Agricultural production is at the mercy of uncertainties driven by climate change, as a result of this most of the major and minor crops are under threat of crop failure due to the severity of its effects on ‘crop fertility’. Plant reproduction is regarded as highly sensitive to such climatic changes, especially under high temperatures stress. Therefore, a key strategy to adapt to ever-increasing global temperature is by improvement and promotion of underutilised crops, one such future crop and the main focus of our research is bambara groundnut (Vigna subterranea [L] Verdc.). The present research was aimed at investigating the effect of temperature stress on plant reproduction, however, there is very limited data on how bambara groundnut genotypes differ in their response to temperature stress with respect to plant reproduction. Therefore, the focus of this research was a systematic study to establish firstly a guide to the reproductive development and, to quantify the impact of high temperature stress on floral development, pollination to fertilization and pod set in bambara groundnut. The main methodology applied to establish the first guide to bambara groundnut flower development and pollen formation was through advanced microscopy techniques (fluorescence and scanning electron microscopy [SCM]). Later, the effect of short duration high temperature stress surrounding flowering time (pre- and post-anthesis) in seven bambara groundnut genotypes (IITA-686, S19-3, AHM-753, Uniswa red, Getso, and DipC), was investigated by applying three days of high temperature stress (36/33°C, day/night) at 100% flowering, before the temperature was returned to control conditions (28/22°C) and maintained until pod harvest. Phenotypic characteristics such as flower morphology, pollen viability and pod set, between control and heat stressed groups, were some of the traits observed to assess the effect among the seven genotypes. RNA sequencing experiment was designed and executed to obtain differential gene expression data under high temperature stress, however breakdown of a freezer prevented the successful completion of the experiment. Firstly, a scale of bambara groundnut flower development was established based on flower size as a unit of measurement, from stage 8 to stage 13, which corresponds to floral organ differentiation and flower opening, respectively. Pollen architecture and development (micro-sporogenesis and micro-gametogenesis) was documented using fluorescence microscopy and SCM. And this study is the first one to link flower phenology to the stages of pollen development through morphological data. Secondly, the effect of short duration high temperature stress was evaluated, it showed that the effect on in vitro pollen germination was significant (p < 0.05) and was seen within 24 h of the application of the heat stress (HT-1) in all genotypes, and correspondingly pod set was significantly (p < 0.05) reduced during heat stress. The genotypes IITA-686, AHM-753 and S19-3 recovered, pollen viability relatively faster and produced pods when the plants were returned to control conditions after heat- stress, in contrast to Uniswa red and Getso, where pod set was severely affected. We could conclude that like most of the legumes bambara groundnut pollen is sensitive to high temperature stress, with temperatures 36/33°C producing significant effects on pollen viability, and also display acclimation capability, when returned to control conditions. We advocate that selection for breeding should start at male gamete level, through in vitro pollen germination to determine tolerant and sensitive genotypes, and the prospects of bambara groundnut pollen thermo-tolerance should be evaluated. Many research experts are considering bambara groundnut as a future crop based on its agro-ecological, cultural, genetic and nutritional importance. This research is one step in contributing to the knowledge of this future crop. This study serves as a guide for future researchers interested in flower development and variation in the process observed within and between bambara groundnut genotypes. Assessing pollen thermo-tolerance can give a direct indication of crop success/ seed yield under heat stress and the methodology is not limited to only temperature stress, that is it could also be adapted in photoperiod, drought and water stress. Investigation of other forms of stress tolerance could ultimately contribute to the development of future crop which could cope with future climatic anomalies.
| Identifer | oai:union.ndltd.org:bl.uk/oai:ethos.bl.uk:757380 |
| Date | January 2018 |
| Creators | Dhanaraj, Bhavya |
| Publisher | University of Nottingham |
| Source Sets | Ethos UK |
| Detected Language | English |
| Type | Electronic Thesis or Dissertation |
| Source | http://eprints.nottingham.ac.uk/49191/ |
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