Abstract
Morning glory was found to be an indicator plant suitable for detecting photochemical oxidants. Typical symptom was small flecks of chlorosis only on the upper surface of the leaves. If the damage was more severe, it became to necrosis. Twelve cultivarieties of morning glory were exposed to the natural photochemical oxidants at Konosu or artificially produced ozone to determine the diffrence of susceptibility among the cultivarieties. Two varieties, Heavenly Blue and Pearly Gate, belonging to Ipomoea tricolor Lam.. were the most susceptible. Among the species of Pharbitis nil Choisy, varieties Scarlet O'hara and Rose Queen were also sensitive. On the other hand, dwarf varieties both Carol Red and Carol Blue, and Uzu type variety Murasaki-jishi were tolerant. Four to five matured leaves between the 10th leaf to the 14th (leaf position was counted from the top of the plant) wete more sensitive than expanding, just expanded young leaves and overmatured leaves during the period from the 15th to 70th leaf stage. Morning glory grown at a normal fertilizer level was more sensitive to photochemical oxidants than that at a lower nutrient level. The plant was less sensitive when water supply was partially withheld than supplied sufficiently.
