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Achieving durable resistance to leaf rust (LR), caused by Puccinia triticina, in wheat has been one of the main objectives of breeding programs. Durability of LR resistance is considered to be associated with adult plant resistance (APR) genes that are quantitatively inherited and whose expression is largely influenced by environment. Our objective was to study the effects and interactions of APR genes Lr34, Lr68 and Sr2 on LR response in Uruguay using two BCF populations ('LE2304*2/Parula' and 'ORL99192*2/Parula'). The experimental material was screened for LR in three artificially inoculated environments (La Estanzuela 2012 and 2013 and Young 2012). Linked molecular markers were used to detect the presence of the genes conferring resistance to LR. Gene Lr34 was fixed in the 'LE2304*2/Parula' population. Lr68+ Sr2 resulted in a reduction of 79 % of the LR area under the disease progress curve (AUDPC), while the presence of Lr68 alone resulted in a reduction of 51 %. In the 'ORL99192*2/Parula' population, the combined effect of Lr34+ Lr68+ Sr2 led to the highest reduction of LR AUDPC (73 %). Individually, Lr34 and Lr68 resulted in a reduction of the LR AUDPC of 14 and 50 %, respectively. Sr2 alone did not reduce LR AUDPC but enhanced the effect of either Lr34 or Lr68. Unlike previous reports Lr68 conferred a higher level of LR resistance than Lr34 in Uruguay. [ABSTRACT FROM AUTHOR]

Most wheat cultivars planted worldwide are susceptible to the stem rust Ug99 race group. To prepare for the potential spread of these races into South America, we aimed to identify genomic regions responsible for resistance to Ug99 race group in germplasm adapted to South America. Two RIL populations from a cross between a stem rust susceptible parent "Baguette 13" and resistant local parents "INIA Tero" and "BR23//CEP19/PF85490" were developed. Phenotypical evaluation was completed at the seedling stage in Uruguay and under field conditions in Uruguay and Kenya. Both RIL populations were genotyped using the GBS approach. Besides Sr24, three other resistance loci in "INIA Tero" were detected on chromosomes 2B, 6A, and 7B. All four QTL were effective to local races, whereas only the QTL on chromosome 2B was effective against the Ug99 race group. Besides Sr31, "BR23//CEP19/PF85490" also carries two other stem rust resistance loci on chromosomes 2B and 6A. All three explained the resistance in Uruguay, while only the QTL on 2B was effective to Ug99 in Kenya. The physical location suggested that the QTL identified on chromosome 2B in both populations may correspond to Sr28, which was confirmed using specific molecular markers. Further studies are needed to determine the relationship between QTL for resistance to local races identified on chromosomes 6A and 7B and previously reported resistance genes and QTL. The results of this study are highly relevant for breeding wheat cultivars with diverse and durable resistance to stem rust. [ABSTRACT FROM AUTHOR]

Wheat yellow (stripe) rust, caused by Puccinia striiformis f. sp. tritici ( Pst ), is one of the most devastating diseases of wheat worldwide. Pst populations are composed of multiple genetic groups, each carrying one or more races characterized by different avirulence/virulence combinations. Since the severe epidemics in 2017, yellow rust has become the most economically important wheat foliar disease in Uruguay. A set of 124 Pst isolates collected from wheat fields in Uruguay between 2017 and 2021 were characterized phenotypically, and 27 of those isolates were subsequently investigated in-depth by additional molecular genotyping and race phenotyping analyses. Three genetic groups were identified, PstS7 , PstS10 , and PstS13 , with the latter being the most prevalent. Two races previously reported in Europe, Warrior ( PstS7 ) and Benchmark ( Pst S10), were detected in four and two isolates, respectively. A third race, known as Triticale2015 ( PstS13 ), that was first detected in Europe in 2015 and in Argentina in 2017 was detected at several locations. Additional virulence to Yr3 , Yr17 , Yr25 , Yr27 , or Yr32 was detected in three new race variants within PstS13 . The identification of these new races, which have not been reported outside South America, provides strong evidence of the local evolution of virulence in Pst during the recent epidemic years., Competing Interests: The author(s) declare no conflict of interest.