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Title: Investigating salt stress resilience in Brassica oleracea
Author: Lawal, Almustapha
ISNI:       0000 0004 7972 4473
Awarding Body: University of Warwick
Current Institution: University of Warwick
Date of Award: 2019
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Soil salinity remains a global problem that affects approximately 20% of irrigated land and reduces plants growth and crop yields. Many of the Brassica oleracea species are important horticultural crops. The work aims to study variation in B. oleracea genotypes in response to salt stress and involves the use of cultivated B. oleracea DHSL150, wild B. oleracea lines and doubled haploid (DH) lines derived from them. Plants were exposed to salt stress through salt-shock using 250 mM NaCl at week-six of their growth. Morphological traits were measured including; plant height, plant fresh/dry weights, leaf fresh/dry weights and leaf area. Na+, K+ and Ca2+ were measured by using inductively coupled plasma mass spectrometry (ICP-MS) from leaf mineral. The results indicate significant variation between the lines, for example growth reduction of -11.74% to - 14.96% was observed in the parent lines and, -1.84% to -11.24% in the DH lines compared against the untreated control. Plant fresh and dry weights exhibited a reduction between -32.92% to -2.15% in the wild S1parent lines and -20.14% in the parent DHSL150 line while their DH lines reduced by -28.52% to -12.42 %. Leaf morphology affects the leaf area, which showed a significant reduction in DHSL150 and four other wild S1 parent lines (p < 0.05) as compared to the untreated control. The leaf area of some DH lines showed no difference compared to the control, however others exhibited a significant reduction (p < 0.05). Analysis of mineral content within leaves revealed significant variation between the B. oleracea genotypes 24 hr post-exposure to salt treatment. The leaf Na+ level showed a significant increase in all the genotypes while K+ and Ca2+ level showed a non-significant reduction 24 hr post-treatment. Two-weeks posttreatment, K+ level were affected. It dropped significantly in some lines especially in DHSL150 thereby affecting K+/Na+ ratio. A significant K+/Na+ xx ratio increase was observed in some wild S1 accessions and DH lines, which indicates resilience to salt stress. A successful strategy for salt tolerance relies on the maintenance of a high K+/Na+ ratio through a mediated active/passive transport systems carried out by ion membrane transporters/channels. The relative gene expression of some selected ion membrane transporters using qPCR was carried out. Relative gene expression of Na+/H+ antiporter (NHX1), and potassium transporters (KT9 & KUP11) increased between treated and the control with B. oleracea wild S1 and DH lines both showing improved K+/Na+ twoweeks post-treatment. Other transporters such as vacuolar H+ adenosine triphosphatase (VATPase -G), and chloride gated channel (V-CLC) also showed increased expression with respect to the untreated control. Variation due to the effects of allelic variants was investigated using genotype-by-sequencing (GBS). A significant variation at different chromosome positions corresponding to the introgressed regions in the DH lines was observed between parent lines. These finding could be significant for plant breeding and development of enhanced varieties of brassica vegetables with salt resilience.
Supervisor: Not available Sponsor: Tertiary Education Trust Fund (Nigeria)
Qualification Name: Thesis (Ph.D.) Qualification Level: Doctoral
EThOS ID:  DOI: Not available
Keywords: QK Botany ; SB Plant culture