L. Hoffmann, and
T. Bohn, Centre de Recherche Public--Gabriel Lippmann, Department Environment and Agro-Biotechnologies; 41, Rue du Brill; L-4422, Belvaux, Luxembourg
Head blight caused by Fusarium graminearum is one of the major diseases of wheat (Triticum aestivum L.) in Luxembourg (2) and there is concern for mycotoxins in diseased grain. Isolates of F. graminearum have been assigned to chemotypes based on the particular toxins produced. Ten wheat fields representing different topoclimatological areas of Luxembourg were surveyed in 2007 and 2008 to determine the frequency and distribution of chemotypes. Partially blighted wheat heads were collected, and diseased grains were plated on Fusarium-selective agar (dichloran-chloramphenicol-peptone) for 12 days at 22 ± 2°C with a 12-h light period. Monoconidial isolates of F. graminearum (79 in 2007 and 85 in 2008) were obtained by conidia dilution on 2% water agar and needle selection under a microscope. F. graminearum isolates showed rapid growth on potato dextrose agar, dense aerial mycelium with red pigment deposits in the plate, macroconidia with five to six defined septa, and a basal cell with the typical foot shape. Microconidia were absent. To confirm species identification, a PCR reaction was carried out using the F. graminearum species-specific primers Fg16F (5′-CTCCGGATATGTTGCGTCAA-3′) and Fg16R (5′-GGTAGGTATCCGACATGGCAA-3′) according to Demeke et al. (1). Chemotype of each isolate was determined according to Ward et al. (4). In particular, PCR primer 12CON (5′ CATGAGCATGGTGATGTC-3′) coupled with primer 12NF (5′-TCTCCTCGTTGTATCTGG-3′) and primer 3CON (5′-TGGCAAAGACTGGTTCAC-3′) coupled with primer 3NA (5′-GTGCACAGAATATACGAGC-3′) identified the nivalenol chemotype, primer 12CON coupled with primer 12-15F (5′-TACAGCGGTCGCAACTTC-3′) and primer 3CON coupled with primer 3D15A (5′-ACTGACCCAAGCTGCCATC-3′) identified the 15-acetylated deoxynivalenol (DON) chemotype, while primer 12CON coupled with primer 12-3F (5′-CTTTGGCAAGCCCGTGCA-3′) and primer 3CON coupled with primer 3D3A (5′-CGCATTGGCTAACACATG-3′) identified 3-acetylated DON chemotype. Reactions were repeated two times and positive controls (provided by Kerry O'Donnell, NRRL collection, Peoria, IL) and a negative control (water) were used in each reaction. Frequency of the nivalenol chemotype was found to be 2.5% in 2007 and 1% in 2008. Interestingly, the nivalenol chemotype was absent in southern Luxembourg. According to this finding, nivalenol was likely to be present at low levels in grain from Reisdorf and Echternach in 2007 (central Luxembourg) and in 2008 from grain of Troisvierges (northern Luxembourg). The remaining isolates in both years belonged to the 15-acetylated DON chemotype and the 3-acetylated DON chemotype was not detected. Compared with a previous report from the Netherlands (3), the nivalenol chemotype in Luxembourg is less frequent and widespread. To our knowledge, this is the first report of the nivalenol chemotype of F. graminearum causing head blight on wheat in Luxembourg.
References:(1) T. Demeke et al. Int. J. Food Microbiol. 103:271, 2005. (2) F. Giraud et al. Plant Dis. 92:1587, 2008. (3) C. Waalwijk et al. Eur. J. Plant Pathol. 109:743, 2003. (4) T. J. Ward et al. Fung. Genet. Biol. 45:473, 2008.