Early Blight

The fungus Alternaria solani causes the disease early blight and is found worldwide in locales with frequent rainfall or heavy dew. Early blight lesions are characterized by concentric rings of brown or black giving a classic target appearance. In addition, a yellow area surrounds the spots which coalesce to engulf the entire leaf, stem, or fruit. Initial efforts focused on incorporating stem resistance, particularly collar rot resistance from S. lycopersicum (Andrus etal. 1942), but also conferred a moderate level of leaf and fruit resistance. Along with additional sources of resistance (Foolad et al. 2000), early blight resistant cultivars have been developed which reduce the frequency of fungicide applications necessary for control, but do not eliminate the need for chemical control (Shoemaker and Gardner 1986; Gardner and Shoemaker 1999). Zhang et al. (2003) identified QTLs associated with early blight resistance in wild tomato species, but Graham et al. (2005) were not successful in identifying resistance from the S. habrochaites ILs (Monforte and Tanksley 2000).

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