Yield response of rice (Oryza sativa L.) genotypes to drought under rainfed lowland: 3. Plant factors contributing to drought resistance

A series of experiments were conducted in drought-prone northeast Thailand to examine the magnitude of yield responses of diverse genotypes to drought stress environments and to identify traits that may confer drought resistance to rainfed lowland rice. One hundred and twenty eight genotypes were grown under non-stress and four different types of drought stress conditions.Under severe drought conditions, the maintenance of PWP of genotypes played a significant role in determining final grain yield. Because of their smaller plant size (lower total dry matter at anthesis) genotypes that extracted less soil water during the early stages of the drought period, tended to maintain higher PWP and had a higher fertile panicle percentage, filled grain percentage and final grain yield than other genotypes. PWP was correlated with delay in flowering (r=−0.387) indicating that the latter could be used as a measure of water potential under stress. Genotypes with well-developed root systems extracted water too rapidly and experienced severe water stress at flowering. RPR which showed smaller coefficient of variation was more useful than root mass density in identifying genotypes with large root system.Under less severe and prolonged drought conditions, genotypes that could achieve higher plant dry matter at anthesis were desirable. They had less delay in flowering, higher grain yield and higher drought response index, indicating the importance of ability to grow during the prolonged stress period.Other shoot characters (osmotic potential, leaf temperature, leaf rolling, leaf death) had little effect on grain yield under different drought conditions. This was associated with a lack of genetic variation and difficulty in estimating trait values precisely.Under mild stress conditions (yield loss less than 50%), there was no significant relationship between the measured drought characters and grain yield. Under these mild drought conditions, yield is determined more by yield potential and phenotype than by drought resistant mechanisms per se.     

Association between aflatoxin contamination and drought tolerance traits in peanut

The current study investigates the association between drought tolerance traits and aflatoxin contamination in peanut grown under long-term drought. Two field experiments were conducted at Khon Kaen University, Thailand using a split–split plot design with three drought stress levels as main plots, 11 genotypes as sub-plots, and two soil inoculations of Aspergillus flavus treatments as sub-sub-plots. The effects of temperature, soil moisture and A. flavus population on kernel colonization and aflatoxin contamination, and drought tolerance traits viz. specific leaf area (SLA) and root length density (RLD) were measured. The results demonstrated that elevated soil temperatures and reduced soil moisture, favored aflatoxin production. Drought in combination with higher levels of A. flavus inoculum load in the soil resulted in an increase in the fungal populations in the soil which in turn resulted in increased kernel colonization and subsequent aflatoxin contamination. A combination of SLA and RLD, and kernel colonization had a significant influence on aflatoxin contamination under drought conditions in both seasons (r = 0.73** and 0.76**). The results revealed that drought tolerance traits (SLA and RLD) could be contributing to resistance to aflatoxin contamination suggesting that a combination of SLA, RLD and kernel colonization could be used as selection criteria in selecting parents for aflatoxin resistance.     

不同生育时期干旱对花生根系生理特性及产量的影响

采用旱棚土柱栽培法,研究了不同生育时期干旱对花生根系生理特性及产量的影响。结果表明:干旱胁迫下,花生根系变长,直径变小,表面积增大,根尖数增多,根系活力下降,根系总吸收面积、根系活跃吸收面积增大,根干物质量、根冠比增大。不同生育时期相比,花针期和结荚期干旱对根系生长发育和根系活力的影响明显大于苗期和饱果期干旱,而根系总吸收面积和活跃吸收面积增幅显著低于苗期和饱果期,表明花针期和结荚期对干旱反应敏感;不同时期干旱明显降低了花生荚果产量,结荚期减产最大,其次为花针期和饱果期,苗期减产最小。     

Rice near-isogenic-lines (NILs) contrasting for grain yield under lowland drought stress

The development of near-isogenic-lines (NILs) is a very important tool for both genetic and physiological dissection of drought resistance in rice. Two pairs of NILs differing for grain yield under drought stress were isolated and characterized for yield, yield related traits, and several physiological traits in a range of contrasting environments. In replicated field trials both NIL pairs differed significantly for grain yield under drought stress but showed similar yield potential, phenology, and yield component traits under non-stress conditions. A polymorphism analysis study with 491 SSRs revealed that both NIL pairs are at least 96% genetically similar. These NILs show that small genetic differences can cause large difference in grain yield under drought stress in rice. In both pairs the drought-tolerant NILs showed a significantly higher assimilation rate at later stages both under stress and non-stress conditions. They also had a higher transpiration rate under non-stress condition. The most tolerant NIL (IR77298-14-1-2-B-10) had significantly higher transpiration rate and stomatal conductance in severe stress conditions. In one pair the tolerant NIL had constitutively deeper roots than the susceptible NIL. In the second pair, which had higher mean root length than the first pair, the tolerant NIL had more roots, greater root thickness, and greater root dry weight than the susceptible NIL. Deeper root length may allow tolerant NILs to extract more water at deeper soil layers. It is concluded that enhanced rooting depth is an important strategy for dehydration avoidance and rice adaptation to drought stress, but root architecture might not be the only mechanism causing the significant yield increase we observed in lowland drought stress environments. To further dissect the drought avoidance mechanisms in rice, analysis of root hydraulic properties may be necessary.     

花生水分胁迫研究II.荚果生长

本文探讨了水分胁迫对结荚期花生荚果发育的影响。为期两年(1997/98和1998/99)的试验是在农牧学院(国立R姫oCuarto大学)试验场开展的。目的是量化与水分胁迫有关的物候因子的变化与花生荚果发育的关系。试验采用的是生育期为150d的兰娜型花生品种。荚果发育水平分别通过成熟度和荚果干重两方面来定性和定量衡量。水分胁迫对荚果发育的影响表现为改变发育起始阶段时间、荚果发育速率和生育期、成熟度和最终产量。两年的试验结果相似,主要结果取自处理S2(开花下针期进行干旱处理),包括花期延长,下针结果期延迟11～13d,降低荚果发育速率(11.5～12.6mg·d 1,对照为17.0mg·d 1),以及降低荚果最终产量。     

Variation in root system architecture and drought response in rice (Oryza sativa): Phenotyping of the OryzaSNP panel in rainfed lowland fields

Root growth at soil depths below 30 cm may provide access to critical soil water reserves during drought in rainfed lowland rice. In this study, the OryzaSNP panel, a set of 20 lines representing genetic diversity in rice used for the discovery of DNA sequence polymorphisms, was evaluated for root characteristics in the field over three seasons varying in drought severity. Root length density (RLD) at a depth of 30–45 cm varied up to 74–92% among genotypes under drought stress (2008–2009 dry seasons), ranging from 0.024 to 0.23 cm cm⁻³ in 2008 and from 0.19 to 0.81 cm cm⁻³ in 2009. Real-time monitoring of soil moisture profiles revealed significant differences among genotypes, and these differences were correlated with RLD at those soil depths. Among the lines evaluated, the Aus isozyme group, particularly the genotype Dular, showed greater drought resistance associated with deep root growth and the highest drought response index (less reduction in yield by drought stress). Since the set of genotypes used in this study has been completely sequenced for SNP markers, the phenotypic information on root growth and drought avoidance responses presented here could be used in initial analysis of the genetic basis of dehydration avoidance traits and in facilitating improvement in drought resistance in rice.     

不同生育时期干旱处理对夏花生生长发育的影响

旱棚盆栽条件下研究了夏花生生长发育和生理性状对土壤干旱的反应，结果表明，水分胁迫使夏花生营养生长及干物质积累量下降，根系体积下降，叶片中叶绿素含量和脯氨酸含量提高。苗期干旱对营养生长影响最大，花针期和结荚期干旱主要影响生殖生长和产量形成，导致产量降低。     

干旱胁迫对花生生长发育和光合产物积累的影响

采用人工控制条件下的防雨棚土柱栽培试验,以不同抗旱类型花生品种为材料,设置充分灌水和中度干旱胁迫处理,对苗期、花针期、结荚期、饱果期和成熟期(播种后30d、50d、75d、103d和132d)5个生育时期地上部不同器官和根系物质积累的影响进行了研究。结果表明,随生育期的进行,除花育22号在全生育期干旱胁迫条件下呈渐升趋势至成熟期最大外,花育23号和花育25号2品种根系干物质积累量均呈"抛物线型"变化趋势。干旱胁迫使花育23号根系干物质积累量峰值出现在结荚期,而花育25号峰值滞后到饱果期。3品种根重和荚果干物质积累量大小顺序均表现为:花育25号花育22号花育23号;通过Logistic方程能很好地拟合各品种地上部各器官、根系及植株生长发育情况。干旱胁迫使花育22号和花育23号两品种最大生长速率(Vm)明显降低,花育25号明显升高,但3品种地上部植株物质积累最大速率出现的时间(Tm)均明显滞后;地上部叶片和茎Vm降低,Tm延长;干旱胁迫使花生光合作用降低,光合产物积累缓慢,植株生长发育迟滞。3品种表现出对干旱胁迫适应性的差异,花育23号品种对水分较为敏感,抗旱性较差,花育25号具有较强的抗旱性。     

氮素用量对菜用大豆生殖生长期根系及鲜荚产量的影响

采用盆栽试验,利用根系扫描分析系统研究了不同氮素用量(0、100、200、300 mg.kg-1)下菜用大豆生殖生长期根系形态动态变化特征,并比较了单株鲜荚产量差异。结果表明:不同氮素用量下生殖生长期菜用大豆根系形态指标均呈单峰曲线变化,峰值出现在开花后21 d;100 mg.kg-1氮素用量能明显促进菜用大豆根系发育和根瘤干物质的积累,促使大豆形成较大的根系表面积,较高的单株产量以及2粒荚和3粒荚数;当氮素施用量增加到200和300mg.kg-1时,根系干物质、根系表面积、根长和单株鲜荚产量均降低;300 mg.kg-1氮素施用量的根体积最大;不施氮处理的根瘤数目和重量最高,形成较多的细根,表现为根系长度最长,根系干物质重最低。     

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

Tolerance of 42 bread wheat genotypes to drought stress after anthesis

The present research characterized yield and yield components of 42 wheat genotypes after terminal drought stress. The experiment was in twice replicated simple rectangular lattice design, conducted at irrigated and terminal stress conditions during 2006-2007. These study genotypes had significant differences for grain yield at level of 1%. Genotypes 4057, Viking/5/Gds/4.., Sabalan and 5041 respectively with 6.313, 6.159, 5.793 and 5.774 t ha(-1) had the highest yield and Gascogen has the lowest yield with 2.561 t ha(-1). Mean of total grain yield for under study genotypes was 5.628 t ha(-1) in non-stress and 3.305 t ha(-1) in drought stress conditions. Drought stress decreased amount of grain yield 2.323 t ha(-1) that was noticeable. Interaction of Genotype x environmental conditions was significant at probability level of 1% for grain yield. Yield of all genotypes in drought condition was lower than non-stress condition. Genotypes Viking/5/Gds/4/Anza/3/Pi.., Sabalan, 4061,4057 and 4041 had more yield in non-stress condition and MV17/Zrn, Sabalan, Saysonz and 4032 in stress condition. Stress intensity pay attention to total grain yield was 42%. Genotypes Viking/5/Gds/4/.. and Sabalan had high grain yield and was better than other genotypes and controls (Toos and Crosse Shahi), according to GMP, STI and MSTI. And had the most amount of stress tolerance index as compared with other genotypes confirms this subject. Correlation of yield with other traits was not significant in non-stress condition. In drought condition, correlation of grain yield with 1000 grain weight and total number of tillers per plant was positively significant. ANOVA showed significant differences between osmotic pressures for coleoptile length, between genotypes for mean and maximum coleoptile length and between interactions of genotypes x osmotic pressures for mean and maximum coleoptile length. Mean comparisons showed the highest total, mean and maximum coleoptile length in -7 bar PEG+I ml L(-1) potassium humate treatments. Genotypes Sardari and Sabalan had the highest amounts of total, mean and maximum coleoptile length. With due attention to interaction genotype x osmotic pressures, genotypes Sardari, Sabalan and 4057 in -7 bar PEG+1 ml L(-1) potassium humate had the most amounts of noted characters than others. In conditions of this experiment, potassium humate caused increase in tolerance rate of genotypes against drought stress.     

大豆不同生殖生长期干旱胁迫条件下施磷对根系形态性状的影响

磷素(P)是提高植物抗水分胁迫能力的重要因子.选取大豆(Glycinemax L. Merrill)品种东农434进行盆栽试验,分别在大豆R1期(初花期)和R4期(盛荚期)进行干旱胁迫处理,解析P在干旱胁迫条件下对根系性状和产量的影响.试验设置4个施P水平,即0、7.3、14.6和29.2 mgkg-1.3个水份处理,即(1)全生育期维持田间持水量(FWC)的65%～75%为对照;(2)R1期控水为FWC的30%～40%;(3)R4期控水为FWC的30%～40%.结果表明,两个时期的干旱胁迫均显著影响根系性状,降低产量,且R4期比R1期严重.磷素营养显著改善干旱胁迫所引起的不利影响,增加根干重、根长、根表面积,进而减少大豆产量的损失.     

Genetic analysis and validation of quantitative trait loci associated with reproductive-growth traits and grain yield under drought stress in a doubled haploid line population of rice (Oryza sativa L.)

Drought is a major constraint for rice production and yield stability in rainfed ecosystems, especially when it occurs during the reproductive stage. Combined genetic and physiological analysis of reproductive-growth traits and their effects on yield and yield components under drought stress is important for dissecting the biological bases of drought resistance and for rice yield improvement in water-limited environments. A subset of a doubled haploid (DH) line population of CT9993-5-10-1-M/IR62266-42-6-2 was evaluated for variation in plant water status, phenology, reproductive-growth traits, yield and yield components under reproductive-stage drought stress and irrigated (non-stress) conditions in the field. Since this DH line population was previously used in extensive quantitative trait loci (QTLs) mapping of various drought resistance component traits, we aimed at identifying QTLs for specific reproductive-growth and yield traits and also to validate the consensus QTLs identified earlier in these DH lines using meta-analysis. DH lines showed significant variation for plant water status, reproductive-growth traits, yield and yield components under drought stress. Total dry matter, number of panicles per plant, harvest index, panicle harvest index, panicle fertility, pollen fertility, spikelet fertility and hundred grain weight had significant positive correlations with grain yield under drought stress. A total of 46 QTLs were identified for the various traits under stress and non-stress conditions with phenotypic effect ranging from 9.5 to 35.6% in this study. QTLs for panicle exsertion, peduncle length and pollen fertility, identified for the first time in this study, could be useful in marker-assisted breeding (MAB) for drought resistance in rice. A total of 97 QTLs linked to plant growth, phenology, reproductive-growth traits, yield and its components under non-stress and drought stress, identified in this study as well as from earlier published information, were subjected to meta-analysis. Meta-analysis identified 23 MQTLs linked to plant phenology and production traits under stress conditions. Among them, four MQTLs viz., 1.3 for plant height, 3.1 for days to flowering, 8.1 for days to flowering or delay in flowering and 9.1 for days to flowering are true QTLs. Consensus QTLs for reproductive-growth traits and grain yield under drought stress have been identified on chromosomes 1 and 9 using meta-QTL analysis in these DH lines. These MQTLs associated with reproductive-growth, grain yield and its component traits under drought stress could be useful targets for drought resistance improvement in rice through MAB and/or map-based positional analysis of candidate genes.     

不同生育期干旱对花生衰老特性及产量的影响

在防雨棚池栽和盆栽条件下,通过人工控水研究了不同生育期干旱对花生衰老特性和产量的影响。研究表明,不同生育期干旱均导致花生叶片叶绿素含量、净光合速率、SOD、POD、CAT活性和花生根系活力的降低,致叶片MDA含量提高,其中花针期和结荚期干旱对花生衰老特性影响最大。干旱处理均导致荚果产量、生物产量降低,花针期和结荚期干旱对花生产量形成影响最大。     

Survival and recovery of tall fescue genotypes: association with root characteristics and drought tolerance

Identification and selection of plant genotypes with survival, recovery and sustainable performance during drought periods is one of the main objectives of plant improvement for arid and semi‐arid regions. This study aimed to evaluate root traits and recovery of tall fescue genotypes after a period of drought stress. A total of twenty four tall fescue genotypes were selected from a wide polycross population and assessed for field drought tolerance based on stress tolerance index (STI) and recovery during 2010–2013. The genotypes were classified as tolerant, moderately tolerant and susceptible based on STI. Then, in 2014, genotypes were assessed in a pot experiment for root characteristics under two levels of moisture environments (control and intense drought stress). In both moisture environments, root length (RL), root area (RA), root volume (RV) and root weight (RW) were negatively correlated with days to recovery (DR). Genotypes that recovered from drought had greater RL, RA, RV and RW than the genotypes unable to recover. Principle component analysis (PCA) was performed to identify genotypes with superior root characteristics, stress tolerance and recovery potential that can be used for future breeding programmes. Results indicated that selection based on combining STI, recovery and extensive root system might improve drought tolerance of tall fescue.     

Yield and yield-attributing traits of rice (Oryza sativa L.) under lowland drought and suitability of early vigor as a selection criterion

Fifteen experiments testing seven sets of genotypes under irrigated non-stress and drought stress situations were conducted from 2004 to 2006 with the objective to study the effect of different severity levels of drought on tolerant and susceptible advanced breeding lines, current varieties, and traditional and improved donors, and to study the effect of selection for high early vigor on yield. With the onset of drought, a yield reduction due to a decrease in biomass was observed in both susceptible and tolerant lines. However, after an initial reduction in yield, tolerant lines were able to sustain a yield loss more effectively than susceptible lines by better maintenance of biomass and higher harvest index. Under intermittent drought stress, genotypes with the ability to maintain higher biomass, reflected in terms of high early vigor recorded 3 wk after transplanting, recorded higher grain yield than genotypes with low early vigor. Lines with high early vigor yielded higher under both irrigated non-stress and intermittent drought stress situations. Under intermittent stress, plants with high vigor, low vigor, or random plants with high or low vigor coming from tolerant × susceptible crosses yielded higher than did the plants with the same vigor coming from susceptible × susceptible crosses. Under both irrigated non-stress and intermittent drought stress situations, early vigor showed significant genetic correlation with grain yield and could be included as an efficient selection criterion to improve yield in the lowlands.     

水分胁迫对秋植花生结荚期同化物运输的影响

在秋播花生开花下针期至饱果成熟期给予不同程度的干旱处理,结果表明,无论是轻度、中度或严重干旱均影响果实的发育,使代谢源中的同化物向代谢库(荚果)中输出减少,植株叶片的含水量下降,蒸腾速率、光合速率及叶绿素含量降低,呼吸速率升高,同时花生经济产量降低。     

Comparison of Root System Development in Two Rice Cultivars During Stress Recovery from Drought and the Plant Traits for Drought Resistance

Summary

A greenhouse experiment was conducted to compare root system development of two upland rice cultivars, IRAT 13 and Senshou, during recovery from drought stress and to identify the plant traits that confer drought resistance. From 62 days after sowing (62 DAS), drought stress was given for 6 d followed by rewatering for 14 d. Root length density (RLD) and root diameter (thickness) were measured at the end of the stress and rewatering periods. Control plants were well-watered throughout the study. Gultivar IRAT 13 had thicker roots and higher relative RLD (ratio of RLD in drought-stressed plants to that in control plants) than under drought stress, and significantly higher root growth recovery after rewatering cultivar Senshou. Related plant traits such as evapotranspiration (ET), leaf and stem dry weights and weight of senescent leaves (dead leaves) in IRAT 13 were significantly more favorable for drought resistance compared to Senshou.     

甘蓝型油菜耐湿性的遗传差异鉴定

9个不同遗传背景的甘蓝型油菜品种（系）在室内进行发芽种子水淹和春季田间模拟湿害条件下，研究油菜对湿害胁迫的耐湿遗传差异。结果表明，不同油菜品种（系）对湿害具有较大的遗传差异。发芽种子湿害胁迫后，耐湿品种中双8号和中双9号等品系（种）具有较强的耐湿性，表现为发芽湿害处理后活力指数、成苗率、相对苗长、相对根长和相对苗重等显著较高，田间湿害后单株有效果数、每角粒数和单株粒重的降低程度显著低于其他品种，而且千粒重显著提高，含油量和蛋白质变化不显著。不耐湿的品种如GH01等活力指数、相对苗长、相对苗重、单株粒重、每角粒数含油量等显著降低，蛋白质含量显著提高。相关分析表明，发芽种子耐湿活力指数与花期田间湿害后的产量性状耐湿指标具有显著或极显著的相关关系。     

Breeding for drought tolerance: Direct selection for yield, response to selection and use of drought-tolerant donors in upland and lowland-adapted populations

Drought is the most important constraint reducing rice yield in rainfed areas. Earlier efforts to improve rice yield under drought mainly focused on improving secondary traits because the broad-sense heritability (H) of grain yield under drought stress was assumed to be low, however gains in yield by selecting for secondary traits have not been clearly demonstrated in rice. In present study, the effectiveness of direct selection for grain yield was assessed under lowland reproductive stage stress at Raipur in eastern India and under upland reproductive stage drought stress at IRRI. The selection under severe stress (in both upland and lowland trials) resulted in greater gains under similar stress levels (yield reduction of 65% or greater under stress) in evaluation experiments than did selection under non-stress conditions, with no yield reduction under non-stress conditions. We observed similar H of grain yield under stress and non-stress conditions, indicating direct selection for yield under drought will be effective under both lowland and upland drought stresses. None of the secondary traits (panicle exsertion, harvest index, leaf rolling, leaf drying) included in our study showed a higher estimate for H than grain yield under stress. Secondary traits as well as indirect selection for grain yield under non-stress situation were predicted to be less effective in improving yield under drought in both lowland and upland ecosystem than direct selection for grain yield under the respective stress situations. The low, but positive values observed for genetic correlation (r_G) between yield under stress and non-stress indicated that it is possible to combine drought tolerance with high-yield potential but low values also indicated that selection for grain yield needs to be carried under stress environments. The study also indicated that under lowland drought stress, the use of highly drought-tolerant donors, as parents in crosses to high yielding but susceptible varieties resulted in a much higher frequency of genotypes combining high-yield potential with tolerance than did crosses among elite lines with high-yield potential but poor tolerance. Breeding strategies that use drought-tolerant donors and that combine screening for yield under managed drought stress with screening for yield potential are likely to result in the development of improved cultivars for drought-prone rainfed rice producing areas.