Submitted to: Crop Science
Publication Type: Germplasm Release
Publication Acceptance Date: December 1, 2000
Publication Date: N/A
Interpretive Summary: Switchgrass is a very important grass, used for livestock grazing and also as a biofuel. In switchgrass, as in many grasses, the first, or primary root (which is present in the embryo) is very short-lived. It is replaced by other roots that arise from a part of the seedling called the crown node. Normally the crown node is located below the soil surface. However, in some cases the crown node is located above the soil surface. When the crown node is located above the soil surface, the seedling often dies because replacement roots cannot begin to grow in air. Crown nodes are located above the soil surface when seedlings don't receive enough light as they develop. We used plant breeding techniques to develop two switchgrass populations which have higher and lower crown nodes when grown in dim light. These populations (called germplasms) have been named TEM-SEC and TEM-SLC, respectively. They should be useful in studying ways in which light influences the developing grass seedling. Also, seedlings of TEM-SLC should survive better in field plantings (especially when light is limiting) because crown nodes (and consequently replacement roots) will be located below the surface of the soil, where moisture is available.
During the germination and emergence process in warm-season grasses, cell division and elongation at the base of the crown node elevates the crown node. When the tip of the coleoptile receives an adequate light stimulus, a signal to the crown node stops cell division and elongation. Under ideal conditions, these factors interact so that final crown node placement is slightly below the soil surface. However, because competition, heavy overcast conditions, and other factors limit light receipt by the coleoptile tip, elongation of the subcrown internode often continues until the crown node is above the soil surface. Adventitious roots, which must replace the primary root present in the embryo, initiate from the crown node. Consequently, seedlings with crown nodes above the soil surface often perish. We conducted three cycles of recurrent selection in dim, continuous light using Alamo switchgrass (Panicum virgatum L.) as the parental material. We saved the ten percent of seedlings with highest and ten percent of seedlings with lowest crown nodes (measuring from the soil surface) to generate two switchgrass germplasms designated TEM-SEC (elevated crown nodes) and TEM-SLC (low crown nodes). When evaluated in the low light environment in which selection was performed, crown nodes of TEM-SLC were significantly lower than those of Alamo, which in turn were significantly lower than those of TEM-SEC. These new germplasms will be useful in elucidating factors involved in seedling photomorphogenesis. Also, TEM-SLC should establish better in light-limited situations.