Salazar Licea, Luis Carlos
(2022)
Understanding the genetic and physiological basis of drought resistance in Bambara groundnut (Vigna subterranea (L.) Verdc).
PhD thesis, University of Nottingham.
Abstract
Bambara groundnut (Vigna subterranea (L) Verdc) is an underutilised African legume commonly known for its resistance to harsh environmental conditions such as drought, and equally known for its high protein content, and thus, having the potential to aid in the pursuit of food security as the climate is constantly changing. As an underutilised crop, Bambara groundnut has been relatively poorly researched in comparison to other more conventional crops such as maize, wheat, soybean, or rice.
To help Bambara groundnut farmers and breeding programs achieve the development of varieties with better agronomical potential, a better understanding of the physiological and genetic mechanisms, in relationship to drought resistance, is needed.
A series of experiments under controlled glasshouse conditions were conducted in order to gain a better understanding of the responses of Bambara groundnut to drought. Drought is defined as when the level of water content in the soil is below a healthy threshold for plants to continue normal physiological and biochemical processes. A selection of genotypes was assessed over a period of three years, in 10 L pots, and an Association Genetics Panel was assessed over one season in 5 L pots. Additionally, the transcriptome of a sub-set of 4 genotypes was studied through RNA-sequence, and a genome wide association study was conducted over the association genetics panel.
A combination of these approaches allowed to have a better understanding on a series of physiological mechanisms where two main approaches were detected, such as, drought tolerance and drought avoidance.
For drought tolerance, several genotypes, such as DodR, S19-3, and TN, showed a higher conservation of their canopy, their efficiency of the photosystem II, relative water content in leaves, and a warmer canopy under drought conditions. Additionally, genes related to several osmo-protectant compounds, and cuticular waxes were differently expressed in response to drought.
For drought avoidance, several genotypes, such as UnisR, Kano2, Kano3, and Gresik, showed a faster and higher rate of leaf senescence, lower efficiency of the photosystem II, lower percentage of relative water content in leaves, and a cooler canopy temperature. However, the recovery rate when irrigation was re-introduced, was significantly higher than the drought tolerant genotypes. Additionally, in the case of Gresik, genes related to stomatal conductance were differently expressed in response to drought.
These findings will help stepping forward in the Bambara groundnut research by narrowing research objectives in future efforts through a selection of specific physiological traits and genes, and subsequent adaptation into breeding programs by marker assistant selection, or gene editing.
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