Fungal Colonizers and Seed Loss in Lodgepole Pine Orchards of British Columbia

Lodgepole pine (Pinus contorta var. latifolia Engelm. ex S. Watson) is an important lumber species in Canada, and seed orchards are expected to meet the increased demand for seed. However, seed production has been consistently low in the Okanagan region orchards of British Columbia, Canada. To determine whether the fungal microbiome contributes to seed loss, histological and molecular approaches were used. Seed production was studied at seven Okanagan orchards, all outside the natural range of lodgepole pine, and at one near Prince George, within its natural range. Seed losses were highest in the Okanagan, compared with Prince George. The role of fungal colonizers in consuming seed during the last stages of maturation is described. Fungal hyphae were frequently observed at all locations in developing seed, particularly once storage substances accumulated. Fungi identified from host tissues using molecular and morphological techniques included Alternaria, Cladosporium, Fusarium, Penicillium, and Sydowia. The opportunistic foliar pathogen Sydowia polyspora, which is known to have a variable biotrophic status, was detected at most orchards within different host tissues (seeds, needles, and conelets), in association with pollen, and in the air column. Reduced seed viability observed in Okanagan orchards is most likely due to a combination of factors, including composition of the fungal microbiome.