Yellow Stunt, a Tobacco Disease Caused by Pythium dissotocum, in Southern Parts of Brazil

Yellow stunt, an emerging disease of tobacco (Nicotiana tabacum), has become increasingly prevalent in tobacco-growing regions in southern Brazil. Major symptoms are moderate to severe stunting, yellowing of leaves, severe wilting, darkened roots, necrosis of stem tissue directly above the soil line, and plant death. Phytophthora glovera was first proposed in 1999 as the primary causal agent of yellow stunt (1), but since then, there has been no data or completion of Koch's postulates to support this. Fifty-six isolates of fungi and fungus-like organisms were obtained from stem and root samples of tobacco plants with typical symptoms of yellow stunt in the Brazilian States of Rio Grande do Sul, Santa Catarina, and Parana during the growing seasons of 2004/05 to 2006/07. They were identified to species level by analysis of the morphological characteristics (2) and sequence of rDNA internal transcribed spacer regions 1 and 2 (ITS1 and ITS2) (3). The isolates were identified as Pythium dissotocum (29), Fusar...