Abstract: Soybean rust occurs in many countries throughout Asia, Australia, Africa, and South America. The causal agents of soybean rust are two closely related fungi, Phakopsora pachyrhizi and P. meibomiae, which are differentiated based upon morphological characteristics of the telia. Determination of the nucleotide sequence of the internal transcribed spacer (ITS) region revealed greater than 99%/95% nucleotide sequence similarity among isolates of either P. pachyrhizi or P. meibomiae, but only 80% sequence similarity between the two species. Utilizing differences within the ITS region, four sets of PCR primers were designed specifically for P. pachyrhizi, and two sets of PCR primers were made specific to P. meibomiae. Classical and real-time fluorescent PCR assays were developed to identify and differentiate between P. pachyrhizi and P. meibomiae.

Abstract: Karnal bunt of wheat is caused by Tilletia indica Mitra. Recently, teliospores morphologically resembling T. indica were isolated from bunted ryegrass seeds and wheat seed washes. Previously developed PCR assays failed to differentiate T. indica from the newly discovered ryegrass pathogen, T. walkeri. The nucleotide sequence of a 2.3-kb region of mitochondrial DNA, previously amplified by PCR only from T. indica, was determined for three isolates of T. indica and for three isolates of T. walkeri. There was greater than 99% identity within either the T. indica group or the T. walkeri group of isolates, whereas there was approximately 3% divergence between isolates of these two Tilletia species. Five sets of PCR primers were made specific to T. indica, and three sets were designed specifically for T. walkeri based upon nucleotide differences within the mtDNA region.