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Cassava sexual reproduction is important for breeding improved cassava cultivars as it is the primary means for genetic recombination. Several challenges hinder successful cassava breeding, including: delay in flower initiation, abortion after successful initiation, low number of flowers produced per inflorescence, low proportion of flowers that are female, and poor fruit and seed set, especially in genotypes with traits of agronomic importance. In this dissertation, I focused on the challenge of flower initiation and low female flower numbers. To evaluate factors affecting flower initiation and genotype by environmental interactions, plants were grown under two Nigerian field environments (Ubiaja and Ibadan) and three controlled temperature conditions (22_C/18_C, 28/24_C and 34/30_C (day/night)). This study showed that the Ubiaja field and 22_C/18_C (day/night) environments were favorable for cassava flowering while the Ibadan field and warmer temperatures had a delaying effect. Early flowering genotypes tended to be environmentally insensitive while late genotypes were sensitive to the delaying effect of unfavorable environments. To elucidate methods by which flower numbers can be increased in the field, treatments with anti-ethylene growth regulator silver thiosulfate (STS) or pruning fork-type branches increased flower abundance without changing female to male ratios. Application of the synthetic cytokinin benzyladenine (BA) increased the percentage of female flowers to over 80%. The three-way treatment combination of pruning + STS + BA produced the largest number of female flowers, with STS and pruning working additively to increase total flower numbers and BA increasing the proportion of female flowers. Transcriptomic analysis of gene expression with RNA-seq showed that all conditions favoring cassava flowering (Ubiaja field, 22_C/18_C and pruning+STS+BA treatments) downregulated expression of flowering repressor gene TEMPRANILLO1. There were also complex changes to abscisic signaling genes under all conditions studied. The transcriptome of the pruning+STS+BA treatment additionally showed downregulated gibberellin signaling. Finally, analysis of vegetative growth and nighttime carbohydrate export from leaf showed that the flower enhancing effect of plant growth regulators did not modify photosynthate partitioning. Based on these recent findings and that of our Cornell-led project, the treatment strategy using pruning+STS+BA to enhance cassava female flower and fruit development offers the potential to enhance breeding productivity by many cassava breeding programs.

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183 pages


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Cassava flowering; Cool ambient temperature; Field transcriptome; Photosynthate partitioning; Plant growth regulators; TEMPRANILLO 1


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Union Local


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Setter, Tim

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Hua, Jian
Björkman, Thomas

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Soil and Crop Sciences

Degree Name

Ph. D., Soil and Crop Sciences

Degree Level

Doctor of Philosophy

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Government Document




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dissertation or thesis

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