Quantitative resistance differences between and within natural populations of Solanum chilense against the oomycete pathogen Phytophthora infestans

Abstract

The wild tomato species Solanum chilense is divided in geographically and genetically distinct populations that show signs of defense gene selection and differential phenotypes when challenged with several phytopathogens, including the oomycete causal agent of late blight Phytophthora infestans. To better understand the phenotypic diversity of this disease resistance in S. chilense and to assess the effect of plant genotype vs. pathogen isolate, respectively, we evaluated infection frequency in a systematic approach and with large sample sizes. We studied 85 genetically distinct individuals representing nine geographically separated populations of S. chilense. This showed that differences in quantitative resistance properties can be observed between but also within populations at the level of individual plants. Data also did not reveal clear indications for complete immunity in any of the genotypes. We further evaluated the resistance of a subset of the plants against P. infestans isolates with diverse virulence properties. This confirmed that the relative differences in resistance phenotypes between individuals were mainly determined by the plant genotype under consideration with modest effects of pathogen isolate used in the study. Thus, our report suggest that quantitative resistance against P. infestans in natural populations of a wild tomato species S. chilense is likely not the result of specific adaptations of hosts to the pathogen but of basal defence responses that depend on the host genotype and are pathogen isolate-unspecific.

Laminarin-triggered defence responses are geographically dependent for natural populations ofSolanum chilense

“…We found no correlation between the observed ROS maxima and the infection frequency observed with P. infestans (Kahlon et al ., 2021) (Pearson’s correlation coefficient of 0.09, p - value=0.37, Table 1). This indicates that ROS production in laminarin-associated quantitative defence responses is insufficient to assess quantitative resistance against P. infestans in S. chilense .…”

“…Leaf discs of the plant LA1963-02 (chosen due to its high resistance observed in Kahlon et al ., 2021) were treated with laminarin and MilliQ-H 2 0 treated leaf discs served as control. Experiments were performed on three different dates in three independent replicates each.…”

“…GLMMs were generated to evaluate the effect of measured immunity components on infection frequency (IF) using glmer() from the package {lme4} (Bartes et al ., 2015). The analyses were done for the 83 plants for which IF scores were available (Kahlon et al ., 2021). We scaled the measured components (ROS, ET, SA, ABA, IAA and PA) in this study with function scale() and used used the binomial variable (y) which is infection outcome, of all the plants performed on three different dates.…”

“…Furthermore, we showed clear quantitative differences in resistance against three common filamentous pathogens (Stam et al ., 2017) in different S. chilense populations. In a recent report (Kahlon et al ., 2021) we showed that such differences in quantitative resistance in geographically distinct locations of S. chilense against P. infestans are predominantly driven by the host genotype.…”

“…In this study, we use a wild tomato species Solanum chilense to elucidate molecular cues behind the diversity in resistance against the oomycete, P. infestans (Stam et al ., 2017; Kahlon et al ., 2021). Both, quantitative and qualitative resistance against P. infestans has been reported in different wild species across the Solanum genus.…”