Some grass seedlings could be killing themselves by emerging from the soil at the wrong time of day—a costly mistake for farmers and ranchers trying to establish forage grasses on rangeland, an Agricultural Research Service scientist says.
The problem occurs if the germinated seed's first plant parts emerge from the soil at night, or if ground cover keeps the emerging part in the dark, says plant physiologist Charles R. Tischler.
"Light is the signal for these particular plant parts to stop growing," Tischler explains. "Since they don't stop when there's no light, they keep pushing the plant tip upward. As a result, the node—the place where roots form on the plant—winds up aboveground, leaving the new roots to die.
"When this happens, you don't get a good stand from your grass seeding, and you lose production on that land for a year as a source of feed for livestock. Also, since the land is bare, it's much more prone to wind and water erosion."
Tischler says experiments on 10 warm-season grasses showed that it's possible to counteract the "suicide tendency" in grasses such as kleingrass, a promising forage species for the Southwest. That would increase the likelihood of the grass successfully taking hold on rangeland.
A grass seedling's life begins when plant parts called the mesocotyl and coleoptile emerge from the seed in the soil.
The role of these two parts is to get the plant up through the soil surface. The mesocotyl grows steadily longer, pushing the coleoptile up toward the surface. Light striking the tip of the emerged coleoptile halts production of a chemical called auxin, which in turn stops the lengthening of the mesocotyl.
To find grasses with sensitivity sufficient to halt excessive elongation even in very faint light, Tischler and colleagues at ARS' Grassland, Soil, and Water Research Laboratory at Temple, Texas, grew warm-season grass species inside boxes with very dim continuous light. The tests included three different grama grasses, a switchgrass, big bluestem, four lovegrasses, a green sprangletop, and kleingrass.
"The kleingrass' node elevation started out quite a bit higher than the lovegrass'," recalls Tischler.
"We collected seeds from all the plants that had shown good sensitivity to the very dim light and had stopped their elongation.
"After three generations of selection in the kleingrass—taking the seeds from the plants with the lowest crown node elevation, growing out those seeds, and repeating this cycle twice more—we had kleingrass with crown node elevation levels closer to those of lovegrass, known for its short elongation and good stand establishment.
"The material we've selected still has to be field-tested," says Tischler. "But it has the potential to increase establishment of grasses in the field, and our procedure should also be of interest to plant physiologists." -- By Sandy Miller Hays, ARS.
Charles R. Tischler was at the USDA-ARS Grassland, Soil, and Water Research Laboratory, 808 East Blackland Road, Temple, TX 76502; phone (254) 770-6500, fax (254) 770-6561.
"Growing the Living Daylights Out of Kleingrass" was published in the April 1995 issue of Agricultural Research magazine.