Germination ecology of Cassava (Manihot esculenta Crantz, Euphorbiaceae) in traditional agroecosystems: Seed and seedling biology of a vegetatively propagated domesticated plant

Cassava is clonally propagated, but Amerindian farmers also use plants from volunteer seedlings to prepare stem cuttings. Although sexual reproduction plays a role in cassava’s evolution it is poorly studied. We examined one aspect of cassava reproductive ecology, seed dormancy and germination. Volunteer seedlings emerge from a soil bank of seeds produced during the previous cycle of cultivation that remain ungerminated through the fallow period, then germinate synchronously after vegetation is slashed and burned. Laboratory experiments showed that germination can be enhanced by mechanical scarification and also by dry heat treatment, suggesting that burning after field clearing could help break dormancy. Germination was also stimulated by high temperatures (35°C) that in nature indicate bare soils, and inhibited by temperatures (25°C) close to those in soil shaded by vegetation and by light. Seeds of both wild and domesticated cassava exhibit physiological dormancy, an adaptation for germination in periodically disturbed habitats. In addition to these preadaptations, preliminary results also suggest specific adaptations of domesticated cassava to the distinctive disturbance regimes of swidden agriculture.