Influences of irrigating methods on shoot and root growth of melons were studied under root confinement culture in a vinyl house from mid-June to late August 2004. The control (plot C) and three root-confined plots (LM, MF and SD) were designed. Plot C unconfined rooting zoon was irrigated by drip-watering at a relative short interval (at most 10 times a day according to the weather) in daytime. Plot LM and SD were also irrigated in the same way as plot C. Plot MF was irrigated by drip-watering at a long interval (at most 4 times a day according to the weather) in daytime. On basis of evapotranspiration rate, all plots were irrigated the same amount of water per day until one week before the harvest time. Prior to transplantation, plot C, LM and MF were sufficiently watered the whole surface of a ridge but plot SD was watered only the central zoon of a ridge. Roots in plot C distributed shallowly and widely. Roots in plot MF and LM also distributed shallowly and the amount of roots was less in plot MF. Roots in plot SD grew most vigorously and distributed most uniformly in a ridge. Fruit weight was relatively larger in plot C and SD than in 2 other plots. The peduncle length was shorter in plot LM than in other plots. The results suggested that the watering management in root confinement culture greatly affected the root growth, root system formation and fruit quality.

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For the maintenance of shoot growth and the survival under the osmotic stress condition, it is considered that the maintenance of root growth, the expansion of root system and the maintenance of water and nutrients absorption have the important key. Root elongation involves both cell elongation and cell production. Additionally, the root system consists largely of many lateral roots and lateral root has an important role for the plant growth under osmotic stress condition. It was suggested that allocation of photosynthate is one of the main factors that regulate lateral root development in root systems. In this paper, we review the previous studies focused on (1) the relationship between root elongation and root osmotic adjustment for the maintenance of turgor pressure under the osmotic stress condition, (2) the effect of osmotic stress for the cell production and root elongation and (3) the role of sugar accumulation for the lateral root development under the osmotic stress condition.

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