Germination, penetration, and infection by Arceuthobium americanum on Pinus banksiana

Information on the establishment of Arceuthobium americanum Nutt. ex Engelm. on its host, jack pine (Pinus banksiana Lamb.), is required to improve knowledge of this critical development stage and improve pest management. Laboratory and field observations on four populations of A. americanum seeds from Alberta collected in 2000 and 2001 and histological observations on one population were used to determine the timing and histopathology of parasite establishment on jack pine. Seed germination remained near zero until 110 d after placing seeds in storage; germination peaked after 230 d in 2001 and between 230 and 320 d in 2002. Interannual variation in germination timing at study sites was high. Interannual variation in percentage of germination was low, as was variation in percentage of germination from different seed sources. Germinated seeds of each seed source were significantly larger (48%) than seeds that did not germinate. Penetration at the base of spur shoots began during June-August and usually continued until June-July of the next year. The odds of infection when the germinant survived until the second growing season were 26-55 times greater than the odds of infection when the germinant withered in the first growing season. Symptoms of infection usually occurred 13-15 months after germination and were consistent for all seed sources and sites.