STRUCTURAL EFFECTS ON FLAX STEMS OF 3 POTENTIAL RETTING FUNGI

Rhizomucor pusillus and Fusarium lateritium, isolated from flax dew-re tted in South Carolina, and Epicoccum nigrum, isolated from flax dew-r etted in the Netherlands, are evaluated for structural modifications o f various cells in their flax stems, particularly the effects on fiber walls and bundles as related to retting. All fungi are effective in d egrading parenchyma tissues and isolating fibers, but F. lateritium an d particularly E. nigrum also degrade the fiber cell walls, including the secondary layers, indicating the potential for over-retting and re duced fiber strength. In contrast, R. pusillus does not appear to atta ck the main portion of the secondary wall, but degrades the most centr al portion of the fiber wall, thus expanding the fiber lumen. Extracel lular enzymes produced by this fungus appear to effectively degrade th e middle lamellae, separating bundles into fibers. The lignified walls of the core cells are partially degraded by F. lateritium but not by R. pusillus or E. nigrum. R. pusillus and E. nigrum appear to partiall y degrade or alter the cuticular surface of the stem, possibly facilit ating hyphal penetration to the internal tissues. These observations o f structural alterations indicate that R. pusillus possesses the best retting abilities. Results are interpreted in light of previous inform ation on the enzymatic profile of these fungi.