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Colonization of Oak Wilt Fungal Mats by Ophiostoma piceae During Spring in Minnesota

The colonization of Ceratocystis fagacearum fungal mats of different ages by Ophiostoma piceae on Quercus spp. was determined in three east-central Minnesota locations during the spring of 1995. The extent of the mat area colonized by O. piceae generally increased with mat age. Subsamples 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 of O. piceae isolation from at least one subsample of an immature mat ranged from 30 to 53% compared with more than 90% for all other mat ages in the three locations. The average number of colony-forming units of O. piceae per square centimeter ranged from 1 × 10³ to 1.2 × 10⁶ 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 averaged 99% for all ages of mats in all locations. The interaction between O. piceae and C. fagacearum on mats, nitidulids, and the oak wound surface is discussed.