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Halo blight in bean plants is not detected

The Halo blight disease of bean plants is highly important in temperate zones like Spain. The seeds are one of the most important sources of transmission of the pathogen, which means the detection of this bacterium in seeds is one of the most efficient control methods.Nevertheless, the blight pathogen can not be detected in Spain using routine techniques.

Halo blight is the common name for the disease caused by the bacteria Pseudomonas syringae pv. phaseolicola. One of the aims of the PhD thesis by agricultural engineer Arantza Rico Martínez, was to find the genetic characterisation of the bacteria in order to make advances in the control of the disease. To this end, 152 diseased beanstalks, obtained from commercial crop fields between 1993 and 2001, were used. The results of the analyses were not the expected ones. Contrary to prevision, the phenotypic and molecular characterisation of the stumps of P. syringae pv. phaseolicola showed that most of them did not produce an antimetabolitic toxin known as phaseolotoxin, described as specific to this patovar and it was shown that they lacked the genes responsible for producing this toxin. This finding is relevant because one of the most effective control methods for the illness is based on the detection of the presence of the genes responsible for the biosynthesis of phaseolotoxin in the seed. Given that neither the toxin nor the genes can be detected, it is impossible to detect the bacteria responsible for halo blight with this method. The importance of the results is greater if analysed in an international context. Given that it is the first time that the existence of a non-toxigenic population of P. syringae pv. phaseolicola with epidemiological importance, has been described which is seen as the main cause of halo blight in Spain. In this sense, a molecular more exhaustive characterisation of the non-toxigenic beanstalks has enabled Arantza Ricos' research group to propose the subdivision of the patovar phaseolicola in two groups differentiated by the possession of the genes responsible for the biosynthesis of phaseolotoxin. Origin of fireblight,Another aim of the thesis was to genetically characterise the Spanish population of the bacteria Erwinia amylovora, cause of the disease known as Fuego bacteriano or fireblight which affects species from the rosacea family (such as fruit trees-apple and pear- and ornamental bushes). The symptoms of this disease are very characteristic: the plant has necrosed leaves, acquiring a burnt physiology. Given the high genetic homogeneity of E. amylovora, very little is known about the epidemiological ways of the dispersion of the disease. So, with the aim of finding out how this pathogen introduces itself, the thesis used various techniques of genetic characterisation. The conclusion drawn is that the observed diversity supports the hypothesis of multiple introductions of the pathogen in Spain and in other European countries. This disease was first detected in Gipuzkoa in 1995.For further information:,Arantza Rico Martinez ,Tel: (+34) 948169717,E-mail: arantza.rico@unavarra.es

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Spain