Abstract
White rust, causal agent oomycete Albugo candida, is a significant disease of the cultivated Brassica species. The Indian gene pool lines of oilseed mustard, Brassica juncea, are highly susceptible to the pathogen. Resistance to A. candida has been reported in the east European gene pool lines of mustard and mapped to LG A4 in line Heera and LG A5 in line Donskaja-IV. A new resistance-conferring locus to A. candida isolate AcB1 has been mapped to LG A6 of B. juncea line Tumida—a Chinese vegetable type mustard using an F1DH mapping population that has been developed from a Tumida × Varuna (susceptible Indian gene pool line) cross. A molecular map containing 8,303 genic and GBS markers was used to map the resistance trait to an interval of 63.0 cM—70.8 cM on LG A6. Genome assemblies of Tumida and Varuna were used to find the genes present within the flanking markers discerned by genetic mapping. The most likely candidate gene in the mapped interval is BjuA046215, a CC-NBS-LRR (CNL) type R gene that encodes a protein with all the specific subdomains of the proteins encoded by such genes. Alleles of BjuA046215 in Varuna and other lines of the Indian and the east European gene pools encode proteins that have truncated LRR domains. Analysis of the syntenic regions in some of the Brassicaceae genomes and phylogenetic analysis of CNL type R genes showed BjuA046215 to be closely related to a recently described white rust resistance-conferring R gene BjuWRR1 in B. juncea Donskaja-IV, both belonging to the CNL-D group of R genes. Related R genes in Arabidopsis thaliana confer resistance to another oomycete, Peronospora parasitica.
Highlights
White rust caused by the biotrophic oomycete Albugo candida is a major disease of oilseed and vegetable crops belonging to the genus Brassica (Saharan and Verma, 1992; Kamoun et al, 2015)
The segregation pattern strongly suggested the presence of a single major locus in Tumida conferring resistance to the white rust disease
We have mapped a novel locus in B. juncea Tumida that confers resistance to white rust disease caused by A. candida
Summary
White rust caused by the biotrophic oomycete Albugo candida is a major disease of oilseed and vegetable crops belonging to the genus Brassica (Saharan and Verma, 1992; Kamoun et al, 2015). The Indian gene pool lines of Brassica juncea (oilseed mustard) are highly susceptible to A. candida (Li et al, 2008; PanjabiMassand et al, 2010; Awasthi et al, 2012) leading to significant yield losses (Lakra and Saharan, 1989; Saharan and Verma, 1992). Resistance to white rust has been reported in the east European gene pool lines of oleiferous mustard (Panjabi-Massand et al, 2010; Awasthi et al, 2012; Arora et al, 2019). Breeding for resistance to white rust in mustard is of critical importance as in India alone the crop is grown in ~6 million hectares of land
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