Detection and quantification of Fusarium culmorum and Fusarium graminearum in cereals using PCR assays

Random amplified polymorphic DNA assays were used to identify amplification products characteristic of either Fusarium culmorum or Fusarium graminearum. Selected fragments were cloned, sequenced and primer pairs were developed which permitted specific detection of F. culmorum or F. graminearum using conventional PCR. Quantitative assays were developed for both F. culmorum and F. graminearum, using competitive PCR. The F. culmorum-specific competitive PCR assay was used to study the effect of inoculum load and timing on stem base disease of winter wheat caused by F. culmorum. The extent of fungal colonization, as measured by fungal DNA content, was greater on plants inoculated earlier in the season and increased with increasing conidial load. The F. graminearum -specific competitive PCR assay was used to study the colonization of wheat grain by trichothecene producing and non-producing isolates of F. graminearum. Colonization of grain by trichothecene producing isolates was greater than that by non-producing isolates, supporting the view that trichothecenes act as virulence factors in the colonization of wheat by F. graminearum. The results from competitive PCR assays were compared with those for visual disease assessment in both instances.