Transcription of genes in the biosynthetic pathway for fumonisin mycotoxins is epigenetically and differentially regulated in the fungal maize pathogen Fusarium verticillioides.

When the fungal pathogen Gibberella moniliformis (anamorph, Fusarium verticillioides) colonizes maize and maize-based products, it produces class B fumonisin (FB) mycotoxins, which are a significant threat to human and animal health. FB biosynthetic enzymes and accessory proteins are encoded by a set of clustered and cotranscribed genes collectively named FUM, whose molecular regulation is beginning to be unraveled by researchers. FB accumulation correlates with the amount of transcripts from the key FUM genes, FUM1, FUM21, and FUM8. In fungi in general, gene expression is often partially controlled at the chromatin level in secondary metabolism; when this is the case, the deacetylation and acetylation (and other posttranslational modifications) of histones are usually crucial in the regulation of transcription. To assess whether epigenetic factors regulate the FB pathway, we monitored FB production and FUM1, FUM21, and FUM8 expression in the presence of a histone deacetylase inhibitor and verified by chromatin immunoprecipitation the relative degree of histone acetylation in the promoter regions of FUM1, FUM21, and FUM8 under FB-inducing and noninducing conditions. Moreover, we generated transgenic F. verticillioides strains expressing GFP under the control of the FUM1 promoter to determine whether its strength under FB-inducing and noninducing conditions was influenced by its location in the genome. Our results indicate a clear and differential role for chromatin remodeling in the regulation of FUM genes. This epigenetic regulation can be attained through the modulation of histone acetylation at the level of the promoter regions of the key biosynthetic genes FUM1 and FUM21, but less so for FUM8.

The ITS region as a taxonomic discriminator between Fusarium verticillioides and Fusarium proliferatum.

The maize pathogens Fusarium verticillioides (Fv) and Fusarium proliferatum (Fp) are morphologically very similar to one another, so Fp isolates have been often mistaken as Fusarium moniliforme (the former name of Fv). The only presently accepted morphological discriminator between these species is the presence/absence of polyphialides. Here, a collection of 100 Fusarium strains, isolated from infected maize kernels on plants grown in north-western Italy, were assigned as Fv or Fp on the basis of the presence/absence of polyphialides. This classification was tested on a subset of isolates by sexual crosses, ITS and calmodulin sequencing and AFLP profiling. An ITS-RFLP assay was extended to the full collection and to a number of Fv and Fp isolates of different geographical origin and hosts. The ITS region is proposed as taxonomically informative for distinguishing between Fp and Fv.

First Report of Leaf Blotch Caused by Marssonina coronaria on Apple in Italy.

During the early summers of 2001 and 2002, in Forno Canavese in northwest Italy, a leaf disease was observed on the old apple cv. Furnas in a domestic orchard. Lesions on the upper side of the leaf were brownish, irregular in size and shape with somewhat dendritic margins, became black, and often coalesced with time. On the underside, lesions were smaller with more definite margins. Beginning in July, scattered acervuli (95 to 170 µm) were observed erupting through the epidermis on the upper side of leaves. Conidia were ampule shaped, 1-septate, constricted at the septum, hyaline, guttulate, and 6.1 to 8.4 × 14.6 to 22.0 µm. Severely diseased leaves abscised prematurely. The fungus was identified as Marssonina coronaria (Ellis & J.J. Davis) J.J. Davis, teleomorph Diplocarpon mali (1) although the conidia were slightly shorter than those originally described for this fungus. Monoconidial isolates were obtained by spreading mini-suspensions of conidia taken from acervuli on malt agar (MA) and transferring single-germinated conidia to MA, potato dextrose agar, V8 agar, or apple leaf agar (ALA). The fungus grew slowly, producing small colonies on V8 and ALA only. On ALA medium, after 3 months incubation at 20 to 22°C, the colonies were 5 to 7 mm in diameter with light brown, irregular margins and dark brown centers bearing acervuli. Conidia from pure cultures were collected, suspended in sterile, distilled water (250,000 ml-1), and sprayed on the leaves of three 'Golden Delicious' apple shoots maintained in a mist chamber at 20 to 25°C for 2 weeks. In two independent experiments, the fungus reproduced symptoms like those observed on 'Furnas' and was reisolated from acervuli. No symptoms were observed on water-treated controls. To our knowledge, apple leaf blotch has not previously been reported in Italy. Although now it is a minor disease, it could become more important in sustainable crops because of its relatively low sensitivity to copper fungicides (2), the only products that can be used under that program. References: (1) Y. Harada et al. Ann. Phytopathol. Soc. Jpn. 40:412, 1974. (2) J. Ruide et al. China Fruits 2:51, 1997.

First Report of Phytophthora cinnamomi on High-Bush Blueberry in Italy.

Beginning in the summer of 1996, a disease of high-bush blueberry (Vaccinium corymbosum L.) appeared on cvs. Sparta and Berkeley in commercial plantings near Cuneo and in a nursery in Pinerolo (northwest Italy). In the field, the disease became evident 5 to 8 months after planting. Symptoms included stunting, pale green-to-reddish leaves, premature defoliation, and root and crown rot. The root system was reduced, with few feeder roots and a dark discoloration of the root cortex. Root, crown, and basal stem rot led to death of the plants. Pieces of the discolored organs were surface-sterilized in sodium hypochlorite (2%) for 5 min, rinsed in sterile water, dried on sterile filter paper, and plated on acidified malt extract agar (pH 4.6) (MEA) and a selective medium for oomycetes (2). Slow-growing colonies developed on MEA, whereas colonies characteristic of Phytophthora spp. grew on the selective medium for oomycetes. Six isolates from plants collected from the field and the nursery were inoculated as V8 juice culture homogenate on the roots of blueberry cv. Berkeley, azalea, and 1-year-old chestnut plants in pots. All six isolates reproduced the symptoms in blueberry and caused root and foot rot in the other hosts. The original fungus was reisolated from all inoculated hosts. The isolates were examined and compared with strain 0229 of P. cinnamomi Rands from the International Mycological Institute. They were identified as P. cinnamomi on the basis of morphological characteristics and total mycelial soluble protein patterns on sodium dodecyl sulfate-polyacrylamide gel electrophoresis. In Italy, blueberry is a new host for this pathogen that was previously observed in rhododendron (1), and recently in chestnut (3) and other forest species. Because of the high risk of spreading the pathogen to areas where susceptible plants are grown, it is recommended that high-bush blueberry nursery stock be tested for the pathogen. References: (1) G. Gullino and A. Garibaldi. La difesa delle piante 10:273, 1987; (2) H. Masago et al. Phytopathology 67:425, 1977. (3) A. M. Vettraino et al. Plant Pathol. 50:90, 2001.