Reproductive Stage Drought Stress Research Articles

Panicle transcriptome of high-yield mutant indica rice reveals physiological mechanisms and novel candidate regulatory genes for yield under reproductive stage drought stress

BackgroundReproductive stage drought stress (RDS) is a major global threat to rice production. Due to climate change, water scarcity is becoming an increasingly common phenomenon in major rice-growing areas worldwide. Understanding RDS mechanisms will allow candidate gene identification to generate novel rice genotypes tolerant to RDS.ResultsTo generate novel rice genotypes that can sustain yield under RDS, we performed gamma-irradiation mediated mutation breeding in the drought stress susceptible mega rice variety, MTU1010. One of the mutant MM11 (MTU1010 derived mutant11) shows consistently increased performance in yield-related traits under field conditions consecutively for four generations. In addition, compared to MTU1010, the yield of MM11 is sustained in prolonged drought imposed during the reproductive stage under field and in pot culture conditions. A comparative emerged panicle transcriptome analysis of the MTU1010 and MM11 suggested metabolic adjustment, enhanced photosynthetic ability, and hormone interplay in regulating yield under drought responses during emerged panicle development. Regulatory network analysis revealed few putative significant transcription factor (TF)-target interactions involved in integrated signalling between panicle development, yield and drought stress.ConclusionsA gamma-irradiate rice mutant MM11 was identified by mutation breeding, and it showed higher potential to sustain yield under reproductive stage drought stress in field and pot culture conditions. Further, a comparative panicle transcriptome revealed significant biological processes and molecular regulators involved in emerged panicle development, yield and drought stress integration. The study extends our understanding of the physiological mechanisms and candidate genes involved in sustaining yield under drought stress.

Impact of root architecture and transpiration rate on drought tolerance in stay‐green sorghum

AbstractSorghum [Sorghum bicolor (L.) Moench] yield loss due to terminal drought stress is common in semiarid regions. Stay‐green is a drought adaptation trait, and a deeper understanding of stay‐green‐associated traits is necessary for sorghum breeding. We hypothesize that the stay‐green trait in sorghum may be associated with the root architecture and transpiration rate under drought stress. The objectives were to (i) identify the relationship among stay‐green‐associated traits, (ii) compare the root system architecture and transpiration rate of stay‐green (B35 and 296B) and senescent (BTx623 and R16) genotypes under drought stress, and (iii) quantify the impacts of reproductive stage drought stress on gas exchange and grain yield of stay‐green and senescent genotypes. A series of drought experiments were conducted with these genotypes. Under drought stress, the stay‐green genotypes had an increased total root length in the top 30–60 cm (18%) and 60–90 cm of soil (45%) than the senescent genotypes. In contrast, under progressive soil drying, stay‐green genotypes had a decreased transpiration rate (9%) than senescent genotypes by an early (∼1 h) partial closure of stomata under high vapor pressure deficit conditions. The increased seed yield (43%) in stay‐green genotypes is due to an increased photosynthetic rate (30%) and individual seed size (35%) than senescent genotypes. Overall, it is concluded that stay‐green phenotypes had two distinct drought adaptive mechanisms: (i) increased root length for increased soil exploration for water and (ii) an early decrease in the transpiration rate to conserve soil moisture. Identifying genomic markers for these traits would accelerate drought‐tolerant sorghum breeding.

Mapping of QTLs associated with yield and related traits under reproductive stage drought stress in rice using SNP linkage map.

Drought stress is a major constraint for rice production worldwide. Reproductive stage drought stress (RSDS) leads to heavy yield losses in rice. The prospecting of new donor cultivars for identification and introgression of QTLs of major effect (Quantitative trait locus) for drought tolerance is crucial for the development of drought-resilient rice varieties. Our study aimed to map QTLs associated with yield and its related traits under RSDS conditions. A saturated linkage map was constructed using 3417 GBS (Genotyping by sequencing) derived SNP (Single nucleotide polymorphism) markers spanning 1924.136cM map length with an average marker density of 0.56cM, in the F3 mapping population raised via cross made between the traditional ahu rice cultivar, Koniahu (drought tolerant) and a high-yielding variety, Disang (drought susceptible). Using the Inclusive composite interval mapping approach, 35 genomic regions governing yield and related traits were identified in pooled data from 198 F3 and F4 segregating lines evaluated for two consecutive seasons under both RSDS and irrigated control conditions. Of the 35 QTLs, 23 QTLs were identified under RSDS with LOD (Logarithm of odds) values ranging between 2.50 and 7.83 and PVE (phenotypic variance explained) values of 2.95-12.42%. Two major QTLs were found to be linked to plant height (qPH1.29) and number of filled grains per panicle (qNOG5.12) under RSDS. Five putative QTLs for grain yield namely, qGY2.00, qGY5.05, qGY6.16, qGY9.19, and qGY10.20 were identified within drought conditions. Fourteen QTL regions having ≤ 10Mb QTL interval size were further analysed for candidate gene identification and a total of 4146 genes were detected out of these 2263 (54.63%) genes were annotated to at least one gene ontology (GO) term. Several QTLs associated with grain yield and yield components and putative candidate genes were identified. The putative QTLs and candidate genes identified could be employed to augment drought resilience in rice after further validation through MAS strategies.

Disentangling the Roles of Plant Water Status and Stem Carbohydrate Remobilization on Rice Harvest Index Under Drought

BackgroundHarvest index is an important component of grain yield and is typically reduced by reproductive stage drought stress in rice. Multiple drought response mechanisms can affect harvest index including plant water status and the degree of stem carbohydrate mobilization during grain filling. In this study, we aimed to dissect the contributions of plant water status and stem carbohydrate mobilization to harvest index. Pairs of genotypes selected for contrasting harvest index but similar biomass and days to flowering were characterized at ICAR-RCER, Patna, India and at IRRI, Philippines.ResultsMultiple traits were related with harvest index across experiments, including mobilization efficiency at both sites as indicated by groupings in principal component analysis, and plant water status as indicated by direct correlations. Biomass-related traits were positively correlated with harvest index at IRRI but biomass was negatively correlated with harvest index at ICER-RCER, Patna. We observed that some pairs of genotypes showed differences in harvest index across environments, whereas other showed differences in harvest index only under drought. Of all time points measured when all genotypes were considered together, the stem carbohydrate levels at maturity were most consistently (negatively) correlated with harvest index under drought, but not under well-watered conditions. However, in the pairs of genotypes grouped as those whose differences in harvest index were stable across environments, improved plant water status resulted in a greater ability to both accumulate and remobilize stored carbohydrate, i.e. starch.ConclusionBy distinguishing between genotypes whose harvest index was improved across conditions as opposed to specifically under drought, we can attribute the mechanisms behind the stable high-harvest index genotypes to be more related to stem carbohydrate remobilization than to plant water status. The stable high-harvest index lines in this study (Aus 257 and Wanni Dahanala) may confer mechanisms to improve harvest index that are independent of drought response and therefore may be useful for breeding improved rice varieties.

Transcriptome and Physio-Biochemical Profiling Reveals Differential Responses of Rice Cultivars at Reproductive-Stage Drought Stress.

Drought stress severely affects the growth and development of rice, especially at the reproductive stage, which results in disturbed metabolic processes, reduced seed-set/grain filling, deteriorated grain quality, declined productivity, and lower yield. Despite the recent advances in understanding the responses of rice to drought stress, there is a need to comprehensively integrate the morpho-physio-biochemical studies with the molecular responses/differential expression of genes and decipher the underlying pathways that regulate the adaptability of rice at various drought-sensitive growth stages. Our comparative analysis of immature panicle from a drought-tolerant (Nagina 22) and a drought-sensitive (IR 64) rice cultivar grown under control (well-watered) and water-deficit/drought stress (treatment, imposed at the reproductive stage) conditions unraveled some novel stress-responsive genes/pathways responsible for reproductive-stage drought stress tolerance. The results revealed a more important role of upregulated (6706) genes in the panicle of N 22 at reproductive-stage drought stress compared to that (5590) in IR 64. Functional enrichment and MapMan analyses revealed that majority of the DEGs were associated with the phytohormone, redox signalling/homeostasis, secondary metabolite, and transcription factor-mediated mitigation of the adverse effects of drought stress in N 22. The upregulated expression of the genes associated with starch/sucrose metabolism, secondary metabolites synthesis, transcription factors, glutathione, linoleic acid, and phenylalanine metabolism in N 22 was significantly more than that in the panicle of IR 64. Compared to IR 64, 2743 genes were upregulated in N 22 under control conditions, which further increased (4666) under drought stress in panicle of the tolerant cultivar. Interestingly, we observed 6706 genes to be upregulated in the panicle of N 22 over IR 64 under drought and 5814 genes get downregulated in the panicle of N 22 over IR 64 under the stress. In addition, RT-qPCR analysis confirmed differential expression patterns of the DEGs. These genes/pathways associated with the reproductive-stage drought tolerance might provide an important source of molecular markers for genetic manipulation of rice for enhanced drought tolerance.

Genetic analysis and traits association study in marker-assisted multi-drought-traits pyramided genotypes under reproductive-stage moisture stress in rice (Oryza sativa L.)

Reproductive-stage drought-stress is a major production constraint in rainfed rice ecosystem. Emergence of marker-assisted breeding strategies for developing drought-tolerant rice varieties are being optimized through exploiting adaptive-traits for their increased contribution towards grain-yield under recurring-drought. Grain-yield is a complex-trait; requires knowledge of genetics and association among yield contributing component-traits. Current study was undertaken using 21 marker-assisted multi-drought-traits pyramided genotypes response for genetic variability and association of traits for grain-yield under aerobic and reproductive-stage drought conditions. Field evaluation was carried-out in two seasons and data was collected on various parameters. Path-coefficient analysis was used as a selection criterion to select yield contributing-traits and found nine phenotypic traits were having a positive direct-effect on grain-yield during both and/or at least one season under both moisture-regimes. The data from summer and Kharif seasons have been pooled within their respective moisture-regimes due to the non-significance of Levene’s test of homogeneity of variances and estimated BLUP values. ANOVA based on BLUP values revealed significant differences for moisture-conditions and also among genotypes. Phenotypic variation via. box-plots and histogram depicted mean phenotypic differences of traits under two moisture-regimes. Majority of the traits possessed high PCV, GCV with high heritability and GAM indicating higher trait expression and additive gene action lead to effectiveness of selection under drought/moisture stress. Grain-yield possessed a positive correlation with all the component-traits under consideration during both moisture-regimes. Selection of genotypes based on these component-traits were rewarding and seems to be better selection-criteria. Finally, we can end-up with superior-genotypes suitable for intermittent-drought conditions.

Drought Tolerant Near Isogenic Lines of Pusa 44 Pyramided With qDTY2.1 and qDTY3.1, Show Accelerated Recovery Response in a High Throughput Phenomics Based Phenotyping.

Reproductive stage drought stress (RSDS) is a major challenge in rice production worldwide. Cultivar development with drought tolerance has been slow due to the lack of precise high throughput phenotyping tools to quantify drought stress-induced effects. Most of the available techniques are based on destructive sampling and do not assess the progress of the plant’s response to drought. In this study, we have used state-of-the-art image-based phenotyping in a phenomics platform that offers a controlled environment, non-invasive phenotyping, high accuracy, speed, and continuity. In rice, several quantitative trait loci (QTLs) which govern grain yield under drought determine RSDS tolerance. Among these, qDTY2.1 and qDTY3.1 were used for marker-assisted breeding. A set of 35 near-isogenic lines (NILs), introgressed with these QTLs in the popular variety, Pusa 44 were used to assess the efficiency of image-based phenotyping for RSDS tolerance. NILs offered the most reliable contrast since they differed from Pusa 44 only for the QTLs. Four traits, namely, the projected shoot area (PSA), water use (WU), transpiration rate (TR), and red-green-blue (RGB) and near-infrared (NIR) values were used. Differential temporal responses could be seen under drought, but not under unstressed conditions. NILs showed significant level of RSDS tolerance as compared to Pusa 44. Among the traits, PSA showed strong association with yield (80%) as well as with two drought tolerances indices, stress susceptibility index (SSI) and tolerance index (TOL), establishing its ability in identifying the best drought tolerant NILs. The results revealed that the introgression of QTLs helped minimize the mean WU per unit of biomass per day, suggesting the potential role of these QTLs in improving WU-efficiency (WUE). We identified 11 NILs based on phenomics traits as well as performance under imposed drought in the field. The study emphasizes the use of phenomics traits as selection criteria for RSDS tolerance at an early stage, and is the first report of using phenomics parameters in RSDS selection in rice.

Performance Evaluation of Sub1 Rice Genotypes for Vegetative Stage Submergence Stress and Reproductive Stage Drought Stress

Performance Evaluation of Sub1 Rice Genotypes for Vegetative Stage Submergence Stress and Reproductive Stage Drought Stress

Genetic Dissection of Epistatic Interactions Contributing Grain Yield Variability in Rice under Drought.

AimsThe aim of the present study was to evaluate the performance of ‘high’-‘low’ yielding pyramided lines (PLs), having the same combinations of qDTYs in Samba Mahsuri, MR219 and IR64-Sub1 genetic backgrounds, and to understand the genetic interactions among QTL and/with genetic background affecting grain yield.BackgroundEpistasis regulates the expression of traits governed by several major/minor genes/QTL. Multiple pyramided lines (PLs) with the same grain yield QTL (qDTYs) combinations but possessing grain yield variability under different levels of reproductive stage drought stress were identified in different rice genetic backgrounds at International Rice Research Institute (IRRI).ObjectivesThe objectives of the present study were to evaluate the performance pyramided lines (PLs) with drought QTL in the backgrounds of Samba Mahsuri, MR219 and IR64-Sub1 under reproductive stage drought stress (RS) and NS (non-stress) conditions, to understand the effect of epistatic interactions among qDTYs and with genetic background on GY under the differential level of stress and to identify the promising drought-tolerant lines with high yield under drought and higher background recovery in different genetic backgrounds.MethodsThe experiments were conducted in 2015 DS (dry season), 2015 WS (wet season) and 2017 DS at IRRI, Los Baños, Philippines, in a transplanted lowland ecosystem under lowland severe stress (LSS), lowland moderate stress (LMS) and lowland non-stress (LNS). The experiments were laid out in alpha lattice design with two replications.ResultsSeveral digenic interactions were found in different genetic backgrounds, 13 interactions in Samba Mahsuri, 11 in MR219 and 20 in IR64-Sub1 backgrounds. Among all digenic interactions, one QTL × QTL interaction, 17 QTL × background and 26 background × background interactions resulted in GY reduction in low yielding PLs in different genetic backgrounds under LSS or LMS. Negative interaction of qDTY3.1, qDTY4.1 and qDTY9.1 with background markers and background × background interactions caused up to 15% GY reduction compared to the high yielding PLs under LMS in the Samba Mahsuri PLs. In MR219 PLs, the negative interaction of qDTY2.2, qDTY3.2, qDTY4.1 and qDTY12.1 with the background marker interval RM314-RM539, RM273-RM349 and RM445-RM346, RM473D-RM16, respectively resulted 52% GY reduction compared to the high yielding PLs under LSS. In IR64-Sub1 PLs, qDTY6.1 interacted with background loci at RM16-RM135, RM228-RM333, RM202-RM287 and RM415-RM558A marker interval under LSS and at RM475-RM525 marker interval under LMS, causing GY reduction to 58% compared to the high yielding PLs.ConclusionHigh yielding PLs in Samba Mahsuri (IR 99734:1-33-69-1-22-6), MR219 (IR 99784-156-87-2-4-1) and IR64-Sub1 (IR 102784:2-89-632-2-1-2) backgrounds without any negative interactions were identified. The identified selected promising PLs may be used as potential drought-tolerant donors or may be released as varieties for drought-prone ecosystems in different countries.

Development of Drought Tolerant Rice Breeding Lines of an Elite Indian Rice (Oryza sativa L.) Variety Improved White Ponni through Molecular Breeding

Changes in climatic conditions especially unpredictable drought occurrences are challenging for food security. The present investigation was carried out to improve the grain yield in Improved White Ponni (IWP) rice under reproductive stage drought stress. This variety is well known for its grain quality. Physiological changes, grain yield and related traits under drought were evaluated in the advanced breeding lines of Improved White Ponni X Apo containing qDTY 3.1. The experiment was conducted at the Department of Rice, Centre for Plant Breeding and Genetics, Tamil Nadu Agricultural university, Coimbatore during 2020. Two superior backcross inbred lines of IWP X Apo, donor parent and recipient parent were raised under water stress in rain out shelter as well as in well irrigated conditions in replications. Soil moisture content was reduced to 12.7% in drought field showing the stress severity. Physiological parameters such as photosynthetic rate, transpiration rate, stomatal conductance, chlorophyll content and relative water content, Yield and related traits such as days to fifty percent flowering, productive tillers, spikelet fertility, grain yield and grain weight were recorded in the BILs and parents during flowering stages. Reduction was observed in all these traits under water stress. However, in comparison with IWP (94.6%) which lacks qDTY 3.1, BILs with qDTY 3.1 showed less reduction in grain yield (63%) and other traits. Earliness was also observed in qDTY 3.1 containing BILs under drought stress (BILs - 106 days, IWP-117 days) and controlled conditions (BILs- 83 days, IWP-107 days) when compared to IWP. Grain quality estimates in the BILs showed similarity to IWP. These BILs need to be evaluated further for confirmation of drought tolerance and they are effective resources for utilisation in drought breeding programmes.

Marker-assisted forward breeding to develop a drought-, bacterial-leaf-blight-, and blast-resistant rice cultivar.

Among the different challenges related to rice (Oryza sativa L.) cultivation, drought, bacterial leaf blight (BLB), and blast are the key stresses that significantly affect grain yield (GY) in rice. To ameliorate this issue, marker-assisted forward breeding (MAFB) coupled with a simultaneous crossing approach was used to combine three drought tolerant quantitative trait loci (QTL)-qDTY1.1 , qDTY3.1 , and qDTY12.1 -four BLB genes-Xa4, xa5, xa13, and Xa21-and one blast-resistance gene, Pi9, in the elite rice cultivar Lalat. The introgression lines (ILs) developed in the current study were phenotypically screened for drought, BLB, and blast resistance at the F7 -F8 generation. Under the reproductive stage (RS) drought stress, the yield advantage of ILs, with major-effect QTL (qDTY) over elite parent Lalat, ranges from 9 to 124% in DS2019 and from 7 to 175% in WS2019. The selected ILs were highly resistant to BLB, with lesion lengths ranging from 1.3 to 3.0 cm and blast scores ranging from 1 to 3. ILs that were tolerant to RS drought, resistant to BLB, and blast disease and had similar or higher yields than Lalat were analyzed for grain quality. Six ILs were found to have similar grain quality characteristics to Lalat including hulling, milling, head rice recovery (HRR), chalkiness, alkali spreading value (ASV), and amylose content (AC). This study showed that MAFB, together with simultaneous crossing, would be an effective strategy to rapidly combine multiple stresses in rice. The ILs developed in this study could help to ensure yield sustainability in rainfed environments or be used as genetic material in future breeding programs.

Response of Primed Rice (Oryza sativa L.) Seeds towards Reproductive Stage Drought Stress

Seed priming could be promoted as a potential alternative in alleviating drought stress challenges in rice cultivation. The present study was conducted as an attempt to verify potential performance of seed priming in improving seedling growth and harvestable grain yield of rice under reproductive stage drought stress (RS). Seed treatments involved were non-primed seeds as control (T1), hydro-primed (T2) and osmo-primed at -1.0 mPa with polyethylene glycol (PEG6000) (T3). Reproductive stage drought stress (RS) was imposed at soil water potential lower than -60 kPa. The well-watered plants served as control of the experiment. In general, seedling growth of T3 was better than T2 and T1 for all growth parameters in both planting seasons. Yield components were significantly lower in RS as compared to well-watered treatment (WW). The agronomic performance of primed seeds in T2 and T3 were not significantly different with T1 under both RS and WW for both planting seasons. As a conclusion, seed priming treatments used in this study was ineffective in improving agronomic performance of rice under RS. Therefore, other alternatives such as development of drought tolerant rice should be highly emphasized in order to minimize the impact of drought on growth and yield of rice plant.

Marker-assisted forward and backcross breeding for improvement of elite Indian rice variety Naveen for multiple biotic and abiotic stress tolerance.

The elite Indian rice variety, Naveen is highly susceptible to major biotic and abiotic stresses such as blast, bacterial blight (BB), gall midge (GM) and drought which limit its productivity in rainfed areas. In the present study, a combined approach of marker-assisted forward (MAFB) and back cross (MABC) breeding was followed to introgress three major genes, viz., Pi9 for blast, Xa21 for bacterial blight (BB), and Gm8 for gall midge (GM) and three major QTLs, viz., qDTY1.1, qDTY2.2 and qDTY4.1 conferring increased yield under drought in the background of Naveen. At each stage of advancement, gene-based/linked markers were used for the foreground selection of biotic and abiotic stress tolerant genes/QTLs. Intensive phenotype-based selections were performed in the field for identification of lines with high level of resistance against blast, BB, GM and drought tolerance without yield penalty under non-stress situation. A set of 8 MAFB lines and 12 MABC lines with 3 to 6 genes/QTLs and possessing resistance/tolerance against biotic stresses and reproductive stage drought stress with better yield performance compared to Naveen were developed. Lines developed through combined MAFB and MABC performed better than lines developed only through MAFB. This study exemplifies the utility of the combined approach of marker-assisted forward and backcrosses breeding for targeted improvement of multiple biotic and abiotic stress resistance in the background of popular mega varieties.

Molecular Breeding for Improving Productivity of Oryza sativa L. cv. Pusa 44 under Reproductive Stage Drought Stress through Introgression of a Major QTL, qDTY12.1.

Increasing rice production is quintessential to the task of sustaining global food security, as a majority of the global population is dependent on rice as its staple dietary cereal. Among the various constraints affecting rice production, reproductive stage drought stress (RSDS) is a major challenge, due to its direct impact on grain yield. Several quantitative trait loci (QTLs) conferring RSDS tolerance have been identified in rice, and qDTY12.1 is one of the major QTLs reported. We report the successful introgression of qDTY12.1 into Pusa 44, a drought sensitive mega rice variety of the northwestern Indian plains. Marker-assisted backcross breeding (MABB) was adopted to transfer qDTY12.1 into Pusa 44 in three backcrosses followed by four generations of pedigree selection, leading to development of improved near isogenic lines (NILs). Having a recurrent parent genome (RPG) recovery ranging from 94.7–98.7%, the improved NILs performed 6.5 times better than Pusa 44 under RSDS, coupled with high yield under normal irrigated conditions. The MABB program has been modified so as to defer background selection until BC3F4 to accelerate generational advancements. Deploying phenotypic selection alone in the early backcross generations could help in the successful recovery of RPG. In addition, the grain quality could be recovered in the improved NILs, leading to superior selections. Owing to their improved adaptation to drought, the release of improved NILs for regions prone to intermittent drought can help enhance rice productivity and production.

Evaluation of Inherited Resistance Genes of Bacterial Leaf Blight, Blast and Drought Tolerance in Improved Rice Lines

Improved rice lines were developed frome three parents with the resistance or tolerance to bacterial leaf blight, blast and drought stress, respectively, using single-, double- and three-way crosses. The improved lines were assessed for agro-morphological and yield traits under non-drought stress (NS) and reproductive-stage drought stress (RS) treatments. The mean comparison of traits measured between parent plants and progenies (improved lines) were similar, and there were significant and non-significant differences among the parents and improved lines (genotypes) under NS and RS. Smilarly, there was significant and non-significant differences in the interaction among both parent varieties and improved lines for NS and RS. Cluster and 3D-model of principal component analysis did not generate categorical clusters according to crossing methods, and there were no exclusive crossing method inclined variations under the treatments. The improved lines were high-yielding, disease resistant, and drought-tolerant compared with their parents. All the crossing methods were good for this crop improvement program without preference to any, despite the number of genes introgressed.

Utilization of genetic diversity and population structure to reveal prospective drought-tolerant donors in rice

Fifty SSR markers were used to assess genetic diversity among 40 drought-tolerant, five moderately drought-tolerant, and three susceptible genotypes to identify new donors for drought tolerance in rice. Out of 50 SSR markers, 17 markers are reported to be linked to major grain yield QTLs under reproductive stage drought stress. 163 (97.7%) out of 167 alleles were found to be polymorphic. The PIC value ranged from 0 to 0.963 with an average of 0.795 per locus. The minor allele frequency varied from 0.312 (RM336) to 0.895 (RM530) with an average of 0.60. The genetic diversity ranged from 0.187 (RM530) to 0.739 (RM336) with an average of 0.51. The cluster analysis grouped all the genotypes into three major clusters at 50% level of genetic dissimilarity. Structure analysis identified two subpopulations among 48 rice genotypes. 81% and 19% of molecular variances were revealed within and among the subpopulations, respectively. The first three principal components explained over 88% of total genetic variation. Two genotypes, Kalakeri and RR-2-6 were identified as new drought-tolerant donors. Kalakeri contributes drought tolerance QTL, qDTY1.1, while RR-2-6 contributes QTLs, qDTY2.2, and qDTY2.3.

Characterization of flowering time response among recombinant inbred lines of WAB638-1/PRIMAVERA rice under reproductive stage drought stress

AbstractNinety-eight high-yielding recombinant inbred lines (RILs) of WAB638-1/PRIMAVERA rice were evaluated with the parents under reproductive stage drought stress. The study aimed at characterizing flowering time response under drought stress and consequently classifying the genetic resources for efficient use in breeding programmes. Two field trials were conducted during the 2016 and 2017 dry seasons using the randomized complete block design with two replications. In 2016, 12 RILs were evaluated with the parents for the rooting attributes under drought stress and well-watered treatments. Analysis of variance revealed a significant (P < 0.05) variation among the genotypes for the traits evaluated. Drought stress reduced most of the characters in this study, including grain yield. However, the inbred lines exhibited considerable tolerance to drought stress as indicated by yield-related stress indexes, including stress susceptibility and drought tolerance indexes. Delayed flowering (FD) was recorded in 75 genotypes (including WAB638-1), while 25 genotypes (including PRIMAVERA) had no delay under drought stress compared to the control. The genotypes were grouped into flowering delay (D) genotypes (FD > 1 d) and no delay (N) genotypes (FD < 1 d), which significantly differ (P ⩽ 0.05) for numbers of days to 50% flowering. The flowering delay genotypes may be suitable for intermittent drought, while genotypes with little or no delay may be selected for terminal drought conditions. There was a significant correlation (r > 0.5) between the root length and number of days to 50% flowering. The study indicated that root parameters, such as the root length, may contribute to the drought adaptation mechanisms of the RILs.

Incorporating Drought and Submergence Tolerance QTL in Rice (Oryza sativa L.)-The Effects under Reproductive Stage Drought and Vegetative Stage Submergence Stresses.

Drought and submergence have been the major constraint in rice production. The present study was conducted to develop high-yielding rice lines with tolerance to drought and submergence by introgressing Sub1 into a rice line with drought yield QTL (qDTY; QTL = quantitative trait loci) viz. qDTY3.1 and qDTY12.1 using marker-assisted breeding. We report here the effect of different combinations of Sub1 and qDTY on morpho-physiological, agronomical traits and yield under reproductive stage drought stress (RS) and non-stress (NS) conditions. Lines with outstanding performance in RS and NS trials were also evaluated in vegetative stage submergence stress (VS) trial to assess the tolerance level. The QTL class analysis revealed Sub1 + qDTY3.1 as the best QTL combination affecting the measured traits in RS trial followed by Sub1 + qDTY12.1. The effects of single Sub1, qDTY3.1 and qDTY12.1 were not as superior as when the QTLs are combined, suggesting the positive interaction of Sub1 and qDTY. Best performing lines selected from the RS and NS trials recorded yield advantage up to 4453.69 kg ha−1 and 6954 kg ha−1 over the parents, respectively. The lines were also found having great tolerance to submergence ranging from 80% to 100%, contributed by a lower percentage of shoot elongation and reduction of chlorophyll content after 14 days of VS. These lines could provide yield sustainability to farmers in regions impacted with drought and submergence while serving as important genetic materials for future breeding programs.

Introgression of qDTY1.1 Governing Reproductive Stage Drought Tolerance into an Elite Basmati Rice Variety “Pusa Basmati 1” through Marker Assisted Backcross Breeding

Drought stress at the reproductive stage in rice is one of the most important cause for yield reduction, affecting both productivity and quality. All Basmati rice varieties, including the popular cultivar “Pusa Basmati 1 (PB1)” is highly sensitive to reproductive stage drought stress (RSDS). We report for the first time, improvement of a Basmati cultivar for RSDS tolerance, with the introgression of a major quantitative trait locus (QTL), “qDTY1.1” into PB1. The QTL was sourced from an aus variety, Nagina 22 (N22). A microsatellite (simple sequence repeat (SSR)) marker “RM 431” located at telomeric end (38.89 mb) of chromosome 1, and located within a 1.04 mb QTL region was employed for foreground selection for qDTY1.1 in the marker assisted backcross breeding process. A set of 113 SSR markers polymorphic between N22 and PB1 were utilized for background selection to ensure higher recurrent parent genome recovery. After three backcrosses followed by five generations of selfing, eighteen near isogenic lines (NILs) were developed, through combinatory selection for agro-morphological, grain and cooking quality traits. The NILs were evaluated for three consecutive Kharif seasons, 2017, 2018 and 2019 under well-watered and drought stress conditions. RSDS tolerance and yield stability indicated that P1882-12-111-3, P1882-12-111-5, P1882-12-111-6, P1882-12-111-7, P1882-12-111-12, P1882-12-111-15 and P1882-12-111-17 were best in terms of overall agronomic and grain quality under RSDS. Additionally, NILs exhibited high yield potential under normal condition as well. The RSDS tolerant Basmati NILs with high resilience to water stress, is a valuable resource for sustaining Basmati rice production under water limiting production environments.

Drought Tolerant near Isogenic Lines (NILs) of Pusa 44 Developed through Marker Assisted Introgression of qDTY2.1 and qDTY3.1 Enhances Yield under Reproductive Stage Drought Stress

Reproductive stage drought stress (RSDS) is detrimental for rice, which affects its productivity as well as grain quality. In the present study, we introgressed two major quantitative trait loci (QTLs), namely, qDTY2.1 and qDTY3.1, governing RSDS tolerance in a popular high yielding non-aromatic rice cultivar, Pusa 44, through marker-assisted backcross breeding (MABB). Pusa 44 is highly sensitive to RSDS, which restricts its cultivation across drought-prone environments. Foreground selection was carried out using markers, RM520 for qDTY3.1 and RM 521 for qDTY2.1. Background selection was achieved with 97 polymorphic SSR markers in tandem with phenotypic selection to achieve faster recurrent parent genome (RPG) recovery. Three successive backcrosses followed by three selfings aided RPG recoveries of 98.6% to 99.4% among 31 near isogenic lines (NILs). Fourteen NILs were found to be significantly superior in yield and grain quality under RSDS with higher drought tolerance efficiency (DTE) than Pusa 44. Among these, the evaluation of two promising NILs in the multilocational trial during Kharif 2019 showed that they were significantly superior to Pusa 44 under reproductive stage drought stress, while performing on par with Pusa 44 under normal irrigated conditions. These di-QTL pyramided drought-tolerant NILs are in the final stages of testing the All India Coordinated Rice Improvement Project varietal trials for cultivar release. Alternately, the elite drought-tolerant Pusa 44 NILs will serve as an invaluable source of drought tolerance in rice improvement.