New QTLs for Spot Blotch Disease Resistance in Wheat (Triticum aestivum L.) Using Genome-Wide Association Mapping

Abstract

Spot blotch disease caused by Bipolaris sorokiniana is a major constraint for wheat production in tropics and subtropics. The introgression of spot blotch resistance alleles to the disease susceptible lines is critical to securing the wheat production in these regions. Although genome-wide association studies (GWASs) for spot blotch were attempted earlier, the present study focused on identifying new quantitative trait loci (QTLs) for spot blotch under natural disease pressure in diverse field conditions. A total of 139 advanced spring wheat lines were evaluated in three environments (three years and two locations) in India and Bangladesh. The GWAS using 14,063 polymorphic genotyping-by-sequencing (GBS) markers identified eight QTLs associated with spot blotch disease resistance belonging to eight chromosomes across the wheat genome. Here, we report the identified marker–trait associations (MTAs), along with the allele effects associated with the disease. The functional annotation of the significant markers identified NBS-LRR, MADS-box transcription factor, and 34 other plant-related protein families across multiple chromosomal regions. The results indicate four promising new QTLs on chromosomes 1A (497.2 Mb), 1D (89.84 Mb), 2B (421.92 Mb), and 6D (6.84 Mb) associated with several disease resistance protein families. These results provide insights into new genomic regions associated with spot blotch disease, and with additional validation, could be utilized in disease resistance breeding efforts in wheat development.

Characterization and Mapping of Spot Blotch in Triticum durum–Aegilops speltoides Introgression Lines Using SNP Markers

“…An oxidative burst is triggered by recognition, accompanied by transcriptional reprogramming and HR, which leads to disease resistance (Thomas and van der Hoorn, 2018). QTL QSb.pau-2A mapped in the present study was found 55 Mb from QTL Q.Sb.bisa.2A (Tomar et al, 2021) and in same genomic region of QTL QSb.bhu-2A (Kumar et al, 2010) and is probably novel as this QTL had been contributed by A. speltoides while previously reported QTL are from cultivated wheat.…”

“…For BLUEs model, the genotypes were considered as fixed effects, while for BLUPs model all the effects were considered as random effects. Considering genotypes as random effects reduces the effect of screening time along with other environmental effects on SB severity (Tomar et al, 2021). The disease severity scores obtained by fitting the BLUPs and BLUEs models were plotted using ggplot2 v3.…”

“…Spot blotch is one of the major constraints to the global wheat production, especially in areas with hot and humid climate (Tomar et al, 2021). To counter the constraints from foliar diseases like SB, there is a need for constantly identifying and introgressing new sources of resistance.…”

“…The continuous distribution of disease severity score in the panel indicated additive effect leading to quantitative nature of resistance. Most of the studies on SB resistance dictate that multiple genes with minor effect control the SB resistance in wheat (Adhikari et al, 2012;Lillemo et al, 2013;Zhuang et al, 2013;Gurung et al, 2014;Lu et al, 2016;Ayana et al, 2018;Kaur et al, 2018;Singh et al, 2018;Tomar et al, 2021). Kumar et al (2008) also suggested that the resistance to SB is polygenic and controlled by a number of loci each having its own additive effect.…”

“…QTL QSb.pau-2B was mapped 20 Mb from another QTL previously mapped in the region (Bainsla et al, 2020) and was found to be flanked by six senescence-associated family protein (DUF581) coding genes. In wheat, if one allele of the gene is involved in senescence, the other is associated with the stay-green trait (Tomar et al, 2021) and the staygreen trait has been reported to positively correlate with wheat leaf blight resistance (Joshi et al, 2006;Rosyara et al, 2008). QTL QSb.pau-3B was found to be linked with Protein FAR1-RELATED SEQUENCE 3 which is known to modulate plant immunity.…”