Black rot of cabbage in The Netherlands: studies on spatial and temporal development.

Black rot in cabbage is caused by the bacterium Xanthomonas campestris pv. campestris . An exploratory survey at farm level suggested that major aspects contributing to black rot development are cultivar, initial inoculum, refuse management, origin of transplants, and seed quality. Black rot development was far more intensive with fresh than with old refuse piles, infected with X.c. pv. campestris . Increased levels of field resistance reduced the development of black rot in time and space.Field resistance to black rot is thought to be composed of several mechanisms. Black rot is hypothesised to be a potentially polycyclic disease. Fast disease development was related to the number of rain days. Secondary foci may appear at short distances from the initial focus but they usually merge with the expanding initial focus.Fast spatio-temporal development was related to high initial inoculum levels. Disease proceeds faster in plots with multi-focal inoculation than in those with uni-focal inoculation. Serious epidemics in Dutch cabbage fields originate from large numbers of foci. Temperatures≥5°C stimulated decomposition of plant debris and subsequently hastened the decline of X.c. pv. campestris . Infestation foci of X.c. pv. campestris in soil dwindled away during winters and became extinct in spring of the successive year. Polyetic development of black rot was not found. Geostatistics was successfully applied to reduce field sampling needed to obtain insight in disease patterns