Approximately two-thirds of the global human caloric intake is derived from just three plants (corn, wheat, and rice). Each of these plants experience substantial yield losses due to the problem of stalk lodging (stalks or stems breaking due to environmental factors). Economic losses due to stalk lodging are estimated to exceed $6 billion annually in the USA alone. Interestingly, the majority of prior research into stalk lodging has focused on the stalk or stem with very little attention given to the role of the leaf sheath. Our goal was to determine the contribution of the leaf sheath on overall plant biomechanics and failure properties.
We analyzed the bending strength of several varieties of hard and soft wheat stems harvested at full maturity. To evaluate biomechanical properties stems were subjected to three-point bending using an Instron Universal testing system with custom fixtures. As such we conducted non-destructive flexure tests on plants both before and after careful removal of leaf sheaths. In addition, destructive failure tests were conducted by grouping stems according to variety and comparing the average strength of plants with leaf sheaths intact to the average strength of plants with leaf sheaths removed.
We found that the leaf sheath accounts for 20% - 50% of the total bending strength of the plant. Similarly, it accounts for 30% - 40% of the total flexural strength. The contribution of the leaf sheath was highly dependent upon the particular hybrid or wheat variety being tested. This indicates that it is possible to target the responsible phenomes, and breed for leaf sheaf strength. These results indicate the need for more in-depth analyses of the leaf sheath with regards to the problem of stalk lodging.