Genome-wide association study dissecting drought resistance-associated loci based on physiological traits in common bean

Genetic improvement of drought resistance is one of the main breeding goals for common bean,so molecular markers must be identified to facilitate drought resistance breeding.In this study,we evaluated the proline,trehalose,raffinose,and stachyose contents of 210 common bean accessions under two watering conditions and found large variations in all four.The coefficients of variation ranged from 21.21%for proline content to 78.69%for stachyose content under well-watered conditions,and from 20.11%for proline content to 50.08%for trehalose content under drought stress.According to our genome-wide association analysis,32 quantitative trait loci were associated with drought resistance,seven of which overlapped with known loci.Four hotspot regions were identified at Pv01,Pv07 and Pv11.A set of candidate genes was identified,including genes encoding MYB,bZIP,bHLH,ERF,and protein kinases.Among these genes,Phvul.001G189400,Phvul.007G273000 and Phvul.008G270500 were annotated as bZIP,ERF and WRKY,respectively.These genes are reportedly involved in drought stress responses in Arabidopsis thaliana and were induced by drought stress in common bean.Significant SNPs in six candidate gene regions formed different haplotypes,and phenotypic analysis revealed significant differences among the haplotypes.These results provide new insight into the genetic basis of drought resistance in common bean and reveal candidate genes and superior natural variations that will be useful for improving common bean.

Grassland-type ecosystem stability in China differs under the influence of drought and wet events

Ecological stability is a core issue in ecological research and holds significant implications forhumanity. The increased frequency and intensity of drought and wet climate events resulting from climatechange pose a major threat to global ecological stability. Variations in stability among different ecosystemshave been confirmed, but it remains unclear whether there are differences in stability within the sameterrestrial vegetation ecosystem under the influence of climate events in different directions and intensities.China's grassland ecosystem includes most grassland types and is a good choice for studying this issue.This study used the Standardized Precipitation Evapotranspiration Index-12 (SPEI-12) to identify thedirections and intensities of different types of climate events, and based on Normalized DifferenceVegetation Index (NDVI), calculated the resistance and resilience of different grassland types for 30consecutive years from 1990 to 2019 (resistance and resilience are important indicators to measurestability). Based on a traditional regression model, standardized methods were integrated to analyze theimpacts of the intensity and duration of drought and wet events on vegetation stability. The resultsshowed that meadow steppe exhibited the highest stability, while alpine steppe and desert steppe had thelowest overall stability. The stability of typical steppe, alpine meadow, temperate meadow was at anintermediate level. Regarding the impact of the duration and intensity of climate events on vegetationecosystem stability for the same grassland type, the resilience of desert steppe during drought was mainlyaffected by the duration. In contrast, the impact of intensity was not significant. However, alpine steppewas mainly affected by intensity in wet environments, and duration had no significant impact. Ourconclusions can provide decision support for the future grassland ecosystem governance.

Physiological Response Mechanism and Drought Resistance Evaluation of Passiflora edulis Sims under Drought Stress

In order to explore the response mechanism of Passiflora edulis Sims to drought stress,the changes in morpho-logical and physiological traits of Passiflora edulis Sims under different drought conditions were studied.A total of 7 germplasm resources of Passiflora edulis Sims were selected and tested under drought stress by the pot culture method under 4 treatment levels:75%–80%(Control,CK)of maximumfield water capacity,55%–60%(Light Drought,LD)of maximumfield water capacity,i.e.,mild drought,40%–45%(Moderate Drought,MD)of max-imumfield water capacity,i.e.,moderate drought and 30%–35%(Severe Drought,SD)of maximumfield water capacity,i.e.,severe drought.On the 40th day of drought treatment,13 indices,including seedling growth mor-phology,physiology,and biochemistry,were measured.The results showed that under drought stress,the height and ground diameter of P.edulis Sims gradually decreased with increasing drought stress,and there were signifi-cant differences in seedling height and ground diameter among the treatments.Drought stress significantly inhib-ited the growth of seven P.edulis Sims varieties.The contents of soluble sugar(SS),soluble protein(SP),proline(Pro),and other substances in P.edulis Sims basically increased with increasing drought stress.With the aggrava-tion of drought stress,the malondialdehyde(MDA)content of P.edulis Sims tended to increase to different degrees,the superoxide dismutase(SOD)activity and peroxidase(POD)activity both tended to increase atfirst and then decrease,and the change in catalase(CAT)activity mostly showed a gradual increasing trend.The con-tents of endogenous hormones in P.edulis Sims significantly differed under different degrees of drought stress.With the aggravation of drought stress,the abscisic acid(ABA)content of P.edulis Sims tended to increase,whereas the contents of gibberellin(GA),indoleacetic acid(IAA),and zeatin nucleoside(ZR)exhibited a down-ward trend.A comprehensive evaluation of the drought resistance of seven P.edulis Sims varieties was conducted based on the principal component analysis method,and the results showed that the drought resistance decreased in the order XH-BL>XH-TWZ>TN1>GH1>ZJ-MT>LP-LZ>DH-JW.

Association and Heritability Studies for Drought Resistance under Varied Moisture Stress Regimes in Backcross Inbred Population of Rice

Drought stress is one of the major constraints affecting rice production and yield stability in the rainfed regions. To understand the physiological basis of drought resistance related component traits, we used a backcross inbred population of rice under three kinds of moisture regimes viz., non-stress, moderate （24.48%） and severe stress （73.97%） conditions which reflect the differential responses of the genotypes to varying stress intensities. The plot yield, 1000-grain weight, panicle exsertion and canopy air temperature difference exhibited high heritability under the control conditions, whereas spikelet sterility and single plant yield exhibited high heritability under the moderate stress conditions. Traits such as days to 50% flowering, plant height and osmotic potential showed high heritability under the severe stress conditions. Plot yield under stress was significantly and positively correlated with harvest index and 1000-grain weight, but negatively associated with leaf rolling score and days to 50% flowering. The drought susceptibility index and drought response index were negatively correlated between each other both under the moderate and severe stress conditions. The derived traits viz., difference in panicle length between the control and the severe stress was associated with osmotic adjustment measured under field conditions. Difference in plant height and panicle length was negatively associated with plot yield under stress.

Physiological and Transcriptome Analysis Illuminates the Molecular Mechanisms of the Drought Resistance Improved by Alginate Oligosaccharides in Triticum aestivum L.

Alginate oligosaccharides(AOS)enhance drought resistance in wheat(Triticum aestivum L.),but the definite mechanisms remain largely unknown.The physiological and transcriptome responses of wheat seedlings treated with AOS were analyzed under drought stress simulated with polyethylene glycol-6000.The results showed that AOS promoted the growth of wheat seedlings and reduced oxidative damage by improving peroxidase and superoxide dismutase activities under drought stress.A total of 10,064 and 15,208 differentially expressed unigenes(DEGs)obtained from the AOS treatment and control samples at 24 and 72 h after dehydration,respectively,were mainly enriched in the biosynthesis of secondary metabolites(phenylpropanoid biosynthesis,flavonoid biosynthesis),carbohydrate metabolism(starch and sucrose metabolism,carbon fixation in photosynthetic organisms),lipid metabolism(fatty acid elongation,biosynthesis of unsaturated fatty acids,alpha-linolenic acid metabolism,cutin,suberine and wax biosynthesis),and signaling transduction pathways.The up-regulated genes were related to,for example,chlorophyll a-b binding protein,amylosynthease,phosphotransferase,peroxidase,phenylalanine ammonia lyase,flavone synthase,glutathione synthetase.Signaling molecules(including MAPK,plant hormones,H_(2)O_(2) and calcium)and transcription factors(mainly including NAC,MYB,MYB-related,WRKY,bZIP family members)were involved in the AOS-induced wheat drought resistance.The results obtained in this study help underpin the mechanisms of wheat drought resistance improved by AOS,and provides a theoretical basis for the application of AOS as an environmentally sustainable biological method to improve drought resistance in agriculture.

Relationship Between Drought Resistance and Betaine Aldehyde Dehydrogenase in the Shoots of Different Genotypic Wheat and Sorghum

不同基因型小麦 (TriticumaestivumL .)和高粱 (SorghumvulgareL .)的抗旱性与其种芽中的甜菜碱醛脱氢酶(BADH)的含量存在密切关系。

Screening of Drought Stress Indicators and Analysis of Drought Resistance in Cultivated Rice Germplasm Resources in Guangxi

This study aimed to screen drought stress indicators and analyze the drought resistance in 105 cultivated rice germplasm resources in Guangxi Zhuang Autonomous Region under drought stress in the whole growth period based on D value of seven morphological traits including panicle neck thickness,effective panicle number per plant,1 000-grain weight,filled grain number per panicle,total grain number,seed setting rate and yield per plant.According to the results,under drought stress,yield per plant exhibited significant positive correlation with panicle neck thickness and exhibited extremely significant positive correlation with other five morphological traits.Based on the identification and evaluation of comprehensive drought-resistance index D value,seven highly drought-resistant cultivated rice varieties were screened,accounting for 6.67％.Upland rice germplasm resources in Guangxi Zhuang Autonomous Region possess strong drought-resistance capacity,which could be used to screen highly drought-resistant rice germplasm materials.This study provided material basis and theoretical reference for breeding drought resistant rice cultivars in Guangxi Zhuang Autonomous Region.

Comprehensive Assessment of Drought Resistance of Proso Millet Germplasm Resources in Shanxi

In order to clarify drought resistance of proso millet applied in field production in Shanxi, we identified its drought resistance during the whole growth period and measured nine traits, including plant height, panicle length, stem diameter, panicle weight, grain weight per spike, straw weight per plant, node numbers of main stem, 1 000-grain weight and effective panicles, under different treatments. Principal component analysis and stepwise regression analysis were used for comprehensive evaluation of drought resistance during the whole growth period and screening the drought index. The results showed that there were correlations among 9 phenotypic traits. The coefficient of variation of panicle weight and straw weight per plant sharply reduced under normal water supply and drought stress. Landrace ＂yellow millet＂ had the strongest drought resistance（D =0.87）, integrated drought D value and membership function value of yield had significant correlation（r =0.515 9, P〈0.05）. Panicle weight and straw weight per plant had significant impact on drought resistance and could be taken as comprehensive indexes of drought resistance identification in growth period.

Analysis of Combining Ability of Drought Tolerance in Maize

By using complete-diallel cross design（Griffing method I）, the influence of the combination of different high-yield genotypes of maize on the drought tolerance of their offspring, the general combining ability, the specific combining ability and the back cross effect of drought tolerance between parents and the main genetic parameters for drought tolerance were analyzed. The result indicated that there were significant differences in general combining ability effects（GCA） of maize; there were highly significant differences in special combining ability effects（SCA）; there was no significant difference in reciprocal effects（R）. There were apparent differences in drought tolerance among six parents; to be specific, Zheng 58 had the highest drought tolerance, while PH4CV had the lowest. Improving drought-tolerant parents with Zheng 58, Ji 853 and Xinzi 8717 had gain superiority effects on the increase of drought tolerance in offspring. The influence of the genetic additive effect on the drought tolerance of offsprings varied with different parents and combinations. Therefore, the expression of drought tolerance inheritance genes was determined only by the additive and non-additive genetic effects but had little relationship with reciprocal effects. The selection of drought tolerance of maize should be conducted at higher generations.

Study on the Correlation Between Leaf Area and Drought Resistance in Different Alfalfa Varieties

[Objective] This study was to reveal the correlation between leaf area and drought resistance in different varieties of alfalfa.[Method] Using various alfalfa varieties as experimental materials,the drought resistance of leaves of drought-stressed alfalfa plants was assessed by measuring the content of free proline for analyzing its correlation with leaf area.[Result] Under drought condition,the drought resistance of alfalfa is directly related to leaf area in a positive correlation.[Conclusion] Leaf area could be used as an institutional assistant index to reflect the resistance of different alfalfa varieties.

Research on Relationship between Recovery Ability after Drought Stress-rewatering and Water Use Efficiency of Winter Wheat Varieties

The study aims at exploring the possibility of using the recovery ability af- ter drought stress-rewatering at vegetative growth stage as the evaluating index in water use efficiency （WUE） of winter wheat varieties. ＇Jing 411 ＇, ＇Jinmai 47＇ and their 34 near isogenic lines （NILs） were used as test materials. Semi-automatic rainproof shelter and the percolating pools were used for simulating drought treat- ment. After suffering severe drought stress, winter wheat crops were rewatered at early jointing stage. The biomass accumulation after rewatering was determined as recovery ability index. In the meanwhile, plant height in the end of vegetative growth stage was measured, and WUE of varieties/lines was also determined. Thereafter, the differences in recovery ability, plant height and the population WUE, together with the correlation between recovery ability and population WUE were analyzed, respectively. The results showed that there were significant differences in recovery ability among some varieties/lines. The recovery ability was affected by both geno- type and environment, and the interaction existed in these two factors. Significant differences existed in plant height and population WUE among the 34 NILs along with their parents. There was a significantly positive correlation between recovery ability and plant height of varieties/lines. Recovery ability and plant height were very significantly and positively correlated with population yield WUE respectively. The re- sults indicated that recovery ability after drought stress-rewatering could be used as an evaluating index of population WUE under drought condition.

Evaluation of Drought Resistance of Olive Varieties from Different Provenances

In order to study olive’s drought resistance in Yunnan province, different varieties of olive trees from Albania, Italy, Spain and Greece were cultured, and leaves from these trees in drought season and rainy season were col ected and determined by physiological indices, such as proline content, relative electric con-ductivity, binding water/free water, relative water content and malon-dialdehyde in leaves. The evaluation of drought resistance with subordinate function showed that：There were no significant differences among drought resistances of varieties and provenances. The change of physiological indices in different varieties showed differ-ent ranges. The drought resistance of seven varieties decreased in order as fol ows：Koroneiki〉 Picual〉 Berat〉 Kaliniot〉 Frantoio〉 Coratina〉 Arbequina.

Comprehensive Evaluation on Drought Resistance of Different Flue-cured Tobacco Cultivars in Bijie Tobacco Growing Area

Based on pot experiments, major agronomic traits, biomass accumulation, leaf water-holding capacity, relative water content, root MDA content, root proline content and other physiological indicators of four different flue-cured tobacco culti-vars under drought stress were investigated, and drought resistance in various flue-cured tobacco cultivars was comprehensively analyzed with subordinate function method, aiming at clarifying the differences in drought resistance among various flue-cured tobacco cultivars. The results indicated that under drought stress, major agronomic traits, fresh and dry mass accumulation, and leaf relative water content of four different flue-cured tobacco cultivars were reduced significantly; the decreas-ing range of Yunyan 87 reached the minimum, fol owed by Bina 1, while Qianxi 1 demonstrated the maximum decreasing range. Leaf water-holding capacity of various flue-cured tobacco cultivars showed a descending order of Yunyan 87 〉 Bina 1 〉Qianxi 1 〉 Jiucaiping 2. MDA content and proline content in roots of various flue-cured tobacco cultivars increased significantly; to be specific, Yunyan 87 and Bina 1 exhibited a slight increase in root MDA content and a significant increase in root proline content, while Jiucaiping 2 and Qianxi 1 showed an opposite trend. Accord-ing to the results of comprehensive analysis with subordinate function method, drought resistance in various flue-cured tobacco cultivars showed a descending or-der of Yunyan 87 〉 Bina 1 〉 Jiucaiping 2 〉 Qianxi 1.

Advance of Rice Drought Resistance,Water Saving Cultivation and Genetic Breeding

The water shortage faced with rice production in China was comprehensively analyzed,and the seasonal as well as spatial and temporal differences were the factors limiting rice production,which would be a severe test for grain production safety.Therefore,solving strategies had been proposed from the following aspects：the improvement of irrigation practices was of significant effect on improving the high efficient utilization of water;the screening of drought resistance cultivars and upland rice cultivation could also greatly improve the ability of drought resistance;the combination of traditional breeding techniques with modern transgenic technology as well as the QTL analysis had made considerable progress on improving the soil moisture productive potential of rice from the perspective of genetics.The development of China＇s rice industry would face greater water scarcity in the future,but the conventional water-saving technologies could only reduce water consume to a certain extent,while the exploration and improvement of the water saving potential of wetland rice to give full play to the biological water-saving function would become the goal of agricultural development in China.

Screening of drought resistance indices and evaluation of drought resistance in cotton(Gossypium hirsutum L.)

Sixteen cotton cultivars widely planted in China were sowed under five different drought concentrations(0,2.5,5,7.5,and 10%)using PEG6000 to screen the indices of drought resistance identification and explore the drought resistance of different cotton cultivars.Eighteen physiological indices including root,stem,and leaf water contents(RWC,SWC,and LWC),net photosynthetic rate(Pn),the maximum photochemical quantum yield(Fv/Fm),the actual photochemical quantum yield(ΦPSII),non-photochemical quenching coefficient(NPQ),leaf water potential(LWP),osmotic potential(Ψs),leaf relative conductivity(REC),leaf proline content(Pro),leaf and root soluble protein contents(LSPC and RSPC),leaf and root malondialdehyde(MDA)contents(LMDA and RMDA),root superoxide dismutase,peroxidase,and catalase activities(RSOD,RPOD,and RCAT)were measured.Results indicated the 18 physiological indices can be converted into five or six independent comprehensive indices by principal component analysis,and nine typical indices(Fv/Fm,SWC,LWP,Pro,LMDA,RSPC,RMDA,RSOD,and RCAT)screened out by a stepwise regression method could be utilized to evaluate the drought resistance.Moreover,the 16 cotton cultivars were divided into four types:drought sensitive,drought weak sensitive,moderate drought resistant,and drought resistant types.The resistance ability of two selected cotton cultivars(drought resistant cultivar,Dexiamian 1;drought sensitive cultivar,Yuzaomian 9110)with contrasting drought sensitivities were further verified by pot experiment.Results showed that the responses of final cotton biomass,yield,and yield composition to drought were significantly different between the two cultivars.In conclusion,drought resistant cultivar Dexiamian 1 and drought sensitive cultivar Yuzaomian 9110 were screened through hydroponics experiment,which can be used as ideal experimental materials to study the mechanism of different cotton cultivars with contrasting drought sensitivities in response to drought stress.

Relationship Between Changes of Endogenous Hormone in Sweet Potato Under Water Stress and Variety Drought-resistance

The IAA, GA3, iPA, ZR and ABA contents in sweet potato leaves under drought conditions were determined by the method of ELISA, and the relationship between these endogenous hormones and drought resistance of different sweet potato varieties were studied. The results showed the IAA, GA3, iPA and ZR contents in sweet potato leaves decreased, but ABA contents increased obviously. The stronger the drought resistance of the variety was, the more IAA, GA3, iPA and ZR contents decreased and the less ABA contents increased. Their relative contents correlated significantly negatively(r were -0.9070, -0.9493, -0.9509, -0.8674 and -0.9117 respectively)to drought-resistability.

A drought resistance index to select drought resistant plant species based on leaf water potential measurements

The water deficit in arid and semi-arid regions is the primary limiting factor for the development of urban greenery and forestation. In addition, planting the species that consume low levels of water is useful in arid and semi-arid regions that have poor water management measures. Leaf water potential(Ψ) is a physiological parameter that can be used to identify drought resistance in various species. Indeed, Ψ is one of the most important properties of a plant that can be measured using a pressure chamber. Drought avoiding or drought resistant species have a lower Ψ than plants that use normal or high levels of water. To determine drought resistance of species that are suitable for afforestation in arid urban regions, we evaluated twenty woody species in the Isfahan City, central Iran. The experimental design was random split-split plots with five replications. The species were planted outdoor in plastic pots and then subjected to treatments that consisted of two soil types and five drip irrigation regimes. To evaluate the resistance of each species to drought, we used the Ψ and the number of survived plants to obtain the drought resistance index(DRI). Then, cluster analysis, dendrogram, and similarity index were used to group the species using DRI. Result indicates that the evaluated species were classified into five groups:(1) high water consuming species(DRI>–60 MPa);(2) above normal water consuming species(–60 MPa≥DRI>–90 MPa);(3) normal water consuming species(–90 MPa≥DRI>–120 MPa);(4) semi-drought resistant species(–120 MPa≥DRI>–150 MPa);and(5) drought resistant species(DRI≤–150 MPa). According to the DRI, Salix babylonica L., Populus alba L., and P. nigra L. are high water consuming species, Platanus orientalis L. and Albizia julibrissin Benth are normal water consuming species, and Quercus infectoria Oliv. and Olea europaea L. can be considered as drought resistant species.

Genetic Analysis on Characteristics to Measure Drought Resistance Using Dongxiang Wild Rice(Oryza rufupogon Griff.) and Its Derived Backcross Inbred Lines Population at Seedling Stage

Drought stress is one of the major constraints to rice （Oryza sativa L.） production and yield stability especially in rainfed ecosystems and is getting worse as the climate changes worldwide. Dongxiang wild rice （DXWR） Oryza rufipogon Griff., contains drought resistant gene. Improving drought resistance of cultivars is crucial to increase and stabilize rice grain yield via transferring resistant gene from species related to rice. In this paper, four upland rice, sixty backcross inbred lines （BILs） derived from BC1F5 of R974//DXWR/R974, and their parents were employed to evaluate drought-resistance at seedling stage in the greenhouse. Nine traits were recorded for assessment of drought resistance, including maximum root length （MRL）, number of roots （NR）, shoot length （SL）, dry root weight （DRW）, fresh root weight （FRW）, root relative water content （RRWC）, leaf relative water content （LRWC）, level for rolling leaf （LRL）, and seedling survivability under repeat drought （SSRD）. Using more than 88% of accumulative contribution resulted from the principal component analysis （PCA）, the nine traits were classified into five independent principal components and the line 1949 showed the highest resistance. Analysis on the stepwise regression equation and correlation demonstrated that MRL, RN, FRW, and RRWC significantly influenced the drought resistance, thus could be used as comprehensive index for drought resistance at the seedling stage. Using the major gene plus polygene mixed inheritance model of quantitative traits, the inheritance of drought-resistance of BIL population at seedling stage was mostly controlled by two independent genes plus polygene. As a result, the DXWR could be precious resources for genetic improvement of drought resistance in cultivated rice.

Influence of drought hardening on the resistance physiology of potato seedlings under drought stress

In this paper, the influence of drought hardening on the growth, development, resistance physiology, leaf microstructure and stomatal behavior of potato seedlings under drought stress was studied, and the mechanism of drought hardening improvement of potato seedling drought resistance was elucidated. We found that drought stress had several adverse effects on potato seedlings, yet drought hardening alleviated the decrease in relative water content（RWC）, net photosynthetic rate（Pn） and chlorophyll content and inhibited the increase in relative electric conductivity and malondialdehyde（MDA） content. Compared with contrast seedlings, drought-hardened seedlings also had enhanced root vigor, increased antioxidant enzyme activity and higher levels of abscisic acid（ABA）, proline（Pro）, soluble sugars and polyamines（PAs） under drought stress. In addition, the stomatal density of potato seedling leaves increased significantly, while the leaf area, stomatal size and stomatal aperture decreased with drought hardening treatment. These changes led to reduced leaf transpiration rate（Tr） and improved water utilization efficiency（WUE）. The changes in leaf microstructure also had a positive effect on the drought resistance of the drought-hardened potato seedlings. So it can be concluded that through increasing the content of some endogenous hormones, osmotic regulatory substances and the activities of antioxidant enzymes, the resistance physiology of drought-hardened potato seedlings was enhanced.

The apple DNA-binding one zinc-finger protein MdDof54 promotes drought resistance

DNA-binding one zinc-finger(Dof)proteins constitute a family of transcription factors with a highly conserved Dof domain that contains a C2C2 zinc-finger motif.Although several studies have demonstrated that Dof proteins are involved in multiple plant processes,including development and stress resistance,the functions of these proteins in drought stress resistance are largely unknown.Here,we report the identification of the MdDof54 gene from apple and document its positive roles in apple drought resistance.After long-term drought stress,compared with nontransgenic plants,MdDof54 RNAi plants had significantly shorter heights and weaker root systems;the transgenic plants also had lower shoot and root hydraulic conductivity,as well as lower photosynthesis rates.By contrast,compared with nontransgenic plants,MdDof54-overexpressing plants had higher photosynthesis rates and shoot hydraulic conductivity under long-term drought stress.Moreover,compared with nontransgenic plants,MdDof54-overexpressing plants had higher survival percentages under short-term drought stress,whereas MdDof54 RNAi plants had lower survival percentages.MdDof54 RNAi plants showed significant downregulation of 99 genes and significant upregulation of 992 genes in response to drought,and 366 of these genes were responsive to drought.We used DAPseq and ChIP-seq analyses to demonstrate that MdDof54 recognizes cis-elements that contain an AAAG motif.Taken together,our results provide new information on the functions of MdDof54 in plant drought stress resistance as well as resources for apple breeding aimed at the improvement of drought resistance.