Quantitative‐genetic analysis of leaf‐rust resistance in seedling and adult‐plant stages of inbred lines and their testcrosses in winter rye

Abstract

AbstractLeaf rust is the most frequent leaf disease of winter rye in Germany. All widely grown population and hybrid varieties are susceptible. This study was undertaken to estimate quantitative‐genetic parameters of leaf‐rust resistance in self‐fertile breeding materials with introgressed foreign leaf‐rust resistances and to analyze the relative importance of seedling and adult‐plant resistance. Forty‐four inbred lines and their corresponding testcrosses with a highly susceptible tester line were grown in a field in four different environments (location‐year combinations) with artificial inoculation. Plots were separated by a nonhost to promote autoinfections and minimize interplot interference. Leaf‐rust severity was rated on three leaf insertions at three dates. The testcrosses showed a considerably higher disease severity than the lines. High correlations (r ≅ 0.9, P = 0.01) existed among the leaf insertions and the rating dates. Large genotypic variation for resistance was found in both the inbred and testcross populations. Genotype‐environment interaction and error variances were of minor importance, thus high entry‐mean heritabilities were achieved. A tight correlation between the inbreds and their corresponding testcrosses was found (r = 0.88, P = 0.01). Heterosis for resistance was significant (P = 0.05), but not very important. In a seedling test with 20—30 single‐pustule isolates, 34 out of 44 inbreds reacted race‐specifically. From the remaining inbred lines, three were medium and seven highly susceptible. In a further greenhouse test with 16 inbreds, seven were susceptible and five were resistant in both seedling and adult‐plant stages. The remaining four lines had adult‐plant resistance. In conclusion, race‐specific leaf‐rust resistance can be selected among inbred lines per se. Lines should also be tested in the adult‐plant stage.