Knowledge of genetic variation in a pathogen population contributes to breeding for disease resistance. The fungus Pyrenophora tritici-repentis, cause of tan spot of wheat, is an important foliar pathogen worldwide. Currently, eight races have been identified in the fungal population prevalent on wheat and alternative hosts. Races 1 through 6 have been observed in North America. However, the fungal population from South America has not been characterized as to race. In this study, 48 single-spore isolates of P. tritici-repentis, recovered from wheat, were obtained from Argentina (10), Brazil (23), and Uruguay (15). Isolates were tested by inoculating individually on 2-leaf stage seedlings of the wheat differentials Glenlea, Katepwa, ND495, 6B365, M-3, and Salamouni in the greenhouse. They were grouped into different races based on necrosis and chlorosis induction on the differentials. Isolates from Argentina were grouped into races 1 and 7; from Brazil into races 1 and 8; and, from Uruguay into races 1 and 2. Results indicate that P. tritici-repentis has a diverse population on wheat in South America. More isolates are under investigation to obtain a comprehensive virulence pattern of the pathogen population in South America. Wheat lines should be screened against all known races to achieve durable resistance in a cultivar release program. The P. tritici-repentis race structure on wheat in Europe needs to be determined, as the pathogen has become a concern for wheat breeders and pathologists.

Nitrogen (N) cycling ecosystem function is crucial in primary productivity but also carry various ecological implications such as N losses to environment. In mountainous soil ecosystems, this important function beside soil characteristics is dependent on the litter produced through plant decay which may play a critical role in shaping the hosted soil microbial communities such as those involved in N cycling processes. This study aims at investigating the effects of plant litter amendment, believed to reduce the nitrogen leaching and improve soil health, on nitrogen cycling microbial communities and processes using litterbag approach at field station of COMSATS, Abbottabad. Plant litter collected from the stands of Pine (Pinus wallichiana) and understory Indigo shrub commonly known as Indigo Himalayan (Indigofera heterentha (Fabaceae) wall), near Abbottabad, native to the lower Himalaya, were applied to indigenous loamy soil in four treatments (i.e. Control, Pine, Indigo and Pine + Indigo). The N cycling processes (involved in nitrous oxide GHG emissions, potential nitrification activity -PNA and denitrification enzyme activity -DEA), through measuring enzymes activities and the abundances of nitrifying -amoA (ammonia oxidizing bacteria -AOB, ammonia oxidizing archaea -AOA) and denitrifying functional guilds (nirS, nosZ) were determined using quantitative PCRs by targeting their corresponding genes. The results revealed that the plant litter significantly influenced both nitrification and denitrification but also the size of microbial communities involved in these two