Soilless culture of watermelon [Citrullus lanatus (Thunb.) matsum. et nakai], and salinity effects on fruit development and soluble solids content

摘要

Watermelon plants were grown in 4 types of soilless culture systems--wet-sheet culture (WSC), rockwool culture (RWC), and deep-flow technique either with aeration (DFT/A) or without aeration (DFT/N)--to determine a suitable soilless culture system for watermelon. The electrical conductivity (EC) of the nutrient solution supplied was maintained at 1.2 dS nT . Shoots were restricted to 2 per plant and were trained vertically. Each plant had 1 fruit. Although shoot growth was greater in DFT at earliergrowth stages, some plants wilted in DFT/N at the fruit development stage. Fruit weight was slightly greater in WSC and DFT/A than in RWC and DFT/N. The total soluble solids (TSS) content of the fruit was similar in WSC, RWC, and DFT/A. From these results, we selected WSC as a suitable soilless culture system for watermelon. The effect of salinity at the fruit development stage on fruit weight and TSS content was investigated in WSC to ascertain whether the quality of the fruit could be improved. The EC of the nutrient solution supplied was 1.2 dS m~(-1) at the vegetative growth stage. It was then set to 1.2 dS m~(-1) (control), 5 or 8 dS m~(-1) (salinity treatments) at 12-13 d after pollination. Fruits were harvested at 40 d after pollination. In the5 and 8 dS m~(-1) treatments, the EC of the nutrient solution in the growing bed increased above that of the solution supplied. The photosynthetic rate of the leaves decreased notably as the salinity increased. Fruit weight was approximately 6 kg in thecontrol and decreased significantly in the 5 and 8 dS m~(-1) treatments. The TSS content of the fruit did not increase with salinity.