Identification of genomic regions associated with Ug99 slow rusting adult plant resistance in wheat (Triticum aestivum L.)

Authors: VIKRAM, PRASHANT - Shree Guru Gobind Singh Tricentenary University; LOPEZ-VERA, ERIC - International Maize & Wheat Improvement Center (CIMMYT); BHAVANI, SRIDHAR - International Maize & Wheat Improvement Center (CIMMYT); THIYAGARAHAN, KARTHIKEYAN - International Maize & Wheat Improvement Center (CIMMYT); Singh, Sukhwinder

Submitted to: Discover Life
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 8/13/2024
Publication Date: 9/27/2024
Citation: Vikram, P., Lopez-Vera, E.E., Bhavani, S., Thiyagarahan, K., Singh, S. 2024. Identification of genomic regions associated with Ug99 slow rusting adult plant resistance in wheat (Triticum aestivum L.). Discover Life. https://doi.org/10.1007/s11084-024-09655-4.
DOI: https://doi.org/10.1007/s11084-024-09655-4

Interpretive Summary: One of resistance breeding's main goals is the efficient application of resistance sources that guarantee endurance. Resistance genes deployed are only sometimes practical or durable due to constantly changing populations of pathogens. One such instance of a disease continuously evolving to overcome host resistance is the fungal pathogen Puccinia graminis Pers. f. sp. tritici (Pgt), which causes stem rust in wheat. Stem rust in wheat is one of the deadliest plant diseases humans have ever encountered (Kislev 1982). It can wipe out entire small-scale farm plots and millions of hectares of susceptible kinds (Roelfs, 1985). The Ug99 race fungus is a major threat to world wheat production, as 90% of the wheat types are susceptible to this race-specific fungus (Singh et al., 2011). Another evidence suggests that the somatic hybridization and nuclear exchange of dikaryons resulted in the emergence of this race-specific dikaryotic fungus, Puccinia graminis f. sp. tritici Ug99 (Li et al., 2019). Rust diseases typically hamper wheat productivity in all wheat-growing regions of the world (Singh et al., 2011). This was mainly because multiple resistance genes have become ineffective due to the rapid racial evolution of virulent pathogens and disease-favoring environmental circumstances (Park et al., 2016). While several effective genetic strategies have been undertaken since the emergence of this virulent fungal race. There have been reports from several locations regarding the rise and spread of novel, highly pathogenic Pgt races that can overcome common resistance genes. For example, the races TPMKC and TTTTF have demonstrated virulence against multiple frequently used Sr genes in the United States (McVey et al., 2002; Jin et al., 2007). Concern has been raised in Africa regarding the emergence of the race TTKSK (also known as isolate Ug99), which was first discovered in Uganda and has virulence for the commonly used resistance gene Sr31 (Pretorius et al., 2007). Since this race also became resistant to other genes such as Sr24, Sr36, Sr9h, and SrTmp, variants within the Ug99 lineage had spread to eastern and southern Africa as well (Jin et al., 2008; Rouse et al., 2014; Patpour et al., 2016). Two Pgt races, namely TRTTF and JRCQC, exhibited virulence against susceptible durum wheat varieties as resistance genes Sr9e and SrTmp became ineffective, as observed in Ethiopia, and a TKTTF race, which is different from the lineage of Ug99 in bread wheat, was reported as well (Olivera et al. 2012; Olivera et al. 2015).

Technical Abstract: Ug99 is a highly destructive race of stem rust fungus known as Puccinia graminis Pers. f. sp. tritici Eriks. & E. Henn. (Pgt). To address this problem, the International Maize and Wheat Improvement Center, Mexico (CIMMYT) has extensively employed adult plant resistance (APR), which combines multiple genes that provide slow rusting resistance. CIMMYT's advanced line, "Diniza," has proven to possess a good level of APR for the Ug99 race group. This study identified the genomic regions responsible for providing APR in the PBW343/Diniza RIL population. The researchers identified four Quantitative Trait Loci (QTLs) that provide slow rusting APR on chromosomes 2B (QSr.cimm-2B), 3BS (QSr.cimm-3BP1 and QSr.cimm-3BP2), and 7DS (QSr.cimm-7D). These QTLs could explain phenotypic variances of 17.0%, 18%, 8.9%, and 11.6%, respectively. Three QTLs, QSr.cimm-2B, QSr.cimm-3BP2, and QSr.cimm-7D, were derived from Diniza, while QSr.cimm-3BP1 was derived from PBW343. The researchers conducted a QTL class analysis to determine the additive or epistatic interactions of the QTL in combinations, suggesting that a combination of several QTLs can effectively reduce disease severity. QSr.cimm-2B is a new QTL that was identified in this study. QSr.cimm-3BP1 and QSr.cimm-7D were co-localized with the previously identified stem rust resistance genes Sr2 and Lr34, respectively. The identified QTL can be combined to enhance stem rust resistance in breeding materials.