A complex of four species of the fungus Stemphyl-lium; S. solani, S.floridanum, S. botryosum,and S. vesi-carum, are responsible for gray leafspot. These fungi are found worldwide on tomatoes and exhibit similar symptoms. Shiny, smooth and gray lesions are found on the underside of leaves and later the foliage has a shot hole appearance. In severe cases, leaves turn yellow, this is followed by leaf drop, and in some cases, defoliation of the entire plant. A single incompletely dominant gene, Sm,isresponsible forthe resistance used today (Hendrix and Frazier 1949). The Sm gene is found on chromosome 11 (Behare et al. 1991) linked to the I and I - 2 genes. A study by Kedar et al. (1967) found gametes with Sm and I were transferred preferentially thereby increasing their use in resistant cultivars.
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