COLONIZATION OF OAK WILT FUNGAL MATS BY OPHIOSTOMA-PICEAE DURING SPRING IN MINNESOTA

The colonization of Ceratocystis fagacearum fungal mats of different a ges by Ophiostoma piceae on Quercus spp. was determined in three east- central Minnesota locations during the spring of 1995. The extent of t he mat area colonized by O. piceae generally increased with mat age. S ubsamples per mat yielding the fungus for the three locations averaged 11 to 27% for immature mats, 65 to 72% for mature mats, and 66 to 96% for aging and declining mats. On a mat-incidence basis, frequencies o f O. piceae isolation from at least one subsample of an immature mat r anged from 30 to 53% compared with more than 90% for all other mat age s in the three locations. The average number of colony-forming units o f O. piceae per square centimeter ranged from 1 x 10(3) to 1.2 x 10(6) and increased with mat age. The extent of C. fagacearum recovery from each mat was lower for aging plus declining mats (P < 0.03) compared with other ages in two locations. On a mat-incidence basis, frequency of C. fagacearum recovery from at least one subsample of a mat average d 99% for all ages of mats in all locations. The interaction between O . piceae and C. fagacearum on mats, nitidulids, and the oak wound surf ace is discussed.