that three selected, resistant lines had distinct mtDNA organization that distinguished them from each other, from T and from N cytoplasm maize. Restriction patterns of the selected resistant lines were similar to those from T cytoplasm mtDNA; these patterns had not been observed in any previous analyses of various sources of T cytoplasm. The mtDNA analyses indicated that the male-fertile, toxin-resistant lines did not originate from selection of N mitochondrial genomes coexisting previously with T genomes in the T cytoplasm line used for selection.Scientific Journal Series Article no. 11,185 of the Minnesota Agricultural Experiment Station and no. 2295 of the Florida Agricultural Experiment Station. Mention of a trademark, proprietary product, or vendor does not constitute a guarantee of warrantly of the product by the U.S. Department of Agriculture and does not imply its approval to the exclusion of other products or vendors that may also be suitable     

Identification of an RFLP marker tightly linked to theHt1 gene in maize

Summary We have identified tight linkage of an RFLP marker to theHt1 gene of maize that confers resistance to the fungal pathogenHelminthosporium turcicum race 1. This was accomplished by the use of four pairs of near isogenic lines (NILs; B73, A619, W153R, and CM105), each differing by the presence or the absence of the geneHt1. SinceHt1 maps to chromosome 2, 26 clones already mapped to this chromosome were labeled and probed against Southern blots of these NILs DNA digested with three restriction enzymes:EcoRI,BamHI, andHindIII. Six markers exhibited an RFLP for at least one pair of NILs. Presumptive linkage was further tested by analyzing the segregation of five of the six markers (one was monomorphic in the cross studied) and resistance toH. turcicum race 1 on 95 F₂ individuals from the cross DF20 × LH146Ht. The results indicate a tight linkage between one of the DNA markers,UMC150B, and theHt1 gene.