The Influence of Ectotrophic Mycorrhizal Fungi on the Resistance of Pine Roots to Pathogenic Infections. I. Antagonism of Mycorrhizal Fungi to Root Pathogenic Fungi and Soil Bacteria

Antagonism of ectotrophic mycorrhizal fungi to <i>Phytophthora cinnamomi</i>, other root pathogenic fungi, and soil bacteria was examined. In agar plate tests, <i>Laccaria laccata</i>, <i>Lactarius deliciosus</i>, <i>Leucopaxillus cerealis</i> var. <i>piceina</i>, <i>Pisolithus tinctorius</i>, and <i>Suillus luteus</i> inhibited growth of nearly half of the 48 different fungal root pathogens. <i>Leucopaxillus cerealis</i> var. <i>piceina</i> inhibited 92% of the test pathogens. Differences in sensitivity of several isolates of <i>P. cinnamomi</i> to inhibitions by this symbiont were not found. Culture filtrates of <i>L. cerealis</i> var. <i>piceina</i> were inhibitory also to growth of <i>P. cinnamomi</i> and soil bacteria. Zoospore germination was inhibited completely in filtrates of this symbiont. Maximum antibiotic production occurred during the rapid growth phase in liquid culture. Length of culture incubation and temperature strongly influenced production of inhibitory substances by <i>L. cerealis</i> var. <i>piceina</i> in liquid culture. It grew best from 10 to 20 C, whereas <i>P. tinctorius</i> grew best from 30 to 35 C in liquid culture.