Abstract
Greenhouse-grown, vegetative ‘Davis’ soybean plants, Glycine max (L.) Merrill, were infested with neonate larvae of the soybean looper, Pseudoplusia includens (Walker), which were allowed to defoliate the plants for 16 d. At 7, 10, 12, 14, and 16 d after infestation (DAI), plants were destructively sampled to measure plant growth and N2-fixing ability (measured using the acetylene-ethylene reduction assay). On the respective sample dates, defoliated plants suffered 13, 37, 43, 62, and 73% defoliation relative to controls. This progressive defoliation caused significant reductions in dry weight of stems by 10 DAI, and of roots and nodules by 14 DAI. Number of nodules and mean dry weight per individual nodule were not affected during the course of the experiment. N2-fixing ability was reduced significantly by 10 DAI, largely because of a significant decrease in nodule specific activity (NSA). Further decreases in N2-fixing ability at 14 and 16 DAI resulted from a combination of decreased nodule weight and decreased NSA.
Published Version
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