Molecular and genetic analysis of defensive responses of Brassica juncea – B. fruticulosa introgression lines to Sclerotinia infection

Abstract

Sclerotinia stem rot caused by Sclerotinia sclerotiorum is a major disease of crop brassicas, with inadequate variation for resistance in primary gene pools. We utilized a wild Brassicaceae species with excellent resistance against stem rot to develop a set of B. juncea - B. fruticulosa introgression lines (ILs). These were assessed for resistance using a highly reproducible stem inoculation technique against a virulent pathogen isolate. Over 40% of ILs showed higher levels of resistance. IL-43, IL-175, IL-215, IL-223 and IL-277 were most resistant ILs over three crop seasons. Sequence reads (21x) from the three most diverse ILs were then used to create B. juncea pseudomolecules, by replacing SNPs of reference B. juncea with those of re-sequenced ILs. Genotyping by sequencing (GBS) was also carried out for 88 ILs. Resultant sequence tags were then mapped on to the B. juncea pseudomolecules, and SNP genotypes prepared for each IL. Genome wide association studies helped to map resistance responses to stem rot. A total of 13 significant loci were identified on seven B. juncea chromosomes (A01, A03, A04, A05, A08, A09 and B05). Annotation of the genomic region around identified SNPs allowed identification of 20 candidate genes belonging to major disease resistance protein families, including TIR-NBS-LRR class, Chitinase, Malectin/receptor-like protein kinase, defensin-like (DEFL), desulfoglucosinolate sulfotransferase protein and lipoxygenase. A majority of the significant SNPs could be validated using whole genome sequences (21x) from five advanced generation lines being bred for Sclerotinia resistance as compared to three susceptible B. juncea germplasm lines. Our findings not only provide critical new understanding of the defensive pathway of B. fruticulosa resistance, but will also enable development of marker candidates for assisted transfer of introgressed resistant loci in to agronomically superior cultivars of crop Brassica.

Development of a Yellow-Seeded Stable Allohexaploid Brassica Through Inter-Generic Somatic Hybridization With a High Degree of Fertility and Resistance to Sclerotinia sclerotiorum

“…fruticulosa, where highly resistant plants with lesion sizes less than 2.5 cm were recorded (Rana et al, 2017). Atri et al (2019) identified 13 loci responsible for S. sclerotiorum resistance on seven different B. juncea chromosomes that were used in the set of B. juncea-B. fruticulosa ILs.…”

“…However, enormous genetic variations do exist in important agronomic traits, including disease resistance within the Brassicaceae family (Warwick, 1993). Camelina sativa, B. desnottesii, Capsella bursapastoris, Diplotaxis catholica, D. erucoides, D. tenuisiliqua, and S. alba are well documented for their resistance to Alternaria brassicae (Brun et al, 1988;Conn et al, 1988;Sharma et al, 2002), where S. alba, Erucastrum cardaminoides, E. abyssinium, B. fruticulosa, D. tenuisiliqua show resistance to Sclerotinia sclerotiorum (Li et al, 2009;Garg et al, 2010;Rana et al, 2017Rana et al, , 2019Atri et al, 2019). Out of these, S. alba was found to be the most promising due to its resistance to major biotic and abiotic diseases that affect rapeseed and mustard, such as Alternaria blight (Kolte, 1985;Brun et al, 1987;Ripley et al, 1992;Sharma and Singh, 1992;Earle, 1995, 1997;Sharma et al, 2002), Sclerotinia stem rot (Kolte, 1985;Li et al, 2009), blackleg, beet cyst nematode (Lelivelt et al, 1993), flea beetles (Bodnaryk and Lamb, 1991) heat, drought (Downey et al, 1975;Primard et al, 1988;Downey and Röbbelen, 1989;Brown et al, 1997;Kumari et al, 2018), and pod shattering (Downey, 1987;Chandler et al, 2005;Wang et al, 2007).…”

Understanding Host–Pathogen Interactions in Brassica napus in the Omics Era

“…These NGS-based SNP genotyping approaches have been applied widely for the QTL mapping of disease resistance traits and identification of candidate genes through genome-wide association studies (GWAS) in Brassica crops ( Table 2 ). Highlights include the discovery of novel disease resistance QTLs/genes at an unprecedented speed, for example, in Blackleg [ 72 , 73 ], Sclerotinia [ 74 , 75 , 76 ] and Clubroot [ 77 , 78 , 79 ]. The other benefit of the application of NGS-based SNP genotyping is the successful breeding of B. napus varieties containing multiple improved traits.…”

Molecular characterization of disease resistance in Brassica juncea – The current status and the way forward

“…However, recently, qualitative cotyledon resistance has been demonstrated in B. juncea genotypes Ringot I and Seeta (Ge et al, 2015) and also in some interspecific crosses involving B. juncea (Barbetti et al, 2014). Perhaps of most significance are the studies by Rana et al (2017) and Atri et al (2019) (Gaur et al, 2016). In Australia, the B. juncea genotypes tested to date are all very susceptible to sclerotinia (Uloth et al, 2015b).…”

“…Introgression from other brassicas, such as B. carinata (Barbetti et al, 2014), three wild crucifers (E. cardaminoides, Diplotaxis tenuisiliqua, and Erucastrum abyssinicum; Garg et al, 2010a) and most recently B. fruticulosa (Rana et al, 2017;Atri et al, 2019) and again E. cardaminoides (Rana et al, 2019), has also been performed to develop resistant B. juncea cultivars by interspecific hybridization.…”