Agricultural Drought Resisting and Hydrological-Ecological Changes Taking Hebei Province in North China as an Example

Drought is usually supposed to be a rainfall deficiency problem. Most studies and practices to mitigate drought disaster are focusing on water development and irrigation, while neglecting that the agriculture system is a compounded human-natural system. Drought situation and tendency is also driven by human coping strategies. This paper takes Hebei Province in north China as an example, studing the spirally interact process of drought resisting and hydrological ecological feedback. The result shows that large scale water projects construction facilitated irrigation. With improved irrigation, farmers enhanced multiple crop index and land-use intensity greatly and increased the sowing area of water consuming crop, winter wheat. At the same time, both crop yield and gross output are raising steadily. Water demand and depletion in agricultural system increase year by year. This gradually leads to highly dependent on over exploitation of water resources, especially overdraw of groundwater. The process deteriorated the stability of hydrological-ecological system and made the ecological environment drying up. Drying up environment is breeding greater vulnerability and risk of drought in the long term. For sustainable development, integrated drought risk management should be based on the balance between sustainable water supply and water demand. The key is to improve agricultural system＇s adaptive and resilient capacity to drought.

Aβ-Carotene Ketolase Gene NfcrtO from Subaerial Cyanobacteria Confers Drought Tolerance in Rice

Nostoc flagelliforme is a terrestrial cyanobacterium that can resist many types of stressors,including drought,ultraviolet radiation,and extreme temperatures.In this study,we identified the drought tolerance gene NfcrtO,which encodes aβ-carotene ketolase,through screening the transcriptome of N.flagelliforme under water loss stress.Prokaryotic expression of NfcrtO under 0.6 mol/L sorbitol or under 0.3 mol/L NaCl stress significantly increased the growth rate of Escherichia coli.When NfcrtO was heterologously expressed in rice,the seedling height and root length of NfcrtO-overexpressing rice plants were significantly higher than those of the wild type(WT)plants grown on½Murashige and Skoog solid medium with 120 mmol/L mannitol at the seedling stage.Transcriptome analysis revealed that NfcrtO was involved in osmotic stress,antioxidant,and other stress-related pathways.Additionally,the survival rate of the NfcrtO-overexpression lines was significantly higher than that of the WT line under both hydroponic stress(24%PEG and 100 mmol/L H_(2)O_(2))and soil drought treatment at the seedling stage.Physiological traits,including the activity levels of superoxide dismutase,peroxidase,catalase,total antioxidant capacity,and the contents of proline,trehalose,and soluble sugar,were significantly improved in the NfcrtO-overexpression lines relative to those in the WT line under 20%PEG treatment.Furthermore,when water was withheld at the booting stage,the grain yield per plant of NfcrtO-overexpression lines was significantly higher than that of the WT line.Yeast two-hybrid analysis identified interactions between NfcrtO and Dna J protein,E3 ubiquitin-protein ligase,and pyrophosphate-energized vacuolar membrane proton pump.Thus,heterologous expression of NfcrtO in rice could significantly improve the tolerance of rice to osmotic stress,potentially facilitating the development of new rice varieties.

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.

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.

Increase in root density induced by coronatine improves maize drought resistance in North China

Drought stress caused by insufficient irrigation or precipitation impairs agricultural production worldwide.In this study,a two-year field experiment was conducted to investigate the effect of coronatine(COR),a functional analog of jasmonic acid(JA),on maize drought resistance.The experiment included two water treatments(rainfed and irrigation),four COR concentrations(mock,0μmol L^(-1);A1,0.1μmol L^(-1);A2,1μmol L^(-1);A3,10μmol L^(-1))and two maize genotypes(Fumin 985(FM985),a drought-resistant cultivar and Xianyu 335(XY335),a drought-sensitive cultivar).Spraying 1μmol L^(-1)COR at seedling stage increased surface root density and size,including root dry matter by 12.6%,projected root area by 19.0%,average root density by 51.9%,and thus root bleeding sap by 28.2%under drought conditions.COR application also increased leaf area and SPAD values,a result attributed to improvement of the root system and increases in abscisic acid(ABA),JA,and salicylic acid(SA)contents.The improvement of leaves and roots laid the foundation for increasing plant height and dry matter accumulation.COR application reduced anthesis and silking interval,increasing kernel number per ear.COR treatment at 1μmol L^(-1)increased the yield of XY335 and FM985 by 7.9%and 11.0%,respectively.Correlation and path analysis showed that grain yields were correlated with root dry weight and projected root area,increasing maize drought resistance mainly via leaf area index and dry matter accumulation.Overall,COR increased maize drought resistance mainly by increasing root dry weight and root area,with 1μmol L-^(-1)COR as an optimal concentration.

Genetic dissection of drought resistance for trait improvement in crops

Reliance on agriculture for food security is a constant in all modern societies.Global climate change and population growth have put immense pressure on sustainable agriculture,exacerbating the effects of environmental stresses.Drought is one of the most pressing abiotic stresses that farmers face,presenting an annual threat to crop growth and yield.Crops have evolved extensive morphological,physiological,and molecular mechanisms to combat drought stress.Drought resistance is a polygenic trait,controlled by a complex genetic network and an array of genes working together to ensure plant survival.Many studies have aimed at dissecting the genetic mechanisms underlying drought resistance.Recent studies using linkage and association mapping have made progress in identifying genetic variations that affect drought-resistance traits.These loci may potentially be engineered by genetic transformation and genome editing aimed at developing new,stress-resistant crop cultivars.Here we summarize recent progress in elucidating the genetic basis of crop drought resistance.Molecular-breeding technologies such as marker-assisted selection,genome selection,gene transformation,and genome editing are currently employed to develop drought-resistant germplasm in a variety of crops.Recent advances in basic research and crop biotechnology covered in this review will facilitate delivery of drought-resistant crops with unprecedented efficiency.

Effects of Tsukamurella tyrosinosolvens P9 on growth,physiology and antioxdant enzyme of peanut under drought stress and after re-watering

Background:The plant-growth-promoting rhizobacterium Tsukamurella tyrosinosolvens is a rare strain of actinomycete,in order to recognize and expand the ecological functions of rare actinomycetes.Methods:In this experiment,we studied the effect of Tsukamurella tyrosinosolvens P9 on the drought resistance of peanut by inoculating peanut seedlings in pots and measuring the growth and physiological indicators of peanut under drought stress and re-watering conditions.Results:The results showed that during drought stress,the relative water content of the soil and leaves,chlorophyll content,and stomatal length,width,and aperture were significantly decreased while the levels of malondialdehyde(MDA),H_(2)O_(2) and stomatal density were significantly increased.Peanut growth was also inhibited.However,inoculation with the P9 strain significantly promoted the growth of peanut under drought stress as plant height,fresh weight,root length and root weight were significantly higher compared with the uninoculated drought stress group.In addition,in P9-inoculated plants,the water and chlorophyll contents were significantly higher and the activities of the antioxidant enzymes CAT and SOD were significantly increased(except during the six days of drought treatment).While the stomatal length,width,and aperture were improved,the levels of MDA and H2O2 were significantly decreased.NBT staining showed that inoculation with P9 reduced O^(2−) accumulation under stress.After re-watering,the physiological indexes of inoculated plants recovered more quickly and grew better.Conclusions:The results showed that T.tyrosinosolvens P9 enhanced drought resistance and improves peanut growth by increasing leaf water content,increasing photosynthesis,regulating stomatal closure,and improving antioxidant enzyme activity.

Genetic dissection of yield-related traits in response to drought stress in common bean

Drought stress severely impairs common bean production.For facilitating drought-resistance breeding in common bean,molecular markers were identified in a genome-wide level marker–trait association study.A panel of 210 common bean accessions showed large variation in 11 agronomic traits at the adult stage(plant height,pod number per plant,seed number per pod,seed number per plant,seed yield per plant,pod length,harvest index,pod harvest index,days to maturity,hundred-seed weight,and seed yield)under two water conditions.The coefficient of variation ranged from 6.21% for pod harvest index to51.00% for seed number per plant under well-watered conditions,and from 4.05% for days to maturity to 40.72% for seed number per plant under drought stress.In a genome-wide association study,119quantitative-trait loci were associated with drought resistance,including 41 adjacent to known loci.Among these loci,12 were found to be associated with at least two traits.Three major loci were identified at Pv01 and Pv02.A set of candidate genes were found that encode MYBs,AREBs,WKRYs,and protein kinases.These results reveal promising alleles that control drought resistance,shedding light on the genetic basis of drought resistance and accelerating future efforts for drought resistance improvement in common bean.

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.

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.

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.

Drought-resistant Hybrid Millet under Watersaving Irrigation in Extreme Drought Area of Dunhuang City

[Objective]This study aimed to select hybrid mil et varieties those can produce high yield under water-saving irrigation conditions. [Method] From 2011 to 2013, drought-resistant experiments on 200 hybrid mil et combinations were carried out in the three consecutive years in Dunhuang City. Plastic film was covered on the soil surface in one treatment （F） and was not in the other treatment （NF）. Irri-gation was only performed once before sowing. At seedling stage, jointing stage, heading stage and fil ing stage, we measured the water contents of soil at 0-20, 20-40, 40-60, 60-80, 80-100 and 100-120 cm deep. Plant height, panicle length, til er number, grain weight per ear, grain weight per plant, grass weight and above-ground biomass were measured from a bulk of eight plants in each plot. Grain yield per plot was measured final y. [Result] Under the only irrigation of 1 200 m3/hm2 before sowing, 18 hybrid mil et combinations exhibited stronger resistance to drought, and four of them： 13DH2, 13DH3, 13DH8 and 13DH9 produced grain more than 3 000 kg/hm2. The yield of hybrid mil et combination 13DH8 was up to 6 000 kg/hm2 under the only irrigation of 1 200 m3/hm2, i.e. 1 m3 of water could produce 5 kg of grain on average. Therefore, application of this cultivation technology could increase arable land of irrigated arid area by several times. In addition, irrigation of 1 200 m3/hm2 is equivalent to 120 mm of rainfal; so this cultivation technology also can be applied in arid area with 200 mm of rainfal . [Conclusion] The cultivation technology can cope with the occurrence of extreme weather, protect water re-sources and enlarge global grain planting area. At the same time, it also ensures food production and food safety.

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.

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.

Relationship Between Soluble Protein,Chlorophyll and ATP in Drought-Resistant Sweet Potato Under Water Stress

Some indices concerning the metabolism of substance and energy in sweet potato leaves under water stress were studied. The results showed an obvious increase in soluble protein content. Compared with control, Chl a, Chl b, total Chl contents and the ratio of Chl a to Chl b all decreased to some extent. ATP content increased in some varieties and decreased in others, but the stronger the drought resistance of the variety , the higher the ATP content. The correlation coefficient(r)of the soluble protein content, ratio of Chl a to Chl b and ATP content as a percentage of the drought-resistant sweet potato control variety are 0. 8968, - 0. 8509 and 0. 8200, respectively, P<0. 01. So these indices can be used to evaluate the drought resistance of different sweet potato varieties.