Sixty-five cvs. of petunia, Petunia hybrida Vilm., were evaluated for sensitivity to ozone and the reduction in damage afforded by applications of growth regulating and other chemicals. Plants were exposed to ozone concn at 15, 30, 45, and 60 parts per hundred million (pphm) in a growth chamber for 1.5, 3, and 6 hr at 25°C, 78-88% relative humidity, and an illumination of 2,000 ft-c. Chemicals which retarded internode elongation and promoted dark green color of the foliage reduced visible injury induced by ozone.4,5 The compounds 2,4-dichlorobenzyltributyl phosphonium chloride (CBBP) and succinic acid 2,2-dimethyl hydrazide (SADH) retarded growth and modified sensitivity of the foliage to ozone. Concentration of SADH needed to reduce injury significantly was at least twice that used to retard stem elongation. Adding L. ascorbic acid and a wax coating to the spray solution increased the protection afforded by SADH. Chemicals which did not retard growth of petunia such as the chemical growth retardants (2-chloroethyl) trimethyl ammonium chloride (chlormequat), α-cyclopropyl-α (4-methoxyphenyl)-5-pyrimidine methanol (ancymidol), and the systemic fungicide methyl 1-butylcarbamoyl-2-benzimidazolecarbamate (benomyl) afforded no protection for ozone treated plants. The 65 cvs. were placed in 6 classes based on an average rating of injury after exposures to 4 doses of ozone. Five cvs. were in the very tolerant class and have most potential for use in the development of new petunia cvs. resistant to ozone and possibly to other phytotoxicants.
Eight cultivars of poinsettia, Euphorbia pulcherrima Willd., were evaluated for sensitivity to α-cyclopropyl-α (4-methoxyphenyl)-5-pyrimidine methanol (ancymidol) and protection from ozone and sulfur dioxide injury afforded by applications of ancymidol and (2-chloroethyl) trimethyl ammonium chloride (chlormequat). Foliar sprays of ancymidol were at least 80 to 500 times and the soil drench 1000 times more active than chlormequat in retarding stem elongation. The diam of the bracts was reduced, but branching increased more on plants treated with ancymidol than on untreated plants. The cv. Annette Hegg (AH) was more sensitive to ozone fumigations than was ‘Eckespoint C-l’ (C-l). Sulfur dioxide also caused more injury to AH than to C-l. Ancymidol and chlormequat reduced visible injury induced by ozone and sulfur dioxide.