INFLUENCE OF SOIL pH AND HUMIDITY ON SURVIVAL OF CEPHALOSPORIUM GRAMINEUM IN INFESTED WHEAT STRAW

Abstract

Cephalosporium gramineum survived in and sporulated most profusely on wheat straws in soil at pH 3.9 to 5.5. Strongly acid (pH 3.3) and alkaline soil (pH 7.6 or greater) reduced survival. The sporodochial stage (Hymenula cerealis) formed at pH values between 3.9 and 8.4, but most abundantly at pH 4.8 to 5.1. While acidity favored both saprophytic survival and sporulation, the pH’s of most wheat lands of Washington are within the pH range favorable for the pathogen.Saprophytic colonization of straw by Trichoderma spp. was favored by acidity (greatest at pH 3.3 to 3.9), and colonization by saprophytic Fusarium spp. by alkalinity (greatest at pH 8.2 to 8.8).Air-dried soil was brought to various relative humidities (RH) over glycerine and water solutions. Cephalosporium gramineum survived best in straw in contact with soil at the lowest RH tested (ca. 82%) and least well at an RH near 90%. Survival was reduced in soils with relative humidities between 90 and 86%, water levels below those of soil at the permanent wilting point for higher plants. Such humidities exist in surface layers of summerfallow and crop lands during portions of the summer in Washington.Penicillium brevi-compactum and P. steckii were the main colonists of the straws at RH values of 95% or lower.