Inheritance mode of seed dormancy in the hybrid progeny of sesame, Sesamum indicum, and its wild relative, Sesamum mulayanum Nair

Sesamum mulayanum is a wild relative of cultivated sesame, Sesamum indicum, and sometimes grows in sesame crop fields as an associated weed. This species shows deep seed dormancy and is characterized by conspicuous purple pigmentation on the lower lip of the corolla. The present study examined the inheritance mode of seed dormancy by using reciprocal progeny from crosses between the two species. The seeds of S.indicum and F₁ (S.indicum×S.mulayanum) showed good germination, but those of S.mulayanum and F₁ (S.mulayanum×S.indicum) showed deep dormancy. The F₂ seeds from both reciprocal crosses showed deep dormancy. These results, combined with the maternal inheritance of seed-coat characteristics, indicated that the seed dormancy of S.mulayanum can be attributed to its seed-coat structure (coat-enhanced dormancy). The F₃ (S.indicum×S.mulayanum) seeds varied in their depth of seed dormancy and those seeds with deep dormancy (<50% germination) and those with no or shallow dormancy (≥50% germination) occurred in the expected ratio of 3:1, indicating that this trait is polygenic but is controlled by a single dominant major gene. The purple pigmentation of the corolla was expressed in both reciprocal F₁ plants and the presence and absence of pigmentation was segregated among the F₂ plants at the expected ratio of 3:1, indicating that this trait is also controlled by a single dominant gene. The segregation of the major gene controlling seed dormancy and that controlling purple pigmentation was not independent (9:3:3:1), indicating that these genes are linked, providing insights on sesame domestication.