Detection of Wheat Stem Rust (Puccinia graminis f. sp. tritici) Race TTKSK (Ug99) in Iran

In 2007, new reports of stem rust caused by Puccinia graminis Pers. f. sp. tritici Eriks. in Lorestan and Hamadan provinces of Iran were considered unusual because stem rust had not been recorded previously in the Hamadan area where winter habit wheat cultivars are grown. Detailed investigations in these areas showed significant levels of stem rust in experimental plots and occasionally in farmers' fields, some that showed moderate to high levels of infection. Race analysis of four stem rust samples collected from Borujerd, Hamadan, and Poldokhtar (southwest) and Kelardasht (north) in 2007 was conducted using a modified North American Pgt differential set representing the resistance genes Sr5, 6, 7b, 8a, 9a, 9b, 9d, 9e, 9g, 10, 11, 17, 21, 24, 30, 31, 36, 38, Tmp, and McN, commercial cultivars, and genotypes known to carry the 1B.1R translocation. A race collected from Borujerd in 1997 was also included for comparison. Tests were carried out under standard controlled conditions (1,2). Two isolates from samples collected from Borujerd and Hamadan in 2007 showed high infection types (ITs 33+ to 4) on differential lines carrying resistance genes Sr5, 6, 7b, 8a, 9a, 9b, 9d, 9e, 9g, 10, 11, 17, 21, 30, 31, 38, and McN, and low ITs of ;C1= to 2=, ;C to ;N1=, and 2+ on lines carrying Sr24, Sr36, and SrTmp, respectively. On the basis of the high/low ITs on the 20 differentials in the modified Pgt differential set of North America, the two isolates of Pgt collected from Borujerd and Hamadan in 2007 were identified as race TTKSK. The two isolates from samples collected from Poldokhtar and Kelardasht in 2007 and the isolate collected from Borujerd in 1997 were identified as races TRFSC, TTJQC, and RRHSC, respectively. Race TTKSK identified in the current study produced high ITs of 3+ to 4 on the wheat genotypes Line E*4/Kavkaz, Fed.*4/Kavkaz, Clement, and Mildress and commercial cultivars Falat (Seri 82), Shiroodi (CIMMYT name Attila and Indian name PBW343), Atrak (Kauz), and MV17, all carrying the 1BL.1RS translocation and further confirming virulence for Sr31. The spread of Ug99 to Kenya (1999 to 2002), Ethiopia (2003), and Yemen (2006) suggests progressive migration from Uganda, following the pattern believed to have occurred for the spread of wheat stripe rust pathogen from East Africa in 1986 to India in 1998 (3). Our results are consistent with the TTKSK race identified in Iran migrating from the new African population. Seedling evaluation of Iranian wheat cultivars and advanced lines to isolates of TTKSK from Iran confirmed full susceptibility. These results reinforce the serious threat of race TTKSK to wheat production in Iran. In conclusion, the occurrence of race TTKSK in Iran, the susceptibility of Iranian wheat cultivars to this race, the presence of environmental conditions conducive to disease epidemics in different parts of the country, and the occurrence of the alternate host barberry in many of the mountainous areas of Iran, indicate a new and serious threat to wheat production in Iran and a potentially serious threat to neighboring countries. References: (1) Y. Jin et al. Plant Dis. 91:1096, 2007. (2) Z. A. Pretorius et al. Plant Dis. 84:203, 2000. (3) R. P. Singh et al. CAB Rev. 1 (No. 054), 2006.