Evaluation of Levels of Non-hypersensitive Resistance in Different Spring Wheat Cultivars to Leaf Rust

Levels and components of non-hypersensitive resistance in wheat (Triticum aestivum L.) to leaf rust (Puccinia triticina) were studied at seedling and adult plant stage in green house and field conditions during 2001 at Wageningen University, The Netherlands. In seedling stage, level of non-hypersensitive resistance or partial resistance was assessed from latency period (LP), infection frequency (IF), percentage of early aborted infection units without plant cell necrosis (EA-N %) and colony diameter of infection units of single-pustule isolates of Puccinia triticina INRA on 12 spring wheat cultivars/lines. In adult plant stage, non-hypersensitive resistance was evaluated from LP and IF of single-pustule isolate of P. triticina on 8 spring wheat cultivars and 4 lines, while in a field experimental area under disease progress curve (AUDPC) was calculated to assess the level of non-hypersensitive resistance in 8 spring wheat cultivars and two lines. In both seedling and adult plant stage, host genotypes varied for all the parameters studied, indicating a variety of genes with minor effect for non-hypersensitive resistance, since non-hypersensitive resistance is considered to be quantitatively inherited. In partially resistant genotypes the fungus showed a longer LP, lower IF, an increase in EA-N% and reduced colony diameter than on highly susceptible genotypes. Differences between genotypes for the level of nonhypersensitive resistance were larger in adult plant stage than in seedling stage. Also variations among the cultivars for area under disease progress curve (AUDPC) were greater than for components of nonhypersensitive resistance in green house experiments. A long LP was associated with a low IF, increased EAN% and reduced colony diameter of infection units, indicating that the mechanism responsible for longer LP, lower IF, higher EA-N% and reduced colony diameter might be controlled by the same genes or closely linked genes. Non-hypersensitive resistance measured in seedling stage for LP and IF showed no correlation with the non-hypersensitive resistance measured in adult plant stage. Adult plant stage IF and colony diameter of fungus isolates significantly associated with AUDPC assessed in the field, however a long LP and high IF at seedling stage, a high IF and increased EA-N % were non-significantly associated with low AUDPC. Apparently, nonhypersensitive resistance measured in field cannot completely be explained from the component analysis data in the green house.