Waterlogging Tolerance Research Articles

Assay of Genetic Architecture for Identification of Waterlogging Tolerant Pigeonpea Germplasm

The experiment was conducted to identify the waterlogging stress tolerant genotypes in pigeonpea. Waterlogging treatment was given to the plants at vegetative stage after treatment the survival rate was assessed. Out of 128 germplasm pool, 38 survived and the survival rate was estimated along with Mahalanobis D2 cluster analysis. The range of survival percentage for both pot and field were found between 26.6 and 73.3 with the standard deviation of 14.82 for pot screening and 14.29 for field screening. The pot survival percentage mean for all 38 accessions were found higher than field survival which clearly indicates that environment poses an effect on the performance of the genotypes. The Mahalanobis cluster analysis revealed five clusters. Out of five clusters, two were found comparatively tolerant than the others. The tolerant germplasm can also be used as donor parents in hybridization programs for development of water logging-tolerant genotypes. The identified tolerant germplasms may be utilized to incorporate waterlogging tolerance in the short-duration pigeonpea pool.

A major QTL controlling the tolerance to manganese toxicity in barley (Hordeum vulgare L.)

Waterlogging stress disturbs plant metabolism through increased ion (manganese and iron) toxicity resulting from the changes in the soil redox potential under hypoxic conditions. Our previous study found a significant correlation between the tolerance to Mn2+ toxicity and waterlogging stress tolerance in barley, suggesting that waterlogging tolerance could be increased by improving the tolerance to Mn2+ toxicity. In this study, a doubled-haploid (DH) population from the cross between barley varieties Yerong and Franklin (waterlogging-tolerant and -sensitive, respectively) was used to identify QTL controlling tolerance to Mn2+ toxicity based on chlorophyll content and plant survival as selection criteria. Four significant QTL for plant survival under Mn2+ stress (QSur.yf.1H, QSur.yf.3H, QSur.yf.4H, and QSur.yf.6H) were identified in this population at the seedling stage. Two significant QTL (QLC.yf.3H and QLC.yf.6H) controlling leaf chlorosis under Mn2+ stress were identified on chromosomes 3H and 6H close to QSur.yf.3H and QSur.yf.6H. The major QTL QSur.yf.3H, located near the marker Bmag0013, explained 21% of the phenotypic variation. The major QTL for plant survival on 3H was validated in a different DH population (TX9425/Naso Nijo). This major QTL could potentially be used in breeding programmes to enhance tolerance to both manganese toxicity and waterlogging.

REPERCUSSIONS OF WATERLOGGING STRESS AT MORPHO-PHYSIOLOGICAL LEVEL ON COTTON AND WAYS TO LESSEN THE DAMAGE TO CROP YIELDS

The volatility of the climate, which is characterized by intermittent heavy rainfall, causes flooding. The problem is exacerbated in soils with limited internal drainage by warm weather patterns. Cotton is commonly grown under these conditions, putting it at risk for yield losses due to summer flooding following heavy rainfall. This requires a deeper understanding of cotton's processes for waterlogging tolerance. This research analyses likely reasons of waterlogging-induced yield loss in cotton, as well as ways for boosting waterlogging tolerance, based on the little information available on cotton and recommendations from other species. The yield penalty is impacted by soil type, phenological stage, and the total time roots were exposed to less than 10% air-filled porosity. In addition to other soil-related issues, an oxygen deficiency in the root zone alters the redox state of nutrients, rendering some inaccessible (such as nitrogen) or potentially poisonous to plants. In addition, xylem-transported root hormones have long been linked to oxygen shortage. Reduced root growth, reduced nutrient uptake and transport, and disturbed hormone signaling are examples of subterranean effects on shoots that impact canopy formation, photosynthesis, and radiation utilization efficiency. Cotton has no evident root aerenchyma reaction and low fermentative activity compared to cereals with greater waterlogging tolerance. We believe that these traits have a significant effect on cotton's susceptibility to prolonged waterlogging. These subsurface components' effects on photosynthesis, shoot functionality, and yield components are discussed. Utilizing management techniques such as fertilizer application, soil aeration, and controlled watering helps prevent waterlogging. Reducing the expression of the genes directing ethylene production and introducing anti-ethylene compounds to limit ethylene biosynthesis are effective methods for preventing yield losses in cotton plants that have become waterlogged.

Does carbon storage confer waterlogging tolerance? Evidence from four evergreen species of a temperate rainforest

Deep shade and waterlogging are two common stressors affecting seedling performance in the understorey of evergreen rainforests. It has been hypothesised that high levels of carbon storage confer shade- and waterlogging tolerances by preventing carbon limitation under such stresses. Whether the tolerance to both stresses is positively or negatively related remains unclear. To explore the role of carbon storage in the relationships of waterlogging and shade tolerance, we investigated the responses to waterlogging and the levels of carbon storage in two species pairs with contrasting shade tolerance: Embothrium coccineum J.R.Forst.&G.Forst. and Gevuina avellana Mol. (Proteaceae) and Nothofagus dombeyi (Mirb.) Oerst. and Nothofagus nitida (Phil.) Krasser (Nothofagaceae). We subjected seedlings to waterlogging or control conditions for 30 days and evaluated survival, relative growth rate (RGR), biomass distribution, leaf chlorophyll fluorescence (Fv/Fm), and concentrations of total soluble sugars, starch and non-structural carbohydrates in different plant tissues. Waterlogging reduced survival, Fv/Fm and RGR in all species; however, the magnitude of reduction of Fv/Fm and RGR was significantly higher in the shade-intolerant species than in their shade-tolerant counterparts. In general, shade-intolerant species had significantly higher non-structural carbohydrate concentrations in waterlogging than in control conditions. By contrast, shade-tolerant species had similar non-structural carbohydrate concentrations under both conditions. Our results indicate that relatively shade-tolerant species performed better under waterlogging. A reduction in non-structural carbohydrates under waterlogging was not observed in any of studied species; rather, shade-intolerant species exhibited non-structural carbohydrate accumulation suggesting that carbon storage does not confer waterlogging tolerance in these species.

Number of tillers in wheat is an easily measurable index of genotype tolerance to saline waterlogged soils: evidence from 10 large-scale field trials in India

Over 100 wheat varieties and breeding lines from India and Australia were screened in alkaline and waterlogged soils in 10 environments over two years at one drained location and two naturally waterlogged locations in India. Mean trial grain yield was reduced up to 70% in the environments where genotypes were waterlogged for up to 15 days at the vegetative stage in alkaline soil relative to plants in drained soils. Agronomic traits (plant height, tiller number, 1000-grain weight) of genotypes were also reduced under waterlogging. At one waterlogged site, up to 68% of the genetic diversity for predicted grain yields under waterlogging could be accounted for by number of tillers (r2 = 0.41–0.68 in 2011 and 2010, respectively) and positive correlations also occurred at the second site (r2 = 0.19–0.35). However, there was no correlation between grain yields across varieties under waterlogging in any trials at the two waterlogged locations. This may have occurred because waterlogged sites differed up to 4-fold in soil salinity. When salinity was accounted for, there was a good correlation across all environments (r2 = 0.73). A physiological basis for the relationship between tillering and waterlogging tolerance is proposed, associated with crown root development. Results are compared with findings in Australia in acidic soils, and they highlight major opportunities for wheat improvement by selection for numbers of tillers when crops are waterlogged during vegetative growth.

Dynamic and epistatic QTL mapping reveals the complex genetic architecture of waterlogging tolerance in chrysanthemum.

37 unconditional QTLs, 51 conditional QTLs and considerable epistatic QTLs were detected for waterlogging tolerance, and six favourable combinations were selected accelerating the possible application of MAS in chrysanthemum breeding. Chrysanthemum is seriously impacted by soil waterlogging. To determine the genetic characteristics of waterlogging tolerance (WAT) in chrysanthemum, a population of 162 F1 lines was used to construct a genetic map to identify the dynamic and epistatic quantitative trait loci (QTLs) for four WAT traits: wilting index (WI), dead leaf ratio (DLR), chlorosis score (Score) and membership function value of waterlogging (MFVW). The h B2 for the WAT traits ranged from 0.49 to 0.64, and transgressive segregation was observed in both directions. A total of 37 unconditional consensus QTLs with 5.81-18.21% phenotypic variation explanation (PVE) and 51 conditional consensus QTLs with 5.90-24.56% PVE were detected. Interestingly, three unconditional consensus QTLs were consistently identified across different stages, whereas no conditional consensus QTLs were consistently expressed. In addition, considerable epistatic QTLs, all with PVE values ranging from 0.01 to 8.87%, were detected by a joint analysis of WAT phenotypes. These results illustrated that the QTLs (genes) controlling WAT were environmentally dependent and selectively expressed at different times and indicated that both additive and epistatic effects underlie the inheritance of WAT in chrysanthemum. The findings of the current study provide insights into the complex genetic architecture of WAT, and the identification of favourable alleles represents an important step towards the application of molecular marker-assisted selection (MAS) and QTL pyramiding in chrysanthemum WAT breeding programmes.

The Evaluation of Alkali Grass (Puccinellia ciliata Bor) Populations in Aydin Province of Turkey

Alkali grass grows in waterlogged, saline and alaline soils. The main problem in these soils is minerals at toxic level. The toxic ions are chloride, sodium and boron. A number of techniques have been investigated for removing toxic metals from the soil. Today, the cost-effective and environmentally technique is phytoremediation, using hyperaccumulator plants. Alkali grass (Puccinellia ciliata Bor) is suggested as a hyperaccumulator plant by the combination of more favourable characteristics with salt and waterlogging tolerance, high biomass value and convincing nutritive value for adverse environmental conditions. For this reason, we collected alkali grass and soil samples from five different locations in Aydın-Muğla highway, Turanlar and Sınırteke villages in Germencik-Aydın. In the soil analysis, we observed that K accumulation varies between root, shoot and panicle at least whereas Na and B shows more variation on whole plant portions among locations. Intense aerenchyma development on the root tips of Puccinellia plant was observed and it is determined as radial lysogenic aerenchyma formation. Average plant height and dry matter values were between 47.2-74.4 cm and 15.61-80.85 g/plant according to locations. The highest plant height value was obtained from the first location whereas the highest dry matter yield was detected in the fifth location. In conclusion, plants from fifth location can be regarded as fodder plants in these areas. Our results indicated that alkali grass can be effective for phytoextraction of sodium and boron from contaminated sites.

Elucidation of the molecular responses to waterlogging in Sesbania cannabina roots by transcriptome profiling

Sesbania cannabina, a multipurpose leguminous crop, is highly resistant to waterlogging stress. However, the scant genomic resources in the genus Sesbania have greatly hindered further exploration of the mechanisms underlying its waterlogging tolerance. Here, the genetic basis of flooding tolerance in S. cannabina was examined by transcriptome-wide gene expression changes using RNA-Seq in seedlings exposed to short-term (3 h) and long-term (27 h) waterlogging. After de- novo assembly, 213990 unigenes were identified, of which 145162 (79.6%) were annotated. Gene Ontology and pathway enrichment analyses revealed that the glycolysis and fermentation pathways were stimulated to produce ATP under hypoxic stress conditions. Energy-consuming biosynthetic processes were dramatically repressed by short and long term waterlogging, while amino acid metabolism was greatly induced to maintain ATP levels. The expression pattern of 10 unigenes involved in phenylpropanoid biosynthesis, glycolysis, and amino acid metabolism revealed by qRT-PCR confirmed the RNA-Seq data. The present study is a large-scale assessment of genomic resources of Sesbania and provides guidelines for probing the molecular mechanisms underlying S. cannabina waterlogging tolerance.

Comparative RNA-seq based transcriptome profiling of waterlogging response in cucumber hypocotyls reveals novel insights into the de novo adventitious root primordia initiation

BackgroundWaterlogging is a serious abiotic stress to plant growth because it results in the decline in the supplement of oxygen to submerged tissues. Although cucumber (Cucumis sativus L.) is sensitive to waterlogging, its ability to generate adventitious roots (ARs) facilitates gas diffusion and increases plant survival when the oxygen concentration is decreased. To gain a better understanding of the molecular mechanisms that enable de novo AR primordia emergence upon waterlogging, the RNA sequencing-based transcriptomic responses of two contrasting cucumber genotypes, Zaoer-N (waterlogging tolerant) and Pepino (waterlogging sensitive), which differed in their abilities to form AR were compared.ResultsMore than 27,000 transcripts were detected in cucumber hypocotyls, from which 1494 and 1766 genes in ‘Zaoer-N’ and ‘Pepino’, respectively, were differentially expressed 2 days after waterlogging. The significant positive correlation between RNA sequencing data and a qPCR analysis indicated that the identified genes were credible. A comparative analysis revealed that genes functioning in carbohydrate mobilization, nitrate assimilation, hormone production and signaling pathways, transcription factors and cell division might contribute to the waterlogging-triggered AR primordia initiation. Ethylene was determined to be an important plant hormone responsible for the cucumber ARs initiation. Additionally, genes encoding cytochrome P450, ankyrin repeat-containing proteins and sulfite oxidases were determined as important in waterlogging acclimation.ConclusionThis research broadens our understanding of the mechanism underlying waterlogging-triggered ARs emergence, and provides valuable information for the breeding of cucumber with enhanced waterlogging tolerance.

MaRAP2-4, a waterlogging-responsive ERF from Mentha, regulates bidirectional sugar transporter AtSWEET10 to modulate stress response in Arabidopsis.

SummaryAs waterlogging and successive events severely influence growth and development of economically important plants, we attempted to characterize the role of a waterlogging‐responsive group I (A‐6) ethylene response factor (MaRAP2‐4) from Mentha arvensis. Waterlogging, ethylene and methyl jasmonate rapidly induced the expression of MaRAP2‐4. MaRAP2‐4 interacted with multiple cis‐elements like dehydration response elements (DRE1/2), anoxia/jasmonic acid response element (JARE) and GCC box showing its involvement in multiple responses. MaRAP2‐4 localizes in the nucleus and acts as a transcriptional activator. Truncation and internal deletion identified a 20 amino acids potential transactivation domain (PLPSSVDAKLEAICQSLAIN) in MaRAP2‐4. MaRAP2‐4 transgenic Arabidopsis showed enhanced waterlogging and subsequent oxidative stress tolerance. Microarray analysis revealed that within up‐regulated genes 483, 212 and 132 promoters carry either single or multiple copies of DRE, JARE and GCC cis‐element/s, respectively. Within these promoters, a large section belongs to carbohydrate metabolism/transport, including many SWEET transporters. Further analysis showed MaRAP2‐4 specifically targets two positions in AtSWEEET10 promoter carrying DRE and/or GCC box that might regulate carbohydrate availability and waterlogging tolerance. These results demonstrate that MaRAP2‐4 is a positive regulator of waterlogging tolerance, and as energy‐consuming processes such as carbohydrate biosynthesis are reduced under waterlogging‐induced hypoxia, sugar transport through SWEETs may be the primary option to make sugar available to the required tissue.

Investigation and taxonomy of wild Fragaria resources in Tibet, China

Tibet is one of the main distribution centers of wild Fragaria species in China. There are abundant, precious and rare wild strawberry resources. This paper focused on the classification, distribution and evaluation of the 65 wild strawberry accessions collected from 17 counties in Tibet. The main taxonomical characters, such as stolon branching, leaflet type, flower sex, fruit shape, status of achene and sepal, and chromosome number were observed for each accession. All accessions were identified and classified into seven Fragaria species and two forms, including F. daltoniana J. Gay (2x), F. nilgerrensis Schlecht. (2x), F. nubicola Lindl. (2x), F. pentaphylla Losinsk. (2x), F. gracilis A. Los. (4x), F. moupinensis (French.) Card. (4x) and F. tibetica Staudt et Dickore. (4x). The two white-fruited forms were F. nubicola f. alba (2x) and F. moupinensis f. alba (4x). The analytic hierarchy process (AHP) method was used to perform a comprehensive assessment on the value of seven Fragaria species and two forms. The results showed that F. nilgerrensis had better fruit quality, disease resistance and waterlogging tolerance than any other species in Tibet. The collection and identification of wild strawberry resources in Tibet would be helpful to improve the fruit quality and stress resistance of modern strawberry cultivars.

Bulked Segregant RNA-seq Reveals Differential Expression and SNPs of Candidate Genes Associated with Waterlogging Tolerance in Maize.

Waterlogging has increasingly become one of the major constraints to maize productivity in some maize production zones because it causes serious yield loss. Bulked segregant RNA-seq (BSR-seq) has been widely applied to profile candidate genes and map associated Single Nucleotide Polymorphism (SNP) markers in many species. In this study, 10 waterlogging sensitive and eight tolerant inbred lines were selected from 60 maize inbred lines with waterlogging response determined and preselected by the International Maize and Wheat Improvement Center (CIMMYT) from over 400 tropical maize inbred lines. BSR-seq was performed to identify differentially expressed genes and SNPs associated with waterlogging tolerance. Upon waterlogging stress, 354 and 1094 genes were differentially expressed in the tolerant and sensitive pools, respectively, compared to untreated controls. When tolerant and sensitive pools were compared, 593 genes were differentially expressed under untreated and 431 genes under waterlogged conditions, of which 122 genes overlapped. To validate the BSR-seq results, the expression levels of six genes were determined by qRT-PCR. The qRT-PCR results were consistent with BSR-seq results. Comparison of allelic polymorphism in mRNA sequences between tolerant and sensitive pools revealed 165 (normal condition) and 128 (waterlogged condition) high-probability SNPs. We found 18 overlapping SNPs with genomic positions mapped. Eighteen SNPs were contained in 18 genes, and eight and nine of 18 genes were responsive to waterlogging stress in tolerant and sensitive lines, respectively. Six alleles of the 18 originated from tolerant pool were significantly up-regulated under waterlogging, but not those from sensitive pool. Importantly, one allele (GRMZM2G055704) of the six genes was mapped between umc1619 and umc1948 on chromosome 1 where a QTL associated with waterlogging tolerance was identified in a previous research, strongly indicating that GRMZM2G055704 is a candidate gene responsive to waterlogging. Our research contributes to the knowledge of the molecular mechanism for waterlogging tolerance in maize.

Constructing Italian ryegrass yield prediction model based on climatic data by locations in South Korea

AbstractA yield prediction model for Italian ryegrass (IRG) was constructed based on climatic data by locations in South Korea using a general linear model. The sample size of the final dataset was 312 during 25 years. The forage crop and climatic data were collected from the reports of two national research projects on forage crops and Korean meteorological administration, respectively. Five optimal climatic variables were selected through the stepwise multiple regression analysis with dry matter yield (DMY) as the response variable. Subsequently, three climatic variables were selected after considering the interpretability of the five variables. The three selected climatic variables were spring accumulated temperature, mean temperature in January and spring rainfall days. Then, the yield prediction model was constructed based on these three climatic variables using general linear model with the cultivated locations as dummy variables. The model constructed in this research could explain 73.6% of variation in DMY of IRG. The goodness‐of‐fit of the model was tested through residual diagnostics and 10‐fold cross‐validation. For climatic variables, the high partial eta squared value of spring accumulated temperature and spring rainfall may reflect the growth characteristics that spring is the main growing period for IRG and IRG has strong waterlogging tolerance and weak drought tolerance. The results may also support the possibility to sow IRG in the subsequent spring if autumnal seeding was missed in South Korea.

A new major-effect QTL for waterlogging tolerance in wild barley (H. spontaneum).

We report the first study on the unique allele from wild barley that can improve waterlogging tolerance in cultivated barley with a substantially higher contribution to aerenchyma formation. Waterlogging is one of the major abiotic stresses that dramatically reduce barley crop yield. Direct selection on waterlogging tolerance in the field is less effective due to its viability to environment. The most effective way of selection is to choose traits that make significant contributions to the overall tolerance and are easy to score. Aerenchyma formation under waterlogging stress is one of the most effective mechanisms to provide adequate oxygen supply and overcome stress-induced hypoxia imposed on plants. In this study, a new allele for aerenchyma formation was identified from a wild barley accession TAM407227 on chromosome 4H. Compared to that identified in cultivated barley, this allele not only produced a greater proportion of aerenchyma but made a greater contribution to the overall waterlogging tolerance. The QTL explained 76.8% of phenotypic variance in aerenchyma formation with a LOD value of 51.4. Markers co-segregating with the trait were identified and can be effectively used in marker assisted selection.

Physiological and morphological responses to permanent and intermittent waterlogging in seedlings of four evergreen trees of temperate swamp forests.

Waterlogging decreases a plant's metabolism, stomatal conductance (gs) and photosynthetic rate (A); however, some evergreen species show acclimation to waterlogging. By studying both the physiological and morphological responses to waterlogging, the objective of this study was to assess the acclimation capacity of four swamp forest species that reside in different microhabitats. We proposed that species (Luma apiculata [D.C.] Burret. and Drimys winteri J.R. et G. Forster.) abundant in seasonally and intermittently waterlogged areas (SIWA) would have a higher acclimation capacity than species abundant in the inner swamp (Blepharocalyx cruckshanksii [H et A.] Mied. and Myrceugenia exsucca [D.C.] Berg.) where permanent waterlogging occurs (PWA); it was expected that the species from SIWA would maintain leaf expansion and gas exchange rates during intermittent waterlogging treatments. Conversely, we expected that PWA species would have higher constitutive waterlogging tolerance, and this would be reflected in the formation of lenticels and adventitious roots. Over the course of 2 months, we subjected seedlings to different waterlogging treatments: (i) permanent (sudden, SW), (ii) intermittent (gradual) or (iii) control (field capacity, C). Survival after waterlogging was high (≥80%) for all species and treatments, and only the growth rate of D. winteri subjected to SW was affected. Drimys winteri plants had low, but constant A and g during both waterlogging treatments. Conversely, L. apiculata had the highest A and g values, and g increased significantly during the first several days of waterlogging. In general, seedlings of all species subjected to waterlogging produced more adventitious roots and fully expanded leaves and had higher specific leaf area (SLA) and stomatal density (StD) than seedlings in the C treatment. From the results gathered here, we partially accept our hypothesis as all species showed high tolerance to waterlogging, maintained growth, and had increased A or g during different time points of waterlogging. Differences in leaf (SLA) and stomata functioning (gs, StD) plasticity likely allows plants to maintain positive carbon gains when waterlogging occurs. The species-specific differences found here were not entirely related to microhabitat distribution.

Physiological and biochemical changes in waterlog tolerant sesame genotypes

An experiment was conducted under pot culture to investigate physiological responses as well as antioxidative enzymes activities that may lead to select sesame genotype (s) which were more waterlogging tolerant at vegetative stage. Four sesame genotypes viz. BD-6980, BD- 6985, BD-6992 and BD-7012 were grown under waterlogged (at vegetative stage) and control (no waterlogged) conditions. Plant height, root length, root volume, root dry weight and leaf area per plant in all the four sesame genotypes significantly decreased due to waterlogging at vegetative stage in comparison to controlled condition. Higher SPAD value (Soil and Plant Analyzer Development) and specific leaf mass were recorded in waterlogged plant than controlled plant during waterlogging period but reverse was the case during recovery period. All the genotypes showed positive indices of waterlogging tolerance in terms of better performance of root, stem, leaf and petiole. Among the genotypes, BD 6980 showed higher waterlogging tolerance in all the components followed by BD 6985. Malondialdehyde (MDA) content was found higher in waterlogged plant of all the four sesame genotypes in both waterlogging period and recovery period than the controlled plant. Antioxidant enzyme activities like Peroxidase (POD), Catalase (CAT), Ascorbate peroxidase (APX), Glutathione peroxidase (GPX) and Superoxide dismutase(SOD) were inconsistent in the present study but most of the antioxidant enzyme activities showed an increasing trend in waterlogged plant than that of control plant in all the genotypes. Comparatively low amount of MDA content and high antioxidant activities of sesame genotype BD 6980 is considered as highly tolerant to waterlogging and other three genotypes are moderately tolerant under water logging condition.SAARC J. Agri., 14(2): 31-45 (2016)

Combining ability, heterosis, genetic distance and their intercorrelations for waterlogging tolerance traits in chrysanthemum

Waterlogging tolerance (WT) is a major objective in chrysanthemum breeding programs, and although certain genotypes with different tolerance levels have been identified, their value as parents for WT breeding is unknown. Here, twelve F1 crosses derived from an incomplete diallel mating scheme were conducted to investigate combining ability and heterosis for WT and their relationships with parental genetic distance. The results showed that the membership function value of waterlogging (MFVW) was controlled by additive and non-additive gene effects, whereas other growth and biomass traits were mainly controlled by non-additive gene effects. The estimated broad and narrow sense heritabilities of the MFVW were 97.5 and 51.5%, respectively. Combining ability analyses indicated that ‘Nannong Xuefeng’ showing the largest general combining ability (GCA) effect for the MFVW was the best combiner, and identified several best cross combinations with high positive specific combining ability (SCA) effects for most WT-related traits. Mid- and high-parent heterosis occurred widely. The three distance measures, based on phenotypic traits (PD), molecular markers (GD) and markers linked with quantitative trait loci (QTL-GD), presented a non-significant correlation with combining ability except for the GD with GCA for the relative root fresh weight. The correlations between the QTL-GD and heterosis were significant for certain traits and generally higher than that of the PD or GD and heterosis. The SCA effects were positively correlated with heterosis for most of the WT traits (0.51 ≤ r ≤ 0.80). The findings benefit understanding the inheritance mode and then achieving desirable improvement for WT in chrysanthemum.

Mapping quantitative trait loci for root development under hypoxia conditions in soybean (Glycine max L. Merr.).

Greatest potential, QTLs for hypoxia and waterlogging tolerance in soybean roots were detected using a new phenotypic evaluation method. Waterlogging is a major environmental stress limiting soybean yield in wet parts of the world. Root development is an important indicator of hypoxia tolerance in soybean. However, little is known about the genetic control of root development under hypoxia. This study was conducted to identify quantitative trait loci (QTLs) responsible for root development under hypoxia. Recombinant inbred lines (RILs) developed from a cross between a hypoxia-sensitive cultivar, Tachinagaha, and a tolerant landrace, Iyodaizu, were used. Seedlings were subjected to hypoxia, and root development was evaluated with the value change in root traits between after and before treatments. We found 230 polymorphic markers spanning 2519.2cM distributed on all 20 chromosomes (Chrs.). Using these, we found 11 QTLs for root length (RL), root length development (RLD), root surface area (RSA), root surface area development (RSAD), root diameter (RD), and change in average root diameter (CARD) on Chrs. 11, 12, 13 and 14, and 7 QTLs for hypoxia tolerance of these root traits. These included QTLs for RLD and RSAD between markers Satt052 and Satt302 on Chr. 12, which are important markers of hypoxia tolerance in soybean; those QTLs were stable between 2years. To validate the QTLs, we developed a near-isogenic line with the QTL region derived from Iyodaizu. The line performed well under both hypoxia and waterlogging, suggesting that the region contains one or more genes with large effects on root development. These findings may be useful for fine mapping and positional cloning of gene responsible for root development under hypoxia.

<b>Relationship between manganese toxicity and waterlogging tolerance in <i>Zea mays</i> L. cv. Saracura

The objective of this study was to evaluate the relationship between excess manganese and waterlogging tolerance in 18 th selection cycle Zea mays L. cv. Saracura plants. Maize plants were transferred to plastic receptacles containing solutions with different concentrations of manganese. Leaves and roots were evaluated at the beginning of treatment and after 7, 14, and 21 days for chlorophyll content, biomass production and antioxidant metabolism. Mn was strongly translocated from the roots to the leaves, triggering a decrease in chlorophyll content. Excess Mn promoted an increase in reactive oxygen species that was accompanied by higher levels of antioxidative enzyme activity and lipid peroxidation. Zea mays L. cv. Saracura efficiently sequestered relatively large amounts of Mn in the leaves, with a significant impact on metabolism; however, we did not observe visual symptoms or a large decrease in biomass production.

In Silico Characterization and Functional Validation of Cell Wall Modification Genes Imparting Waterlogging Tolerance in Maize.

Cell wall modification (CWM) promotes the formation of aerenchyma in roots under waterlogging conditions as an adaptive mechanism. Lysigenous aerenchyma formation in roots improves oxygen transfer in plants, which highlights the importance of CWM as a focal point in waterlogging stress tolerance. We investigated the structural and functional compositions of CWM genes and their expression patterns under waterlogging conditions in maize. Cell wall modification genes were identified for 3 known waterlogging-responsive cis-acting regulatory elements, namely, GC motif, anaerobic response elements, and G-box, and 2 unnamed elements. Structural motifs mapped in CWM genes were represented in genes regulating waterlogging stress-tolerant pathways, including fermentation, glycolysis, programmed cell death, and reactive oxygen species signaling. The highly aligned regions of characterized and uncharacterized CWM proteins revealed common structural domains amongst them. Membrane spanning regions present in the protein structures revealed transmembrane activity of CWM proteins in the plant cell wall. Cell wall modification proteins had interacted with ethylene-responsive pathway regulating genes (E3 ubiquitin ligases RNG finger and F-box) in a maize protein-protein interaction network. Cell wall modification genes had also coexpressed with energy metabolism, programmed cell death, and reactive oxygen species signaling, regulating genes in a single coexpression cluster. These configurations of CWM genes can be used to modify the protein expression in maize under waterlogging stress condition. Our study established the importance of CWM genes in waterlogging tolerance, and these genes can be used as candidates in introgression breeding and genome editing experiments to impart tolerance in maize hybrids.