Submitted to: Crop Science
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: January 21, 1998
Publication Date: N/A
Interpretive Summary: Seedlings of warm season grasses have two different root systems. One is called the primary root, which develops from the embryo of the seed. A few days after the seedling begins growth, the other system arises at the base of the shoot (which is called the crown). These roots are called crown, or adventitious roots. For crown roots to develop, the crown needs to be below the surface of the soil, where moisture is available. If crown roots do not develop, the seedling eventually dies. Location of the crown is determined by how much light is available to the developing seedling. Plant breeders have developed plant populations which, when grown in dim light, have crowns either (1) at or below soil level, or (2) elevated more than a centimeter above soil level. A series of experiments using different amounts of light were conducted on these two plant populations. Results of these experiments indicate that the seedlings with low crown placement in dim light are much more sensitive to light, and under normal conditions a much lower amount of light is needed for the crown to be located below the soil surface. Also, in seedlings with high crown placement in dim light, under normal conditions a much higher amount of light is needed to keep the crown below the soil surface. These results will be useful in helping determine how grass seedlings respond to light, and how plant breeding may be used to develop grasses in which seedling establishment is better than in existing varieties.
Excessive crown node elevation of panicoid seedings is a major limitation to establishment. Crown node placement at or above the soil limits the probability of adventitious root development at the crown node. Seedlings often emerge but perish when secondary roots are not formed. Kleingrass (Panicum coloratum L.) and switchgrass (Panicum virgatum L.) germplasm with low (LC) and elevated (EC) crown node placement has been developed. We evaluated this germplasm for crown node elevation and coleoptile length in darkness and under continuous low light levels ranging from 0 to 26.8 umol m**- 2s**-1 (400 to 700 mm wavelength). In darkness, coleoptiles of LC seedlings were significantly longer than coleoptiles of EC seedlings and crown node elevation was higher for EC than for LC seedlings. Kleingrass EC seedlings required 5 times more light than unselected seedlings to produce similar crown node elevations, whereas LC seedlings required 5 to 10 times less light for the same response. For switchgrass, differences in light requirement were less pronounced. LC germplasm has been selected for a lower light requirement for deetiolation, greater coleoptile elongation and a decreased rate of subcoleoptile internode elongation. EC germplasm has been selected for increased subcoleoptile internode elongation, increased light requirement for deetiolation and a shorter coleoptile.