The protective effect of mycorrhizae common in East Tennessee on loblolly pine (Pinus taeda L.)

Six loblolly pine stands in East Tennessee were surveyed for fungi possibly mycorrhizal with loblolly pine. Fifty-three species of fungi Were collected and identified including Boletus brevipes, Boletus luteus, Cenococcum graniforme, Laccaria laccata, and Pisolithius tinctorius which have previously been shown to be mycorrhizal with loblolly pine. Pure cultures of twelve of the collected species were obtained and tested in synthetic culture with loblolly pine. Agaricus placomyces, Amanita rubescens, Amanita yerna, and Boletus bicolor entered into mycorrhizal relationships with loblolly pine.

Five mycorrhizal fungi, Amanita rubescens, Boletus bicolor, Cenococcum graniforme, Laccaria laccata, and Pisolithius tinctorius, were assayed in plate antagonism tests against thirteen soil-borne pathogens. The presence of mycorrhizal fungi inhibited the growth of the pathogens in 70% of the tests. Boletus bicolor displayed the strongest antagonism inhibiting 90% of the pathogens tested.

Boletus bicolor, Laccaria laccata, and Pisolithius tinctorius were used to test the protection provided live roots by mycorrhizae from pathogens. Sterile loblolly pine seedlings were grown, inoculated with mycorrhizal fungi, and subsequently inoculated with pathogens. Using height growth as an indicator, it was concluded that two of the three mycorrhizal fungi used protected the seedlings from attack by Sclerotium bataticola, Fomes annosus, and Rhizoctonia soIani.