Nitrogen supply exerts a major/minor switch between two QTLs controlling Plasmodiophora brassicae spore content in rapeseed

Abstract

Clubroot, caused by Plasmodiophora brassicae, is a worldwide disease affecting Brassica. Until now, the detection of genetic factors (QTLs) implicated in clubroot resistance has been based on estimates of disease index. However, as the amount of resting spores released in soil after club disintegration influences clubroot epidemics and resistance‐breaking dynamics, its genetic control may deserve specific attention. In a previous report, it was shown that nitrogen fertilization modulated quantitative partial resistance toward clubroot symptom development in rapeseed. The present work aimed to identify genetic factors involved in the control of resting spore production and to assess their regulation by nitrogen supply. A flow cytometer method was adapted for rapidly estimating resting spore content in a large series of samples. Linkage analysis was conducted to detect QTLs implicated in resting spore production in a Brassica napus doubled haploid progeny from the cross Darmor‐bzh × Yudal. DH lines inoculated with the P. brassicae isolate eH were grown under low‐ and high‐nitrogen supply. Under low‐nitrogen conditions, resting spore production was reduced compared to high‐nitrogen conditions, regardless of genotypes. Genetic architecture controlling resting spore production and clubroot symptom development was similar. Under high‐nitrogen conditions, resting spore production was controlled by one major QTL (C09a) and a few small‐effect QTLs. By contrast, two major QTLs (C02 and C09a) controlled resting spore production under low‐nitrogen conditions. This work highlighted a large see‐saw effect between the relative contribution of the C09a QTL (high effect under high‐nitrogen conditions) and the C02 QTL (high effect under low‐nitrogen conditions), with possible implications in resistance breeding.

Resolution of quantitative resistance to clubroot into QTL-specific metabolic modules

“…4B). The moderate-effect QTL C09_Pb and the major-effect QTL C09_DI, both detected at 59 cM, colocalized with the major resistance locus, first described as Pb-Bn2 by Manzanares-Dauleux et al (2003) and further reported by Laperche et al (2017) and Aigu et al (2018). Four additional minor QTLs were found to be involved in the control of DI; these were located on chromosomes A01, A10, C02, and C03.…”

“…Moreover, Darmor- bzh and Yudal displayed compatible interactions with isolate eH, and accordingly it is expected that both genotypes would show some metabolic responses associated with susceptibility. Conversely, previous studies (Laperche et al , 2017; Aigu et al , 2018) have highlighted that both Darmor- bzh and Yudal harbour resistance alleles at different QTLs, and consequently both genotypes were expected to exhibit metabolic features associated with resistance (the mechanisms of which could be either similar or different in the two accessions). To extend the understanding of the relationship between partial resistance and metabolic traits, it was necessary to compare the mapping of QTLs associated with the control of disease traits and metabolic profiles in the two genotypes.…”

“…The objective of the present study was to relate quantitative genetics to both metabolomics and pathogen-resistance traits, to get new insights into the metabolic modules associated with allelic variations at each QTL involved in the control of partial resistance. This work was focused on the progeny derived from two parental genotypes: Darmor- bzh , which displays a high level of partial resistance to the P. brassicae isolate eH, mainly controlled by the locus PbBn1 , and Yudal, which shows an intermediate level of resistance to eH, controlled by several QTLs (Manzanares-Dauleux et al , 2003; Laperche et al , 2017; Aigu et al , 2018). We started the study with a histological and PCR-based evaluation of pathogen development over the duration of infection, to identify the earliest time point at which post-invasion partial resistance was distinguishable between the two parental genotypes.…”

Quantitative resistance to clubroot infection mediated by transgenerational epigenetic variation in Arabidopsis

“…() had already evoked a possible link between temperature, clubroot response and epigenetics when studying the Arabidopsis mutant tu8 (mutant in the LIKE HETEROCHROMATIN PROTEIN 1 LHP1 ) which presented different levels of response to clubroot depending on the temperature conditions. Similar environmental effects on the modulation of QTL controlling clubroot response also have been shown with nitrogen supply variations in B. napus (Laperche et al ., ; Aigu et al ., ) and with flooding in Arabidopsis (Gravot et al ., ). Here, our analyses suggested that the temperature effect was partly triggered by the interaction with the plant epigenome for the traits Rbi and Pb.…”

The effect of nitrogen fertilization on the incidence of olive fruit fly, olive leaf spot and olive anthracnose in two olive cultivars grown in rainfed conditions

“…From the studies conducted up to the present, we can find quite different results, but in some of them nitrogen fertilization was found to increase the incidence of several diseases. For instance, it was reported that high amounts of nitrogen fertilization increased the infection of winter wheat (Triticum aestivum) by fusarium foot and root disease (Fusarium culmorum) (Hemissi et al, 2018), resting spore production of clubroot caused by Plasmodiphora brassica on rapeseed (Brassica napus) (Aigu et al, 2018), fusarium head blight (Fusarium sp.) and related mycotoxin accumulation on winter wheat (Heier et al, 2005), powdery mildew (Erysiphe graminis hordei) in winter barley (Hordeum vulgare) (Oerte and Schönbeck, 1990) or gummy stem blight (Didymella bryoniae) on watermelon (Citrullus lanatus) (Santos et al, 2009).…”