Effects of Temperature and dl-Strigol on Seed Conditioning and Germination of Witchweed (Striga asiatica)1

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Abstract
Seed conditioning and germination in witchweed (Striga asiatica (L.) Kuntze) were temperature-dependent. With higher conditioning temperatures, shorter conditioning time was required for germination with terminal dl-strigol (strigol) treatment at 30 °C. Maximum germination (80–100%) was obtained by conditioning in water at 20, 25, 30 and 35 °C for 14, 7, 5 and 3 d, respectively, and terminally treating with 10−6 M strigol at 30 °C. Seeds conditioned in 10−8 M strigol instead of water germinated much less with the same terminal strigol treatment. Generally, conditioning was slower when seeds were conditioned in strigol rather than water. The reduction in germination rate by pretreatment in strigol or pretreatment at low temperatures could be overcome by increasing the terminal strigol concentration in the germination test. Conditioned seeds did not germinate at 10 and 15 °C with a terminal 10−6 M strigol treatment but yielded close to maximum germination at 25, 30 and 35 °C with the same terminal strigol treatment. To obtain maximum germination, both the minimum conditioning temperature and the minimum germination temperature for conditioned seeds were 20 °C. Factors such as conditioning time, and strigol concentration and temperature during conditioning and/or germination determine whether seeds remain in the conditioning phase or shift to a germination phase.