Giovanna Delogu

Fusarium culmorum: causal agent of foot and root rot and head blight on wheat

UNLABELLED Fusarium culmorum is a ubiquitous soil-borne fungus able to cause foot and root rot and Fusarium head blight on different small-grain cereals, in particular wheat and barley. It causes significant yield and quality losses and results in contamination of the grain with mycotoxins. This review summarizes recent research activities related to F. culmorum, including studies into its population diversity, mycotoxin biosynthesis, mechanisms of pathogenesis and resistance, the development of diagnostic tools and preliminary genome sequence surveys. We also propose potential research areas that may expand our basic understanding of the wheat-F. culmorum interaction and assist in the management of the disease caused by this pathogen. TAXONOMY Fusarium culmorum (W.G. Smith) Sacc. Kingdom Fungi; Phylum Ascomycota; Subphylum Pezizomycotina; Class Sordariomycetes; Subclass Hypocreomycetidae; Order Hypocreales; Family Nectriaceae; Genus Fusarium. DISEASE SYMPTOMS Foot and root rot (also known as Fusarium crown rot): seedling blight with death of the plant before or after emergence; brown discoloration on roots and coleoptiles of the infected seedlings; brown discoloration on subcrown internodes and on the first two/three internodes of the main stem; tiller abortion; formation of whiteheads with shrivelled white grains; Fusarium head blight: prematurely bleached spikelets or blighting of the entire head, which remains empty or contains shrunken dark kernels. IDENTIFICATION AND DETECTION: Morphological identification is based on the shape of the macroconidia formed on sporodochia on carnation leaf agar. The conidiophores are branched monophialides, short and wide. The macroconidia are relatively short and stout with an apical cell blunt or slightly papillate; the basal cell is foot-shaped or just notched. Macroconidia are thick-walled and curved, usually 3-5 septate, and mostly measuring 30-50 × 5.0-7.5 μm. Microconidia are absent. Oval to globose chlamydospores are formed, intercalary in the hyphae, solitary, in chains or in clumps; they are also formed from macroconidia. The colony grows very rapidly (1.6-2.2 cm/day) on potato dextrose agar (PDA) at the optimum temperature of 25 °C. The mycelium on PDA is floccose, whitish, light yellow or red. The pigment on the reverse plate on PDA varies from greyish-rose, carmine red or burgundy. A wide array of polymerase chain reaction (PCR) and real-time PCR tools, as well as complementary methods, which are summarised in the first two tables, have been developed for the detection and/or quantification of F. culmorum in culture and in naturally infected plant tissue. HOST RANGE Fusarium culmorum has a wide range of host plants, mainly cereals, such as wheat, barley, oats, rye, corn, sorghum and various grasses. In addition, it has been isolated from sugar beet, flax, carnation, bean, pea, asparagus, red clover, hop, leeks, Norway spruce, strawberry and potato tuber. Fusarium culmorum has also been associated with dermatitis on marram grass planters in the Netherlands, although its role as a causal agent of skin lesions appears questionable. It is also isolated as a symbiont able to confer resistance to abiotic stress, and has been proposed as a potential biocontrol agent to control the aquatic weed Hydrilla spp. USEFUL WEBSITES http://isolate.fusariumdb.org/; http://sppadbase.ipp.cnr.it/; http://www.broad.mit.edu/annotation/genome/fusarium_group/MultiHome.html; http://www.fgsc.net/Fusarium/fushome.htm; http://plantpath.psu.edu/facilities/fusarium-research-center; http://www.phi-base.org/; http://www.uniprot.org/; http://www.cabi.org/; http://www.indexfungorum.org/

Optically active nitrogen ligans: III. Enantioface-discriminating transfer hydrogenation of acetophenone catalyzed by rhodium(I) complexes with chiral 2-(2′-pyridyl)pyridines

Abstract The reduction of acetophenone by hydrogen transfer from isopropranol is catalyzed by rhodium(I) complexes containing optically active 2-(2′-pyridyl)pyridines. Optical yields up to 15% have been obtained.

Optically active phenanthrolines in asymmetric catalysis. III. Highly efficient enantioselective transfer hydrogenation of acetophenone by chiral rhodium/3-alkyl phenanthroline catalysts.

Abstract The in situ catalysts prepared from [Rh(Diol)Cl]2 (Diol = 1,5-Hexadiene or 1,5-Cyclooctadiene) and 3-alkylphenanthrolines display an extremely high catalytic activity in the transfer hydrogenation of acetophenone. Turn over rates up to 10,000 cycles-per-hour (c/h) have been recorded in 2-propanol solution at 83°C in the presence of KOH as a promoter. Asymmetric inductions up to 655 e.e. are obtained with the ligand 3c bearing a chiral trimethylpropyl substituent. This is an extraordinarily high value in view of the long distance existing between the chiral carbon atom and the reactive site of the catalyst. Experimental evidences suggest that in the asymmetric process the most active and stereoselective catalytic species might be a rhodium hydride complex containing two phenanthroline ligands in a chiral C2 array.

Hydrocarbonylation of unsaturated nitrogen compounds. Synthesis of N-protected aminoacid derivatives from N-substituted phthalimides

Abstract The hydrocarbonylation of some β-substituted N -vinylphthalimides catalysed by Rh or Pd complexes has been investigated. The reaction is strongly affected by the nature of the substituent and is completely prevented when two substituents are present. The addition of carbon monoxide, when it occurs, takes place with complete selectivity and its direction can be regulated to a large extent by selecting the reaction parameters. The hydrocarbonylation of N -allylphthalimide occurs under mild conditions but the control of the regioselectivity is much less efficient.

Optically active phenanthrolines in asymmetric catalysis. IV, Enantioselective hydrosilylation of acetophenone by rhodium/chiral alkyl phenanthroline catalysts

Abstract Thein situ catalysts prepared from [Rh(Cod)Cl]2 (Cod = 1,5-cyclooctadiene) and chiral alkylphenanthroline ligands1–6 display a remarkable activity in the asymmetric hydrosilylation of acetophenone affording, after hydrolysis, the expected 1-phenylethanol in high yield and complete selectivity. High enantioselectivities, up to 76%, were obtained in the presence of 2-substituted derivatives5 and6, whereas 3-alkylphenanthrolines1–4 gave e.e.s not higher than 6%. High chemical yields, but modest enantioselectivities (10–20% e.e.) were recorded with the potentially terdentate ligands7–10. Chiral alkylphenanthrolines were poorly efficient ligands in the asymmetric Ni-catalysed cross-coupling of α-methylbenzylmagnesium chloride with vinyl bromide.

Optically active phenanthrolines in asymmetric catalysis. II: Enantioselective transfer hydrogenation of acetophenone by rhodium/alkyl phenanthroline catalysts

Abstract Three new alkyl phenanthrolines containing a norpinanyl substituent as the common chiral target, have been synthesized and tested as ligands in the rhodium-catalyzed asymmetric transfer hydrogenation of acetophenone. A marked catalytic activity was observed, but the highest optical yield was 24% e.e.

Altered trichothecene biosynthesis in TRI6-silenced transformants of Fusarium culmorum influences the severity of crown and foot rot on durum wheat seedlings

An RNA silencing construct was used to alter mycotoxin production in the plant pathogenic fungus Fusarium culmorum, the incitant of crown and foot rot on wheat. The transformation of a wild-type strain and its nitrate reductase-deficient mutant with inverted repeat transgenes (IRTs) containing sequences corresponding to the trichothecene regulatory gene TRI6 was achieved using hygromycin B resistance as a selectable marker. Southern analysis revealed a variety of integration patterns of the TRI6 IRT. One transformant underwent homologous recombination with deletion of the endogenous TRI6 gene, whereas, in another transformant, the TRI6 IRT was not integrated into the genome. The TRI6 IRT did not alter the physiological characteristics, such as spore production, pigmentation or growth rate, on solid media. In most transformants, a high TRI6 amplification signal was detected by quantitative reverse transcription-polymerase chain reaction, corresponding to a TRI6-hybridizing smear of degraded fragments by Northern analysis, whereas TRI5 expression decreased compared with the respective nontransformed strain. Four transformants showed increased TRI5 expression, which was correlated with a dramatic (up to 28-fold) augmentation of deoxynivalenol production. Pathogenicity assays on durum wheat seedlings confirmed that impairment of deoxynivalenol production in the TRI6 IRT transformants correlated with a loss of virulence, with decreased disease indices ranging from 40% to 80% in nine silenced strains, whereas the overproducing transformants displayed higher virulence compared with the wild-type.

Asymmetric hydroformylation of styrene by rhodium(I) catalysts with chiral ligands containing sulfur donors

Rhodium(I) complexes containing the atropisomeric sulfur ligands 1,1′-binaphthalene-2,2′-dithiol 1(binas) or the relevant dimethyl sulfide 2(Me2binas) are efficient catalysts for the highly regioselective hydroformylation of styrene.

Optically active phenanthrolines in asymmetric catalysis. Rhodium-catalyzed asymmetric transfer hydrogenation of acetophenone

Abstract The catalyst formed in situ from [Rh(1,5-cyclooctadiene)Cl]2 and (+)-(S)-3-s-butyl-1,10-phenanthroline promotes the asymmetric transfer hydrogenation of acetophenone in isopropanol solution; optical yields of up to 31% are obtained.

Natural and Natural-like Phenolic Inhibitors of Type B Trichothecene in Vitro Production by the Wheat (Triticum sp.) Pathogen Fusarium culmorum

Fusarium culmorum, a fungal pathogen of small grain cereals, produces 4-deoxynivalenol and its acetylated derivatives that may cause toxicoses on humans or animals consuming contaminated food or feed. Natural and natural-like compounds belonging to phenol and hydroxylated biphenyl structural classes were tested in vitro to determine their activity on vegetative growth and trichothecene biosynthesis by F. culmorum. Most of the compounds tested at 1.5 or 1.0 mM reduced 3-acetyl-4-deoxynivalenol production by over 70% compared to the control, without affecting fungal growth significantly. Furthermore, several compounds retained their ability to inhibit toxin in vitro production at the lowest concentrations of 0.5 and 0.25 mM. Magnolol 27 showed fungicidal activity even at 0.1 mM. No linear correlation was observed between antioxidant properties of the compounds and their ability to inhibit fungal growth and mycotoxigenic capacity. A guaiacyl unit in the structure may play a key role in trichothecene inhibition.