Resistance of the Wheat Cultivar 'Renan' to Septoria Leaf Blotch Explained by a Combination of Strain Specific and Strain Non-Specific QTL Mapped on an Ultra-Dense Genetic Map.

Camilla Langlands-Perry,Safa Ben Krima,Pierre Sourdille,Thierry C. Marcel,Romain Valade,Murielle Cuenin,Christophe Bergez,Sandrine Gélisse

doi:10.3390/genes13010100

Abstract

Quantitative resistance is considered more durable than qualitative resistance as it does not involve major resistance genes that can be easily overcome by pathogen populations, but rather a combination of genes with a lower individual effect. This durability means that quantitative resistance could be an interesting tool for breeding crops that would not systematically require phytosanitary products. Quantitative resistance has yet to reveal all of its intricacies. Here, we delve into the case of the wheat/Septoria tritici blotch (STB) pathosystem. Using a population resulting from a cross between French cultivar Renan, generally resistant to STB, and Chinese Spring, a cultivar susceptible to the disease, we built an ultra-dense genetic map that carries 148,820 single nucleotide polymorphism (SNP) markers. Phenotyping the interaction was done with two different Zymoseptoria tritici strains with contrasted pathogenicities on Renan. A linkage analysis led to the detection of three quantitative trait loci (QTL) related to resistance in Renan. These QTL, on chromosomes 7B, 1D, and 5D, present with an interesting diversity as that on 7B was detected with both fungal strains, while those on 1D and 5D were strain-specific. The resistance on 7B was located in the region of Stb8 and the resistance on 1D colocalized with Stb19. However, the resistance on 5D was new, so further designated Stb20q. Several wall-associated kinases (WAK), nucleotide-binding and leucine-rich repeats (NB-LRR) type, and kinase domain carrying genes were present in the QTL regions, and some of them were expressed during the infection. These results advocate for a role of Stb genes in quantitative resistance and for resistance in the wheat/STB pathosystem being as a whole quantitative and polygenic.

Highlights

Bread wheat (Triticum aestivum) is a staple food in many countries worldwide and is an economically important crop
Transgressive individuals can be observed for the great majority of studied traits indicating that despite Chinese Spring being susceptible to both fungal strains, it can carry small effect resistance quantitative trait loci (QTL)
This study showed that the resistance in Renan to Septoria tritici blotch (STB) is quantitative and polygenic

Summary

Introduction

Bread wheat (Triticum aestivum) is a staple food in many countries worldwide and is an economically important crop. Septoria tritici blotch (STB) is the most common disease of wheat and is caused by the ascomycete fungus Zymoseptoria tritici (formerly Mycosphaerella graminicola). Major resistance gene Stb was the first cloned gene specifying resistance to STB [23] It encodes a wall-associated kinase-like protein, which detects the presence of a matching apoplastic effector. Renan is resistant to a number of diseases such as cereal rusts, eyespot, septoria leaf blotch, and fusarium These resistances result in part from the introgression of two chromosomal fragments from Aegilops ventricosa which carry the resistance gene to eyespot Pch, on chromosome 7D, and resistance genes to rusts Lr37, Yr17, and Sr38 [27,28,29] on chromosome 2A.

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