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.

In order to devise a scheme for the identification and differentiation of agrobacteria, 50 strains of Agrobacterium, mostly those maintained in the National Collection of Plant Pathogenic Bacteria, were separated into four clusters when subjected to numerical taxonomic analysis. For the two major clusters, regardless of the phytopathogenic effect of the strains, we would adopt the species names A. tumefaciens and A. rhizogenes. A third cluster merits the use of the specific name A. rubi whilst a hitherto unrecognized fourth cluster of yellow‐pigmented isolates may constitute a fourth species in the genus. The species name A. radiobacter is rejected as this species is synonymous with A. tumefaciens and the latter, being the type species of the genus, takes priority. To indicate the phytopathogenic effect of strains within our four Agrobacterium clusters we would use the terms: saprophytic state, tumourigenic state and rhizogenic state. Revised descriptions, without regard to phytopathogenic effect, are given for A. tumefaciens, A. rhizogenes and A. rubi.

Summary. Bacteria isolated from pink‐coloured grains of English wheat were identified as Erwinia rhapontici, and were identical with isolates made by Luisetti & Rapilly (1967) from wheat with a similar disorder in France. Pink grain was reproduced with English and French isolates and with authentic cultures of E. rhapontici when developing grain of wheat plants was inoculated, but only after wounding.

SUMMARY An immunofiuorescent (fluorescent antibody or FA) staining technique was used to detect Erwinia amylovora (Burrill) Winslow et al. in plant tissue, but in preliminary trials it failed to do so in a majority of preparations from fireblight‐infected plants. Differential centrifugation greatly improved the rate of detection of E. amylovora in plant tissue. Ctiltures of E. herbicola subsp. ananas (Serrano) Dye, E. stewartii (Smith) Dye, E. rhapontici (Millard) Burkholder and two plant isolates (probably Pseudomonas fiuorescens (Trevisan) Migula and E. herbicola subsp. herbicola (Lohnis) Dye) cross‐reacted with E. amylovora in the FA stain. Of these only the Ps. fiuorescens isolate and a different plant isolate of E.h. subsp. herbicola cross‐reacted with E. amylovora anti‐serum in the slide agglutination test. Use of absorbed E. amylovora antiserum completely eliminated cross reactions in the slide agglutination test, but only partly removed cross reactions in the FA stain. Immunofluorescence appeared to be more sensitive but less reliable than conventional plating methods for fireblight diagnosis.