INHERITANCE OF STEM RUST RESISTANCE AND OTHER CHARACTERISTICS IN DIPLOID OATS, AVENA STRIGOSA

Abstract

With the appearance and rapid increase of the highly virulent race 6AF of stem rust (Pucciszin grnmiszis Pers f. sp. nves~ne Eriliss. and Henn.) in North America (Stewart, et nl., 1962; Green, 1963) emphasis has been placed on finding new sources of resistance. McKenzie and Green ( 1965) reported on the inheritance of gene H which confers resistance to race 6AF; however, some biotypes of 6AF have been found that can attack plants with this gene. The successful transfer of crown rust resistance from the diploid Avenn strigosn Schreb. to the hexaploid A . sativn L. (Zillinsliy and Dericlt, 1960; Dyclt and Zillinsky, 1963) and the urgent need for additional sources of stem rust resistance has prompted work on transferring the excellent stem rust resistance of A . strigosn to hexaploid oats. This report presents data on the inheritance of resistance to stem rust in diploid oats and the association of stem rust resistance with other characters. Materials and Methods T h e identity of the parental strains, their stem and crown rust reactions and morphologic descriptions are given in Table I. Only the parental characteristics used for genetic analysis are shown. Tests of rust reaction were conducted on F, plants or F, lines in the greenhouse during the winter months. For stem rust inoculations, an oil suspension of urediospores was sprayed on seedlings in the first-leaf stage. For crown rust inoculation, a water suspension was used on I+ to 2-leaf stage seedlings. Approximately 25 seedlings were used of each F3 line. Races 1, 2, 2F, 6, 6A, 6AF (Eastern), 6AF (Western), 6F, 7, 7A, 8, 8AF and 13A of stem rust and races 264 and 294 of crown rust were used. For classification of growth habit, about 30 seeds of each of the F, lines from the cross C.D. 4482 x C.I.3078 were sown in the field. Plants or lines classified as prostrate remained prostrate throughout the summer and failed to head. Seedlings of crosses C.D.4482 x C.I. 3078 and C.D. 3820 x C.D. 7994 were classified for plant pubescence. Basal attachment (wild or sucker mouth vs. normal), and pubescence and nonpubescence (glabrous) of the Iernrna were classified in the C.D. 4482 x C.I. 3078 cross. In crosses between A. weistii Steud. or A. hirtula Lag., having a suclter mouth or wild base, with A. brevis Roth. or A. strigosn, having a normal base, Jones (1940) observed four different basal types which he designated and described as follows: XY typical wild type on both primary and secondary florets; Y base of primary floret similar to wild type, but suclter mouth restricted, base of secondary floret similar to normal type; X a pedicel remains adherent to base of primary floret, rachilla remains attached to secondary floret when separated from primary as occurs in the species A. sterilis L.; xy normal base. The A. brevis (C.D. 4482) used as the parent with the normal base in cross C.D. 4482 x C.I. 3078 rarely produces a secondary floret under conditions in which the F? population was grown. Thus many of the F2 plants produced primary florets only, making it impossible to