Virulence and genotypic diversity of the wheat stem rust pathogen ( <i>Puccinia graminis</i> f. sp. <i>tritici</i> ) in Jordan and the response of durum wheat genotypes to infection

Although WSR has been commonly observed and studied in the Middle East, in Jordan the last reports date from the late 1980s. The objectives of this research were to conduct a national survey of WSR in Jordan, assess the race composition and genotypic diversity of the Pgt population and to evaluate a 162 durum wheat genotypes for stem rust response against isolates of two major Pgt races recovered from stem rust samples collected in this study. A total of 78 WSR live samples and 74 dead samples from 49 fields were collected in 2018. In addition, three historical samples were analyzed. One hundred Pgt isolates derived from the live samples were race-typed and 14 representatives of the identified races were genotyped with a 17 core SNP assay that distinguish major genetic clades. The dead and the historical Pgt samples were all SNP genotyped. Five races were identified from the live samples: PKTTF, TKFTF, TKFTP, TKKTF, and TTRTF. The most frequent race was TKKTF (75%) followed by TKFTF (14%), and TTRTF (9%), whereas races PKTTF and TKFTP were detected from only one isolate each. Selected Pgt isolates representing the five races identified were differentiated into five known genetic clades/sub-clades: III-B, race TTRTF; IV-C, race PKTTF; IV-E.1, race TKFTP; IV-E.2, race TKKTF; and IV-F, race TKFTF. The dead samples were genotyped as clades: IV-E.2 (73.7%), III-B (18.1%), and IV-E.1, IV-F, and Co-A22 at frequencies less than 4%. Minor allelic variations at one or two SNP loci were observed among the dead samples. The dead sample genotyped as Co-A22 was identical to European reference isolates from the early 1980s. From the 36 single uredinial pustules derived from the historical samples, two genotypes were detected: clade III-A and, Co-A22. Seedling resistance was observed in durum wheat landraces and cultivars to two of the major races identified in Jordan, as 52 (32.1%) and 99 (61.1%) genotypes evaluated exhibited a resistant response to races TTRTF and TKKTF, respectively. Infection types in the range of '2-' to '2+' were predominant in this germplasm. Forty-six (28.4%) accessions were resistant to both races, including 1 cultivar and 45 landraces.