Damage Responses in Wild and Cultivated Annual Graminoids: The Role and Defense Status of the Flag Leaf

Abstract

We studied the effects of artificial removal of leaf area and seeds on the performance of three annual grass species, Hordeum vulgare, Setaria italica, and Setaria viridis, grown in two densities. The value of a particular leaf to a plant in relation to its defense status was assessed using food preference trials. The results obtained for H. vulgare in the first study year were in accordance with the hypothesis that the flag leaf is important in ensuring the proper development of the ear and is thus better defended against herbivores. Removal of the flag leaf in an early developmental phase decreased significantly the number and total dry mass of grains per plant. The flag leaf was preferred by the test herbivore less often than the lower leaf of the same plant, which may reflect the stronger defense status of the flag leaf. In the second study year, however, when the same treatments were performed at a later developmental phase, leaf or seed removal had no significant effects on reproduction. In Setaria spp., we could not detect significant effects of leaf or seed removal on the reproductive traits studied. Unlike the cultivated S. italica, S. viridis produced tillers. Tiller production was promoted by both low density and seed removal, whereas flag leaf removal after the appearance of the ear decreased tillering significantly. The importance of plant developmental stage and cultivation history for damage responses is discussed.