Improving growth and structure of root system after transplanting in plug-grown seedlings

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Plug-grown seedlings in a plug tray can be easily overgrown, because of the tightly-restricted root zone. Depression of root activity was found in overgrown cabbage seedlings by evaluation of respiration and bleeding sap rate of the root system. For analysis of root growth in plug-grown seedlings just after transplanting, cabbage seedlings were transplanted in pots filled with sand and grown for two weeks under controlled environment in a phytotron glass room. Subsequent growth of new roots sticked out of a root clump was examined by image analysis of the root system dug out from sand. The delay of transplanting depressed elongation and development of vigorous anchoring roots after transplanting, although volume of new roots was supplemented with a rapid increase in fine roots by branching frequently. Thus, the seedlings overgrown in a plug tray could not become deeply-rooted plants after transplanting, and they might be intolerant of drastic changes in root environment. Coating the tray with a copper compound for preventing formation of a root clump improved subsequent root growth of overgrown seedlings to some extent. Such a new methodology may help to make a plug technique applicable to wide regions in the world for agricultural plant production.