Lethal symptoms observed in hybrid seedlings from crosses between N. occidentalis and N. tabacum progenitors.
(A–C) Hybrid seedlings from the cross N. occidentalis ♀×N. sylvestris ♂ at 24°C. The seedlings showed apparently normal growth at 3 days after germination (DAG) (A). The hypocotyl turned brown at 18 DAG (B), and the seedlings turned completely brown and died at 61 DAG (C). (D–F) Hybrid seedlings from the cross N. occidentalis ♀×N. tomentosiformis ♂ at 24°C. Although the seedlings exhibited apparently normal growth, root growth nearly stopped at 2 DAG (D), and the color of cotyledons and hypocotyl faded at 5 DAG (E). The seedlings turned completely brown and died at 16 DAG (F). (G–I) N. sylvestris grown at 24°C. N. sylvestris grew normally and did not show lethal symptoms at 3 (G), 10 (H), or 30 DAG (I). (J–L) N. tomentosiformis grown at 24°C. N. tomentosiformis also grew normally and did not display any lethal symptoms at 3 (J), 10 (K), or 30 DAG (L). Scale bars = 1 mm.