Seed Dormancy and Germination in Ecotypes of Johnsongrass

We studied germination of seeds of 44 morphologically distinct, vegetative ecotypes of johnsongrass ( Sorghum halepense (L.) Pers.). Seeds of most ecotypes were highly dormant. Without low temperature pretreatment, best germination occurred with continuous fluorescent light, a KNO 3 substratum, and an alternating 20 to 35 C temperature regime. Pretreatment of the seeds for 2 weeks at 10 C, followed by a temperature shift to 40 C for 2 hr was effective in breaking seed dormancy. Germination of each of 12 ecotypes, from harvests in each of 2 years, was markedly similar. Interpretation of the evidence suggests that seed dormancy is largely imposed by the relative degree of mechanical restriction afforded by the seed coat.