Identification of the Germination Self-inhibitor from Uredospores of Puccinia striiformis

MACKO, V., E. J. TRIONE, and S. A. YOUNG. 1977. Identification of the germination self-inhibitor from uredospores of Puccinia striiformis. Phytopathology 67:1473-1474. The endogenous germination inhibitor from uredospores a germination assay employing fresh, water-washed, stripe of the stripe rust fungus, Puccinia striiformis, was identified rust uredospores. The chemical structure was confirmed by as methyl cis-3,4-dimethoxycinnamate. The inhibitor was chromatography in several systems and by mass extracted from field-collected spores with water, partitioned spectrometry. The ED50 of the cis-form of the inhibitor was 4 into ether, and purified by thin-layer and gas ng/ml, whereas the trans-isomer had little or no activity as a chromatography. The inhibitor activity was monitored with germination inhibitor. Additional key words: wheat. Stripe rust, which is caused by Puccinia striiformis inhibitor was extracted from the uredospores by stirring West., is a serious disease of wheat in many parts of the them in water (8 g/ 100 ml) at 22 C. After the spores were world. In the United States it is common in the Pacific removed by filtration, they were extracted with water two intermountain areas and occasionally causes severe more times. The filtrates were pooled and extracted three losses; e.g., on wheat cultivar Pitic 62 in Northern times with an equal volume of diethyl ether. The crude California in 1974 and on Yamhill wheat in Western ether extract was evaporated to near dryness with a rotary Washington in 1975. vacuum evaporator at 22 C. The residue was taken up in a An important aspect in understanding the development small volume of diethyl ether (1 mg equivalent of spores of Puccinia striiformis is the characterization of per 2 uliters ether), spotted on silica gel thin-layer regulatory mechanisms of dormancy and activation chromatography plates, and developed in benzene:ether processes of uredospore germination (3). The presence of (8:2, v/v). The silica gel plate was air-dried and then an endogenous germination inhibitor has been reported divided into 10 equal zones that were scraped off in these spores, but the active principle was not identified separately, eluted with methanol, and tested for (9). Recent studies have emphasized the specific roles of inhibitory activity. germination inhibitors in control of fungal spore For the bioassay, a measured volume of the solution to germination (1, 6). With a view toward defining these be tested was placed in a small test tube. The solvent was control mechanisms in P. striiformis, we have studied the evaporated with the aid of an air stream at room chemical nature and biological activity of the selftemperature. Water (1 ml) was added to each tube and inhibitor from uredospores of this fungus. stirred vigorously. Aliquots (0.5 ml) of this aqueous extract were placed into each of two small vials and about 500 stripe rust uredospores were floated on the surface of MATERIALS AND METHODS the solution in each vial. The uredospores previously had been stirred in double-distilled water for 15 min before About 180 g of fresh uredospores were collected from they were transferred to the bioassay vials. The spores stripe rust lesions on field-infected wheat in June 1975 by were incubated in the dark on the test solutions at 10 C for a vacuum-trap method. The spores were stored in liquid 16 hr before the number of germinating spores was N2 for 2 mo. In a preliminary experiment, the germination determined microscopically. Experimental data were collected only if the germination of the control spores was