The Mechanism of Drought Tolerance in Potato Varieties

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The relationship between the drought tolerance and the root system was investigated with two maincrop potato varieties (Norin 1 and Konafubuki) cultivated in Hokkaido area. In the first experiment, the varietal difference in root system was identified under the field conditions ; the total root length at the maximum developmental stage of root system was 15.9 km/m^2 in Norin 1 and 11.1 km/m^2 in Konafubuki. In the second experiment with the grafting plants between these two varieties grown in pots, it was clarified that the varietal difference in the amount of roots was mainly due to the inherent characteristic in the stock. In the third experiment, the diurnal change in water absorption rate (WAR) was compared between two varieties grown in pots under different soil water conditions. Although the amount of roots less affected the WAR dt the wet plot, the restriction of WAR at the dry plot was larger in Konafubuki than in Norin 1. Finally, in the fourth experiment conducted under field conditions with different soil water treatments, the relationships of the root system with the reduction of transpiration rate and dry matter production at the dry soil condition relative to the wet soil condition was quantitatively identified.From these results, we concluded that the varietal difference in the root system related to the drought tolerance in potato. A genetic improvement of the amount of roots will be valuable to increase a drought tolerance of potato varieties. In addition, the present results suggested that even if deep soils were plentifully wet, some shortage of water inevitably occurred in potato plants when surface soils became dry. The root within surface soils may be superior to those in deep soils with respect to water absorption ability.