Many of the economically important rice cultivars including ‘Khao Dawk Mali 105’ (KDML105) or jasmine rice, one of the world’s famous rice exported from Thailand suffers from drought due to erratic rainfalls and limited irrigation. To improve drought tolerance and reserve genetic background of KDML105, chromosome segment substitution lines (CSSL) containing drought tolerant quantitative trait loci (DT-QTL) has been previously developed by backcrossing between KDML105 and drought tolerant donor, IR58586-F2-CA-143 (DH212). To understand the physiological responses related to drought tolerance in CSSL lines compared to parents, two CSSLs namely CSSL1-16 and CSSL1-18, respectively were used in this study. Twenty-one-d-old hydroponically grown plants were subjected to 20% PEG for 0, 7, 14 d and then recovered from stress for 3 d. The results indicated that CSSL lines especially, CSSL1-16 showed better performance under drought stress compared to their recurrent parent. Drought tolerance superior CSSL1-16 line was indicated by high water status (high relative water content and leaf water potential), good osmotic adjustment, high proline and greater membrane stability. Moreover, this line was able to resume growth after stress recovery whereas other lines/cultivar could not recover. Similarly, drought tolerant donor showed high water status suggesting that well-maintained plant water status was associated with drought tolerant trait. It could be concluded that the highest drought tolerant line was CSSL1-16 followed by DH212, CSSL1-18 and KDML105. It would be interesting to go further into introgressed section in CSSL1-16 to identify potential candidate genes in DT-QTL for breeding drought tolerant rice in the future.
Silicon (Si) is considered a beneficial element for rice (Oryza sativa L.) The objective of this work was to investigate the effects of Si in the form of nanoparticles on growth and physiology of rice under salt stress. Silica nanoparticles (SNPs) were synthesized from rice husk by sol-gel method. The prepared SNPs powders were agglomerated in semi-spherical nanosized particles with diameters in the range of 60-135 nm. Three rice cultivars namely 'Pokkali', 'KDML105' and 'IR29' were grown for 30 d in plastic pots, and then divided into four groups i.e., control, SNPs, NaCl and NaCl + SNPs. Foliar spray of 120 mg L -1 SNPs was given to the SNPs and NaCl + SNPs groups for 4 d. After that the plants in NaCl and NaCl + SNPs groups were exposed to 150 mM NaCl for 17 d. The salt-stressed plants suffered significant reductions in biomass, net photosynthesis rate (PN), and maximal quantum efficiency of photosystem II (PSII) photochemistry (Fv/Fm) while three stress indicators (malondialdehyde, hydrogen peroxide [H2O2] and proline) considerably increased. The SNPs mitigated the adverse effects of salt stress by increasing PN (18% to 116% increase) and lowering H2O2 (8% to 31% reduction) in all cultivars, compared with the values under salt stress, while proline was reduced by 7% in 'KDML105' and 19% in 'IR29'. The H2O2 content was regulated by the increased activities of antioxidant enzymes, notably catalase, peroxidase and ascorbate peroxidase. The application method and concentrations of SNPs used for rice plants under stress should be further optimized for the highest benefit of growth and yield in the field conditions.
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