Abstract
The success of sustainable crop production depends on our ability to select or create varieties that can allocate resources to both growth and defence. However, breeding efforts have emphasized increases in yields but have partially neglected defence traits against pests. Estimating the costs of multiple defences against tuber herbivores and the tradeoffs among them, as well as understanding the relationship between yield and multiple defences is still unknown but relevant to both basic and applied ecology. Using twenty commercial potato varieties available in Colombia and the tuber herbivore Tecia solanivora, we tested whether high yielding varieties show a reduction in three types of defence: constitutive and induced resistance, as well as tolerance. Specifically, we determined (1) the costs in terms of yield of all three defences, (2) the possible tradeoffs among them, and (3) if oviposition preference was related to the expression of these defences. We detected no costs in terms of yield of constitutive and induced resistance to tuber damage. We did, however, find evidence of costs of being able to tolerate tuber herbivory. While we found no tradeoffs among any of the estimated defences, there was a positive correlation between aboveground compensatory growth and tolerance in terms of tuber production, suggesting that after damage there are no shifts in the allocation of resources from aboveground to belowground biomass. Finally, we found that females laid more eggs on those varieties with the lowest level of constitutive resistance. In conclusion our findings suggest that in potatoes, breeding for higher yields has not caused any reduction in constitutive or induced resistance to tuber damage. This is not the case for tolerance where those varieties with higher yields are also less likely to tolerate tuber damage. Given the high incidence of tuber pests in Colombia, selecting for higher tolerance could allow for high productivity in the presence of herbivores. Finding mechanisms to decouple the tolerance response from yield should be a new priority in potato breeding in Colombia to guarantee a higher yield in both the presence and absence of herbivores.
Highlights
Sustainable crop production depends on our ability to decrease pest pressure while simultaneously increasing yield
By studying the response of twenty commercial potato varieties available in Colombia, including varieties of Solanum tuberosum and S. phureja, to the tuber damage of the Guatemalan potato moth Tecia solanivora we evaluated the following: (1) we examined the presence of genetic variation for both resistance and tolerance to tuber herbivory; (2) we determined the costs associated with the expression of all types of defence and the possible tradeoffs among them, and (3) we assessed oviposition preference for all the varieties used and whether this preference was related to the expression of defence
Twenty commercial potato varieties available in Colombia were included in the study: five varieties belonging to the species S. phureja (Criolla Colombia, Criolla Galeras, Criolla Guaneña, Criolla Latina and Criolla Paisa) and 15 varieties of S. tuberosum (Betina, Capiro, Esmeralda, Monserrate, Nevada, Parda Pastusa, Pastusa Suprema, Punto Azul, Purace, Roja Nariño, Rubı, Toquerreña, Unica, V1 and Yungay)
Summary
Sustainable crop production depends on our ability to decrease pest pressure while simultaneously increasing yield. Resistance mechanisms can be constitutive or induced, whereas tolerance mechanisms are always triggered by herbivore attack These defence mechanisms often co-occur within the same genotype or individual, and they are assumed to be costly, given that investment in defence should reduce the amount of resources available for growth and reproduction [2]. As for the presence of tradeoffs among defences, meta-analyses have shown negative correlations between constitutive and induced resistance [11] but no tradeoffs between resistance and tolerance [12]. Most of these studies have focused on the expression of defences to aboveground herbivores, and relatively little is still known about the costs and tradeoffs of plant defences to root or tuber herbivores [13]
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