Fusarium eumartii growth in resistant and susceptible oak species

Fusarium eumartii is a fungus associated with declining Quercus robur, in which it is found in the vessels. The response of oak species to infection is known to vary: Q. robur is susceptible, but Quercus cerris and Quercus pubescens are resistant. An experiment was carried out in 1996 and repeated in 1997, to examine how F. eumartii colonization differed in oak species that were susceptible or resistant to the fungus by counting the number of vessels with mycelium at various distances from the inoculation site in infected seedlings and by determining the amount of viable fungus in infected tissue. Infected vessels with mycelium were counted on sections (10 µm thick) cut at 0, 2, 4, 6, 8 and 10 cm from the inoculation site on 1-year-old inoculated seedlings as well as on sections cut every 2 cm to the seedling tip. The amount of viable fungus was determined by counting the colony forming units (CFUs) in stem segments from the same seedlings. Quercus robur seedlings had the greatest number of infected vessels and the greatest number of CFUs. Forty days after inoculation, the extent of vertical fungal spread was 28.12 cm in Q. robur, 3.15 cm in Q. cerris and 3.00 cm in Q. pubescens. The greatest number of CFUs was found in Q. robur at day 5 after inoculation. Analysis of variance confirmed the results.