Fungal Degradation Properties of Young Small Diameter Genetically Modified Quaking Aspen (Populus tremuloides)

Abstract

Three studies were conducted to evaluate the fungal degradation properties of young transgenic aspen trees (Populus tremuloides). The first study focused on development of methods of decaying small diameter tree samples. The second and third studies focused on the mass loss differences and cellulose and lignin degradation between trees with different lignin types and contents.

In the first study, two methods for rapid laboratory fungal decay tests of very young small diameter (5-15 mm) hybrid poplar (Populus nigra x Populus maximowiczii), yellow poplar (Liliodendron tulipifera), and willow (Salix sp.) trees were examined using the white rot fungi Trametes versicolor and Ceriporiopsis subvermispora. An agar plate method and a modified soil-agar block method were compared using non-standard size stem parts. The agar plate method did not prove to be suitable for testing materials when limited numbers of samples are available because of the extremely high variation of mass loss values. Mass loss using the modified soil-agar block technique was comparable to established methods for small and large blocks using extended colonization periods.

In the second study, one-year old quaking aspen (Populus tremuloides) trees including a control wild type aspen and three lines of transgenic trees were analyzed for resistance to lignin selective white rot fungal decay. The transgenics had reduced lignin content through transfer of an antisense -4CL gene, changed syringly/guaiacyl ratio through insertion of a sense CAld5H gene, and modified lignin content and syringyl/guaiacyl through simultaneous insertion of -4CL and CAld5H genes. Mass loss was used to examine differences between genetic lines. The small diameter transgenic trees were decayed using lignin selective white rot fungus Ceriporiopsis subvermispora. A modified soil-agar block method was used with a forty day colonization time. The transgenic lines with higher S/G lignin ratio exhibited a higher mass loss percentage compared to the wild type and other transgenic lines.

In the third study, the transgenic lines were analyzed for resistance to three types of fungal decay. The small diameter transgenic trees were tested using simultaneous white rot fungus Trametes versicolor, lignin selective white rot fungus Ceriporiopsis subvermispora and a brown rot fungus Poria placenta. A modified soil-agar block method was used to decay the samples. Near infrared spectroscopy and chemical analysis determined loss of cellulose and lignin variations between transgenic genotypes. Near infrared transmittance was successful in predicting the cellulose and lignin percentages of the decayed material. The reduced lignin content lines did not affect the rate of lignin decay for all fungi tested. Lignin decay rates were reduced by the increased S/G ratio lines for all fungi tested.