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Adaptation of Four Pathogens to Semi-Arid Habitats as Conditioned by Penetration Rate and Germinating Spore Survival. Esther Bashi, Department of Life Sciences, Bar Ilan University, Ramat Gan, Israel; J. Rotem, Division of Plant Pathology, Volcani Center, Bet Dagan, Israel, and Department of Life Sciences, Bar Ilan University. Phytopathology 64:1035-1039. Accepted for publication 1 March 1974. DOI: 10.1094/Phyto-64-1035.

The ability of some plant pathogens to cause disease epidemics in semi-arid habitats with short wet periods was studied. Stemphylium botryosum f. sp. lycopersici in tomatoes infected equally well after either a long wetting period or after several short, moist periods interrupted by dry ones; its germ tubes survived the interval between moisture periods. In Phytophthora infestans, rapid penetration of potato leaves compensated for sporangial sensitivity to desiccation. Conidia of Alternaria porri f. sp. solani penetrated potato leaves rapidly and were drought resistant, although infection was higher after a continuous wet period then a few short ones. Uromyces phaseoli in beans develops in semi-arid habitats only in humid seasons because of its comparatively slow infection rate and low survivability between short wet periods.