Abstract
Infestation of white tip nematode in paddy rice have lately increased in the greater part of Japan, and gradual permeation of newly developed mechanical transplanting rice culture have been considered as a possible cause of the increased infestation. In order to confirm this, some observations on the nematode populations were made in comparison between the mechanical transplanting (MT) culture and ordinary hand transplanting (HT) culture. In nursery bed for the MT culture, in which seeds are always sowed densely on a special medium in standardized plastic box and germinated under higher temperature condition than those of the ordinary cultures, the majority of the nematodes originated from the infected seeds reinvaded the young seedlings and active reproduction of the nematodes were observed. On the other hand, only a few nematodes reinvaded the ordinary beds for the HT culture. In field trials on dissemination of the nematodes from infected plants (inoculm) to healthy plants, the earlier inoculations were more effective than later ones for the nematode dissemination in both cultures, but the degrees of the dissemination were significantly higher in MT culture, in which more younger seedlings were used, than in HT culture. From these results, it could be concluded that the occurrence of the nematode would more severe in newly developed MT cult ure than ordinary cultures.
