Herbivory and Maternal Effects: Mechanisms and Consequences of Transgenerational Induced Plant Resistance

Many plants induce defenses against herbivores following initial attack. Maternal effects associated with herbivory could mediate induced defenses across generations of plants if damaged plants produce more resistant progeny than undamaged plants. I report that wild radish plants (Raphanus raphanistrum) damaged by herbivores (Pieris rapae) or treated with a chemical elicitor of induced resistance (jasmonic acid) during the vegetative growth stage, induced resistance of the plants' progeny compared to controls. Conversely, clipping of leaves with scissors, which results in loss of photosynthetic area but not induced resistance, tended to increase susceptibility of progeny plants to P. rapae compared to controls. Progeny plants exhibited further induced resistance when damaged as seedlings, although maternally induced plants were less inducible than maternal-control plants. Herbivory in the maternal generation also affected the growth of progeny plants in two ways: (1) seed mass, which was influenced by maternal herbivory, strongly positively correlated with early plant growth; and (2) when seed mass was accounted for, maternal herbivory still had an effect on plant growth, but these effects varied by plant family. Taken together, these results demonstrate that the defensive phenotype of plants is determined, in part, by the maternal environment, and that this allocation can affect the growth trajectories of progeny.