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Peronospora radiide Bary 1863, a new record in Israel, was found in January 1985 to be the cause of a downy mildew of cultivated marguerite daisies, cv. ‘Scheine von Nizza’ (a cultivar ofArgyranthemum frutescens: Anthemideae: Compositae), grown in an unheated greenhouse in the Coastal Plain. The same fungal species was found in February 1986 on the very common, wildChrysanthemum coronarium(Anthemideae), 13 km distant from the previous year’s location. Conidia of the fungus on ‘Nizza’ leaves had average dimensions similar to those on ‘Nizza’ flowers, but differed in variance (minimal and maximal length and width) and 40% of them had papillate apicesvs4% in conidia from flowers. The average length and width of conidia from both leaves and flowers of ‘Nizza’ were slightly above those already described forP. radiiin the literature. The conidia fromCh. coronariumhad average lengths, widths and quotients significantly higher than those from ‘Nizza’ and from the previously published data, extending the range to 43.8 x 24.3 μm, quotient: 1.83vsthe highest published averages of 34.2 x 23.74 μm, quotient: 1.70. OnCh. coronarium, the dimensions of conidia had great variance within samples from the same plant and differed significantly even between plants at the same time and location, showing this fungus to have more variability than was previously known. Oospores, known elsewhere for this species, were not found in Israel.

The downy mildews of maize, sorghum and pearl millet are among the most destructive diseases in the tropics and subtropics. The pathogens causing the diseases are Peronosclerospora sorghi, P. heteropogoni, P. philippinensis, P. sacchari, P. maydis and Sclerospora graminicola. In spite of an increase in research on graminaceous downy mildews during the last decade, broad gaps in information still exist which prevent their adequate control. Information on seed transmission, collateral hosts as sources of inoculum and effects of environment on the conidial and oospore phases of these diseases is reviewed, and some of the important information gaps are discussed.