小白菜花叶病流行及其介体种群时空动态的模糊聚类分析

利用模糊聚类分析方法对小白菜花叶病介体蚜虫种群增长和病害流行的时空动态分别进行分析,并对介体种群增长和病害流行时空动态进行概述。田外带毒介体扩散迁入,花叶病开始发生,在病害流行初期,由于介体在本田内未建立种群,来自田外的带毒有翅蚜虫在田内随机扩散,导致病害的空间扩展迅速,病样方率逐渐上升,病株率伴随上升,每病样方多为1株病株;在病害流行前期,随着介体的进一步迁入和定殖,病害的空间扩展加快,病样方率迅速上升,样方内病株数量增加,病害严重度上升缓慢;在病害流行中期,田内介体种群密度上升,有翅介体在田内大量扩散,导致病株遍及全田,病样方率接近饱和,病害的增长以病株率上升为主;在病害流行后期,病株率接近饱和,严重度迅速上升,然后超于平缓。

APPLICATION OF FUZZY CLUSTER ANALYSIS TO TEMPORAL AND SPATIAL DYNAMICS OF CHINESE-SMALL-CABBAGE MOSAIC DISEASE AND ITS VECTORS

The temporal and Spatial dynamics of the aphid vectors (Myzzus persicae and Rhopalasiphum pseudobrassicae) of the Chinese-small-cabbage mosaic disease were outlined by means of fuzzy cluster analysis. At the early stage of the epidemic aphids mainly of alatae immigrating from the outside of the field were of low density and poisson distribution, but sometimes low aggregations were observed. After the colonization of the aphids in the field, the infestation increased greatly in a short time, but soon the rate of infestation began to decrease; the density of aphids, however, still continued to increase, resulting in a high aggregation in the season. When the aphid-infested plants reached 90%, the rate of infestation was greatly slow down; the aggregation became lower than before, being stable. The size of the aphid population continued to increase to a peak just before harvest of the crop.The dynamic of disease progress was also studied with a Fuzzy cluster analysis. At the early stage of the epidemic the inoculum (virus) was carried and spread by the immigrating alatae with a random distribution, which resulted in a random distribution of diseased plants in the field. Due to the rapid spatial spread of the disease, there was a rapid increase in number of diseased sampling units, which was paralleled by an increase in percentage of diseased plants in the field. However, at the beginning there was often only 1 diseased plant per sampling unit. Owing to the immigration and colonization of the vectors, inter-and intra-unit spread of disease occurred simultaneously and was accompanied with an increase of disease severity. The migration of vectors in the field facilitate the spread of diseased plants all over the field, resulting in a rapid increase of diseased sampling units to 100% and diseased plants as well. At the last stage of the epidemic, nearly all plants were infected and thus the disease progress was then reflected in the iacresease of severity.