Diversity in viral resistance emerges from host genotype and infection order effects

Maija Jokinen, Hanna Susi , Anna-Liisa Laine

• While viruses are predicted to be the most diverse group of parasites wild plant hosts encounter, the extent and mechanisms maintaining viral resistance diversity remains poorly understood. Here, we test the hypothesis that allocation trade-offs maintain genetic variation in viral resistance and assess whether phenotypic resistance variation may may arise from altered expression under multiple viral attack. • We inoculated clones from 24 Plantago lanceolata genotypes with two viruses to quantify intraspecific variation among host genotypes and test possible trade-offs in resistance to either of the viruses. Furthermore, we performed subsequent viral inoculations to investigate if prior viral infection changes host resistance phenotype. • We found striking intraspecific variation in resistance among the 24 host genotypes against the two studied viruses, with limited evidence for trade-offs maintaining this variation. We also found that prior infection by Plantago lanceolata enamovirus altered the host resistance phenotype, rendering the host more vulnerable to subsequent infection. • Jointly, our results show that intraspecific variation in resistance may have a substantial role in mitigating viral infections in wild hosts. Furthermore, our results highlight the importance of arrival order for the resistance phenotype and for shaping viral coinfections.