Abstract
Within several plant species, a high variation in the composition of particular defence metabolites can be found, forming distinct chemotypes. Such chemotypes show different effects on specialist and generalist plant enemies, whereby studies examining interactions with pathogens are underrepresented. We aimed to determine factors mediating the interaction of two chemotypes of Bunias orientalis (Brassicaceae) with two plant pathogenic fungal species of different host range, Alternaria brassicae (narrow host range = specialist) and Botrytis cinerea (broad host-range = generalist) using a combination of controlled bioassays. We found that the specialist, but not the generalist, was sensitive to differences between plant chemotypes in vivo and in vitro. The specialist fungus was more virulent (measured as leaf water loss) on one chemotype in vivo without differing in biomass produced during infection, while extracts from the same chemotype caused strong growth inhibition in that species in vitro. Furthermore, fractions of extracts from B. orientalis had divergent in vitro effects on the specialist versus the generalist, supporting presumed adaptations to certain compound classes. This study underlines the necessity to combine various experimental approaches to elucidate the complex interplay between plants and different pathogens.
Highlights
Within several plant species, a high variation in the composition of particular defence metabolites can be found, forming distinct chemotypes
A high variation in chemical defence profiles can be found within plant species, in which so-called chemotypes are formed, that differ in the composition of a certain metabolite class[7,8,9,10]
Plants from one chemotype, collected in the Caucasus region where the species potentially originates[26], showed lower abundance of various herbivores and pathogens in a field common garden and were of lower host quality for a generalist herbivore in a laboratory experiment than plants of another chemotype, which was collected in the species’ invasive range in northern parts of Eurasia[23,25]. It is unclear whether differences in pathogen infection spot abundance represent the impact of infection on the plants and whether chemotype susceptibility of B. orientalis differs in dependence of the degree of host specificity of the pathogens
Summary
A high variation in the composition of particular defence metabolites can be found, forming distinct chemotypes Such chemotypes show different effects on specialist and generalist plant enemies, whereby studies examining interactions with pathogens are underrepresented. Orientalis29,30), and may moderately tolerate various classes of defence metabolites These well-studied species could naturally come into contact with B. orientalis, and are suitable models to investigate interactions of chemotype traits with fungal attackers with potentially different adaptations to the host chemistry under controlled conditions. Due to their different host range, A. brassicae and B. cinerea are in the following referred to as ‘specialist’ and ‘generalist’, respectively
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