We showed that a bacterial avirulence (avr) gene function, avrPpiA1, from the pea pathogen Pseudomonas syringae pv pisi, is recognized by some, but not all, genotypes of Arabidopsis. Thus, an avr gene functionally defined on a crop species is also an avr gene on Arabidopsis. The activity of avrPpiA1 on a series of Arabidopsis genotypes is identical to that of the avrRpm1 gene from P.s. pv maculicola previously defined using Arabidopsis. The two avr genes are homologous and encode nearly identical predicted products. Moreover, this conserved avr function is also recognized by some bean and pea cultivars in what has been shown to be a gene-for-gene manner. We further demonstrated that the Arabidopsis disease resistance locus, RPM1, conditioning resistance to avrRpm1, also conditions resistance to bacterial strains carrying avrPpiA1. Therefore, bean, pea, and conceivably other crop species contain functional and potentially molecular homologs of RPM1.

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Polymerase chain reaction (PCR) amplification with random decamer primers, and primers targeted to conserved repetitive sequences were used to investigate the genetic relationship between strains of Ralstonia solanacearum that cause the ‘moko’ and ‘bugtok’ vascular wilt diseases of banana and plantain (Musa spp.). The closely related bacteria R. pickettii, Pseudomonas syzygii and the banana blood disease bacterium were also included in this study. Data from several PCR fingerprints were collated by cluster analysis and principal coordinate analysis. Random Amplified Polymorphic DNA (RAPD) analysis divided the isolates into three groups. Group 1 contained a subset of Central American R. solanacearum moko strains. Group 2 consisted of the blood disease bacterium, P. syzygii and some R. solanacearum isolates from clove trees whilst group 3 comprised South‐east Asian moko and bugtok isolates as well as another subset of Central American moko strains. Fingerprinting by PCR amplification with repetitive primers (rep‐PCR) produced groupings broadly concurrent with those obtained from RAPDs. Both sets of groupings supported previous subdivisions made within R. solanacearum on the basis of tRNA fingerprints and 16 S rRNA sequences, and the data lend support to the renewed description of the blood disease bacterium either as a separate species or as a subspecies within R. solanacearum.

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