The influence of water stress on starch production seems to be dependent on the growth stage of the plant.
Mature plants are able to adapt by initiating regulatory mechanisms enabling them to
withstand prolonged stress conditions.
By reducing leaf canopy and establishing a root system to utilize deep soil water, older plants are able to maintain photosynthetic activity.
The plants, after surviving the stress conditions, will recover quickly by forming new leaves, the energy for this process is obtained by utilizing reserved starch.
The net effect is a reduction in starch content.
In contrast, water stress at the start of plant development does not seem to elicit a regulatory mechanism, starch is, therefore, not effectively synthesized and the plants will not develop.
On removing the stress plants start growing and accumulating starch.
Starch content remains lower than normal despite the application of sufficient
water (maximal starch content was 12.6–21.1% and 25.9–30.3% for roots of with and without initial water stress at 10 and 8 months, respectively).
Varieties responded differently to the adverse conditions, of the six varieties R90 and KU 50 recovered the quickest after stress conditions were removed.
These two varieties also had the highest starch content under both trial conditions
and are recently developed varieties that are distributed to Thai farmers.