Abstract
Cassava (Manihot esculenta), a major food staple in the tropics and subtropics, thrives even in environments undergoing threatening climate change. To satisfy the increasing demand for crop improvement and overcome the limitations of conventional breeding, the introduction of inbreeding techniques such as the production of doubled haploid lines via androgenesis or gynogenesis offers advantages. However, comprehensive studies on cassava flower bud biology or structural development are lacking and precise structural and biological information is a prerequisite to enhance the efficiency of these techniques. The floral biology of three selected cassava lines was studied, focusing on morphology, phenology and pollen biology (quantity, viability and dimorphism). Histological studies were also conducted on microsporogenesis/microgametogenesis and megasporogenesis/megagameto-genesis to generate precise developmental data for these lines. Male and female cyathia have distinct developmental phases. Pollen viability was high during immature stages of plant development; however, pollen mortality was common at later stages. Pollen trimorphism in male gametophytes towards the larger or smaller pollen size, as compared with normal size, was observed. Ten characteristic events were identified in male gametogenesis and six in female gametogenesis that were correlated with flower bud diameter. Male gametophyte diameter at different developmental stages was also determined. Results indicate that the three lines did not differ significantly, except regarding a few morphological aspects such as plant height, flower colour and number of male cyathia. Pollen grains were initially viable, but viability decreased drastically at later stages of growth. Abnormal meiosis or mitosis triggered pollen trimorphism. The demonstrated sequential events of reproductive development generated valuable information at the cellular level, which will help close the current information gap for cassava improvement via breeding programmes and doubled haploid plant production.
Highlights
Cassava (Manihot esculenta), known as tapioca, manioc, mandioca and yuca, is one of the most important root crops cultivated in the tropics and subtropics around the world (Raji et al 2009)
Histological studies were conducted on microsporogenesis/microgametogenesis and megasporogenesis/megagametogenesis to generate precise developmental data for these lines
Ten characteristic events were identified in male gametogenesis and six in female gametogenesis that were correlated with flower bud diameter
Summary
Cassava (Manihot esculenta), known as tapioca, manioc, mandioca and yuca, is one of the most important root crops cultivated in the tropics and subtropics around the world (Raji et al 2009). It belongs to order Malpighiales and family Euphorbiaceae, and its relatives in the Euphorbiaceae family include commercially important plants such as rubber tree (Hevea brasiliensis), castor oil plant (Ricinus comunis) and ornamental plants such as Euphorbia spp. Cassava is a food staple for .800 million people in South America, the Caribbean, Africa and Asia It ranks fourth as the source of human energy (Alves 2001), especially in Africa (Groll et al 2001).
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