Ikuo Kadota

Pseudomonas plantarii sp. nov., the Causal Agent of Rice Seedling Blight

An aerobic, gram-negative bacterium that causes seedling blight of rice was isolated from diseased rice seedlings and bed soil in nursery boxes in Chiba and Niigata Prefectures, Japan. The cells are nonsporeforming and nonencapsulated straight rods (0.7 to 1.0 by 1.4 to 1.9 μm) that occur singly, in pairs, or in short chains and are motile with one to three polar flagella. The bacterium displays the characteristics of the genus Pseudomonas and can be clearly differentiated from Pseudomonas glumae and Pseudomonas avenae, which are known to cause seedling diseases in rice grown in nursery boxes, and from other bacteria. The deoxyribonucleic acid base composition is 64.8 mol% guanine plus cytosine. A new species, Pseudomonas plantarii sp. nov., is proposed. The type strain is NIAES 1723 (JCM 5492, AZ 8201). All strains of the new species produce the disease-causing substance tropolone (a nonbenzenoid aromatic compound with a seven-membered ring) and a reddish brown pigment which was considered to be a derivative of the substance.

Bacterial Blight of Welsh Onion : A New Disease Caused by Xanthomonas campestris pv. allii pv. nov.

In June of 1998, a new bacterial disease was observed on Welsh onion in Okinawa Prefecture, Japan. Infected plants in nursery boxes were stunted with tip dieback, and heavily infected plants died. In fields, the disease appeared on leaves as irregular gray spots or elliptical spots with creases in the center. These spots enlarged and spread rapidly continued cloudy or rainy weather, and formed blight lesions on outer leaves. Yellow mucoid bacterial colonies were consistently isolated from these lesions. The causal bacterium was identified as a pathovar of Xanthomonas campestris on the basis of bacteriological properties. The bacterium was pathogenic to Welsh onion, onion, but nonpathogenic to chive, Chinese chive and hyacinth. Of Liliaceae plants, which contain Welsh onion and onion, only hyacinth has been reported as a host for the genus Xanthomonas, namely X. campestris pv. hyacinthi. However, strains of X. campestris pv. hyacinthi were not pathogenic against either Welsh onion or onion. From these results, the bacterium isolated from Welsh onion is considered to be a new pathovar of X. campestris, and the name of X. campestris pv. allii pv. nov. is proposed. A strain MAFF 311173 is designated as the pathotype strain.