Browsing by Subject "Seed testing"

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Untersuchungen zur bakteriellen Erkrankung Acidovorax valerianellae an Feldsalat
(2012) Braje, Inga; Hinrichs-Berger, Jan
The aim of this study was to contribute to clarifying the epidemiology of the phytopathogenic bacterium Acidovorax valerianellae on corn salad [Valerianella locusta (L.)]. To this end, research was conducted on infection conditions, cultivar sensitivities, transmission paths and seeds. Based on these results, control strategies shall be demonstrated. The tests performed under infectious conditions revealed that the infection of A. valerianellae is dependent on temperature, leaf age, inoculum concentration and leaf moisture, as well as the relative humidity. Inoculation was possible at temperatures between 10 °C and 30 °C. It was possible for leaves of any age to be infected. Moreover, infection was independent of the inoculum concentration, and occurred between 102 and 107 cfu/ml. The speed of infection and the characteristics of the symptoms increased with increasing temperature, leaf age and inoculum concentration. Both the duration of leaf moisture and the relative humidity played a crucial role in the infection process. Under dry conditions, inoculated corn salad plants developed no symptoms. However, infestation increased significantly under humid conditions or during humid periods. Five hours of leaf moisture sufficed for an infection to occur. It was demonstrated that targeted dry growth conditions with short leaf moisture periods constitute an option for controlling A. valerianellae. All 13 tested commercial corn salad cultivars were prone to A. valerianellae. However, the resistance of the wild type V. rimosa was confirmed. For this reason, it seems advisable to cross the wild type with commercial cultivars. A. valerianellae endured for up to eleven months in the soil. Some of the corn salad cultivars cultivated immediately (and one up to eleven months, respectively) after infected plants were severely infected. The number of infected plants decreased in line with increased rotting of infected old plant material. A cultivation break of at least twelve months and the rotation of crops therefore appear to be appropriate ways to eliminate A. valerianellae from the soil. No alternative hosts were detected in the experiments or in the literature. In addition, this study revealed that A. valerianellae is transmitted via seeds. It is therefore important to focus on healthy seeds to prevent the further dissemination of this hazardous disease to uncontaminated crop land. Seeds with natural A. valerianellae contamination were tested using a variety of decontamination methods. Warm water treatment (43 °C for 20 minutes, 55 °C for 20 minutes, 60 °C for 5 minutes) or hot steam treatment (66 °C for 105 seconds) managed to reduce the contamination rate. However, it was not possible to completely eliminate the bacterium. In summary, sowing healthy seeds after a cultivation break of at least twelve months and under dry growth conditions may reduce the infestation of corn salad with A. valerianellae.