Methods for studying population structure, including sensitivity to the fungicide silthiofam, of the cereal take-all fungus, Gaeumannomyces graminis var. tritici

• Published in: Plant pathology 2005-10, Vol.54 (5), p.686-698
• Main Authors: Freeman, J, Ward, E, Gutteridge, R.J, Bateman, G.L
• Format: Article
• Language: English
• Subjects: Biological and medical sciences; Control; Fundamental and applied biological sciences. Psychology; Fungal plant pathogens; fungicide resistance; Gaeumannomyces graminis var. tritici; genetic polymorphism; genetic variation; host plants; host-pathogen relationships; internal transcribed spacers; molecular sequence data; nucleotide sequences; PCR; Phytopathology. Animal pests. Plant and forest protection; plant pathogenic fungi; populations; ribosomal DNA; silthiofam; soil fungi; soilborne disease; take‐all; Triticum aestivum; wheat; winter wheat
• ISSN: 0032-0862; 1365-3059
• DOI: 10.1111/j.1365-3059.2005.01252.x

Field isolates (n = 144) of the wheat take‐all fungus Gaeumannomyces graminis var. tritici (Ggt) were tested for sensitivity to silthiofam, a take‐all‐specific fungicide used as a seed treatment, and identified as A‐ or B‐type by PCR–RFLP analysis of nuclear rDNA. A possible association was identified between polymorphisms in ITS2 of the nuclear rDNA and sensitivity to silthiofam. A Ggt‐specific PCR assay was developed which simultaneously identified isolates of Ggt as A‐ or B‐type, based on the polymorphisms in the nuclear rDNA. A highly significant correlation between Ggt type using the PCR assay and sensitivity to silthiofam was demonstrated in a collection of 358 isolates from three field experiments designed to test the effects of seed‐treatment fungicides on take‐all and Ggt populations in winter wheat. In one experiment the percentages of silthiofam‐sensitive and B‐type isolates were significantly less in populations from plots sown with silthiofam‐treated seed in two consecutive years than in populations from plots sown with nontreated seed. However, silthiofam still provided a significant amount of control of take‐all. The natural occurrence of fungicide‐insensitive isolates, up to about 30% in soils in which the fungicide had never been used, is unusual. The new PCR assay provides a useful tool for studying the population structure of Ggt, and may provide a novel method for assessing the incidence of insensitivity to silthiofam (the target site for which has not yet been identified) in field populations of Ggt.