Abstract
We investigated the effects of grafting Cucurbita maxima Duchesne ex Lam. cv. Kurokawa-delicious plants onto rootstocks of Cucurbita moschata Duchesne ex Poir. cv. Shima-kabocha on growth and yield under high-temperature conditions, and analyzed the bleeding rate based on the root pressure and the relative water content in leaves. The self- and cross-grafted plants of Kurokawa-delicious were planted in a glasshouse in early July (average temperature: 29.1°C). In plants grafted onto Shima-kabocha rootstocks, main stem elongation and leaf development were improved, and the harvested fruits weight per plant was significantly higher compared to that of self-grafted plants. Plants grafted onto Shima-kabocha rootstocks and grown in pots in the glasshouse for 11 days in late August (average temperature: 28.5°C) had a higher bleeding rate per unit root dry weight than self-grafted plants, suggesting that physiological activity in the root systems of Shima-kabocha rootstocks was higher. In self-grafted plants grown for 4 days under a temperature regime of 35/30°C (day/night), the relative water content of leaves was significantly lower than in plants grown at 25/20°C, whereas in plants grafted onto Shima-kabocha rootstocks, the relative water contents at 35/30°C and 25/20°C were similar, and greater than that of self-grafted plants grown at 35/30°C. Thus, the greater activity in the root system and higher relative water content in leaves of plants grafted onto Shima-kabocha rootstocks could maintain a high photosynthetic rate, resulting in improved growth and yield under high-temperature conditions.
