Reproductive biology of cassava landraces

Abstract

The knowledge of the reproductive biology of cassava (Manihot esculenta) is essential for the development of genetic improvement programs and understanding the domestication process. This study evaluates aspects of sexual reproduction, such as floral morphology, pollination ecology, production and viability of pollen grains, apomixis, seed production and seed germination of cassava landraces collected in gardens of "caboclos" and Indians of the Amazon region and São Paulo State, both in Brazil. The aspects of the reproductive biology were studied from field evaluations and collection of flower buds and seeds. The experiments were carried out in Piracicaba, SP. Alteration was verified in the floral morphology of the landrace DG-55, which showed hermaphrodite flowers, and DG-65 and variety Mantiqueira, which presented smaller number of ovules per ovary. Honeybee (Apis mellifera) was the main pollinator of cassava. There was significant variation in the number and viability of pollen grains. The superior anters of the masculine flower presented, significantly, large number of pollen grains. Apomixis was not detected. A larger number of fruits with two or three seeds were detected. However, seeds originating from fruits with a single seed presented higher germination rates. The morphological alterations in the floral structure influenced the seed production and viability. The variation observed in the aspects of the reproductive biology, was probably due to differentiated selective pressure to which the landraces were submitted along the domestication process.