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The Relationship of Sporulation to Photosynthesis in Some Obligatory and Facultative Parasites. Y. Cohen, Division of Plant Pathology, The Volcani Institute of Agricultural Research, Bet Dagan, Israel; J. Rotem, Division of Plant Pathology, The Volcani Institute of Agricultural Research, Bet Dagan, Israel. Phytopathology 60:1600-1604. Accepted for publication 2 June 1970. DOI: 10.1094/Phyto-60-1600.

Exposure of host plants to light conditions favoring photosynthesis, or blocking this process by chemical means, revealed a causal relation between photosynthesis and sporulation of fungal parasites. Extending the photoperiod from 6 to 48 hr before exposing Pseudoperonospora cubensis on cucumbers to dark and moist conditions resulted in an increase in subsequent sporulation. A similar increase in sporulation was also associated with increases in light intensity and temp of incubation, as well as with illumination of the plants with the light spectra most effective for photosynthesis. In Uromyces phaseoli on beans and in Phytophthora infestans on potatoes, the highest sporulation followed the longest photoperiods to which the plants had been exposed. When dichlorophenyl-dimethylurea (DCMU) was applied to suppress photosynthesis of tobacco and cucumbers infected with Peronospora tabacina and P. cubensis, respectively, its effect on the subsequent sporulation depended on whether it had been applied before or after exposure of the plants to a light period. In the first case, few or no spores were formed; in the second case there was normal sporulation. When DCMU was applied at various dates after inoculation to beans, potatoes, and tomatoes infected with U. phaseoli, P. infestans, and Alternaria porri f. sp. solani, respectively, the lowest sporulation of the first two parasites was associated with the earliest date of DCMU application, while the reverse was true for the last species. It was concluded that photosynthesis is an essential condition for sporulation in obligatory parasites, but varies in its effect in facultative parasites.

Additional keywords: reproduction, host-parasite relationships.