FREQUENCY OF THE TELEOMORPH OF PHAEOSPHAERIA NODORUM ON WINTER WHEAT IN NORTH CAROLINA, USA

Authors: Cowger, Christina; SILVA-ROJAS, HILDA - COLEGIO DE POST-GRADUADOS

Submitted to: Phytopathology
Publication Type: Abstract Only
Publication Acceptance Date: 3/1/2004
Publication Date: 6/1/2004
Citation: Cowger, C., Silva-Rojas, H. 2004. Frequency of the teleomorph of phaeosphaeria nodorum on winter wheat in north carolina, usa. Phytopathology.

Interpretive Summary: Ascocarps of Phaeosphaeria nodorum, which causes Stagonospora nodorum blotch of winter wheat, have not been previously reported in the northeastern or southeastern U.S. despite prolonged searching. We sampled tissues from living wheat plants or wheat debris in Kinston, North Carolina, each month except June from May to October 2003. Altogether, over 1,000 fruiting bodies were examined microscopically and tallied as P. nodorum pycnidia or ascocarps, “empty,” or “other fungi.” P. nodorum ascocarps were present each month after May at a frequency of 0.8%-5.4%, and comprised a significantly higher percentage of fruiting bodies from wheat heads than of those from lower stems and leaves. Because the reproductive structures of P. nodorum are easily confused with those of the morphologically similar P. arenaria, the internally transcribed spacer (ITS) regions of Phaeosphaeria isolates from Kinston and Plymouth, NC, were sequenced and compared to known sequences of both species. The results will be presented. The mating type of each isolate in the sequencing sample was also determined, and an approximate balance was found between mating type 1 and mating type 2. We conclude that in the North Carolina P. nodorum population, sexual reproduction plays a role in initiation of new epidemics and the creation of adaptively useful genetic variability, although its relative importance in structuring this population is still unknown.

Technical Abstract: Ascocarps of Phaeosphaeria nodorum, which causes Stagonospora nodorum blotch of winter wheat, have not been previously reported in the northeastern or southeastern U.S. despite prolonged searching. We sampled tissues from living wheat plants or wheat debris in Kinston, North Carolina, each month except June from May to October 2003. Altogether, over 1,000 fruiting bodies were examined microscopically and tallied as P. nodorum pycnidia or ascocarps, “empty,” or “other fungi.” P. nodorum ascocarps were present each month after May at a frequency of 0.8%-5.4%, and comprised a significantly higher percentage of fruiting bodies from wheat heads than of those from lower stems and leaves. Because the reproductive structures of P. nodorum are easily confused with those of the morphologically similar P. arenaria, the internally transcribed spacer (ITS) regions of Phaeosphaeria isolates from Kinston and Plymouth, NC, were sequenced and compared to known sequences of both species. The results will be presented. The mating type of each isolate in the sequencing sample was also determined, and an approximate balance was found between mating type 1 and mating type 2. We conclude that in the North Carolina P. nodorum population, sexual reproduction plays a role in initiation of new epidemics and the creation of adaptively useful genetic variability, although its relative importance in structuring this population is still unknown.