Iron‐Deficiency Chlorosis of Soybean Cultivars Injured by Plant Cutoff and Defoliation1

Abstract

A preliminary observation indicated that iron‐deficiency cholorosis of soybeans [Glycine max (L.) Merr.] grown on calcareous soil may have been accentuated after hail injury that occurred during vegetative growth. The objective of our experiment was to determine the effect of plant cutoff and defoliation on the chlorosis expressed by new leaf tissue that develops after injury occurs. Ten soybean cultivars that differed in resistance to iron‐deficiency chlorosis were grown on a calcareous soil during 2 years. Plants were treated at the V1 to V5 stages of development by removing the main stem above the cotyledonary node, removing the main stem above the unifoliolate node, or complete defoliation. Chlorosis was increased an average of 0.9 score by plant cutoff above the cotyledons, 0.6 score by cutoff above the unifoliolates, and 0.2 score by defoliation. For each type of injury, the stage of development when the treatment was imposed had a significant effect on the change in chlorosis expressed during one or both years. The differences in response among cultivars and the year ✕ cultivar, treatment ✕ cultivar, and year ✕ treatment ✕ cultivar interactions were significant. The increase in chlorosis from plant injury may cause yield loss in addition to that resulting from the injury per se. Artificial plant injury may be a useful tool in selection for improved genetic resistance to iron‐deficiency chlorosis.