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Growth, nutrition and genetic factors that affect pigmentation of wood-sapstain fungi Fleet, Carlos Antonio

Abstract

In this thesis, we examine several factors, including growth, nutrition and genetic identity, which affect pigmentation of sapstain fungi that discolour softwood in Canada from both chemical and molecular approaches. The presented results suggest that there are some chemical and physical factors to living host tissue that may stimulate growth and pigmentation by Ceratocystis resinifera. It was observed that reduced fungal growth on wood with closed border pits was concatenate with reduced consumption of wood nutrients. Nutrients in wood (such as mannose or TG-bound glycerol and fatty acids) play an important role in pigmentation and growth, but it appears that other factors, such as changes to wood ultrastructure or other biochemical factors, are also critical. Thus, some explanation for the differences in fungal distribution between logs and lumber may lie in the access that fungal species have to the host nutrients. Additionally, the presence of the DHN melanin biosynthesis pathway was demonstrated in all tested sapstain fungi using both chemical inhibitors (including tricyclazole, carpropamid and cerulenin) and molecular techniques. Furthermore, since no fungus has ever been found, to our knowledge, to have more than one melanin synthesis pathway, we can speculate with some confidence that the tested species only use the DHN pathway for melanin production. In addition, partial DNA sequences for the genes encoding scytalone dehydratase (SD), 1,3,8-trihyhydroxynaphthalene reductase (3HNR), 1,3,6,8-tetrahydroxynaphthalene reductase (4HNR) and polyketide synthase (PKS) were obtained from species of Ceratocystis and Ophiostoma and found to have homology with known respective DHN biosynthesis gene sequences. Sequence analysis of the partial SD amino acid sequences showed greater than 80% similarity among the sapstain species, and corresponded well with known parsimony analyses of sapstain fungi based on rDNA sequences. Sequence analysis for the genes encoding 3HNR and PKS showed that these sequences had lower interspecies similarities than the gene encoding SD. It is anticipated that this information will contribute to the development of safe and effective means to control sapstain by both researchers and the forest products industry.

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