Discolouration of vascular bundles and the poor root quality of radish is caused by a micro-organism. This was shown in research by Wageningen UR Greenhouse Horticulture. It is still unclear whether this is Xanthomonas or a different pathogen. The research is financed by the Product Board for Horticulture.
Three radish growers were recently facing unknown root problems. This was the reason why Wageningen UR Greenhouse Horticulture did last winter start an investigation, together with PPO Flower Bulbs in Lisse, into the identification of the cause of this problem.
Infested plant material and soil has been studied by using molecular techniques. In a bio-test symptoms could already be observed in the treatments with infested soil after one or two weeks. The radish leaves started wilting and the roots of all plants were more or less discoloured. A noteworthy excessive root growth was observed as well. The quality of the root was poor: not straight, a lot of root growth. Tubers also showed different shapes and they were smaller. And the plants showed a lower production as well.
Bacterium
Infested tubers, mixed through the soil in the form of pulp, were unable to infest radiated soil. The bio-test showed the presence of a micro-organism in the non-radiated soil, which is responsible for the discolouration of the vascular bundles.
Tubers with a slight vascular discolouration have been analysed for the presence of pathogens. The first molecular analyses showed a Xanthomonas-type of bacterium of which four different isolates have been brought in pure culture; these will this spring be tested on plant material to investigate whether this is causing the vascular discolouration.