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Development of the Stem and Crown Rust Fungi on Leaves, Sheaths, and Peduncles of Oats. J. K. Kochman, Former Teaching Fellow, Department of Botany, University of New England, Armidale, New South Wales 2351, Australia, senior author now Plant Pathologist, Department of Primary Industries, P.O. Box 102, Toowoomba, Queensland 4350, Australia.; J. F. Brown, Associate Professor, Department of Botany, University of New England, Armidale, New South Wales 2351, Australia. Phytopathology 65:1404-1408. Accepted for publication 27 June 1975. DOI: 10.1094/Phyto-65-1404.

The development of Puccinia coronata f. sp. avenae and Puccinia graminis f. sp. avenae was studied quantitatively, using histological methods, on leaves, sheaths, and peduncles of two commercial oat cultivars (Algerian and Garry) and on the naturalized weed species Avena sterilis. No major differences were observed in the percentage germination of urediniospores of both rusts on the different hosts or on the various parts of the host. The frequency of appressorium formation by crown rust was less on sheaths than on leaves. Appressoria failed to develop on the peduncles of the hosts examined. Minor differences were observed in appressorium formation by stem rust on the various plant parts. Crown rust had a greater ability to produce appressoria on leaves than stem rust, whereas on sheaths and peduncles the reverse was true. The frequency of penetration from appressoria by crown rust was less on sheaths than on leaves. Penetration by stem rust was lower on sheaths and peduncles than on leaves of Algerian and A. sterilis but was similar on Garry. Penetration frequency of both rusts was lowest on Garry, intermediate on A. sterilis and highest on Algerian. It is suggested that differences in penetration frequency may be a component of the "slow rusting" character.