Previous View
 
APSnet Home
 
Phytopathology Home


VIEW ARTICLE

Sclerotial Inoculum Density of Phymatotrichum omnivorum and Development of Phymatotrichum Root Rot in Cotton. Stuart D. Lyda, Associate Professor, Department of Plant Sciences, Texas A&M University, College Station 77843; Earl Burnett, Research Soil Scientist, USDA, ARS, Blackland Conservation Research Center, Temple, Texas 76501. Phytopathology 60:729-731. Accepted for publication 30 November 1969. DOI: 10.1094/Phyto-60-729.

Sclerotia of Phymatotrichum omnivorum were produced in sterile soil culture and recovered by wet sieving. They were air-dried and added to screened Houston Black clay to establish known inoculum densities. Maximum disease in cotton occurred with 125 to 625 sclerotia/kg of dry soil when the soil was maintained at 28 C. When the sclerotial inoculum was uniformly distributed throughout the soil, increasing densities to 3,125 and 15,625/kg of dry soil gave progressively less disease than 625/kg. Disease incidence was ascertained by number of dead plants. There was a delay in the rate of disease development when these same levels of sclerotia were centrally positioned within the soil; however, the final percentage of dead plants was the same as for 125 or 625 sclerotia/kg soil. Sufficient numbers of sclerotia survived air-drying and screening of the soil from the highest level of sclerotial infestation in the inoculum density tests to cause 100% plant kill when the soil was replanted to cotton.