Summary. The differential value of 15 characteristics was studied for the determination of plant pathogens in the fluorescent group of the genus Pseudomonas. All but 2 of the 161 pathogenic cultures and the 15 nonpathogenic cultures examined could be placed in one of 5 groups on the basis of tests for: oxidase, potato soft rot, arginine dihydrolase, levan production and a hypersensitivity reaction in tobacco leaves. Tests for production of acid from sucrose, nitrate reductase and a lipase for margarine were useful as subsidiary determinants. Aesculin hydrolysis, gelatinase and tyrosinase tests, and the production of a blue fluorescent pigment were of little or no value at the group level, and hydrolysis of Tween 80 and the catalase reaction had no differential value. With the exception of Ps. tolaaii and two cultures of questionable pathogenicity, the pathogens studied could be separated readily from the few nonpathogens studied. A determinative scheme for plant pathogenic fluorescent pseudomonads is proposed to serve until the taxonomy of the group is better understood.

A disease of mature tomato plants is described, the symptoms of which include brown discoloration and/or necrosis and collapse of the pith. These are sometimes accompanied by vascular browning, external dark brown to black stem lesions, bacterial flux from stem wounds and adventitious root formation. The disease, which appears to be favoured by high humidity and/or free water on the plant surfaces and by high N fertiliser, has been widespread on many glasshouse holdings in England since 1971 but has caused severe loss on only a few. It is thought to be caused by a new species of the genus Pseudomonas for which the name P. corrugata Roberts and Scarlett is proposed.* Present address: ADAS, Kenton Bar, Newcastle-upon-Tyne. t Reprint requests should be sent to RAL.

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