Infraspecific variation demonstrated in Phomopsis leptostromiformis using cultural and biochemical techniques

Growth and toxin production of phomopsin A and ochratoxin A forming fungi under different storage conditions in a pea (Pisum sativum) model system

Phomopsins are mycotoxins mainly infesting lupines, with phomopsin A (PHOA) being the main mycotoxin. PHOA is produced by Diaporthe toxica, formerly assigned as toxigenic Phomopsis leptostromiformis, causing infections in lupine plants and harvested seeds. However, Diaporthe species may also grow on other grain legumes, similar to Aspergillus westerdijkiae as an especially potent ochratoxin A (OTA) producer. Formation of PHOA and OTA was investigated on whole field peas as model system to assess fungal growth and toxin production at adverse storage conditions. Field pea samples were inoculated with the two fungal strains at two water activity (aw) values of 0.94 and 0.98 and three different levels of 30, 50, and 80% relative air humidity.After 14 days at an aw value of 0.98, the fungi produced 4.49 to 34.3 mg/kg PHOA and 1.44 to 3.35 g/kg OTA, respectively. Strains of D. toxica also tested showed higher PHOA concentrations of 28.3 to 32.4 mg/kg.D. toxica strains did not grow or produce PHOA at an aw values of 0.94, while A. westerdijkiae still showed growth and OTA production.Elevated water activity has a major impact both on OTA and, even more pronouncedly, on PHOA formation and thus, proper drying and storage of lupins as well as other grain legumes is crucial for product safety.

Phomopsins: an overview of phytopathological and chemical aspects, toxicity, analysis and occurrence

Phomopsis leptostromiformis, and its teleomorph Diaporthe toxica, is a lupin pathogen that causes stem blight in young lupins and, as a saprophyte, has been detected on dead lupine material. Under favourable conditions, the fungus produces phomopsins (PHOs), a family of macrocyclic hexapeptide mycotoxins capable of binding tubulin through the tripeptide side chain. The toxic effects appear largely confined to the liver. In particular, the ingestion of PHO contaminated lupin stubble has been linked to lupinosis, a debilitating disease of sheep (the most sensitive animal) characterised by disorientation, blindness, lethargy, and eventually death. The chemical structures of PHO A, B and D have been identified. Analytical methods to determine PHOs are mainly enzyme-linked immunosorbent assays or chromatographic separations, in combination with ultraviolet and mass spectrometric detection. The data about the PHOs occurrence are limited to Australia, restricted to lupin seed. Only one survey has been carried out on lupin seeds and flours from the Swiss market. Not many strategies have been developed to limit lupin seed contamination. Efforts devoted to control lupinosis in Australia focused on the development of cultivars resistant to Phomopsis infection. There are few examples in literature of decontamination or detoxification of PHOs; moreover, they have been shown to be resistant to extensive processing, including cooking. Australia and New Zealand are the only countries that included PHOs in their mycotoxin regulations, with a limit of 5 µg/kg in lupin seeds and derived products. Phomopsins are poorly studied mycotoxins and risk assessment on PHOs has not been done at the European level. The collection of all available scientific data was requested by EFSA in a specific project and partners involved considered it of general interest preparing this review to highlight the limited available information, which indicate that the assessment of potential risk related to PHOs is currently not feasible.

Cytology of irregular growth forms of Ophiostoma ulmi and Ophiostoma novo-ulmi growing through millipore filter membranes and sterilized elm wood sections

When Ophiostoma ulmi or Ophiostoma novo-ulmi are grown on either 0.22- or 0.45-μm millipore filter membranes placed on impoverished agar medium, the fungus grows through these membranes and takes on various irregular pleomorphic growth forms (P-forms). Links of continuity between these forms and the more regular ones have been shown using light, confocal, and transmission electron microscopy. Tests with labelled probes, such as gold-complexed wheat germ agglutinin for chitin and β-exoglucanase for cellulosic β-1,4-glucans, have indicated that in P-forms deposition of chitin is much altered but is less so in the case of cellulosic glucan. The cytology of these forms compared with the regular fungal ones is also very different, particularly with reference to mitochondria and nuclei. Also, numerous vesiculate structures were noted in the rarely septate P-forms. Similar irregular forms with opaque contents were produced by these fungi when they were grown on sterilized elm wood sections. When these latter samples were fixed by high-pressure freezing, the following main features were noted: fungal cells with a very thin wall, slightly labelled for chitin but more intensely for cellulosic glucans; well-preserved structures, such as plasmalemma and endoplasmic reticulum; and a slightly opaque, fibril-containing extracellular sheath. Differences in labelling for galactose, whether of wall layers or cell contents, were also observed in regular and P-forms. Electron opaque bodies that labelled strongly for galactose were also numerous in P-forms in some samples.Key words: transmission electron microscopy, high-pressure freezing, gold labelling, extracellular sheaths, wall constituents.