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, 12 (4), e0175361
eCollection

Identification and Validation of QTLs for Seedling Salinity Tolerance in Introgression Lines of a Salt Tolerant Rice Landrace 'Pokkali'

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Identification and Validation of QTLs for Seedling Salinity Tolerance in Introgression Lines of a Salt Tolerant Rice Landrace 'Pokkali'

Teresa B De Leon et al. PLoS One.

Abstract

Salinity is a major threat to rice production worldwide. Several studies have been conducted to elucidate the molecular basis of salinity tolerance in rice. However, the genetic information such as quantitative trait loci (QTLs) and molecular markers, emanating from these studies, were rarely exploited for marker-assisted breeding. To better understand salinity tolerance and to validate previously reported QTLs at seedling stage, a set of introgression lines (ILs) of a salt tolerant donor line 'Pokkali' developed in a susceptible high yielding rice cultivar 'Bengal' background was evaluated for several morphological and physiological traits under salt stress. Both SSR and genotyping-by-sequencing (GBS) derived SNP markers were utilized to characterize the ILs and identify QTLs for traits related to salinity tolerance. A total of eighteen and thirty-two QTLs were detected using SSR and SNP markers, respectively. At least fourteen QTLs detected in the RIL population developed from the same cross were validated in IL population. Analysis of phenotypic responses, genomic composition, and QTLs present in the tolerant ILs suggested that the mechanisms of tolerance could be Na+ dilution in leaves, vacuolar Na+ compartmentation, and possibly synthesis of compatible solutes. Our results emphasize the use of salt injury score (SIS) QTLs in marker-assisted breeding to improve salinity tolerance. The tolerant lines identified in this study will serve as improved breeding materials for transferring salinity tolerance without the undesirable traits of Pokkali. Additionally, the lines will be useful for fine mapping and map-based cloning of genes responsible for salinity tolerance.

Conflict of interest statement

Competing Interests: The authors have declared that no competing interests exist.

Figures

Fig 1
Fig 1. Graphical genotypes of 72 introgression lines developed from Bengal x Pokkali cross.
Each row denotes a line selected for a chromosomal segment. Blue and white segments represent Bengal and Pokkali segments, respectively. Lines were genotyped using 107 SSR markers.
Fig 2
Fig 2
Frequency distribution of introgressed Pokkali segments (segment length and % donor genome) in the selected introgression lines using SSR (A) and SNP (B) markers.
Fig 3
Fig 3. Comparison of salinity-tolerance QTLs detected in Pokkali introgression lines by single marker analysis (SMA) and stepwise regression-based likelihood ratio test (LRT).
(A) Numbers of QTLs detected by SSR markers. (B) Number of QTLs detected by SNP markers. (C) Common QTL identified by SSR and SNP markers.

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Grant support

This research was supported by the National Institute of Food and Agriculture, U.S. Department of Agriculture (Grant No. 2013-67013-21238) and the Louisiana Rice Research Board. The funders had no role in study design, data collection and analysis, decision to publish, or preparation of the manuscript.
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