147 AUSTRALIAN RUST STUDIES. XII. Specialization within Ueomyces stkiatus Scheoet. on Trigonella suavissima LiNDL. and Medicago sativa L. By W. L. Waterhouse, The University of Sydney. (Plate viii.) [Read 26th August, 1953.] Synopsis. Uromyces striatus Schroet. on Trigonella suavissima Lindl. in western New South Wales 'was found to attack lucerne (Medicago sativa L>. ). Comparisons of the reactions of several species of Trigonella from overseas with those of numerous species of Medicago show that the two rusts represent distinct physiologic races. There is evidence that they are also different from the U.S.A. rust. In many cases individual plant progenies of a species gave quite different results. All four groups of the possible combinations of resistance and susceptibility to the two races were found. No correlation was found between these groups and the recognized iDotanical groups of these species. A striking case of variegation in a plant of M. hispida ■Gaertn. occurred, and the progeny of one of the shoots yielded albinotic seedlings. Introduction. In 1939 a collection of Trigonella suavissima Lindl. at the flowering stage was lorwarded from Lake Menindie, N.S.W., for examination because of heavy rust attack on leaves and stems. A similar submission was made in 1950. Determinations showed that the rust conformed to the description of Uromyces striatus Schroet. A culture was maintained first on the original host plants which had been sent in the growing condition, and later on seedlings of T. suavissima in pots, in order that the host range might be studied. Specialization Studies. Uredospores transferred to lucerne (Medicago sativa L.) growing in pots gave full infections, and from these, transfers back to the Trigonella were made. The susceptibility of lucerne was unexpected. Because of the importance of lucerne as a crop and pasture plant, and of the medics in pastures, it is important to know the host ranges of pathogens that attack them. For comparative studies, a culture of lucerne rust from an infected crop at Lismore, N.S.W., was maintained on lucerne in a different plant house. For these preliminary studies, seed of Trigonella spp. from overseas was used, together with a quantity of host material of Medicago spp. that was kindly made available by Mr. F. W. Hely, of the C.S.I.R.O. Over a period of years he has studied .an extensive collection obtained from world sources, sorting out variants, and making many single plant selections. All the seed used came from single plants he had saved. In no case was there any evidence of heterogeneity in the rust reactions shown. Seed was scarified with sandpaper, germinated between blotting paper, and then transferred to pots, and kept in the plant house until the seedlings had reached the inoculation stage. The leaves were atomized with water, uredospores transferred to the wetted leaves, and the pots then kept in a saturated atmosphere for 36-48 hours, after which they were placed on the plant house benches. Rust development was at its best after about three weeks, but weather conditions caused variations in this time. In both rusts there was a noticeable slowing-down of rust development in the winter, but comparisons between summer and winter readings showed no differences in the type of susceptible or resistant reactions that developed.
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