First report of Eutypella species associated with dying cotton (Gossypium hirsutum L.)

A rapid increase in the number of Gossypium hirsutum L. plants suddenly wilting and dying in a commercial cotton field in Central Queensland initiated this study. The aim was to characterise fungal species recovered from discoloured vascular tissue of dead plants and determine if they contributed to their death. Isolations were consistently dominated by one fungus based on culture morphology. Identification was established on sequences of the internal transcribed spacer (ITS) region of ribosomal DNA and revealed that the isolates all belong to Diatrypaceae, with high homology to Eutypella scoparia. Further analyses showed that there were two distinct Eutypella species present in the isolates, which are quite different from E. scoparia from the sequence dissimilarity due to the presence of ITS1 and ITS2 insertions. In diseased root samples, community profiling showed two operational taxonomic units (OTUs) related to E. scoparia were the most abundant fungi accounting for 45 to 99% of all sequences. Pathogenicity tests showed that a Eutypella isolate when inoculated into the stem of healthy G. hirsutum using two inoculation methods caused cankerous growth and necrosis of vascular tissue, typical of trunk disease. The fungus caused a red-brown streaking of the vascular tissue like that observed in diseased field plants. This study shows that the fungal isolates, which form a distinct group within the Eutypella, are associated with the root and stem of dying G. hirsutum and were the dominant fungi of diseased roots. This is the first known case of Eutypella affecting cotton worldwide and is considered an expansion of this genus' host range.