- Title
- Genetics, physiology, proteomics of quality protein maize inbred lines under drought and heat stress
- Creator
- Pfunde, Cleopatra Nyaradzo
- Subject
- Corn Drought-tolerant plants Proteomics
- Date
- 2016
- Type
- Thesis
- Type
- Masters/Doctoral
- Type
- Crop Science
- Identifier
- http://hdl.handle.net/10353/11696
- Identifier
- vital:39098
- Description
- When plants perceive heat stress alone or in combination with drought, they activate several responses to synchronize development and molecular activities to ensure survival. In this study, a multidiscipline approach was adopted to investigate the plant genetics, proteomics and physiology for understanding the mechanisms underlying the adaptive response to combined drought and heat stress. The quality protein maize (QPM) inbred lines used had varied degrees of tolerance to both heat stress alone and in combination with drought. The overall objective of this study was to identify drought and heat tolerant germplasm that combine well under drought and heat stress for use in breeding programs to develop new QPM varieties. Initially, the genetic diversity among available inbred lines was estimated using two molecular markers, simple sequence repeats (SSRs) and single nucleotide polymorphisms (SNPs). The results indicated that moderate diversity exists among the QPM inbred lines which can be exploited to generate high performing hybrids. Cross combinations between QS26 and CIM2 and those between QS6 and CIM14 were selected as crosses likely to give substantial heterosis in the field because of the high genetic distances that were found between them using SNPs. Screening of inbred lines for drought and heat tolerance was done at the early germination and seedling stages. Differences in heat tolerance at both stages of growth were observed. Heat tolerant inbred lines at early germination stage had longer coleoptiles and radicles after recovery. The following inbred lines exhibited acquired thermo-tolerance, QS6, CIM7, QS17 and QS19, while CIM12, QS1, CIM21 and QS32 showed basal thermo-tolerance. At the early seedling stage inbred lines with significant differences (P< 0.001) in morpho-physiological traits were noted under heat stress alone and under combined drought and heat stress. However, no significant differences were noted for morpho-physiological measurements in the control treatment. Electron transport rate, sub-stomatal CO2, and stomatal conductance were significantly (P<0.001) reduced in response to combined drought and heat stress. Thus, drought coupled with heat stress resulted in stomatal closure, decreased photosynthetic rate, enhanced respiration and increased leaf temperature for susceptible inbred lines. The combined effects of drought and heat stress were more deleterious than the individual effect of heat stress alone as indicated by the reduction in dry weight. Based on the physiological parameters, biomass and tolerance indices, inbred lines QS22, CIM18 and QS6 showed tolerance to combined drought and heat stress, while CIM18, QS14 and QS30 exhibited thermo-tolerance. Inbred line CIM18 showed cross tolerance to combined drought and heat stress, and to heat stress alone. Further investigations into the comparative proteomic analysis of CIM18 (tolerant) with QS21 (susceptible) under combined drought and heat stress at seedling stage revealed that photosynthetic and stress related proteins were upregulated in CIM18. In addition, the abundance of heat shock proteins such as HSP70 and sHSP 17.8 kDa meant that CIM18 was better able to maintain cellular homeostasis and metabolism. The presence of metabolism related proteins meant that the energy needs of photosynthesis and other activities were met under drought and heat stress. Anti-oxidant enzymes such as glutathione s transferase were responsible for detoxification of reactive oxygen species induced by oxidative stress. These proteins mediated tolerance to combined stress in CIM18. The proteins that were micro-sequenced have previously been identified in individual drought and heat stress studies. The expression of these proteins under combined stress indicated that mechanisms from both stresses were pooled to confer tolerance in CIM18. Accordingly, the study proposes that CIM18 is a drought and heat tolerant QPM inbred line and is recommended for inclusion in breeding programs aimed at the development of drought and heat tolerant varieties. QPM has the potential to improve human nutrition in several rural households. The combining ability analysis of inbred lines revealed that GCA effects under combined drought and heat stress were significant for ears per plant, chlorophyll content, canopy temperature, anthesis silking interval, days to 50percent silking and ear length. Specific combining ability effects were significant for grain yield, days to 50percent anthesis, chlorophyll content and senescence. The study revealed that non-additive gene action was more important in determining grain yield under combined drought and heat stress. Inbred lines L2, L3, L7 and L3, L7 and L11 were good sources of genes for high grain yield under well-watered and combined drought and heat stress respectively. Cross combinations L3 x L13 (3.05 t/ha) and L5 x L9 (2.95 t/ha) were the best performing single cross hybrids for grain yield while cross combination L2 x L10 (1.33t/ha) was the least performing hybrid under combined stress conditions. Under well-watered conditions, the highest yielding crosses were between L2 x L13 (6.51t/ha) and L2 x L8 (6.46 t/ha). The inbred lines identified as sources of drought and heat tolerance and the high yielding cross combinations maybe useful for improving tolerance by generating hybrids or synthetic QPM maize varieties. The inbred lines which exhibited tolerance to both drought and heat stress were genetically diverse and were able to maintain photosynthesis and hence growth during stressful conditions. The ability of these genotypes to accumulate biomass or produce yield under stressful conditions highlights underlying mechanisms which need to be further exploited. While partial proteomic work was done in this study, a more comprehensive study looking into greater depth at the genes responsible for these mechanisms is paramount to fully utilize and/or transfer these genes to other desirable genotypes.
- Format
- 235 leaves
- Format
- Publisher
- University of Fort Hare
- Publisher
- Faculty of Science and Agriculture
- Language
- English
- Rights
- University of Fort Hare
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