Seed dormancy in sorghum

Abstract

Seed dormancy in sorghum varieties and hybrids was investigated during the three years from 1963 through 1965. These investigations were conducted at Texas A&M University, College Station, Texas. Seeds of the following varieties and hybrids were used: Martin (B398), Feterita (Tx09), Kafir (A3197 and B3197), Shallu and hybrids of A3197 x Shallu. On the basis of the results obtained from these investigations, four mechanisms were proposed to be functioning in dormancy. The first mechanism was associated with loss of initial seed moisture and functioned until the initial seed moisture was reduced to approximately 28% or less. This mechanism apparently functioned in seeds of all the varieties and hybrids investigated, and it was the only mechanism that functioned in seeds of Tx09. The second mechanism was associated with completion or cessation of active growth and functioned until maximum dry weight of the seeds was attained. This mechanism functioned in seeds of all the varieties and hybrids except Tx09. The third mechanism functioned in seeds which had attained maximum dry weight and in which the moisture content was less than 28%. This mechanism was affected by the rate of seed development. Dormancy was either more pronounced or more persistent in seeds which developed more rapidly. The third mechanism functioned in the pericarp and was active in seeds of all the varieties and hybrids except Tx09, A3197, and B3197. The fourth mechanism also functioned in seeds which had attained maximum dry weight and in which the moisture content was less than 28%. This mechanism was associated with the presence of a brown, cellular testa and a brown pericarp in the hybrid seeds, and functioned only in the brown, hybrid seeds. Dormancy resulting from the third and fourth mechanisms persisted as long as seven months in seeds stored at 2 to 4 C but only for one to two three months in seeds stored at 22 to 25 C. moisture inhibition was not restricted in dormant seeds of Shallu and F₂ hybrid seeds. An unidentified, water soluble growth inhibitor was present in the F₂ hybrid seeds. This inhibitor did not prevent germination but inhibited seedling growth after the radicle emerged. The inhibitor was presumed to be in the pericarp and testa.