Effect of Ethrel on Seasonal Activity of Three Enzymes and Lodging Resistance in Soybeans1

‘Hark,’ ‘Chippewa,’ and ‘Corsoy’ soybeans [Glycine max (L.) Merr.] were grown in field plots in 1969 and 1970. 2‐chloroethylphosphonic acid (Ethrel) at concentrations of 0 to 1000 ppm was applied as a foliar spray when third trifoliolate leaves were 75% expanded. Plants were assayed during the growing season for phenylalanine ammonia lyase (PAL) (4.3.1.a) and peroxidase (1.11.1.7) activity in the stem, and nitrate reductase (NR) (1.6.6.1) activity in the leaves. Acid‐detergent fiber and lignin analyses along with anatomical observations were performed on the stems. Plants were rated for extent of lodging and seed yields were determined. NR activity peaked on July 6, PAL activity peaked during mid‐July, and peroxidase activity peaked in mid‐ to late August. Peroxidase activity increased in response to Ethrel, particularly in the internodes where lodging was first evident in control plants. PAL activity increased in response to Ethrel during the seasonal peak in enzyme activity. Corsoy lodged more than did the other varieties, but lodging was reduced in all varieties. Seed yield was not reduced by Ethrel, indicating that this growth substance may be of use to decrease harvest losses of soybean seed due to lodging.