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THE USE OF GRAFTING FOR IMPROVING SALINITY TOLERANCE IN TOMATO PLANTS
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Abdalla, Reham Mohamed
Doctor of Philosophy
Date of Defense:
December 07, 2016
Kathleen Brown, Dissertation Advisor
Michael Orzolek, Committee Chair
Kathleen Brown, Committee Member
Elsa Sánchez, Committee Member
Jack Watson, Outside Member
THE USE OF GRAFTING FOR IMPROVING SALINITY TOLERANCE IN TOMATO PLANTS Soil salinity is one of the major abiotic stresses causing yield reductions in agriculture worldwide. Grafting was proposed to improve tomato tolerance to salinity. The first experiment aimed at assessment of the survival rates and growth performance of tomato scion/rootstock combinations. Our results showed that ‘Arnold’, ‘Taurino’, and ‘Maxifort’ had the highest survival rates. Most self-grafted plants had lower survival rates than the hetero-grafts. Genotypes with excellent survival rates were selected for salinity screening. In the screening experiment, 21 wild and cultivated genotypes were treated with 0, 50, 100, 150 mM NaCl for 16 days. ‘Ironman’ was the most vigorous genotype. ‘LA3120’ was less vigorous than ‘Ironman’ under salinity but limited Na+ transport to the shoot, whereas ‘LA1630’ transported more Na+ to the shoot. Genotypes with high vigor and/or low shoot DW reduction under NaCl treatments were selected as potential rootstocks. In the grafting experiment, grafted plants were treated with 0 or 75 mM NaCl for 25 days. Under salinity, percent reduction of shoot DW ranged from ~-4% in Moneymaker/Resistar to ~40% in Moneymaker/Ironman. ‘Moneymaker’ /‘AR’ was the most vigorous combination. ‘Moneymaker’/‘LA1630’ had the highest leaf Na+ concentration, whereas ‘Moneymaker’/‘LA3120’ had the lowest leaf Na+ concentration. Rootstock had a key role in controlling the salt tolerance mechanism of the scion. In the sap experiment, Na+ and K+ concentrations were measured in the stem sap below and above the graft union. Plants were grown for 10 days under 75 mM NaCl treatment. Most grafted plants had lower sap Na+ concentrations than in non-grafts. In hetero-grafts, sap Na+ concentration was higher in the below- graft segment than in the above-graft segment. Self-grafts, had similar Na+ concentrations in the two positions. In all graft combinations, K+: Na+ ratio was higher in the above-graft segment than in the below graft segment. These studies show that the extent and mechanisms of salt tolerance vary among commercial tomato cultivars, and that grafting of compatible genotypes helps restrict Na+ movement to the shoot. Salt-tolerant rootstocks from this project can be used by farmers under saline conditions.
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