| The majority of vascular plants harbour specialized fungi, known collectively as endophytes, within their living tissues. The foliar endophytes of Pinus strobus L. (eastern white pine) are not well studied. In this thesis, aspects of the biology of white pine phyllosphere fungi were investigated. The distribution of endophytes between sites, trees, branches, needle age classes, and needle positions was heterogeneous at all levels except branches. Asymptomatic needles observed using light microscopy and TEM showed that Lophodermium spp. endophytes exhibited specialized hyphal structure. Hyphae were dorsiventrally appressed, highly lobed and usually situated in the middle lamella between the epidermis and hypodermis. In incubated samples, hyphal morphology became more regular and growth rate and needle colonization increased as senescence proceeded. To study endophyte activity during the period of natural senescence, needles were sampled weekly through August and September. Needles were cleared, stained and examined microscopically. Needles that had suffered severe prior biotic or abiotic attack were dropped early in the senescing period. Shortly thereafter, endophyte activity increased in remaining needles provoking host defence responses. By the time abscission occurred, the majority of the needle tissue was colonized. To assess the size of individual infections, needles were divided into one mm segments, placed on agar medium, and random amplified polymorphic DNA (RAPD) profiles generated from emerging isolates. Results demonstrated that Lophodermium isolates originated from separate infection events, were discrete and localized along the needle, and reached lengths of a few mm. Infection sizes corresponded to those observed in microscopic and cultural studies. In addition to endophytes per se, unique fungi were found inhabiting the epistomatal chambers in needles of white pine. These fungi were neither epiphytes nor endophytes but adapted to the particular niche found in the stomata, one that is transitional between the phylloplane and the endophytic space. They were documented using light microscopy, SEM, and TEM. The distribution of stomatal fungi is not homogeneous over the range of white pine in south-central Ontario. |
