THE MECHANICS OF ANCHORAGE IN WHEAT TRITICUM-AESTIVUM L .2. ANCHORAGE OF MATURE WHEAT AGAINST LODGING

The root system of mature wheat Triticum aestivum Maris Dove is dominated by the 7 to 15 adventitious roots which emerge from the perimeter of the stem base, pointing radially outwards and downwards. The basal, coronal region of these roots is thick and unbranched, attached to a rhizosheath of earth by a dense covering of root hairs and stiffened in bending by lignification of outer layers of the cortex. Root lodging of plants involves bending of the coronal roots at their base and axial movement of leeward and windward roots through the soil; their resistance to these motions provide moments resisting lodging. A model of anchorage was produced by summing the resistance of each root to both forms of motion to give two anchorage components. The model was tested in a series of mechanical experiments in which simulated lodging was followed by loading of individual roots; results supported the anchorage model and suggested that in the experimental conditions the two components of anchorage were approximately equal in magnitude. The stem was about 30% stronger than the anchorage system. The coronal anchorage roots made up 4.4% of total dry mass; it is suggested that anchorage could be improved either by increasing investment in this region or by altering root orientation. Sequential development of seminal and adventitious root systems is related to the changes in anchorage requirement with age.