2007 Volume 6 Issue 4 Pages 541-546
A simple new estimation method for water status in satsuma mandarin (Citrus unshiu Marcow.) was developed, expecting to improve irrigation in the summer and early autumn seasons and increase fruit quality. As a patch test, a “Water Stress Indicator” stuck on the abaxial side of the leaf changed color depends on the water status of the satsuma mandarin tree. The indicator is based on the fact that Cobalt(II) chloride changes its color by hydration reaction; if there is sufficient moisture, the light blue turns to a light red. To determine the appropriate condition of this indicator usage, the relationship between the diurnal change of transpiration and the leaf water potential (LWP) before sunrise was investigated. There was a clear difference in the transpiration rate of satsuma mandarin leaves around midday on a comparison of satsuma mandarin trees under various water statuses. If the transpiration rate was above the cut off (3 μg·cm−2·s−1), LWP should be −0.8 MPa or more. Together with these results, the indicator should be stuck on the abaxial side of a leaf that receives sufficient sunshine around noon. Under this condition, if the indicator color turns light red within 5 min, the satsuma mandarin tree tested is not under water stress. The "Water Stress Indicator" would facilitate visual estimation of the water state from summer to early autumn.
