Significance of host complexity and diversity for race‐specific leaf‐rust resistance in self‐fertile synthetic rye populations

Abstract

Leaf rust (Puccinia recondita Rob. ex. Des.) is the most frequently occurring leaf disease in German winter rye (Secale cereale L.). To test the usefulness of race-specific resistance genes, the effects of increased host diversity and complexity by producing two-and fourline synthetics from inbred lines carrying different resistance genes were analysed. Thirty-three synthetics along with two full-sib families and one hybrid variety were tested in 17 environments in Germany under natural infections. For comparison, the parent lines of the synthetics were evaluated in 11 environments. Only two synthetics and the full-sib families were resistant across all environments. Observed resistance levels of the synthetics were highly correlated (r ¼ 0.83, P ¼ 0.01) with those predicted from the parental values. Host complexity had a minor effect in two-line synthetics only. In conclusion, the effectiveness of race-specific leafrust resistances among environments, and increasing the host complexity and diversity does not lead to a higher resistance level than that expected from the resistances of the parents.

Diversity, spatial variation, and temporal dynamics of virulences in the German leaf rust (Puccinia recondita f. sp. secalis) population in winter rye

“…For example, populations from EWE2001, HOH2002 and GL2002 had some frequent virulences against P53 or S4084, that occurred rarely at any other location and even at the same locations in other years. These results of seedling tests were substantiated by a virulence analysis at the adult-plant stage of 11 differentials at 11 field environments in the same seasons (Wilde et al 2006). Here, as well, we observed a high diversity of virulences and the composition of rust populations varied considerably among environments.…”

“…Considering the breakdown of stripe rust resistance gene Yr17 in wheat within 3 years of commercially growing resistant cultivars (Bayles et al 2000), the testing procedures for monogenic resistances should be as rigorous as possible. A companion study clearly illustrated that even highly heterogeneous synthetic populations of rye could not compete with the high pathogen diversity and spatial fluctuations of leaf-rust populations in rye fields (Wilde et al 2006). …”

“…It is, therefore, necessary to find new, highly effective, and environmentally stable race-specific resistance genes. However, according to the large number of virulences already existing in the present-day leaf-rust populations, even gene deployment or pyramiding strategies will not provide sufficiently durable resistance (Wilde et al 2006). More durable resistance might be achieved by an additional selection for racespecific adult-plant and/or quantitative resistances.…”

“…This was especially demonstrated in the spring-sown winter rye experiment. We planted 33 self-fertile rye synthetics containing race-specific resistances of varying complexity in four field environments (Wilde et al 2006). This model experiment was designed as a worst-case scenario where the naturally occurring leaf-rust populations could parasitize rye plants that remained in the vegetative growth stage during the whole season.…”

“…These genotypes were developed for and described in detail in a companion study (Wilde et al 2006) where we wanted to test the effect of heterogeneous genotypes (simulating cultivar mixtures) on the rye leaf rust popula- Table 1 Key for the rating of leaf rust symptoms of rye according to Frauenstein and Reichel (1978) Infection type Infection symptoms Detached leaf-segment test and disease assessment…”