Identification and mapping of a novel blackleg resistance locus LepR4 in the progenies from Brassica napus × B. rapa subsp. sylvestris

Abstract

Blackleg, caused by Leptosphaeria maculans, is one of the most economically important diseases of Brassica napus worldwide. Two blackleg-resistant lines, 16S and 61446, were developed through interspecific hybridization between B. napus and B. rapa subsp. sylvestris and backcrossing to B. napus. Classical genetic analysis demonstrated that a single recessive gene in both lines conferred resistance to L. maculans and that the resistance alleles were allelic. Using BC(1) progeny derived from each resistant plant, this locus was mapped to B. napus linkage group N6 and was flanked by microsatellite markers sN2189b and sORH72a in an interval of about 10 cM, in a region equivalent to about 6 Mb of B. rapa DNA sequence. This new resistance gene locus was designated as LepR4. The two lines were evaluated for resistance to a wide range of L. maculans isolates using cotyledon inoculation tests under controlled environment conditions, and for stem canker resistance in blackleg field nurseries. Results indicated that line 16S, carrying LepR4a, was highly resistant to all isolates tested on cotyledons and had a high level of stem canker resistance under field conditions. Line 61446, carrying LepR4b, was only resistant to some of the isolates tested on cotyledons and was weakly resistant to stem canker under field conditions.

Molecular mapping of qualitative and quantitative loci for resistance to Leptosphaeria maculans causing blackleg disease in canola (Brassica napus L.)

“…Other genomic regions that we have identified for blackleg resistance (Table 2) may be the same as reported previously (Delourme et al 2008;Diederichsen et al 2005;Pilet et al 1998). For example, the QRlm.wwai-A2 and QRlm.wwai-A10 may correspond to race-specific major genes LepR2 and LepR1/LepR3 (Yu et al 2005(Yu et al , 2008. However, it was difficult to compare loci conferring blackleg resistance due to the different marker systems used in the mapping studies (Kaur et al 2009;Yu et al 2005).…”

“…These studies evaluated blackleg resistance on the basis of pathogen infection on cotyledons, stem (canker), and survival under field conditions. To date, 14 major loci (Rlm1-10 and LepR1 to LepR4) conferring resistance to specific races of L. maculans have been identified (Delourme et al 2006a;Rimmer 2006;Yu et al 2005Yu et al , 2008.…”

Frequency of avirulence genes inLeptosphaeria maculansin western Canada

“…A set of differential genotypes (varieties or lines) with previously characterized resistance genes in B. napus or Brassica juncea L. genetic backgrounds were chosen for the study: 'Westar' -no resistance genes (Delourme et al, 2004), 'MT29 ' -Rlm1,9 (Delourme et al, 2008), 'Samouraï' -Rlm2,9 (Rouxel et al, 2003b), '22-1-1' -Rlm3 (Delourme et al, 2004), 'Falcon' -Rlm4 (Rouxel et al, 2003b), '150-2-1' -Rlm5 (Stachowiak et al, 2006), FalconMX -Rlm4,6 andDarmorMX -Rlm6,9 (Chèvre et al, 1997;Balesdent et al, 2006), '23-2-1' -Rlm7 (Delourme et al, 2004), 'Darmor' -Rlm9 (Delourme et al, 2004), 'Westar 74' -Rlm10 (Chèvre et al, 1996;Chèvre, personal communication) and 'Surpass 400 ' -Rlm1, LepR3 (Van de Wouw et al, 2008;Yu et al, 2008). Since 'MT29' and 'Samouraï' each contain Rlm9 as well as Rlm1 and Rlm2, respectively, these lines could not be used to discriminate the presence of AvrLm1 and AvrLm2 in those isolates with AvrLm9.…”

Improving blackleg disease management ofBrassica napusfrom knowledge of genetic interactions withLeptosphaeria maculans†

“…In Canada, work on B. napus material derived from crosses with B. rapa subsp. sylvestris L. elucidated four resistance genes: LepR1, LepR2, LepR3 and LepR4 (Yu et al, 2005(Yu et al, , 2007(Yu et al, , 2008.…”