Title: INFLUENCE OF HOST AND NON-HOST PLANTS UPON POPULATIONS OT ' VERTICILL]UM DAHLIAE IN SOIL THESIS OF

The incitant of Verticilliurn wilt of pepperrnint (Verticilliurn dahliae IOeb.) causes disease symptorns only in the genera Mentha (the rnints) and Monarda. This fungus is unable to grow saprophyt-ically through natural soil. V. dahliae survives in soil by coloniz-ing and forrning rnicrosclerotia in susceptible plants, living root tis-sue of rrrany resistant plants, and, to a lirnited extent, non-living plant residues Fluctuations in populations of V. dahliae in the rhizosphere and penetration of the roots of host and non-host plants were studied in the greenhouse. Rhizosphere soil was collected frorn plants and diluted into ethanol-streptornycin agat (ESA) by standard soil dilu-tion techniques. Rhizosphere soils f rorn all plants tested had signi-ficantly higher populations of V. dahliae than did non-rhizosphere soils. V. dahliae populations in non-rhizosphere soil always re-rnained relatively stable over an eight week period. Resistant an