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Untersuchungen zum Befall des Winterrapses mit Phoma lingam (Tode ex Fr.) Desm. und zur Durchführung von Resistenzprüfungen in Feldversuchen

Wittern, I., Krüger, W., Heitefuss, R.
Phytopathologische Zeitschrift 1985 v.112 no.2 pp. 173-190
Brassica napus var. napus, Leptosphaeria maculans, autumn, cultivars, field experimentation, leaves, linear models, root crown, stems, Germany
The resistance of winter oilseed rape cultivars to Phoma lingam (root collar and stalk rot) was studied in field trials under the climatic conditions of northern Germany for two years. The scoring was carried out with individual plants, which were taken from the plots. Representative results were obtained when 30 plants per plot were evaluated. If the scoring was carried out in the field according to the symptoms on the stems results were different from those where the scoring was carried out according to the symptoms on the root collar. In the autumn symptoms were mostly found on the leaves and only to a slight degree on the root collar, but no clear cut differences between the cultivars could be found. Susceptible cultivars showed a high increase of infection starting from the middle of March. This let to a clear differentiation between susceptible and resistant* cultivars from April and May onwards. Since the infection increased until harvest the most accurate evaluation of resistance by scoring was possible in July. A heavy infection was found on one experiment in June with plants which had already developed their stems in autumn. This did not affect the different susceptibility of the cultivars to P. lingam. Resistant cultivars showed a low percentage of plants with heavy infections by P. lingam. Jet Neuf, a resistant cultivar, showed 10% and Quinta, a more susceptible cultivar, showed 60% of heavily infected plants. The disease index at the various experimental sites had an influence on the differentiation of the cultivars. Susceptible cultivars under high infection pressure reacted much more with an increase of infections than resistant cultivars. This relationship was characterized by a linear regression between the individual infection of a cultivar and the average infection of all cultivars at one site.