Interactive impacts of a herbivore and a pathogen on two resistance types of Barbarea vulgaris (Brassicaceae)

Abstract

It is well known that pathogens and arthropod herbivores attacking the same host plant may affect each other. Little is known, however, about their combined impact on plant fitness, which may differ from simple additive expectations. In a 2-year common garden field experiment, we tested whether the pathogen Albugo sp. (white blister rust) and the herbivorous flea beetle Phyllotreta nemorum affected each other's performance on two resistance types (G-type and P-type) of the crucifer Barbarea vulgaris ssp. arcuata, and whether biomass, reproduction and survival of the plants were affected by interactive impacts of the antagonists. Most of the insect-resistant G-plants were severely affected by white rust, which reduced biomass and reproductive potential compared to the controls. However, when also exposed to flea beetles, biomass loss was mitigated in G-plants, even though apparent disease symptoms were not reduced. Most of the insect-susceptible P-plants were resistant to white rust; however, the number of flea beetle mines tended to increase in plants also exposed to Albugo, and biomass at the last harvest was slightly lower in the combined treatment. Thus, interactive impacts of the herbivore and pathogen differed between the two resistance types, with an antagonistic combined impact in G-plants, which lasted surprisingly long, and a slight synergistic impact in P-plants.

Resistance and susceptibility to powdery mildew, root-knot nematode, and western flower thrips in two types of winter cress (Brassicaceae)

“…cruciferarum in the G-and P-types is opposite in the case of the oomycete A. candida, for which the G-type is the most susceptible type (Christensen et al, 2014;Heimes et al, 2014;van Mölken et al, 2014). The case of resistance to the rust A. candida is the only one in which resistance to a herbivore is detected in the P-type rather than in the G-type, which besides showing resistance to the mildew E. cruciferarum and the thrips F. occidentalis as we report here, is already well-known as resistant to P. xylostella and P. nemorum (Agerbirk et al, 2003b;Badenes-Pérez et al, 2014b;Idris and Grafius, 1994).…”

“…However, the P-type is often resistant to the oomycete pathogen causing white rust, Albugo candida (Pers.) Kuntze (Peronosporales: Albuginaceae), while the G-type is mostly susceptible to it (Christensen et al, 2014;Heimes et al, 2014;van Mölken et al, 2014). Within B. vulgaris, two biochemically distinct forms that are morphologically indistinguishable have also been found (Agerbirk et al, 2015;van Leur et al, 2006).…”

Does fungal infection increase the palatability of oilseed rape to insects?

“…In Brassica rapa, the infection with a biotrophic fungal pathogen Erysiphe cruciferarum did not affect the pupal weight and mortality of Pieris brassicae caterpillars, but fungal infection with subsequent infestation indirectly and negatively affected the incidence of natural enemies by reducing the emission of VOCs. 79 Another study on Brassicaceae plants demonstrated an interaction effect of an insect herbivore and a fungal pathogen, and how this differs on two resistant host cultivars of Barbarea vulgaris 80 : the insect-resistant genotype was severely infected by a biotrophic fungus Albugo spp., which reduced plant biomass loss when subsequently infested by Phyllotreta nemorum flea beetles. However, the reverse effect was observed in the insectsusceptible genotype, where Albugo spp.…”