Widespread occurrence of the aecial stage of sunflower rust caused by Puccinia helianthi in North Dakota and Minnesota in 2008.

摘要

To determine the prevalence of aecial stage of sunflower rust pathogen, P. helianthi, in the primary growing regions of North Dakota (ND), and Minnesota (MN), USA, surveys were conducted in 75 sunflower fields in 18 counties between 22 and 24 July in ND and 34 fields in 8 counties between 17 and 31 July in MN. The incidence of aecia and uredinia were determined by visual observation of a minimum of 20 plants scouted in a 'W' pattern in the field. Rust was found in 31 and 53% of fields in ND and MN, respectively. In fields were rust was found, both aecia and uredinia were observed in 37% of the fields, eacia in only 29% of the fields, and uredinia in 34% of the fields. Although it is uncertain why aecia were widespread in 2008, night temperatures in Mohall, ND, where aecia were first observed, reached the dew point temperature on 51 of 61 days in June and July, suggesting that dew or fog likely formed. Thus, favourable condition for germination and infection early in the growing season indicate widespread occurrence of rust was likely a result of local inoculum sources. The early appearance of aecia is cause for concern for two reasons: significant yield loss can occur when rust appears early in the growing season: and the presence of aecia suggest that the pathogen completed its sexual cycle. When P. helianthi completes its life cycle it is likely that a greater diversity of races will result.