There are three different tomato diseases in the United States, supposed to be caused by three different species of Fusarium. They are the "summer blight" of California, the "yellow blight" of the Pacific Northwest, and "Fusarium wilt," which is one of the most serious tomato diseases in the southern states. Each of these geographical sections is subject to exceed¬ ingly high temperatures, and it has been observed that in periods of very high air and soil temperatures the Fusarium diseases cause the most serious damage. Edgerton (3) has recently published his observations on the relation of high temperatures to the Fusarium wilt disease. It is for this disease that the writer has attempted to determine definite temperature limits. The work herein described was carried on entirely under greenhouse conditions in the "Wisconsin soil-temperature tanks," the primary object being to study the effects of (1) different soil temperatures and (2) different air temperatures upon the development of the disease. The influence of other environmental conditions on the development of the disease, and detailed observations, hitherto unrecorded, as to the nature of the disease have been described also.
The FungusThe causal organism of the wilt disease under discussion is a vascular parasite of the tomato (Lycopersicum esculentum Mill.) which may live and retain its pathogenicity in the soil for considerable periods. Pure cultures of this fungus, designated as Fusarium lycopersici Sacc., were obtained from S. H. Essary of Tennessee, and in addition, isolations were made by the author from infected soil and infected plants sent from Maryland, Tennessee, Ohio, and Indiana.When inoculations were made with these various isolations, it was found that, under greenhouse conditions at least, some produced much more serious wilting than others. After a series of preliminary inoculation experiments, therefore, one Indiana isolation was chosen for the temperature experiments. This strain was not so virulent a parasite as a Maryland isolation, but it produced the disease under a wide range of temperatures and was about equal in virulence to several other strains from Indiana,