Informations et ressources scientifiques
sur le développement des zones arides et semi-arides

Titre : Germination and stand establishment of pearl millet and sorghum of different seed qualities under field conditions in Botswana and controlled high-temperature environments

Auteur : Mortlock, Miranda Yolanda

Université de soutenance : Kansas State University

Grade : Doctor of Philosophy (PhD) 1988

Résumé
Larger and/or denser millet (Pennisetum glaucum (L.) R. Br.) and sorghum (Sorghum bicolor (L.) Moench.) seed has shown improved field establishment in Kansas. Soil temperatures are high in the semi-arid tropics and thus studies of seed quality under controlled supraoptimal temperatures and in the field were conducted. Seed quality effects on germination of Senegal Bulk pearl millet and ’Segaolane’ sorghum were examined on a thermogradient plate. Timing and duration of a 40 to 45 C stress on early germination were studied. Early millet establishment was determined at three constant high temperatures in a growth chamber and under two regimes of diurnal fluctuating temperatures. Dryland planting on four dates, two late-planted, irrigated trials and a dry/wet planting trial examined establishment and yield in Botswana. Soil temperatures at 2, 5 and 10 cm depths were recorded. Large ($>$2.6 mm diameter), dense ($>$1.26 g cm$\sp-3$ density), and bold (large and dense) ’Serere 6A’ millet seed was tested. Control seed was unseparated. For comparison with seed separated for density by flotation, a washed control was included. Bold millet and dense sorghum ($>$1.29 g cm$\sp-3$) were compared with control seed on 11 farmer fields using traditional planting methods. Under controlled constant temperature environments a seed size by temperature by time interaction occurred for germination of both crops. Medium sized millet seed showed higher germination over a wider constant temperature range than other seed sizes. With 1 or 2 h of high temperature stress, dense and large sorghum seed had higher radicle emergence at 24 h ; however, there were no differences between seed sizes and densities at 4 or 8 h duration of stress. As millet seed size increased, plumule length (at 48 h) decreased. At constant 43 C, dense millet seeds had higher emergence than light seed. Seedlings were taller from larger or denser seed. Under high diurnal soil temperatures large seeds had lower emergence but higher dry weights than small seed. In Botswana, bold millet or dense sorghum seed did not significantly improve establishment in on-farm trials. In broadcast plots 10.6% of viable millet seed and 18.4% of viable sorghum seed emerged. Under these severe conditions, seed quality effects were not great enough to be of value in improving traditional stand establishment.

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