OPTIMIZING SILVER THIOSULFATE APPLICATIONS ON CASSAVA TO BLOCK ETHYLENE EFFECTS AND IMPROVE FLOWER RETENTION FOR BREEDING PURPOSES
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Cassava is the fourth largest staple crop in the world, and it serves as a main carbon source for
human nutrition in Africa, South America, and Southeast Asia. However, its poor flower set and lack
of flowering synchrony makes it hard to breed improved genotypes with higher production and
superior qualities. Previous findings indicated that applying silver thiosulfate (STS) could improve
cassava flower retention and might be useful in cassava breeding. However, at the rates used it might
induce severe phytotoxicity on the plants, and there is concern silver may accumulate in the soil. The
goal of this research was to find better strategies to apply STS and reduce plant phytotoxicity.
Experiments with ethephon showed that ethylene was responsible for cassava flower abortion and
senescence. STS inhibited ethylene signaling thus protecting the flowers from abortion and
senescence. Compared to wide-scale spraying of STS to mature leaves, localized STS application to
the apex was equally effective for flower retention, and it requires less silver. To develop an optimal
protocol, tests were conducted to find 1) the best timing for STS applications; 2) the number of
applications required for better flowering; 3) the best placement for STS application; and 4) the best
concentration for STS application on cassava. Overall, the findings indicate that optimal STS
treatment is when it starts at least several days before bud appearance, and with a continued supply
during flowering. STS application to the young leaves in the apex avoids excess application and
phytotoxicity. STS dosage requires optimization: it needs to be sufficiently high for substantial
flowering benefit, and low enough to avoid phytotoxicity. These findings indicate that STS could
serve as a potentially valuable tool for cassava breeders in managing flowering
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2017-05-30
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Agriculture; Agronomy; Plant sciences
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Committee Chair
Setter, Tim
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Miller, William
Degree Discipline
Soil and Crop Sciences
Degree Name
M.S., Soil and Crop Sciences
Degree Level
Master of Science
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Government Document
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dissertation or thesis