Unidirectional trichomes in rice and prickles in Andropogon virginicus protect meristems from herbivory

Abstract

AbstractMany grasses (Poaceae) defend their basal meristems with silicified trichomes, prickles, and spines. These leaf features are often unidirectional, pointing from the leaf base to the tip. They have been hypothesized to direct small herbivores away from vulnerable meristems, making grasses tolerant of the loss of leaf tissue. The aim of this study was to determine whether leaves of rice (Oryza sativa L.) and broomsedge (Andropogon virginicus L.) with silicified non‐glandular trichomes and prickles experience more chewing damage to leaf tips than to leaf bases, and whether the unidirectional leaf features were responsible for this pattern. Rice and A. virginicus leaves received 4× and 3× more chewing damage, respectively, to tips than middle sections, and 3× and 8× more damage to middle sections compared to basal sections. Removing trichomes and prickles from half of each leaf did not increase the overall frequency of damage to those leaves. However, removing silicified structures caused herbivores to increase the frequency of damage to leaf sections without trichomes and prickles, including basal leaf sections. Leaves of A. virginicus were experimentally folded in half such that the middle section was above the tip and basal sections; folded leaves received more damage to tips and bases than to middle sections. This indicates that herbivores do not choose to feed on the tallest leaf tissue but are likely influenced by the orientation of the silicified leaf features. Previous studies have shown variation in silicified structures on the leaves of many crop species. As these structures are involved in directing herbivores away from basal meristems, they should be considered as targets for crop breeding.