Quantitative resistance increases the durability of qualitative resistance to Leptosphaeria maculans in Brassica napus

Abstract

Summary• It has frequently been hypothesized that quantitative resistance increases the durability of qualitative (R-gene mediated) resistance but supporting experimental evidence is rare. To test this hypothesis, near-isogenic lines with ⁄ without the Rgene Rlm6 introduced into two Brassica napus cultivars differing in quantitative resistance to Leptosphaeria maculans were used in a 5-yr field experiment.• Recurrent selection of natural fungal populations was done annually on each of the four plant genotypes, using crop residues from each genotype to inoculate separately the four series of field trials for five consecutive cropping seasons. Severity of phoma stem canker was measured on each genotype and frequencies of avirulence alleles in L. maculans populations were estimated.• Recurrent selection of virulent isolates by Rlm6 in a susceptible background rendered the resistance ineffective by the third cropping season. By contrast, the resistance was still effective after 5 yr of selection by the genotype combining this gene with quantitative resistance. No significant variation in the performance of quantitative resistance alone was noted over the course of the experiment.• We conclude that quantitative resistance can increase the durability of Rlm6. We recommend combining quantitative resistance with R-gene mediated resistance to enhance disease control and crop production.

Identification and mapping of quantitative resistance to late blight (Phytophthora infestans) in Solanum habrochaites LA1777

“…Quantitative resistance in plants has been shown to be more durable (Brun et al 2010;Palloix et al 2009). In S. habrochaites a high level of quantitative resistance to several isolates has been found ).…”

“…Not all QTLs were identified in each experiment and in all lines with overlapping introgressions, indicating that most QTLs have a limited effect and interactions between QTLs as well as between QTLs and environment play a role in obtaining a high level of resistance. Combining QTLs and single resistance genes can be beneficial for durability of the resistance to several fungi (Brun et al 2010;Palloix et al 2009;Stall et al 2009). Therefore we suggest to develop combinations of several QTLs or QTLs and single genes, not only from one wild species but also from different wild species.…”

“…Quantitative resistance is often non racespecific and more durable than qualitative resistance governed by R-genes (Brun et al 2010;Palloix et al 2009;Robert et al 2009). For resistance to late blight, research in potato has been since 1970 focusing on introducing quantitative resistance (Wastie 1991), in spite of the fact that already eleven single R-genes were known.…”

Spatio‐temporal connectivity and host resistance influence evolutionary and epidemiological dynamics of the canola pathogen Leptosphaeria maculans

“…This approach allowed us to explicitly characterize the dynamics of adaptive change in variable L. maculans populations exposed to different selective pressures (host resistance genes). Previous field studies used only a single pathogen population, either exposed to different hosts (Brun et al., 2000, 2010; Delourme et al., 2014) or to contrasting stubble management practices (Daverdin et al., 2012). Our results clearly show that host resistance is the most important driver of variation in pathogen population composition (Table 3).…”

“…Resistance efficacy for blackleg has proven difficult to maintain in all major cropping regions as this pathogen has repeatedly evolved infectivity against nearly all major resistance genes released so far (Brun et al., 2010; Li, Sivasithamparam, & Barbetti, 2003; Rouxel et al., 2001; Sprague et al., 2006), sometimes with almost complete yield loss (Sprague et al., 2006). Deployment of new resistance genes to date has been largely ad hoc following discovery and introduction via breeding pathways, resulting in a predictable temporal sequence of pathogen evolutionary adaptation (Van de Wouw et al., 2017).…”