[Effects of root exudates of squash grafted with cucumber shoot on seed germination]

Cucumber (Cucumis statirus L.) is commonly cultivated by grafting on squash (Cucurbita moschata) in commercial production. The effects of root exudates of squash grafted with cucumber on seed germination rate of cucumber and squash were tested. In this study, the exudates of cucumber-grafted squash roots were continuously collected with XAD-4 resin, and were further diluted with distilled water to make 5%, 10%, 20% and 40% concentrations. Cucumber and squash seeds were used for bioassay. The seeds were germinated in glass petri dishes with 2 filter papers at bottoms and containing 5 mL the diluted root exudates. The results showed that the exudates of cucumber-grafted squash roots significantly inhibit germination rate, radicel and hypocotyl elongation in cucumber and squash, and the inhibitory rate positively correlate with the concentration of the grafted cucumber root exudates. So grafted cucumber still have allelopathy. The exudates of cucumber-grafted squash roots significantly stimulated IAA oxidase activity in cucumber and squash. As a result, they decrease IAA level in cucumber and squash, and restrained their growth. The exudates of cucumber-grafted squash roots also decrease significantly the activities of amylase and alpha-amylase in cucumber and squash, and this decrease effects were strengthening with the increasing of the concentration of the grafted cucumber root exudates. So the exudates of cucumber-grafted squash roots can inhibit the hydrolysis and utilization of starch in cucumber and squash, and thereby suppress germination and seedling growth.