ABSTRACT

Phomopsis species were isolated from cotton and soybean tissues in the southeastern United States. Fungal isolations determined Phomopsis longicolla and P. phaseolina colonized roots, petioles, leaves, and pod tissues of soybean, whereas a Pho-mopsis sp. was isolated from roots, petioles, leaves, and boll tissues of cotton. Morphological and cultural differences were found between the cotton Phomopsis isolates and the two soybean pathogens, P. phaseoli and P. longicolla. Toothpick inoculations determined that all three species produced symptoms on cotton and soybean. Symptoms were more severe for each species on the primary host. Restrictive fragment length polymorphism analyses of polymerase chain reaction (PCR) fragments were used to distinguish Phomopsis isolates from soybean and cotton. Specific primers were used to amplify a 550 base pair sequence known as the Internal Transcribed Spacer (ITS) Region, a mitochondrial rRNA gene. PCR fragments from forty-nine Phomopsis isolates were sequenced. DNA sequence analyses displayed distinct variation between Phomopsis isolates from cotton and soybean. This is noteworthy because the naming of Phomopsis species thus far has been strongly based on plant hosts.