Viability and dissemination of Pantoea ananatis, etiological agent of Maize White Spot disease

Maize white spot (MWS) is a disease widely spread in maize production regions in Brazil and causes serious economic damages to the culture. Little is known about the dissemination, growth and development conditions of the MWS causal agent, the bacterium Pantoea ananatis. The objective of this work was to determine the viability of this bacterium, as well as its distribution in the plant. P. ananatis after isolated was stored in both, Nutrient Broth (NB) medium and in mineral oil. For the viability tests, the cultures stored in NB were maintained at 12ºC and –6ºC and the cultures stored in mineral oil were maintained at room temperature. The isolate remained viable for seven months in NB medium at the two temperatures assessed, and four months when stored in mineral oil. The presence of the P. ananatis bacteria was analyzed in, 1) soil samples collected close to rhizosphere, 2) in seeds from plants severely attacked by MWS, 3) foliar segments of healthy plants and 4) the stem of healthy plants. P. ananatis was found surviving epiphytically on the leaf surface and its population increased with plant age, air relative humidity, and decreasing of temperature. This agent was not found neither rhizosphere nor in seeds, but it was isolated in low quantity in maize stem. P. ananatis resides epiphytically on leaves and, due to several factors, may trigger injuries to its host. All epiphytic isolates were characterized in regards to ice nucleation activity, a characteristic of this pathogen.