No abstract

This work was carried out in the Northwestern Loess Plateau (NLP), one of two main large-scale apple production areas in China. It is to investigate the role of nematodes in apple production areas, which cause apple replant disease (ARD). Soil samples from total eight sites in NLP were collected twice, in summer and autumn, respectively. The nematodes were extracted by washing-sifting-sucrose centrifugation and total nematodes in each sample were counted with the aid of an anatomical lens (40×). Furthermore, a sub-sample of one quarter of each nematode suspension was observed with a Motic microscope (400 and 1000×) and each nematode was identified to genus level using diagnostic keys. The results indicated that the characteristics of the nematode community did not vary significantly in four different types of soils. Especially, the diversity indices of nematode community did not show obvious differences. In addition, the analysis of nematodes with different feeding habits revealed that the overall number of Pratylenchus penetrans nematodes in the replanted orchard in NLP were far below the density threshold that could jeopardize apple trees. Thus, it appeared that the nematodes were not the leading causal agent for ARD in NLP.