Effect of Leaf Rust on Yield Components of Winter Rye Hybrids and Assessment of Quantitative Resistance

Leaf rust ( Puccinia recondita f. sp. secalis ) is common in all winter rye growing areas, but little is known about its effect on yield in hybrid rye. Ten single crosses without any hypersensitive response to leaf rust were grown at three environments (Hohenheim, 1991; Halle, 1991; Hohenheim, 1992) in an inoculated and a non‐inoculated, fungicide protected, treatment block. Resistance traits were mean leaf rust ratings of the upper three leaves (F‐2, F‐1, F) assessed with 10 arbitrarily, chosen tillers per plot at four assessment dates, selected leaf rust rating on two leaves at one assessment date, and area under disease progress curve (AUDPC). Additionally, kernel number per head, grain weight per head and thousand kernel weight were assessed on the individual tillers in three environments and plot yield and thousand kernel weight of the thresheld plot samples in two environments. Correlations among AUDPC values and mean leaf rust ratings on the respective leaves and selected leafrust rating were high (r∼0.9, P = 0.01). Resistance among the upper three leaves was closely correlated (r∼0.9, P = 0.01) for AUDPC value and mean leaf rust rating. Leaf rust epidemics significantly reduced grain weight per head, plot yield and thousand kernel weight in three environments; kernel number per head was not significantly affected. Thousand kernel weight was reduced on average by 14% ranging from 11 to 27% among single crosses. Significant genotypic variation was observed for the affected yield components at Hohenheim 1991 and 1992. Genotype‐year interaction variance was large in the combined analysis for yield components. Quantitative resistance can be assessed by visual rating of maximal two leaves at one optimal assessment date. Relative, thousand kernel weight from thresheld plot samples can be used additionally as resistance trait when disease severity is high enough during kernel filling.