A new leaf blotch disease of sudangrass caused by Pantoea ananas and Pantoea stewartii

An unreported disease of sudangrass (Sorghum sudanense) was observed in com mercial fields in Imperial Valley of California. Symptoms included light-co lored necrotic streaks, and white or tan irregular blotches, often associat ed with reddish purple to dark brown margins. Pantoea ananas was consistent ly isolated from the blotches with reddish margins, while Pantoea stewartii or mixtures of both species were isolated from necrotic streaks without re ddish margins. Fourteen seed samples harvested in different locations were assayed and found to be 0.0 to 3.6% infested with P. ananas. Seed transmiss ion may be a means by which the pathogen is introduced. Symptoms in inocula ted plants appeared as early as 2 and as late as 20 days after inoculation, depending on the inoculum level, methods of inoculation, temperature, and available moisture. The initial symptoms caused by inoculations with both b acteria were similar, but as symptoms progressed, P. ananas was associated with white streaks or irregular necrotic blotches often surrounded by a red dish or purplish hue. P. stewartii was associated with light-colored necrot ic streaks. A synergistic or antagonistic relationship was not observed bet ween the two pathogens in co-inoculations. In host range studies, both bact eria caused disease on sorghum and sudangrass at similar levels of severity . P. ananas was also pathogenic on corn and oat. P. stewartii from sudangra ss was pathogenic on corn but did not cause wilting that was observed with Stewart's wilt strains of P. stewartii from corn. The sudangrass strains of P. stewartii also infected oat and triticale, while the Stewart's wilt str ains did not. Both Il ananas and P. stewartii from sudangrass grew at relat ively high temperatures (43 and 37 degrees C, respectively) and caused dise ase at elevated temperatures and conditions of relative humidity similar to those in the Imperial Valley during late summer when epidemics of the dise ase were common.