GENETIC DISSECTION OF SEEDLING AND REPRODUCTIVE STAGE SALINITY TOLERANCE IN RICE USING SALT TOLERANT CULTIVAR MTU 1061
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Date
2022-08-11
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guntur
Abstract
The present investigation was undertaken with an aim to identify salinity tolerance lines in F2 population through phenotyping (seedling and reproductive stages) and genotyping (detect presence of salt tolerance QTLs).
The present study entitled “Genetic Dissection of Seedling and Reproductive Stage Salinity Tolerance in Rice Using Salt Tolerant Cultivar MTU 1061” was conducted at Regional Agricultural Research Station, Maruteru, with main objective of development and genotyping of mapping population (234 F2 lines) to identify the chromosomal regions relating to seedling and reproductive stage salinity tolerance and phenotyping of the 234 F2:3 progenies for seedling and reproductive stage salinity tolerance.
234 F2:3 lines derived from a cross between a high yielding salt susceptible rice cultivar Sri Druthi (MTU 1121) and salt tolerant variety Indra (MTU 1061) were evaluated for salt tolerance at both stages namely seedling and reproductive stages using hydroponics and pot culture experiment respectively under salinity stress (EC @ 6 and 12 dSm-1). Data on seven seedling salinity tolerance traits viz., salt injury score (SIS), shoot Na+ concentration, shoot K+ concentration, Na/K ratio, shoot length (cm), root length (cm), shoot dry weight (g) and eight yield contributing traits viz., plant height at maturity, days to flowering, panicle length, number of filled grains per panicle, number of total grains per panicle, spikelet fertility, grain yield/plant and productive tillers per plant were recorded.
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A set of 234 F2:3 lines were evaluated for salt tolerance at seedling stage in a hydroponics experiment taken up during Rabi 2018-19 and Kharif 2019. The F2:3 population and parents showed a wide range of variation for different morpho-physiological traits in response to salt stress. Based on modified standard evaluation score (1-9) for visual salt injury at seedling stage, one line was highly tolerant, forty were tolerant, one hundred fifteen were moderately tolerant, seventy-one were susceptible and the rest seven were highly susceptible. Whereas, donor parent MTU 1061 showed tolerant (score of 3) and recipient parent MTU 1121 showed susceptible reaction (score of 9). In F2:3, shoot Na+ concentration, shoot K+ concentration, Na/K ratio, shoot length (cm), root length (cm) and shoot dry weight (g) ranged from 11.39 ppm to 40 ppm, 4.52 ppm to 17.94 ppm, 1.50 to 5.00, 6.58 cm to 30.59 cm, 6.42 cm to 19.00 cm and 0.07 g to 2.31 g, respectively. In this study, at seedling stage the F2:3 lines had high Na+ and high K+ concentration in the shoot suggesting that homeostasis between Na+ and K+ plays a key role in the seedling stage tolerance to salt stress.
Screening of 234 F2:3 lines at reproductive stage was taken up during Rabi 2019-20 using pot culture experiment. Parents and the F2:3 population showed a high variation for different evaluated yield traits in response to salt stress (EC @ 12 dS/m). Grain yield per plant is the best indicative score for tolerance at reproductive stage. Out of the 234 F2:3 lines, five were highly tolerant (grain yield/plant >2.5 g), forty-five were tolerant (grain yield/plant 1.5 g – 2.5 g) and the rest one hundred eighty-four were susceptible (grain yield/plant <1.5 g). Whereas, donor parent MTU 1061 was highly tolerant (grain yield/plant 2.83 g) and recipient parent MTU 1121 showed susceptible reaction (grain yield/plant 0.72 g). In F2:3, plant height, days to flowering, panicle length, number of filled grains per panicle, number of total grains per panicle, spikelet fertility, productive tillers per plant ranged from 46 cm to 102 cm, 92 to 106, 14 cm to 22 cm, 10 to 296, 116 to 459, 6 to 73 and 2 to 5, respectively.
In seedling and reproductive stages, a total of 234 F2:3 lines derived from MTU 1061 / MTU 1121 were evaluated for salinity tolerance. Out of the 234 F2:3 lines only seven lines were tolerant in both stages i.e., in seedling stage based on SIS and NaK ratio, in reproductive stage based on grain yield / plant. The selected lines with salinity tolerance at both the stages will be further advanced and will be evaluated in yield trials under stress and non stress conditions. And selected tolerant F2:3 lines (seven lines) will be valuable material for further fine mapping and introgression into elite genotypes to develop salt tolerant varieties.
To identify the chromosomal regions relating to seedling and reproductive stages salinity tolerance, the F2 mapping population (234 F2 lines) was developed by making cross between MTU 1061 (donor) and MTU 1121 (recipient). The two parental lines MTU 1061 and MTU 1121 were screened for parental polymorphism using 1,001 SSR markers spanning all the 12 chromosomes. Among 1,001 SSR markers, 104 markers (10%) were
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polymorphic. The molecular linkage map was constructed using 104 polymorphic markers spanning a total map length of 2956.12 cM using kosambi mapping function using IciMapping V.4.1 software. QTL mapping was carried out using Interval Mapping (IM), Inclusive Composite Interval Mapping (ICIM) and Interval Mapping for Epistatic Mapping (IM-EPI) methods in both seedling and reproductive stages.
QTL analyses were conducted for seven seedling salinity tolerance traits in the F2:3 population using interval mapping (IM) and inclusive composite interval mapping (ICIM). A total of 49 additive QTLs were detected by IM for all seven traits whereas 51 additive QTLs were detected by ICIM. A total of 257 pairs of interactive epistatic QTLs were detected by Interval Mapping for Epistatic Mapping (IM-EPI) method. Forty-nine QTLs detected in IM were same as with ICIM. In both methods (IM and ICIM), out of the 49 QTLs, two novel QTLs for SIS score, four QTLs for shoot Na+ concentration, two QTLs for shoot K+ concentration, 16 QTLs for NaK ratio, 17 QTLs for shoot length, six QTLs for root length and two QTLs for shoot dry weight were detected with phenotypic variance ranging from 0.1% to 11%. Compared to IM method, extra two QTLs (qDWT-6-1 and qDWT-9-1) detected for shoot dry weight on chromosomes 6 and 9 in ICIM method. qDWT-6-1 which had a phenotypic variance of 11% and this QTL was detected in the region between RM50 – RM3431 on chromosome 6 which had LOD ≥ 2. In IM-EPI method, 257 pairs of interactive epistatic QTLs were detected, out of 257 pairs of epistatic QTLs, 32 pairs of QTLs for SIS score, 21 pairs of QTLs for shoot Na+ concentration, 15 pairs of QTLs for shoot K+ concentration, 52 pairs of QTLs for NaK ratio, 60 pairs of QTLs for shoot length, 72 pairs of QTLs for root length, five pairs of QTLs for shoot dry weight. One hundred and ten epistatic QTLs were co-localized with 39 additive QTLs for seven seedling salinity tolerant traits.
Among salinity tolerance traits, Na+/K+ ratio, an important ion balancing parameter for the salt tolerance, was controlled by 16 QTLs were mapped on chromosomes 1, 3, 4, 6, 7, 8, 9, 10 and 12 detected by IM and ICIM. All QTLs were with small effects with phenotypic variance ranging from 0.5% to 1%. Out of the 16 QTLs, one of the QTL qNaK-1-1 position was corresponding to Saltol locus on chromosome 1.
QTL analyses were conducted for eight yield contributing traits under reproductive stage salinity in the F2:3 population using interval mapping (IM) and inclusive composite interval mapping (ICIM). A total of 32 additive QTLs were detected by IM for all eight traits whereas 25 additive QTLs were detected by ICIM. A total of 201 pairs of interactive epistatic QTLs were detected by Interval Mapping for Epistatic Mapping (IM-EPI) method. Twenty-five QTLs detected in ICIM were same as with IM. Out of 25 QTLs, two QTLs for plant height, two QTLs for days to flowering, seven QTLs for number of filled grains per panicle, two QTLs for number of total grains per panicle, three QTLs for spikelet fertility, seven QTLs for grain yield per plant and two QTLs for productive tillers per plant. Compared to ICIM method, additional seven QTLs were detected in IM method, five QTLs (qDFL-6-1, qDFL-6-2, qDFL-7-
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1, qDFL-9-2 and qDFL-11-1) for days to flowering, one QTL (qGY-12-1) for grain yield per plant and one QTL (qPT-12-1) for productive tillers per plant. All additive QTLs were minor with a phenotypic variance ranging from 0.2% to 7% detected by IM and ICIM. In IM-EPI method, 201 pairs of interactive epistatic QTLs were detected, out of 201 pairs of epistatic QTLs, eight pairs of QTLs for plant height, 35 pairs of QTLs for days to flowering, five pairs of QTLs for panicle length, 43 pairs of QTLs for number of filled grains per panicle, eight pairs of QTLs for number of total grains per panicle, 38 pairs of QTLs for spikelet fertility, 42 pairs of QTLs for grain yield per plant and 22 pairs of QTLs for productive tillers per plant. Forty-nine epistatic QTLs were co-localized with 19 additive QTLs for six reproductive salinity tolerant traits.
At seedling stage, the phenotypic responses, genomic composition, and QTLs identified from the study indicated that Na/K ratio is the key factor for salinity tolerance. The mechanisms of tolerance might be due to homeostasis between Na+ and K+ or Na+ compartmentation. In reproductive stage phenotypic responses and QTLs identification indicated that grain yield per plant under stress is the key factor comparative to remaining parameters such as number of spikelets, filled spikelets and unfilled spikelets. It can be concluded from the study that tolerance at the seedling stage is not necessarily associated with tolerance at the reproductive stage and vice versa. The tolerant F2:3 lines will be a valuable pre-breeding material for use in rice breeding programs and also provide an opportunity for functional genomics studies to provide molecular insights into salt tolerance mechanisms in MTU 1061.
Description
GENETIC DISSECTION OF
SEEDLING AND REPRODUCTIVE
STAGE SALINITY TOLERANCE IN
RICE USING SALT TOLERANT
CULTIVAR MTU 1061