Abstract:

Brassica rapa var. chinensis and Brassica rapa var. glabra were employed as experimental materials, with the sampling methods such as aggregation index, m^*-m regression analysis and Taylor’s power law, and the spatial distribution pattern and characteristic of clubroot disease under greenhouse cultivation were analyzed, and the sampling techniques were studied to further improve the investigation and prediction ability of the disease. The result showed that the disease developed severe when the test area was closer to the center of the greenhouse, and relatively light when it was near the edge in the two crops. Test of aggregation index showed that the main trends of clubroot disease were fitted to uniform distribution under the condition of heavy occurrence, but aggregation distribution would also occur in the lower occurrence area. Regression analysis of m^*-m and Taylor’s power law indicated that the individual colony was the basal component of the spatial distribution of clubroot disease and they attracted each other slightly. The distribution pattern of individual colony tended to be uniform distribution, and this trend was increased with the increasing disease grade of individual plant in the two crops. On the basis of the above analysis, the optimal theoretical sampling model and sequential sampling model of clubroot disease in the two crops were presented. This study results were helpful to improve efficiency in the investigation and sampling of clubroot disease, and it provided evidence for early-forecast and prevention decision.

Key words: greenhouse cultivation, Brassica rapa var. chinensis, Brassica rapa var. glabra, clubroot disease, spatial distribution pattern, sampling technique, aggregation index methods, optimal theoretical sampling model