209 AUSTRALIAN RUST STUDIES. PHYSIOLOGIC RACE DETERMINATIONS AND SURVEYS OF CEREAL RUSTS. By W. L. Waterhouse, The University of Sydney. (Plate ix.) [Read 30th July, 1952.] Synopsis. In continuation of earlier work, studies of the life histories and specialization phenomena have been made of the stem and leaf rusts of wheat, oats, barley, and rye. The host range has had to be extended to other grasses in many cases. In general the aecidial stages of the pathogens are unimportant here. The carry-over of the rust takes place in the uredospore stage on self-sown plants of the cereal host or some-times on susceptible grasses. The physiologic races and, in certain cases, the biotypes of these rusts, have been deter-mined during a long period of years and their occurrence surveyed for Australia and New Zealand. The bearing of this work on breeding programmes is emphasized. General. Cereal rusts do enormous damage throughout the world. In Australia, studies have been in progress for a number of years, and although results of earlier work have been published (Waterhouse, 1929, 1930, 1933, 1934, 1935, 1936, 1938, 1939, 1951; Waterhouse and Watson, 1941; Watson and Waterhouse, 1949), a detailed account of the later investigations has not been given for some time. This paper is designed to bring up to date the results that have been obtained with the following rusts: stem and leaf rust of wheat, stem and leaf rust of oats, leaf rust of rye, and leaf rust of barley. Results of work on certain grass rusts are not included here. STEM RUST OF WHEAT. Introduction. Weather conditions in recent years have again been responsible for heavy crop losses from disease attack, and these have directed attention to the continuing import-ance of the wheat rust problem. Butler (1948) estimated that the New South Wales losses caused by stem rust in the 1947-1948 season amounted to £7,000,000, and pointed out that this would have been much greater had it not been for the cultivation of several resistant varieties in some areas. Further heavy losses have occurred since. Apart altogether from rust, other organisms have done much damage under the favour-able conditions. It is difficult to give a true assessment of particular losses: some put down to stem rust may well have been due to other causes. Life History. Aecidial Stage. Earlier work with Puccinia graminis tritici E. & H. (Waterhouse, 1929, 1936, 1938) has shown that the Australian position is unique in many ways. For example, the rust does not regularly develop the aecidial stage on the barberry. To date only one record of the natural occurrence of this stage has been made (Waterhouse, 1934). Nevertheless controlled work in the plant house has shown that the barberry is a potential source of danger, and the growing of susceptible species is rightly proscribed. Material sent from other countries for examination has consistently given good germinations of teleutospores which have been over-wintered abroad before being forwarded by air mail in the spring. There have been a few cases, e.g., wheat straw from Greece, in which all attempts have failed to break the dormancy, either by exposing to winter conditions on the Tablelands, or by artificial freezing and thawing, material t
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