Heather Fell, Ajisa Muthayil Ali, Rachel Wells, Georgia K. Mitrousia, Hugh Woolfenden, Henk-jan Schoonbeek, Bruce D. L. Fitt, Christopher J. Ridout & Henrik U. Stotz

Theoretical and Applied Genetics April 2013; vol. 136, Article number: 71

 Key message

Quantitative disease resistance (QDR) controls the association of the light leaf spot pathogen with Brassica napus; four QDR loci that were in linkage disequilibrium and eight gene expression markers were identified.

Abstract

Quantitative disease resistance (QDR) can provide durable control of pathogens in crops in contrast to resistance (R) gene-mediated resistance which can break down due to pathogen evolution. QDR is therefore a desirable trait in crop improvement, but little is known about the causative genes, and so it is difficult to incorporate into breeding programmes. Light leaf spot, caused by Pyrenopeziza brassicae, is an important disease of oilseed rape (canola, Brassica napus). To identify new QDR gene loci, we used a high-throughput screening pathosystem with P. brassicae on 195 lines of B. napus combined with an association transcriptomics platform. We show that all resistance against P. brassicae was associated with QDR and not R gene-mediated. We used genome-wide association analysis with an improved B. napus population structure to reveal four gene loci significantly (P = 0.0001) associated with QDR in regions showing linkage disequilibrium. On chromosome A09, enhanced resistance was associated with heterozygosity for a cytochrome P450 gene co-localising with a previously described locus for seed glucosinolate content. In addition, eight significant gene expression markers with a false discovery rate of 0.001 were associated with QDR against P. brassicae. For seven of these, expression was positively correlated with resistance, whereas for one, a HXXXD-type acyl-transferase, negative correlation indicated a potential susceptibility gene. The study identifies novel QDR loci for susceptibility and resistance, including novel cryptic QDR genes associated with heterozygosity, that will inform future crop improvement.

See https://link.springer.com/article/10.1007/s00122-023-04243-y

Figure 3: Effects of SNPs at GWA markers that were in linkage disequilibrium on QDR against P. brassicae. Box plots were generated in R. The box represents the lower (25%) and upper (75%) quartiles with the median shown as a bar. The whiskers extend to the most extreme data point that is no more than 1.5 times the interquartile distance from the box. Outliers may extend beyond the whiskers. Jitters illustrate individual measurements. Resistance alleles were heterozygous in three cases or homozygous in one case. Asterisks indicate significant differences at P < 0.05 (*), 0.001 (***) or P < 0.0001 (****).