Adaptation to resistant hosts increases fitness on susceptible hosts in the plant parasitic nematode Globodera pallida

Abstract

Trade-offs between virulence (defined as the ability to infect a resistant host) and life-history traits are of particular interest in plant pathogens for durable management of plant resistances. Adaptation to plant resistances (i.e., virulence acquisition) is indeed expected to be associated with a fitness cost on susceptible hosts. Here, we investigated whether life-history traits involved in the fitness of the potato cyst nematode Globodera pallida are affected in a virulent lineage compared to an avirulent one. Both lineages were obtained from the same natural population through experimental evolution on resistant and susceptible hosts, respectively. Unexpectedly, we found that virulent lineages were more fit than avirulent lineages on susceptible hosts: they produced bigger cysts, containing more larvae and hatching faster. We thus discuss possible reasons explaining why virulence did not spread into natural G. pallida populations.

Keywords: Experimental evolution; fitness benefit; life‐history traits; selection; trade‐off; unnecessary virulence.

Figure 1

Percentage of females produced for each Globodera pallida lineage on the resistant potato cultivar Iledher and for the positive controls on the susceptible potato cultivar Désirée. Lineages having evolved on Désirée (Gp‐Désirée‐6x, Gp‐Désirée‐8x, Gp‐Désirée‐10x) and on Iledher (Gp‐Iledher‐6x, Gp‐ Iledher‐8x, Gp‐ Iledher‐10x) are indicated in grey and black, respectively. White bars correspond to the percentage of females produced by the three avirulent lineages (Gp‐Désirée‐6x, Gp‐Désirée‐8x and Gp‐Désirée‐10x) on Désirée. Letters represent the homogenous groups identified by the Tukey contrasts test at the 5% threshold.

Figure 2

Means (± standard error) of (A) the number of cysts (#Cysts), (B) the size of cysts (Size_cysts), (C) the number of larvae (#Larvae), (D) the length of larvae (Length_larvae), (E) the hatching probability (P) and (F) the mean hatching time (HT) for the virulent and the avirulent Globodera pallida lineages at each generation (6x and 10x). F and P are indicated for each comparison and significant vir/avir effects are highlighted in bold.