Pathogenic diversity in Puccinia striiformis f. sp. tritici isolates from Pakistan

225 Puccinia striiformis f.sp. tritici isolates collected from wheat growing areas of Pakistan during 2013-2016 were analyzed using 18 near isogenic yellow rust differentials. Seventy eight races were identified among collection in which 20 were common (n > 2). Rest of the races were very rare and encountered only once (n=1). Races 574212, 574232, 474232, 474233, 574213 and 434232 were most frequent (n> 15). Pathogenic diversity analysis of the collection reveal high diversity (H =3.57) of the P. striiformis population of pakistan. On the basis of phenotypic response to yellow rust genes, the most frequent races could be grouped into 5 diverse groups. Distinct grouping was also observed in rarely encountered isolates. Most of the races were highly complex and 80% isolates had complexity ranging from 8 to 11. Virulence frequency for Yr6, Yr7, Yr8, Yr17, Yr27, Yr43 & YrExp2 remained above 80% while that of Yr1, Yr9 and Yr44 remained over 40%. Partial virulence was detected for Yr5, while virulence to Yr10, Yr15, YrSP was found in < 4% isolates. Paper discuss spatial and temporal distribution of P. striiformis races in Pakistan.