Population structure of plant-pathogenic Fusarium species in overwintered stalk residues from Bt-transformed and non-transformed maize crops
Bt-transformed maize contains genes from Bacillus thuringiensis encoding for insecticidal crystal proteins. Less insect damage on Bt maize stalks can cause a reduced infection by Fusarium species through plant injuries. This could affect the presence of plant-pathogenic Fusarium species on maize residues which serve as an inoculum source for subsequent crops. We collected overwintered maize stalks of four different Bt maize hybrids and their corresponding non-Bt lines in two consecutive years in a field trial in Germany. Fusarium spp. were isolated from 67% of 648 collected maize stalks. Identification with new multiplex PCR assays showed that F. graminearum, F. avenaceum, and F. proliferatum were the most abundant Fusarium species, isolated from 42%, 26%, and 15% of the stalks, respectively. Species abundances varied between varieties and collection years. No consistent difference was found between Bt and non-Bt stalks. Fusarium graminearum isolates were subject to a population genetic structure analysis with eight newly developed microsatellites. Significant association of loci and overrepresentation of repeated multilocus haplotypes indicated a substantial asexual component of reproduction, supporting selection of haplotypes. The data suggested selection of particular F. graminearum haplotypes by collection years but not by maize Bt transformation. Haplotypic changes between years caused no divergence in the distribution of alleles, suggesting that gene flow beyond the field scale prevented substructuring. We present evidence for gene flow between our saprophytic F. graminearum population on maize residues and a wheat-pathogenic population from a field 100 km distant.
KeywordsBt maize residues Cry1Ab protein Microsatellites Saprophytic Fusarium survival PCR-based identification Population genetic structure
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We gratefully acknowledge V. Heitz and K. H. Dannemann for permission to sample on their field trial, T. Miedaner for providing the German F. graminearum population, H-R. Forrer, F. Mascher and M. Lorito for providing reference strains of Fusarium species, M. S. Saharan, O. Bucher, and R. Heusser for technical assistance, B. McDonald, C. Linde, and P. Brunner for comments on the manuscript. This research was supported by the Swiss National Center of Competence in Research (NCCR Plant Survival, Neuchâtel).
- de Luna L, Bujold I, Carisse O, Paulitz TC (2002) Ascospore gradients of Gibberella zeae from overwintered inoculum in wheat fields. Canadian Journal of Plant Pathology-Revue Canadienne De Phytopathologie 24: 457–464Google Scholar
- Demeke T, Clear RM and Patrick SK (2004) Polymerase chain reaction based assays for the detection and identification of Fusarium species in mycelial cultures and grains. In: Canty SM, Boring T, Wardwell J and Ward RW (eds) Proceedings of the 2nd International Symposium on Fusarium Head Blight, 11–15 December, Orlando, FL, USA. (pp. 559–563) Michigan State University, East Lansing, MI, USAGoogle Scholar
- Edwards SG, Pirgozliev SR, Hare MC, Jenkinson P (2001) Quantification of trichothecene-producing Fusarium species in harvested grain by competitive PCR to determine efficacies of fungicides against Fusarium head blight of winter wheat. Applied and Environmental Microbiology 67: 1575–1580PubMedCrossRefGoogle Scholar
- James C (2005) Global Status of Commercialized Biotech/GM Crops: 2005. ISAAA Briefs No. 34, ISAAA: Ithaca, NY, USAGoogle Scholar
- Khonga EB, Sutton JC (1988) Inoculum production and survival of Gibberella zeae in maize and wheat residues. Canadian Journal of Plant Pathology-Revue Canadienne De Phytopathologie 10: 232–239Google Scholar
- Kommendahl T, Windels CE (1981) Root-, stalk- and ear-infecting Fusarium species on corn in the USA. In: Nelson PE, Toussoun TA, Cook RJ (eds) Fusarium: Diseases, Biology and Taxonomy. Pennsylvania State University Press, University Park, PA, USA, pp. 94–103Google Scholar
- Miedaner T, Schilling AG, Geiger HH (2001) Molecular genetic diversity and variation for aggressiveness in populations of Fusarium graminearum and Fusarium culmorum sampled from wheat fields in different countries. Journal of Phytopathology-Phytopathologische Zeitschrift 149: 641–648CrossRefGoogle Scholar
- Naef A, Senatore M, Défago G (2006a) A microsatellite based method for quantification of fungi in decomposing plant material elucidates the role of Fusarium graminearum DON production in the saprophytic competition with Trichoderma atroviride in maize tissue microcosms. FEMS Microbiology Ecology 55: 211–220CrossRefGoogle Scholar
- Nei M (1987) Molecular Evolutionary Genetics. Columbia University press, New York, USAGoogle Scholar