Influence of Soil Moisture on Longevity of Cotton Root-rot Sclerotia »

The fungus Phymatotrichum omnivorum (Shear) Duggar, the cause of cotton root rot, has three known stages in its life history, namely, (i) a vegetative or Ozonium stage (^),^ (2) a conidial or Phymatotrichum stage {!), and {S) a sclerotial stage (4). Several investigators have shown that the sclerotia, or hold-over bodies, are usually present in the soil wherever the disease is found, and play an important part in the persistence and overwintering of the fungus. Dana {2) found viable sclerotia that had survived a fallow treatment of more than 2 years, and King and Hope {3) found that a large proportion of sclerotia were viable after being maintained for 2}^ years in soil cultures in the laboratory, Neal {2), King, Loomis, and Hope (5), and Dana {2) reported that the viability of sclerotia of ordinary size was destroyed when they were exposed to drying for a very short time. King, Loomis, and Hope {5) found that a large proportion of sclerotia were viable after immersion for 120 days in water, and Taubenhaus, Ezekiel, and Lusk (7) found that flooding field plots for 120 days failed to eradicate the disease, although they observed that the vegetative stage of the fungus was no longer viable after submergence in saturated soil for 3 days. Additional information concerning the influence of soil moisture on the germinating powers of sclerotia seemed desirable. An experiment was conducted, therefore, in which the sclerotia were buried for varying periods in soils maintained at different definite moisture contents. EXPERIMENTAL PROCEDURE