Downloaded from www.microbiologyresearch.org by IP: 54.70.40.11 On: Thu, 13 Dec 2018 14:52:28 Journal of General Microbiology (1 987), 133, 2393-2399. Printed in Great Britain 2393 Isolation and Partial Characterization of Three Classes of Mutant in Pseudomonas syringize Pathovar pisi with Altered Behaviour towards Their Host, Pisum sativum ByAFSHAN N. MALIK,lt ALAN VIVIAN1*$ AND JOHN D. TAYLOR2 School of Biological Sciences and Environmental Health, Thames Polytechnic, Wellington Street, London SE18 6PF, UK Institute of Horticultural Research, Wellesbourne, Warwick CV3.5 9EF, UK (Received 2 April 1987; revised 6 May 1987) Mating with Escherichia cofi strain SMlO carrying the Tn5 vector pSUP2011 was used to mutagenize Pseudomonas syringae pv. pisi strain 299A. The resulting transconjugants were each tested by stem-inoculation into several pea (Pisum sativum) cultivars. Three classes of mutant, which probably resulted from insertion of part or all of RP4-2-Tc :: Mu into the genome of strain 299A, showed reduced virulence towards one or more pea cultivars. The single class I mutant was avirulent on all pea cultivars tested and had lost the ability to induce a hypersensitive response in tobacco (Nicotiana tabacum) cv. White Burley; the single class I1 mutant induced a hypersensitive response on all pea cultivars and tobacco; class I11 mutants showed reduced virulence towards pea cv. Early Onward, while remaining fully virulent towards other normally susceptible pea cultivars, and inducing a hypersensitive response in tobacco. INTRODUCTION Pseudomonas syringae pv. pisi causes bacterial blight of peas (Pisum sativum) (Lawyer, 1984). In common with some other plant-pathogenic pseudomonads, this organism exhibits a well- defined race structure and strains can be distinguished on the basis of differential interaction with a range of host cultivars (Taylor, 1986). The interactions of host and pathogen are essentially of two kinds : compatible and incompatible. A compatible interaction resdts in the establishment of the pathogen and development of disease symptoms in the host. An incompatible interaction results in the induction of host defences leading to the development of a hypersensitive response (HR) in the host. HR limits the development of the pathogen and results in a localized necrotic lesion close to the site of infection (Klement, 1963). HR also develops when plant-pathogenic bacteria are introduced into the leaves of a non-host plant such is tobacco (Nicotiana tabacum). In an attempt to investigate genes involved in pathogenicity we have used the transposon vector pSUP2011 (Simon et al., 1983) to mutagenize the race 1 strain, 299A, of P. syringae pv. pisi. A rapid stem-inoculation technique permits screening of mutagenized transconjugants against a range of pea cultivars. This paper describes the isolation and initial characterization of three classes of mutant affected in their ability to cause disease in one or more pea cultivars. t Present address : Department of Haematology and Oncology, Institute of Child Health, 30 Guilford Street, $ ' Present address : Science Department, Bristol Polytechnic, Coldharbour Lane, Frenchay, Bristol BS16 lQY, Abbreviation : HR, hypersensitive response. London WClN IEH, UK. UK. 0001-4120 0 1987 SGM