Variations in leaflet orientation among soybean cultivars

Significant variation was observed among five cultivars of soybeans (Glycine max L., Merr.) in the degree of leaflet orientation at two stages of growth. The degree of leaflet orientation of Ogden, Forrest, Essex, York and Dare was measured hourly beginning at 7:00 a.m. and continuing until 7:00 p.m. (EST) and 8:00 p.m. (EOT) during V10 and R3, respectively. The cultivars tended to change the vertical inclination of the center leaflets of a trifoliolate while keeping the horizontal inclination relatively constant, whereas, the reverse was true of the side leaflets. Maximum variation in leaf movement was noted from 10:00 a.m. until 5:00 p.m. During the V10 stage of growth Ogden and Essex exhibited the greatest amount of orientation while Forrest and Dare were intermediate and York exhibited the least response. During R3 Ogden attained and maintained the highest angle of orientation of the center leaflet followed by Essex and Forrest. Dare and York changed very little. Forrest, Dare and York exhibited the most horizontal movement of the side leaflets CR3) followed by Ogden and Essex which exhibited less movement. More variation was observed during the reproductive stage of growth than was observed during the vegetative stage. Analyses indicate that sufficient statistical information about the variation can be attained from two-days' measurements. Potassium levels were significantly higher (P > .01) in the pulvini of plants collected in the "tense" state than those from plants collected when pulvini were in the "relaxed" stage. The shifts in potassium concentration in the pulvinus apparently has some role in the bending and straightening of the pulvinus which in turn moves the leaflet. Some differences were observed among cultivars in the fine structure of the pulvinus but these differences could not be adequately defined in this study. The effects of light intensity, sun angle and ambient temperature on leaflet orientation of the soybean cultivars were negligible based on correlation and regression values.