A Leaf Spot and Blight of Greenhouse Tomato Seedlings Incited by a Herbaspirillum sp.

Abstract

A leaf spot and blighting were observed on leaves of tomato transplants from a producer in Florida in 2001 and 2002. A nonfluorescent bacterium was isolated consistently from affected tissue. The typical bacterium was a gram negative, strictly aerobic, slightly curved rod with one or two flagella. Sequence analysis of the 16S rRNA indicated that two representative strains, F1 and SE1, had greater than 99% nucleotide sequence identity with Herbaspirillum huttiense and H. rubrisubalbicans. The cellular fatty acid composition of the total of 16 tomato strains was very similar to H. huttiense and H. rubrisubalbicans. Based on carbon utilization, six of nine strains tested with the Biolog system were identified as Herbaspirillum spp. The tomato strains were oxidase positive and grew at 40°C, but were negative for levan production, pectate hydrolysis, and arginine dihydrolase activity. Based upon this polyphasic analysis, we concluded that the strains were most closely related to H. huttiense, although placement in this species would require further analyses. However, the tomato strains and H. rubrisubalbicans, but not H. huttiense, caused confluent necrosis when infiltrated at high concentrations into tomato leaves and were able to produce leaf spot symptoms on inoculated tomato seedlings in the greenhouse. Using pulsed-field gel electrophoresis, we determined that there was considerable variability between the strains collected in 2001 and 2002.