A mechanical study of retting in glyphosate treated flax stems ( Linum usitatissimum)

Abstract

The process of retting (the dissociation of the fibre bundles from the central stele by the action of microbes) in two varieties of flax ( Linum usitatissimum; cvs. Laura and Escalina) was investigated by studying the morphology and mechanics of plants after treatment with a translocated herbicide, glyphosate. The mechanical changes in the stems were measured on a weekly basis, by carrying out a series of mechanical peel and tear tests on the stem tissue of mature plants. There was a pronounced drop in the moisture content of the stem 14 days after application of the herbicide, from a moisture content of ≈60 to 10%. This was consistent with the onset of senescence and subsequent dehydration of the plant tissues. The dehydration of the stem tissues corresponded with an increase in the work required to peel the fibre bundles from the secondary phloem tissue, from 212±7.9 to 539±22 J m −2 ( P<0.001). However, 27 days after application of the herbicide there was a more gradual but significant drop in the work required to peel the stem, by ≈45% to a mean work to peel of 297±19.8 J m −2. This is thought to be a result of the retting process. This study indicates that peel tests can be used to measure mechanical changes in the interface between the fibre bundles (primary phloem tissue) and the secondary phloem tissue. It enables the progression of retting to be monitored and allows comparisons to be made to determine the optimum harvest time for flax.