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Abstract
Salinity critically limits rice metabolism, growth, and productivity worldwide. Improvement of the salt resistance of locally grown high-yielding cultivars is a slow process. The objective of this study was to develop a new salt-tolerant rice germplasm using speed-breeding. Here, we precisely introgressed the hst1 gene, transferring salinity tolerance from “Kaijin” into high-yielding “Yukinko-mai” (WT) rice through single nucleotide polymorphism (SNP) marker-assisted selection. Using a biotron speed-breeding technique, we developed a BC3F3 population, named “YNU31-2-4”, in six generations and 17 months. High-resolution genotyping by whole-genome sequencing revealed that the BC3F2 genome had 93.5% similarity to the WT and fixed only 2.7% of donor parent alleles. Functional annotation of BC3F2 variants along with field assessment data indicated that “YNU31-2-4” plants carrying the hst1 gene had similar agronomic traits to the WT under normal growth condition. “YNU31-2-4” seedlings subjected to salt stress (125 mM NaCl) had a significantly higher survival rate and increased shoot and root biomasses than the WT. At the tissue level, quantitative and electron probe microanalyzer studies indicated that “YNU31-2-4” seedlings avoided Na+ accumulation in shoots under salt stress. The “YNU31-2-4” plants showed an improved phenotype with significantly higher net CO2 assimilation and lower yield decline than WT under salt stress at the reproductive stage. “YNU31-2-4” is a potential candidate for a new rice cultivar that is highly tolerant to salt stress at the seedling and reproductive stages, and which might maintain yields under a changing global climate.
Highlights
Projected climate change will aggravate a variety of abiotic stresses of rice plants, including salinity, heat, drought, and submergence, reducing world rice production [1,2,3,4]
We examined important physiological and biochemical parameters of the BC3F3 generation that confer salt tolerance and evaluated the phenotype under salt stress and normal field conditions
We introgressed the salt-tolerance hst1 gene from “Kaijin” into the genetic background of the high-yielding “Yukinko-mai” by three backcrosses followed by two rounds of self-fertilization (Figure 1A)
Summary
Projected climate change will aggravate a variety of abiotic stresses of rice plants, including salinity, heat, drought, and submergence, reducing world rice production [1,2,3,4]. We must increase global rice production by at least 70% to feed the anticipated 9.6 × 109 people by 2050 [5,6] Under these conditions, the improvement of the salinity tolerance of locally grown high-yielding rice cultivars is one of the most promising breeding objectives by which to meet global food demand. The Saltol [18,19] and SHOOT K+ CONCENTRATION 1 [20,21] genes have been identified from major quantitative trait loci (QTLs) of salt-tolerant landraces Pakkali and Nona Bokra, respectively These QTLs have been introgressed into some widely grown, high-yielding rice cultivars to improve salt tolerance [22,23,24,25,26], but the rate of improvement is slow
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