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An outbreak of Fusarium Head Blight of durum wheat occurred in 2004 being localized in sub-humid and higher semi-arid region of Northern Tunisia. A mycological survey carried out throughout these regions, revealed that 78% of the prospected fields were infested. Results of the morphological and molecular identification, showed that the most common species isolated from diseased wheat spikes was Microdochium nivale var. nivale (63.5%), followed by Fusarium culmorum (26%), F. pseudograminearum (9%) and F. avenaceum (1.5%). To evaluate mycotoxin content of naturally infected grain, the amounts of trichothecene mycotoxin deoxynivalenol (DON) in harvested grain from 45 fields were quantified by RIDASCREEN DON Enzyme Immunoassay Kit (ELISA). This study showed that the infection levels in freshly harvested grain were very low and the maximum deoxynivalenol (DON) level of the positive samples was 53 ppb. This is the first report on the natural occurrence of DON in naturally infected wheat grain sampled from Northern Tunisia.

Fusarium pseudograminearum is one of the major pathogens causing crown rot of wheat in the semi-arid and arid areas in Tunisia. In this study, the molecular diversity of 74 isolates of F. pseudograminearum representing three populations from Tunisia and a set of isolates from the world collection was investigated. The potential mycotoxin-producing ability was tested by PCR using primer pairs specific for the Tri3, Tri7 and Tri13 genes. Results indicated that all the isolates are potentially DON and ⁄ or 3-AcDON producers. The mating-type idiomorphs were identified using diagnostic PCR primer for MAT1-1 and MAT1-2. Both mating types were recovered from the same region and in some cases from the same field. Restriction analysis of the nuclear ribosomal DNA (nrDNA) intergenic spacer region (IGS) revealed 11 haplotypes, five of which were identified in the world collection. The analysis of population structure using the combined IGS and MAT data revealed that the total gene diversity (H T = 0.108) was mostly attributable to diversity within populations (H S = 0.102) and that the genetic differentiation among the four populations was low (G ST = 0.09). The analysis of molecular variance (amova amova) showed that 15% of the variability was between the Tunisian populations and the world collection. These findings indicate that quarantine measures should be in place to limit the introduction of new populations of F. pseudograminearum into Tunisia.

Emex spinosa (L.) is a common weed in cereal crops and pastures in northern Tunisia. The build up of the seed bank from a cropping-grazing farming system makes chemical and cultural controls inefficient. Biological control as part of integrated weed management may improve weed control. Diseased seedlings were collected from several locations in northern Tunisia during field surveys. Symptoms were small, circular, light brown leaf spots varying in size (1.75 to 3.5 mm in diameter) with a definite dark brown border on both sides of leaves that wilted and died. Microscopic observations showed conidiophores and conidia within and around the spots. Pure cultures from single conidia were obtained on carrot leaf extract agar. The fungus was identified as Cercospora tripolitana on the basis of identification keys described by Chupp (1). Conidia, borne on unbranched, fasciculated conidiophores, were elongate, hyaline, multiseptate, 110 to 150 × 1.8 to 3.7 μm (average 130 to 2.5 μm), and had truncate bases. For pathogenicity testing, six plants were sprayed with a spore suspension of 6 × 105 conidia/ml. Controls were sprayed with sterile distilled water. Plants were placed in a growth chamber at 22°C, 95% relative humidity, and 18/6 h of light/dark and monitored for symptoms. Ten days after inoculation, symptoms identical to those observed in the field were observed on inoculated plants. Control plants did not develop any symptoms. Four weeks later, diseased leaves turned yellow and died. The fungus was reisolated from symptomatic plants according to Koch's postulates. Although C. tripolitana has been previously reported in North and South Africa, to our knowledge, this is the first report of the fungus as a pathogen on E. spinosa under Tunisian agroecological conditions, making it a promising candidate for weed control. Reference: (1) C. Chupp. A Monograph of the Fungus Genus Cercospora. C. Chupp, Ithaca, New York, 1953.