Partial resistance of some wheat cultivars and candidate lines against stem rust (Puccinia graminis f. sp. tritici)

Background and Objectives Among biotic stresses, stem (black) rust, caused by Puccinia graminis f. sp. tritici is considered to be the most destructive disease of wheat in some countries and its damage reaches 100% in the years of epidemic on susceptible cultivars. Lack of durable resistance in wheat cultivars is the main reason for the black rust epidemics that can limit wheat production in some parts of the world. Today, it is possible to manage rusts with effective and new fungicides. However, growing resistant cultivars is the most effective, economical, and environmentally safe approach for disease management. Therefore, this study was performed in order to identify potential sources of partial resistance to black rust, which is a stable and non-race specific. Materials and Methods The partial resistance parameters including coefficient of infection (CI), final disease severity (FDS), apparent infection rate (r) and relative area under disease progression curve (rAUDPC) were assessed in a set of twenty six wheat genotypes along with susceptible control (Mixture of McNair and line; CD-90-12) during 2018-2019 cropping year. This study was conducted in field plots at Ardabil Agricultural Research Station (Iran). All genotypes were evaluated under natural infection conditions against race population having virulence to resistance genes; Sr25, Sr5, Sr6, Sr7a, Sr9e, Sr13, Sr23, Sr28, Sr29, Sr30, Sr33, Sr34, Sr37, SrDP2, SrGT, SrWLD, SrH and SrTmp. Seedling reaction was also appraised under greenhouse conditions against TKTTF (two isolates) and TTTTF pathotypes. Results The results showed that genotypes Gascogne, MV17 and Gonbad having low levels of CI, FRS, r and rAUDPC were considered as the group with desirable level of partial resistance. Nine cultivars/lines showed moderate values ​​of resistance parameters and were considered as genotypes with moderate level of partial resistance for stem rust. Six lines had low partial resistance and the rest of the lines were grouped in susceptible group without any partial resistance. Discussion Genotypes Zare, Gascogne, Gonbad, N-91-9, and N-91-15 due to susceptible reaction (at least against to one pathotype) at seedling and moderately resistant to moderately susceptible response at the adult plant stage are likely to have the more number of partial resistance genes. Genotypes with desirable and moderate levels of partial resistance identified from this study can be used to introduce candidate varieties or in wheat breeding programs to stem rust.