| Inheritance of leaf rust reaction among the eight differential
varieties of wheat By E. G. HEYNE and C. O. JOHNSTON Kansas Agric. Exp. Sta. and U. S. Dept. Agric., Manhattan, Kansas All eight of the leaf rust differential varieties have 21 pairs of chromosomes and intercross readily. Malakof, Democrat, Hussar and Mediterranean have a winter habit of growth and Carina, Loros, Webster and Brevit have a spring habit of growth. All possible crosses have been made among the eight varieties and to Pawnee and Wichita winter wheats. The study is divided into three phases; 1) conventional genetic procedure studying the response of the F1, F2 and F3 generations, 2) monosomic analysis, and 3) transferring the rust resistant factors of the eight differential varieties into a common genetic background by backcrossing to Wichita, a variety susceptible to all races of leaf rust for which it has been tested. Studies made to date on seedling reaction indicate that one or two factors generally explain the difference in reaction between any two varieties. Generally when the reaction of the resistant parent is of a high type (0; zero fleck) and susceptible parent a 4-type the F1 reaction is intermediate but of a resistant reaction (2 or 2+ response). The only case of complete dominance observed so far has been in the cross Webster x Mediterranean. Webster is highly resistant to race 5 and the F1 reacts like Webster and in the F3 segregating lines the ratio is 3 highly resistant to one susceptible. Mediterranean and Democrat have similar response to all races and in the progeny from this cross no segregation was observed in F3 lines for the races used, indicating that those two varieties have the same factors for resistance. Brevit and Carina have similar responses but for reaction to race 9 they appear to have different alleles. Brevit and Hussar have a similar reaction to race 9 probably due to two factors closely linked. In tests involving Pawnee winter wheat the same factor governs resistance to races 9, 10, ll, 13, 19, 20, 31 and 93. It has been shown by monosomic analysis that the factor for resistance to race 9 of Pawnee is located on chromosome X. The F1 generation of Carina and Webster crossed with the 21 Chinese monosomics indicated that resistance of both varieties to race 15 was dominant and no monosomic analysis of rust reaction was possible in the F1 generation. The F2 generation of Carina x Webster gave no segregation for reaction to race 5. This is as far as the monosomic analysis for leaf rust inheritance has progressed. First and second backcrosses are now being made to Wichita. Several more backcrosses to Wichita will be made before detailed studies of leaf rust reaction will be attempted. The response of Carina, Brevit and Hussar to some races is variable, probably due to environment. It will be of particular interest to study the response of the Wichita backcross material when the factors of these three varieties have been transferred to a common genetic background. |