Drought Stress In Rice Research Articles

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Phyllosphere bacteria plays important role in mitigating biotic and abiotic stress. This study aimed to use phyllosphere bacterium of rice to enhance drought tolerance. Bacterial isolates obtained from rice phyllosphere were investigated for their plant growth promoting activities and role in alleviation of drought stress in rice. The isolates were identified as Bacillus altitudinis FD48, Bacillus pumilus FS20 and Bacillus aquimaris MD02 based on 16S rRNA gene sequence. B. altitudinis FD48 was found to produce indole acetic acid (IAA) (2.82 µg/ml) compared to other two isolates even under PEG induced drought conditions. However, under normal conditions, B. altitudinis FD48 produced 8.0 µg/ml. Quantitative estimation of 1-aminocyclopropane-1-carboxylate (ACC) deaminase activity was found to be 192 n moles a-ketobutyrate mg-1 h-1 and positive for accD gene. B. altitudinis FD48 increased the root and shoot length of rice under in vitro conditions and also improved the germination percentage of rice seeds at different concentration of PEG 6000. Inoculation of rice with plant growth promoting, drought tolerant B. altitudinis FD48 increased relative water content, chlorophyll stability index and membrane stability index compared to control (uninoculated plants) when the plants were subjected to drought by discontinuing water for 8 days after 30 days of germination. Similarly, rice treated with B. altitudinis increased proline content, phenolics content, catalase activity and reduced malondialdehyde (MDA) content in plants. Ethylene emission was significantly reduced by B. altitudinis FD48 inoculation under drought condition when compared with control. This study suggests that the isolate B. altitudinis FD48 may be used at field level to mitigate drought stress in rice. Key words: Proline content, drought, 1-aminocyclopropane-1-carboxylate (ACC) deaminase, plant growth promoting bacteria, phenolics content, indole acetic acid (IAA).

Physiological and Proteomic Analysis of the Rice Mutant cpm2 Suggests a Negative Regulatory Role of Jasmonic Acid in Drought Tolerance.

It is widely known that numerous adaptive responses of drought-stressed plants are stimulated by chemical messengers known as phytohormones. Jasmonic acid (JA) is one such phytohormone. But there are very few reports revealing its direct implication in drought related responses or its cross-talk with other phytohormones. In this study, we compared the morpho-physiological traits and the root proteome of a wild type (WT) rice plant with its JA biosynthesis mutant coleoptile photomorphogenesis 2 (cpm2), disrupted in the allene oxide cyclase (AOC) gene, for insights into the role of JA under drought. The mutant had higher stomatal conductance, higher water use efficiency and higher shoot ABA levels under severe drought as compared to the WT. Notably, roots of cpm2 were better developed compared to the WT under both, control and drought stress conditions. Root proteome was analyzed using the Tandem Mass Tag strategy to better understand this difference at the molecular level. Expectedly, AOC was unique but notably highly abundant under drought in the WT. Identification of other differentially abundant proteins (DAPs) suggested increased energy metabolism (i.e., increased mobilization of resources) and reactive oxygen species scavenging in cpm2 under drought. Additionally, various proteins involved in secondary metabolism, cell growth and cell wall synthesis were also more abundant in cpm2 roots. Proteome-guided transcript, metabolite, and histological analyses provided further insights into the favorable adaptations and responses, most likely orchestrated by the lack of JA, in the cpm2 roots. Our results in cpm2 are discussed in the light of JA crosstalk to other phytohormones. These results together pave the path for understanding the precise role of JA during drought stress in rice.

Association Mapping of Yield and Yield-related Traits Under Reproductive Stage Drought Stress in Rice (Oryza sativa L.)

BackgroundThe identification and introgression of major-effect QTLs for grain yield under drought are some of the best and well-proven approaches for improving the drought tolerance of rice varieties. In the present study, we characterized Malaysian rice germplasm for yield and yield-related traits and identified significant trait marker associations by structured association mapping.ResultsThe drought screening was successful in screening germplasm with a yield reduction of up to 60% and heritability for grain yield under drought was up to 78%. There was a wider phenotypic and molecular diversity within the panel, indicating the suitability of the population for quantitative trait loci (QTL) mapping. Structure analyses clearly grouped the accessions into three subgroups with admixtures. Linkage disequilibrium (LD) analysis revealed that LD decreased with an increase in distance between marker pairs and the LD decay varied from 5–20 cM. The Mixed Linear model-based structured association mapping identified 80 marker trait associations (MTA) for grain yield (GY), plant height (PH) and days to flowering (DTF). Seven MTA were identified for GY under drought stress, four of these MTA were consistently identified in at least two of the three analyses. Most of these MTA identified were on chromosomes 2, 5, 10, 11 and 12, and their phenotypic variance (PV) varied from 5% to 19%. The in silico analysis of drought QTL regions revealed the association of several drought-responsive genes conferring drought tolerance. The major-effect QTLs are useful in marker-assisted QTL pyramiding to improve drought tolerance.ConclusionThe results have clearly shown that structured association mapping is one of the feasible options to identify major-effect QTLs for drought tolerance-related traits in rice.

The APETALA2/ethylene-responsive factor transcription factor OsDERF2 negatively modulates drought stress in rice by repressing abscisic acid responsive genes

SUMMARYAPETALA2/ethylene-responsive factor (AP2/ERF) family transcription factors play a vital role in plant growth and in response to hormones and abiotic stresses. In the current research, it is reported that OsDERF2, one of the drought-responsive ERF, is a member of the DREB sub-family. OsDERF2 is a nuclear-localized protein and has transcriptional activity in yeast. Expression of OsDERF2 was induced by drought and inhibited by abscisic acid (ABA). However, OsDERF2 RNA interference (RNAi) knock-down transgenic lines enhanced tolerance to drought stress at seedling stage and were much more sensitive to ABA treatment, which may result from the increased ABA level in vivo. The basic leucine zipper (bZIP) transcription factor family plays an important role in the ABA signalling pathway of abiotic stress. Quantitative real-time polymerase chain reaction analysis revealed that the bZIP family gene OsbZIP20 and ABA-response gene OsABA45 were up-regulated 25 times and 120 times, respectively, in OsDERF2 RNAi knock-down lines under drought stress, which were up-regulated five and seven times in wild type under drought stress. The current data reveal that OsDERF2 negatively modulates drought stress response in an ABA-mediated pathway through regulating gene expression of other ABA-response transcription factors.

MicroRNAs regulate the main events in rice drought stress response by manipulating the water supply to shoots.

MicroRNAs (miRNAs) are small endogenous regulatory RNAs that are involved in a variety of biological processes related to proliferation, development, and response to biotic and abiotic stresses. miRNA profiles of rice (Oryza sativa L. cv. IR64.) leaves in a partial root zone drying (PRD) system were analysed using a high-throughput sequencing approach to identify miRNAs associated with drought signalling. The treatments performed in this study were as follows: well-watered ("wet" roots, WW), wherein both halves of the pot were watered daily; drought ("dry" roots, DD), wherein water was withheld from both halves of the pot; and well-watered/drought ("wet" and "dry" roots, WD), wherein one half of each pot was watered daily, the same as in WW, and water was withheld from the other part, the same as in DD. High-throughput sequencing enabled us to detect novel miRNAs and study the differential expression of known miRNAs. A total of 209 novel miRNAs were detected in this study. Differential miRNA profiling of the DD, WD and WW conditions showed differential expression of 159 miRNAs, among which 83, 44 and 32 miRNAs showed differential expression under both DD and WD conditions. The detection of putative targets of the differentially expressed miRNAs and investigation of their functions showed that most of these genes encode transcription factors involved in growth and development, leaf morphology, regulation of hormonal homeostasis, and stress response. The most important differences between the DD and WD conditions involved regulation of the levels of hormones such as auxin, cytokinin, abscisic acid, and jasmonic acid and also regulation of phosphor homeostasis. Overall, differentially expressed miRNAs under WD conditions were found to differ from those under DD conditions, with such differences playing a role in adaptation and inducing the normal condition. The mechanisms involved in regulating hormonal homeostasis and involved in energy production and consumption were found to be the most important regulatory pathways distinguishing the DD and WD conditions.

Clustering and evolutionary analysis of small RNAs identify regulatory siRNA clusters induced under drought stress in rice.

MotivationDrought tolerance is an important trait related to growth and yield in crop. Until now, drought related research has focused on coding genes. However, non-coding RNAs also respond significantly to environmental stimuli such as drought stress. Unfortunately, characterizing the role of siRNAs under drought stress is difficult since a large number of heterogenous siRNA species are expressed under drought stress and non-coding RNAs have very weak evolutionary conservation. Thus, to characterize the role of siRNAs, we need a well designed biological and bioinformatics strategy. In this paper, to characterize the function of siRNAs we developed and used a bioinformatics pipeline that includes a genomic-location based clustering technique and an evolutionary conservation tool.ResultsBy comparing the wild type Nipponbare and two drought resistant rice varities, we found that 21 nt and 24 nt siRNAs are significantly expressed in the three rice plants but at different time points under a short-term (0, 1, and 6 hrs) drought treatment. siRNAs were up-regulated in the wild type at an early stage while the up-regulation was delayed in the two drought tolerant plants. Genes targeted by up-regulated siRNAs were related to oxidation reduction and proteolysis, which are well known to be associated with water deficit phenotypes. More interestingly, we found that siRNAs were located in intronic regions as clusters and were of high evolutionary conservation among monocot grass plants. In summary, we show that siRNAs are important respondents to drought stress and regulate genes related to the drought tolerance in water deficit conditions.Electronic supplementary materialThe online version of this article (doi:10.1186/s12918-016-0355-3) contains supplementary material, which is available to authorized users.

Roles of plant hormones and anti-apoptosis genes during drought stress in rice (Oryza sativa L.).

We previously identified the rice (Oryza sativa) senescence-associated gene OsSAP which encodes a highly conserved protein involved in anti-apoptotic activity. This novel Bax suppressor-related gene regulates tolerance to multiple stresses in yeast. Here, we show the effects of drought stress on leaf and root tissues of plants over-expressing OsSAP in relation to the levels of phytohormones, abscisic acid (ABA), jasmonic acid (JA), indole-3-carboxylic acid (ICA), gibberellic acid (GA3), and zeatin. Results showed that rice plants over-expressing SAP were tolerant to drought stress compared to wild type and the plants over-expressing AtBI-1, which is a homolog of the human Bax inhibitor-1 in Arabidopsis. ABA and JA levels in OsSAP and AtBI-1 transgenic plants consistently increased up to at least 3 days after drought treatment, whereas lower GA3 levels were recorded during early drought period. Comparison between control and transgenic plants overexpressing anti-apoptosis genes OsSAP and AtBI-1 resulted in different patterns of hormone levels, indicating that these genes are involved in the plant responses to drought stress and present an opportunity for further study on drought stress tolerance in rice and other plant species.Electronic supplementary materialThe online version of this article (doi:10.1007/s13205-016-0564-x) contains supplementary material, which is available to authorized users.

Genome-Wide Differences in DNA Methylation Changes in Two Contrasting Rice Genotypes in Response to Drought Conditions.

Differences in drought stress tolerance within diverse rice genotypes have been attributed to genetic diversity and epigenetic alterations. DNA methylation is an important epigenetic modification that influences diverse biological processes, but its effects on rice drought stress tolerance are poorly understood. In this study, methylated DNA immunoprecipitation sequencing and an Affymetrix GeneChip rice genome array were used to profile the DNA methylation patterns and transcriptomes of the drought-tolerant introgression line DK151 and its drought-sensitive recurrent parent IR64 under drought and control conditions. The introgression of donor genomic DNA induced genome-wide DNA methylation changes in DK151 plants. A total of 1190 differentially methylated regions (DMRs) were detected between the two genotypes under normal growth conditions, and the DMR-associated genes in DK151 plants were mainly related to stress response, programmed cell death, and nutrient reservoir activity, which are implicated to constitutive drought stress tolerance. A comparison of the DNA methylation changes in the two genotypes under drought conditions indicated that DK151 plants have a more stable methylome, with only 92 drought-induced DMRs, than IR64 plants with 506 DMRs. Gene ontology analyses of the DMR-associated genes in drought-stressed plants revealed that changes to the DNA methylation status of genotype-specific genes are associated with the epigenetic regulation of drought stress responses. Transcriptome analysis further helped to identify a set of 12 and 23 DMR-associated genes that were differentially expressed in DK151 and IR64, respectively, under drought stress compared with respective controls. Correlation analysis indicated that DNA methylation has various effects on gene expression, implying that it affects gene expression directly or indirectly through diverse regulatory pathways. Our results indicate that drought-induced alterations to DNA methylation may influence an epigenetic mechanism that regulates the expression of unique genes responsible for drought stress tolerance.

Morphophysiological and molecular effects of drought stress in rice

Drought is a major abiotic stress that adversely affects the rice growth, mostly in the rainfed ecosystem that ultimately affects the biomass production and yield. Rice needs to adapt a series of physiological mechanisms with complicated regulatory network to fight and cope up with the unfavourable conditions due to drought stress. Morphological and physiological response in rice include inhibition of seed germination, slower growth rate, low root and shoot length, lower chlorophyll content, stomatal closure, lower rate of photosynthesis, yield reduction etc. Stress condition further results in development of response at the molecular level by the generation of reactive oxygen species (ROS) such as O2*-, H2O2, 1O2, OH* etc. which incites oxidative stress in the plants. Oxidative stress is overcome by the inherent capacity of plants to produce antioxidant species which may be enzymatic or non-enzymatic in nature. If however antioxidant defence mechanism cannot overpower the ROS generated, they cause oxidative damage to the plant tissues such as lipid peroxidation, protein oxidation, DNA damage, etc. resulting in cell death. Unlike other stresses, drought affects the physiology and biochemistry of the rice which adversely affects in the morphology and consequently delimits the yield of the plant. Therefore, understanding the morphological, biochemical and molecular mechanisms involved in rice against drought is utmost necessary for rice breeders to improve the rice for drought tolerant/resistance varieties for future green revolution. In this review, an attempt has been made to highlight the complex regulatory network involved in rice against drought with special emphasis on morphological, physiological and molecular mechanisms and to discuss the prospective and challenges for future plant breeders.

Transcriptome profiling of drought responsive noncoding RNAs and their target genes in rice.

BackgroundPlant transcriptome profiling has provided a tool for understanding the mechanisms by which plants respond to stress conditions. Analysis of genome-wide transcriptome will provides a useful dataset of drought responsive noncoding RNAs and their candidate target genes that may be involved in drought stress responses.ResultsHere RNA-seq analyses of leaves from drought stressed rice plants was performed, producing differential expression profiles of noncoding RNAs. We found that the transcript levels of 66 miRNAs changed significantly in response to drought conditions and that they were negatively correlated with putative target genes during the treatments. The negative correlations were further validated by qRT-PCR using total RNAs from both drought-treated leaves and various tissues at different developmental stages. The drought responsive miRNA/target pairs were confirmed by the presence of decay intermediates generated by miRNA-guided cleavages in Parallel Analysis of RNA Ends (PARE) libraries. We observed that the precursor miR171f produced two different mature miRNAs, miR171f-5p and miR171f-3p with 4 candidate target genes, the former of which was responsive to drought conditions. We found that the expression levels of the miR171f precursor negatively correlated with those of one candidate target gene, but not with the others, suggesting that miR171f-5p was drought-responsive, with Os03g0828701-00 being a likely target. Pre-miRNA expression profiling indicated that miR171f is involved in the progression of rice root development and growth, as well as the response to drought stress. Ninety-eight lncRNAs were also identified, together with their corresponding antisense transcripts, some of which were responsive to drought conditions.ConclusionsWe identified rice noncoding RNAs (66 miRNAs and 98 lncRNAs), whose expression was highly regulated by drought stress conditions, and whose transcript levels negatively correlated with putative target genes.Electronic supplementary materialThe online version of this article (doi:10.1186/s12864-016-2997-3) contains supplementary material, which is available to authorized users.

Overexpression of RSOsPR10, a root-specific rice PR10 gene, confers tolerance against drought stress in rice and drought and salt stresses in bentgrass

RSOsPR10 was originally identified as a rice root-specific pathogenesis-related protein whose production was induced by drought and salinity stresses, but not by low temperature or abscisic acid. Our previous studies revealed that RSOsPR10 expression is up-regulated by jasmonic acid, and strongly inhibited by salicylic acid. Immunohistochemical experiments indicated RSOsPR10 is expressed in the root cortical cells. In the present study, we generated RSOsPR10-overexpressing lines of rice and bentgrass to examine the physiological roles of RSOsPR10 in plants. RSOsPR10-overexpressing rice plants were highly tolerant against drought stress, but not against salinity. In contrast, RSOsPR10-overexpressing bentgrass plants were tolerant against drought and salinity stresses. There was little difference between transgenic and wild-type plants regarding phenotype or above-ground growth rates. However, the root mass of the transgenic rice and bentgrass plants was significantly greater than that of the wild-type plants. Therefore, RSOsPR10 is likely involved in mediating environmental stress tolerance through an increase in root growth and development.

Ocimum sanctum leaf extract induces drought stress tolerance in rice

ABSTRACTOcimum leaves are highly enriched in antioxidant components. Thus, its leaf extract, if applied in plants, is believed to efficiently scavenge ROS, thereby preventing oxidative damage under drought stress. Thus, the present study was performed in kharif 2013 and rabi 2014 season to evaluate the effect of aqueous leaf extract of Ocimum sanctum against drought stress in 2 rice genotype under glass house conditions. Here we show that various morpho- physiological (chlorophyll fluorescence, leaf rolling score, leaf tip burn, number of senesced leaves and total dry matter) and biochemical parameters (proline, malondialdehyde and superoxide dismutase content) were amended by Ocimum treatment in both the seasons. Application of Ocimum extract increased expression of dehydrin genes, while reducing expression of aquaporin genes in drought stressed rice plant. Thus, application of Ocimum leaf extract under drought stress can be suggested as a promising strategy to mitigate drought stress in economical, accessible and ecofriendly manner.

Over-expression of a NAC 67 transcription factor from finger millet (Eleusine coracana L.) confers tolerance against salinity and drought stress in rice.

BackgroundNAC proteins (NAM (No apical meristem), ATAF (Arabidopsis transcription activation factor) and CUC (cup-shaped cotyledon)) are plant-specific transcription factors reported to be involved in regulating growth, development and stress responses. Salinity responsive transcriptome profiling in a set of contrasting finger millet genotypes through RNA-sequencing resulted in the identification of a NAC homolog (EcNAC 67) exhibiting differential salinity responsive expression pattern.MethodsFull length cDNA of EcNAC67 was isolated, characterized and validated for its role in abiotic stress tolerance through agrobacterium mediated genetic transformation in a rice cultivar ASD16.ResultsBioinformatics analysis of putative NAC transcription factor (TF) isolated from a salinity tolerant finger millet showed its genetic relatedness to NAC67 family TFs in related cereals. Putative transgenic lines of rice over-expressing EcNAC67 were generated through Agrobacterium mediated transformation and presence/integration of transgene was confirmed through PCR and southern hybridization analysis. Transgenic rice plants harboring EcNAC67 showed enhanced tolerance against drought and salinity under greenhouse conditions. Transgenic rice plants were found to possess higher root and shoot biomass during stress and showed better revival ability upon relief from salinity stress. Upon drought stress, transgenic lines were found to maintain higher relative water content and lesser reduction in grain yield when compared to non-transgenic ASD16 plants. Drought induced spikelet sterility was found to be much lower in the transgenic lines than the non-transgenic ASD16.ConclusionResults revealed the significant role of EcNAC67 in modulating responses against dehydration stress in rice. No detectable abnormalities in the phenotypic traits were observed in the transgenic plants under normal growth conditions. Results indicate that EcNAC67 can be used as a novel source for engineering tolerance against drought and salinity stress in rice and other crop plants.Electronic supplementary materialThe online version of this article (doi:10.1186/s12896-016-0261-1) contains supplementary material, which is available to authorized users.

The NF-YA transcription factor OsNF-YA7 confers drought stress tolerance of rice in an abscisic acid independent manner

The mechanisms of plant response and adaptation to drought stress require the regulation of transcriptional networks via the induction of drought-responsive transcription factors. Nuclear Factor Y (NF-Y) transcription factors have aroused interest in roles of plant drought stress responses. However, the molecular mechanism of the NF-Y-induced drought tolerance is not well understood. Here, we functionally analyzed two rice NF-YA genes, OsNF-YA7 and OsNF-YA4. Expression of OsNF-YA7 was induced by drought stress and its overexpression in transgenic rice plants improved their drought tolerance. In contrast, OsNF-YA4 expression was not increased by drought stress and its overexpression in transgenic rice plants did not affect their sensitivity to drought stress. OsNF-YA4 expression was highly induced by the stress-related hormone abscisic acid (ABA), while OsNF-YA7 was not, indicating that OsNF-YA7 mediates drought tolerance in an ABA-independent manner. Analysis of the OsNF-YA7 promoter revealed three ABA-independent DRE/CTR elements and RNA-seq analysis identified 48 genes downstream of OsNFYA7 action putatively involved in the OsNF-YA7-mediated drought tolerance pathway. Taken together, our results suggest an important role for OsNF-YA7 in rice drought stress tolerance.

Overlap between Signaling Pathways Responsive to Xanthomonas oryzae pv. oryzae Infection and Drought Stress in Rice Introgression Line Revealed by RNA-Seq

Rice bacterial blight, caused by Xanthomonas oryzae pv. oryzae (Xoo), and drought stress are common reducers of rice yields in some regions of Asia and Africa. The rice introgression line H471 exhibits broad-spectrum dual resistance to Xoo and drought tolerance. To obtain a deeper understanding of crosstalk between signaling pathways in response to Xoo infection and drought stress, whole-genome transcriptome analyses of H471 and its recurrent parent Huang-Hua-Zhan (HHZ) were performed. A set of significant KEGG pathways involved in dual stress resistance were inferred by comparing H471 and HHZ samples under Xoo infection and drought stress using the gene set enrichment analysis method. We detected 178 genes that were differentially expressed in H471 common in response to the dual stresses when compared with HHZ, including genes for signaling perception and transduction, transcription regulation, and stress response. Putative common co-regulatory networks were constructed using 39 of the differentially expressed genes from the three different functional groups. These results will be a valuable source of information for further investigations on crosstalk between signaling pathways responsive to Xoo infection and drought stress in rice.

Photosynthetic diffusional constraints affect yield in drought stressed rice cultivars during flowering.

Global production of rice (Oryza sativa) grain is limited by water availability and the low ‘leaf-level’ photosynthetic capacity of many cultivars. Oryza sativa is extremely susceptible to water-deficits; therefore, predicted increases in the frequency and duration of drought events, combined with future rises in global temperatures and food demand, necessitate the development of more productive and drought tolerant cultivars. We investigated the underlying physiological, isotopic and morphological responses to water-deficit in seven common varieties of O. sativa, subjected to prolonged drought of varying intensities, for phenotyping purposes in open field conditions. Significant variation was observed in leaf-level photosynthesis rates (A) under both water treatments. Yield and A were influenced by the conductance of the mesophyll layer to CO2 (g m) and not by stomatal conductance (g s). Mesophyll conductance declined during drought to differing extents among the cultivars; those varieties that maintained g m during water-deficit sustained A and yield to a greater extent. However, the variety with the highest g m and yield under well-watered conditions (IR55419-04) was distinct from the most effective cultivar under drought (Vandana). Mesophyll conductance most effectively characterises the photosynthetic capacity and yield of O. sativa cultivars under both well-watered and water-deficit conditions; however, the desired attributes of high g m during optimal growth conditions and the capacity for g m to remain constant during water-deficit may be mutually exclusive. Nonetheless, future genetic and physiological studies aimed at enhancing O. sativa yield and drought stress tolerance should investigate the biochemistry and morphology of the interface between the sub-stomatal pore and mesophyll layer.

Genetic diversity and population structure in a rice drought stress panel

A drought stress panel composed of diverse accessions selected from upland, aerobic, rainfed lowland and irrigated lowland environments, was assembled to serve as germplasm for aerobic adaptation breeding. Aerobic rice requires significant levels of tolerance to drought stress due to intermittent water deficit and high soil impedance caused by aerobic conditions. Genomic information may be utilized to investigate the nature of the panel to guide varietal improvement. Using 153 simple sequence repeat and 384 single nucleotide polymorphism markers, the aim of the study was to compare the allelic properties of the two marker types, infer population structure of the panel, and estimate kinship among the accessions. There was a general agreement between the results derived from the two marker types. Marker alleles were found to occur at low frequencies, as the panel was composed mostly of improved accessions with some landraces. The panel clustered intojaponica(JA),aus(AU), upland-adaptedindica(UL) and lowland-adaptedindica(LL) subpopulations. The AU and JA subpopulations were more divergent from the rest of the subpopulations than were the LL and UL subpopulations. Average marker-based kinship for related accessions was less than 0.20, indicating a low degree of genetic relatedness in the panel. Within the LL and UL subpopulations, the low levels of kinship imply that there is still much genetic gain to be expected from utilizing the accessions in breeding. Thus, an understanding of the genetic variation in the panel suggests focusing on improving the mean in the short term, and tapping into the exotic alleles from the AU and JA subpopulations when genetic gain declines.

Grain yield QTLs with consistent-effect under reproductive-stage drought stress in rice

In this study, consistent-effect QTLs associated with grain yield under drought stress were identified using two mapping populations derived from crossing Kali Aus, a drought-tolerant rice landrace from India with mega varieties IR64 and MTU1010 as recipient parents. Two populations were phenotyped for yield and yield-component traits under reproductive-stage drought-stress and non-stress conditions in the 2011 and 2012 dry seasons (DS) at IRRI. Bulk-segregant analysis, followed by whole genotyping with selected markers, was used to identify significant markers putatively linked with high grain yield under drought. Six polymorphic markers RM246, RM450, RM250, RM232, RM518, and RM19 were found significant in bulk segregant analysis (BSA) of the Kali Aus/IR64 mapping population. Eight polymorphic markers RM495, RM572, RM246, RM211, RM250, RM231, RM3, and RM340 were found significant in the Kali Aus/MTU1010 mapping population. Analysis revealed major-effect grain yield QTLs qDTY2.3 and qDTY2.2 under drought stress consistently over two seasons in the Kali Aus/IR64 and Kali Aus/MTU1010 populations, respectively. qDTY2.3 explained 9% of phenotypic variance, with an additive effect of 451kgha−1 whereas qDTY2.2 explained 6% of phenotypic variance, with an additive effect of 121kgha−1. The QTLs showed consistent effect over two years of combined stress conditions. The two consistent-effect QTLs qDTY2.2 and qDTY2.3 can be used to improve the grain yield of mega varieties IR64 and MTU1010, respectively, across varying severity of drought stress through marker-aided backcrossing and thus provide farmers with improved varieties that effectively combines high yield potential with good yield under drought.

Nitrogen application enhanced the expression of developmental plasticity of root systems triggered by mild drought stress in rice

Background The promoted root growth under developmental plasticity triggered specifically by mild drought stress (MDS) is known to contribute to maintained water uptake and dry matter production (DMP).