Differences in the pathogenicity of French isolates of Ralstonia solanacearum were found using standardized root inoculations of tomato, aubergine and tobacco. Aggressiveness was assessed by comparing percentage wilted plants over 12 days, following root inoculation of tomato and aubergine, expressed as the mean of four independent replicates for each. The isolates could be separated into four aggressiveness groups on these hosts. None of them provoked any symptoms after root inoculation of tobacco, but they did induce a typical hypersensitive response, or disease symptoms, when infiltrated into tobacco leaves of tolerant or susceptible cultivars, respectively. Samples taken from stems of symptomless tobacco demonstrated high percentages of latent infections. The development of wilting symptoms was strictly correlated with large numbers of the bacterial parasite in xylem vessels and was thus related to the invasiveness of the bacterial strain. Root inoculation with an Hrp‐ mutant strain of R. solanacearum induced protection against subsequent inoculation by a pathogenic strain. The more invasive the Hrp‐ mutant strain, the more protection it gave. Thus aggressiveness should be assessed with a view to epidemiological studies and control measures, since it is an important characteristic of R. solanacearum isolates.
Lane, Egham TW20 9TY (United Kingdom) Recent outbreaks of bacterial wilt disease in Europe have alerted the potato industry to the destructive nature and potential threat of this disease. At present, little is known about the diversity of the pathogen and yet this information is vital if accurate disease forecasting and control are to be achieved. In an initial attempt to address this issue, the genetic diversity amongst 43 isolates of Ralstonia solanacearum race 3 biovar 11 of European origin has been determined. Two genomic fingerprinting methods were used to study the population; macro-restriction analysis of genomic DNA resolved by pulsed-field gel electrophoresis and rep-PCR. In addition a smaller subset of isolates has been studied using amplified restriction fragment polymorphism. The relative success and resolution of each method has been assessed and will be discussed. Results relating the findings of this study to previous research on genetic diversity within race 3 biovar I1 populations of worldwide origin are presented (Smith et al., 1995). In conclusion, it is hoped to demonstrate that the results of this study could serve as a valuable reference point from which future research initiatives specifically on the epidemiology and control of bacterial wilt disease in Europe could be derived. Diversite genetique des isolats de Ralstonia solanacearum sur pornrne de terre en EuropeLes ricents foyers de flitrissement bactkrien en Europe ont alert6 l'industrie de la pomme de terre sur la nature destructrice et la menace potentielle de cette maladie. La diversit6 du pathogkne est peu connue mais cette information est vitale pour mettre en place des prkvisions et une lutte adaptbes. Dans une Ctude prkliminaire, la diversit6 gCnCtique de 43 isolats de la race 3, biovar 11 de R. solanacearum d'origine europeenne a Ct C dCterminCe. Deux mCthodes d'empreintes ghomiques ont Ct C utilisees pour Ctudier la population: analyse de 1' ADN gCnomique par macro-restriction suivie d'une Clectrophorkse sur gel champ pulsC et rep-PCR. De plus, un sous-groupe d'isolats plus restreint a Ct C CtudiC par polymorphisme de longueur des fragments de restriction de I'ADN gCnomique. La rkussite de chaque mCthode et sa pricision ont Ctk CvaluCes et sont discutCes. Des risultats mettant en relation cette Ctude avec des Ctudes antkrieures sur la diversit6 gCnCtique dans des populations de la race 3 biovar I1 de diverses origines (Smith, J.J. et al. 1995) sont prCsentCs. En conclusion, on espkre dbmontrer que les risultats de cette Ctude peuvent servir de point de dipart a de futurs projets de recherche sur I'CpidCmiologie et la lutte contre le flhtrissement bacdrien en Europe. renernulrecKoe pa3noo6pa3ue cpedu u3on~rnoe Ralstonia solanacearum u3 Kaprnocpem 6 Eepone HenaBHue oqarn 6 a~~e p u a n b~o r o Y B J T A~W I B b p o n e npenynpenunu KapTo4enbHoe npow3~oncr-BO o AecrpymnBHoM xapamepe u noTeHqnanbHoi4 yrpose moro 3a60ne~mm. B Hamonmee Bpem oqem MUIO U~B~C T H O o pa3~006pa3nu naToresa, HO TeM He MeHee ma nH OPMWWI m e w xu3-HeHH...
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