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Resistance

Infection Processes of Puccinia recondita in Slow- and Fast-Rusting Wheat Cultivars. Tae Soo Lee, Postdoctoral research associate, Department of Botany and Plant Pathology, Purdue University, West Lafayette, IN 47907; Gregory Shaner, professor, Department of Botany and Plant Pathology, Purdue University, West Lafayette, IN 47907. Phytopathology 74:1419-1423. Accepted for publication (submitted for electronic processing) . Copyright 1984 The American Phytopathological Society. DOI: 10.1094/Phyto-74-1419.

Development of Puccinia recondita from spore germination to uredinia formation in 11 wheat cultivars was studied histologically to determine whether the long latent period and small uredinia in slow-rusting cultivars are due to reduced mycelial growth in leaf tissue. Six sequential samples of flag leaves (24- 216 hr after inoculation) were treated with an optical brightener (Uvitex BOPT) and observed with a fluorescence microscope. Percentages of urediniospore germination, germinated urediniospores forming appressoria, and appressoria forming substomatal vesicles were the same for fast-rusting cultivars (Morocco, Suwon 92, Monon, and P72482), an intermediate slow-rusting cultivar (SW 210), and slow-rusting cultivars (Suwon 85, SW 72469, P6028, CI 13227, and L574-1), as well as for a hypersensitively resistant cultivar (P68130). However, at each sampling time the colonies in slow-rusting wheats were smaller and had fewer haustorial mother cells than colonies in fast-rusting wheats. Although the colony growth rates of P. recondita on fast-rusting and slow-rusting cultivars were different, formation of uredinial beds, from which uredinia develop, in both groups of cultivars began when the average colony area was 0.12- 0.14 mm². The longer time required for colonies to reach this incipient stage of sporulation on slow-rusting cultivars would explain their long latent period.