Root characteristic system improves drought tolerance in orchardgrass

Plant genotypes with higher drought tolerance through improved root characteristics are poorly studied in orchardgrass. In the current research, 30 orchardgrass genotypes were polycrossed and the resulting half‐sib families evaluated under both normal and water stress environments. Under water stress conditions, values for most root traits decreased at 0–30 cm soil depth, while at 30–60 cm depths, the root length (RL), root area (RA), root volume, percentage of root dry weight (RDW) and the ratio of root to shoot were increased. We identified drought‐tolerant genotypes with a high combining ability for root characteristics and a high yield potential. High estimates of heritability as well as genetic variation for root traits indicated that phenotypic selection would be successful in order to achieve genetic progress. Indirect selection to improve dry matter yield was most efficient when selecting for RL and RDW under water stress conditions. Significant associations between a drought tolerance index and RL, RA and root volume confirmed the importance of these traits in conferring drought tolerance of orchardgrass.     

不同氮肥利用效率水稻基因型剑叶光合特性

选用氮肥利用高效型和低效型具有代表性的12个粳稻品种,研究225 kg hm^-2施氮条件下水稻剑叶光合特性的差异及其与氮肥利用效率、水稻结实性的相互关系。结果表明,齐穗后,氮高效基因型水稻的叶绿素含量、叶片含氮量、净光合速率、光合功能期和叶绿素荧光动力学参数中的最大光化学效率(F_v/F_m)、PS II的潜在活性(F_v/F_o)、实际光化学效率(Φ_PSII)、光化学猝灭系数(q_P)和非光化学猝灭系数(q_N)均显著高于氮低效基因型。相关性分析表明,齐穗后不同时期,剑叶中叶绿素含量、叶片含氮量、净光合速率、剑叶的光合功能期和叶绿素荧光动力学参数值(F_v/F_m、F_v/F_o、Φ_PSII、q_P、q_N)与水稻的氮肥利用效率、结实性均呈极显著的正相关。由此说明,与氮低效基因型相比,氮高效基因型水稻生育后期具有较好的光合特性,较长的光合功能期;同时,其PSII反应中心更加稳定,具有更大的光能转化为电化学能的潜力,非光化学猝灭对光合机构也有更好的保护作用。因而,其在促进植株光合物质积累,提高结实性的同时能通过地上部与地下部的调节反馈增强植株对氮肥的吸收利用。     

Genotype selection for physiological responses of drought tolerance using molecular markers in polycross hybrids of orchardgrass

The present study aimed to assess the effect of contrasting levels of molecular and phenotypic diversity among polycross parents of orchardgrass on the performance of synthetic progeny with respect to physiological responses and drought tolerance. Four polycross groups each composed of six parental plants were evaluated under normal irrigation and drought stress conditions. A number of 923 inter simple sequence repeats and sequence related amplified polymorphism markers and several phenotypic traits were used to select contrasting levels of diversity (high and low) in parental genotypes. Highly significant correlation was observed between molecular distance and progeny performances at both normal irrigation and drought stress conditions. High molecular diversity among polycross parents led to a significant yield advantage of first generation progeny with averages of 34.40% for normal irrigation and 48.10% for drought stress conditions. Also crosses between genetically distant parents produced progeny with considerable drought tolerance and yield stability. Positive associations between phenotypic distance of parents and progeny performance were found for most physiological traits at both moisture regimes but phenotypic distances had weak association with forage yield, stress tolerance index and yield stability of progeny. Significant associations between drought tolerance index and some physiological traits confirmed the importance of these traits in conferring drought tolerance of orchardgrass. Our results underscore the effectiveness of marker‐assisted polycross breeding to improve drought tolerance and yield stability through physiological traits in orchardgrass.     

Assessment of Groundnut under Combined Heat and Drought Stress

In semi‐arid regions, particularly in the Sahel, water and high‐temperature stress are serious constraints for groundnut production. Understanding of combined effects of heat and drought on physiological traits, yield and its attributes is of special significance for improving groundnut productivity. Two hundred and sixty‐eight groundnut genotypes were evaluated in four trials under both intermittent drought and fully irrigated conditions, two of the trial being exposed to moderate temperature, while the two other trials were exposed to high temperature. The objectives were to analyse the component of the genetic variance and their interactions with water treatment, year and environment (temperature) for agronomic characteristics, to select genotypes with high pod yield under hot‐ and moderate‐temperature conditions, or both, and to identify traits conferring heat and/or drought tolerance. Strong effects of water treatment (Trt), genotype (G) and genotype‐by‐treatment (GxTrt) interaction were observed for pod yield (Py), haulm yield (Hy) and harvest index (HI). The pod yield decrease caused by drought stress was 72 % at high temperature and 55 % at moderate temperature. Pod yield under well‐watered (WW) conditions did not decrease under high‐temperature conditions. Haulm yield decrease caused by water stress (WS) was 34 % at high temperature and 42 % under moderate temperature. Haulm yield tended to increase under high temperature, especially in one season. A significant year effect and genotype‐by‐environment interaction (GxE) effect were also observed for the three traits under WW and WS treatments. The GGE biplots confirmed these large interactions and indicated that high yielding genotypes under moderate temperature were different to those at high temperature. However, several genotypes with relatively high yield across years and temperature environments could be identified under both WW and WS conditions. Correlation analysis between pod weight and traits measured during plant growth showed that the partition rate, that is, the proportion of dry matter partitioned into pods, was contributing in heat and drought tolerance and could be a reliable selection criterion for groundnut breeding programme. Groundnut sensitivity to high‐temperature stress was in part related to the sensitivity of reproduction.     

Traits related to drought resistance in common bean

Common bean (Phaseolus vulgaris L.) is grown in regions where water deficits during reproductive development significantly reduce yield. The purpose of this study was to evaluate the association of specific phenological and physiological traits with drought resistance in common bean. Five genotypes were grown under and near a rain shelter in 1988, and an additional 16 progeny lines were included in 1990. Drought stress determined by the drought intensity index was severe (0.78) in 1988 and more moderate (0.63) in 1990. Water stress reduced the expression of most traits with the exception of days to flower and leaf moisture retention capacity. Seed yield among genotypes was reduced from 22 to 71% due to drought. Yield under stress was correlated with yield under nonstress in 1990 and negatively correlated with the drought susceptibility index in 1988. Yield components which exhibited the largest differential genotypic responses to stress were pod and seed number, whereas seed size was more stable. Genotypic variation was detected in all the partitioning indexes, chiefly harvest index and relative sink strength, and the heritability estimates for these traits were high. The limited genetic variability observed among water relations traits and their role in water conservation would restrict their potential use in the selection for drought resistance in common bean. The differential correlations between phenological, biomass and partitioning traits and the indexes for yield and drought susceptibility would suggest that the most effective approach in breeding for drought resistance in common bean would be based first on selection for high geometric yield followed by selection among the high-yielding individuals for low to moderate levels of the drought susceptibility index. This revised version was published online in July 2006 with corrections to the Cover Date.     

局部根区灌溉对裸燕麦光合特征曲线及叶绿素荧光特性的影响

为探讨局部根区不同灌溉方式下裸燕麦(Avena nuda L.)光合能力下降的生理机制,采用盆栽及渗水盘供水方法,比较了交替根区灌溉(APRI)、固定根区灌溉(FPRI)和常规灌溉(CTRI)下,裸燕麦旗叶相对叶绿素含量(SPAD值)、光合特征曲线及叶绿素荧光动力学特性的差异。与CTRI处理相比,局部根区灌溉(包括APRI和FPRI处理)降低了叶片SPAD值、净光合速率(P_n)和初始羧化速率(CE),但APRI处理未明显降低初始量子效率(α)、PSII最大量子效率(F_v/F_m)、PSII实际光化学效率(Ф_PSII)、电子传递效率(ETR)和光化学效率 (q_P)。在2种局部根区灌溉模式中,APRI较FPRI显著提高了叶片SPAD值(P<0.05),而且APRI的叶片最大净光合速率(P_max)、α、光饱和点(LSP)、光能利用率(LUE)、C_i/C_a、CE、CO₂饱和点(C_i,sat)、初始荧光(F_o)、最大荧光(F_m)、Ф_PSII、ETR、q_P和非光化学效率(NPQ)均高于FPRI。APRI和FPRI的光合速率降低与气孔因素有关,FPRI光合速率降低还与PSII结构损伤有关;局部根区灌溉提高了裸燕麦干旱胁迫逆境下的耐受能力,APRI有利于保持更高的光合速率。     

Physiological and Molecular Characterization of Faba bean (Vicia faba L.) Genotypes for Adaptation to Drought Stress

Faba bean (Vicia faba L.) is one of the most important and drought sensitive grain legumes. Drought stress is thus one of major constraints in global faba bean production. In this study, twenty local and exotic faba bean genotypes were characterized on physiological and molecular basis. Seeds of faba bean genotypes (six per pot) were sown in poly venyl chloride pots. After seedling emergence, soil moisture was maintained at 100%, 50% and 25% of field capacity designated as well watered, moderate drought and severe drought, respectively. Drought stress significantly influenced the leaf area, leaf temperature, stomatal conductance, relative leaf water contents, grain yield and water‐use efficiency. Faba bean genotypes also differed for the leaf area, leaf temperature, relative leaf water contents, grain yield and water‐use efficiency. Faba bean genotypes Kamline and L.4 were better equipped to curtail water loss, maintain tissue water status, produce stable grain yield and had better water‐use efficiency under mild and severe drought stress, and may be used in breeding programmes. Amplified fragment length polymorphism markers showed high potential in detecting polymorphism and estimating genetic diversity among faba bean genotypes. Unweighted pair group method with arithmetic mean cluster analysis of the genotypes illustrated considerable association between molecular diversity, genetic background and geographic origin. In crux, high polymorphic rate and polymorphism information content values, together with the low genetic similarity observed among tested genotypes suggests a high level of heterogeneity, which may be used in breeding programmes to assemble different drought tolerance mechanisms in one genotype.     

Physiological traits related to drought tolerance in tall fescue

The physiological basis of genetic variation in drought response and its association with yield and related indices is not clear in tall fescue. In this study thirty genotypes of tall fescue (Festuca arundinacea Schreb.) were sampled from a polycross population and evaluated under two levels of irrigation in 2010 (normal and intense stress) and 2011 (normal and mild stress). Physiological traits including relative water content (RWC), total chlorophyll (TChl), chlorophyll a (Chla), chlorophyll b (Chlb), Chla/Chlb, carotenoids (Car), TChl/Car and proline content along with forage yield, agro-morpholgical traits and selection indices (stress tolerance index, STI and drought susceptibility index, DSI) were studied. Large variation and moderate to high heritability was estimated for most of the studied traits. Intense drought condition decreased chlorophyll content while mild stress significantly increased it. In the other hand intense drought stress increased Chla/b while mild stress didn’t change it. Under mild drought stress condition STI was positively correlated with RWC while under intense drought stress condition STI was positively correlated with chlorophyll content. Although proline content was significantly increased in both intense and mild drought stress conditions, no relationship was found between proline accumulation with forage yield and STI. Applications of principle component analysis for screening suitable genotypes are also discussed.     

水分胁迫对糜子植株苗期生长和光合特性的影响

选取耐旱性不同的糜子品种陇糜4号(强抗旱)、晋黍7号(旱敏感)和5283黄(中等抗旱),采用盆栽控水试验,调查不同水分处理对糜子苗期主要性状和光合参数的影响。结果表明：(1)水分胁迫下各品种的株高、叶面积、根重、叶绿素含量、根系活力均呈下降趋势,且陇糜4号的降幅小于5283黄和晋黍7号。(2)水分胁迫下,3个品种的固定荧光值(F_o)和非光化学猝灭系数值(q_N)均显著增加,在重度胁迫后,陇糜4号、5283黄和晋黍7号的F_o值分别比对照增加24.6%﹑34%和40.8%,q_N值分别增加0.956、1.083和2.183,且表现为旱敏感品种晋黍7号的增加幅度大于强抗旱品种陇糜4号;各品种的可变荧光(F_v)、最大荧光(F_m)、最大光化学量子产量(F_v/F_m)、PSII的潜在活性(F_v/F_o)、光化学猝灭系数(q_P)值均因水分胁迫而降低。在中度和重度胁迫时,与正常灌水相比差异达显著水平,降幅以晋黍7号>5283黄>陇糜4号。(3)各品种的净光合速率、蒸腾速率、气孔导度及胞间CO₂浓度均因水分胁迫而下降,强抗旱品种陇糜4号各值的变化幅度均小于中等抗旱品种5283黄和旱敏感品种晋黍7号,表明陇糜4号的光合参数受水分胁迫的影响最小,较高的电子传递速率和较强的光能转化能力是陇糜4号适应干旱环境的重要生理特性。(4)水分胁迫导致糜子叶片对强光的敏感性增加,干旱和光抑制对光系统II造成的叠加伤害随干旱加重和品种抗旱性减弱而加剧,因此,对强光下的糜子幼苗应及时补水,以避免干旱和高光强的叠加伤害。     

玉米叶片光合作用和渗透调节对干旱胁迫的响应

以2个不同抗旱性玉米品种郑单958 (抗旱性强)和陕单902 (抗旱性弱)为材料,采用盆栽控水试验,设置3个干旱处理(轻度干旱、中度干旱、重度干旱)和正常灌水,研究了干旱胁迫对2个玉米品种气体交换、叶绿素荧光参数和渗透调节物质的影响。结果显示, 重度干旱造成2个玉米品种叶片光合机构紊乱,破坏细胞膜完整性;同时增加了渗透调节物质,这对增强叶片的保水能力,维持光合速率有重要的作用。但与陕单902相比,干旱胁迫下郑单958表现出较高的最大净光合速率(P_nmax),表观量子效率(AQY),光饱和点(LSP),最大电子传递速率(J_max),最大羧化速率(V_cmax),PSII的实际量子产量(Φ_PSII)和光化学猝灭系数(q_P);较高的脯氨酸(Pro)和可溶性糖含量(SS);较低的丙二醛含量(MDA)。这些结果表明,干旱胁迫下抗旱品种郑单958具有较强的渗透物质能力,减轻细胞膜质过氧化程度,维持较高的光合性能是其适应干旱环境的生理基础。     

Thresholds for leaf expansion and transpiration response to soil water deficit in a range of sunflower genotypes

The sunflower (Helianthus annuus L.) crop in southern Europe suffers from intense and frequent periods of water deficit. Minimisation of water loss in response to water deficit is a major aspect of drought tolerance and can be achieved through the lowering of either leaf area expansion rate or transpiration per unit leaf area (stomatal conductance). During three greenhouse pot experiments, leaf expansion (LE) and transpiration (TR) rates were monitored as the soil dried progressively for about 15 days. This study aimed to quantify the response of these two physiological processes to water deficit, expressed as the fraction of transpirable soil water (FTSW): response thresholds (onset of decline) were estimated on 25 sunflower genotypes from different generations of selection history. From these relationships, the thresholds below which LE and TR started to decrease from the control were calculated: little change was observed until FTSW was close to 0.6 for leaf expansion and 0.4 for daily transpiration. Variability in the response of all genotypes for expansion and transpiration control was better described using specific thresholds for each genotype rather than generic thresholds for sunflower. The ranking of genotypes was found to be unaffected for transpiration rate control, but this was not the case for leaf expansion. Identified response thresholds were not mutually correlated, suggesting that sunflower controls leaf expansion and transpiration rate independently. Neither was correlated with the release date of the genotype, suggesting that these traits were not subject to selection within evaluation environments.     

QTLs for chlorophyll and chlorophyll fluorescence parameters in barley under post-flowering drought

Drought is one of the major factors limiting barley yields in many developing countries worldwide. The identification of molecular markers linked to genes controlling drought tolerance in barley is one way to improve breeding efficiency. In this study, we analyzed the quantitative trait loci (QTL) controlling chlorophyll content and chlorophyll fluorescence in 194 recombinant inbred lines (RILs) developed from the cross between the cultivar ‘Arta’ and Hordeum spontaneum 41-1. Five traits, chlorophyll content, and four chlorophyll fluorescence parameters, namely initial fluorescence (F_o), maximum fluorescence (F_m), variable fluorescence (F_v), and maximum quantum efficiency of PSII (F_v/F_m) which are related to the activity of the photosynthetic apparatus, were measured under well-watered and drought stress conditions at post-flowering stage. QTL analysis identified a total of nine and five genomic regions, under well-watered and drought stress conditions, respectively, that were significantly associated with the expression of the five target traits at post-flowering stage. No common QTL was detected except one for chlorophyll content, which was identified in both growth conditions, demonstrating that the genetic control of the expression of the traits related to photosynthesis differed under different water conditions. A QTL for F_v/F_m, which is related to the drought tolerance of photosynthesis was identified on chromosome 2H at 116 cM in the linkage map under drought stress. This QTL alone explained more than 15% of phenotypic variance of maximum quantum yield of PSII, and was also associated with the expression of four other traits. In addition, another QTL for F_v/F_m was also located on the same chromosome (2H) but at 135.7 cM explaining around 9% of the phenotypic variance under drought conditions. The result presented here suggest that two major loci, located on chromosome 2H, are involved in the development of functional chloroplast at post-flowering stage for drought tolerance of photosynthesis in barley under drought stress. If validated in other populations, chlorophyll fluorescence parameters could be used as selection criteria for drought tolerance.     

水分胁迫对4份含大茎野生种57NG208血缘F2代甘蔗材料叶绿素荧光动力参数的影响

为研究不同水分胁迫对大茎野生种57NG208血缘F2代材料叶绿素荧光动力参数的影响,以4份大茎野生种57NG208与南涧果蔗正反交后代为材料,在抗旱温室设计桶栽抗旱试验,测定其叶绿素含量及叶绿素荧光动力参数,运用隶属函数法对其抗旱性进行综合分析。结果表明：水分胁迫下,甘蔗叶片SPAD值、最大荧光（Fm）、潜在光化学效率（Fv/F0）和最大光化学效率（Fv/Fm）均降低,初始荧光（F0）除云瑞15-58外则升高,说明水分胁迫伤害了光系统Ⅱ(PSⅡ),使得潜在光化学效率（Fv/F0）和最大光化学效率（Fv/Fm）降低 ,光合电子传递受阻;灰色关联度分析表明,中度、重度水分胁迫下,5个光合生理指标与甘蔗抗旱性的关联度大小不一致。中度水分胁迫下,各指标与甘蔗耐旱性间的关联密切程度依次为：F0＞Fv/Fm＞SPAD值＞Fv/F0＞Fm,关联系数分别为0.8649、0.6664、0.6582、0.6006、0.5952;重度水分胁迫下,其关联度依次为 SPAD值＞Fv/F0＞Fm＞Fv/Fm＞F0,关联系数分别为 0.9290、0.8829、0.8473、0.7636、0.6326;相关分析表明,SPAD值与潜在光化学效率（Fv/F0）呈正相关,与其余3指标呈负相关,初始荧光（F0）与最大荧光（Fm）和最大光化学效率（Fv/Fm）呈正相关,潜在光化学效率（Fv/F0）与最大光化学效率（Fv/Fm）呈负相关;4份参试材料的叶绿素荧光参数和叶绿素含量的变化存在材料间差异,整个处理过中对水分胁迫的适应性依次是云瑞15-80>云瑞15-84>云瑞15-85>云瑞15-79。     

Breeding drought tolerant cowpea: constraints,accomplishments, and future prospects

This review presents an overview of accomplishments on different aspects of cowpea breeding for drought tolerance. Furthermore it provides options to enhance the genetic potential of the crop by minimizing yield loss due to drought stress. Recent efforts have focused on the genetic dissection of drought tolerance through identification of markers defining quantitative trait loci (QTL) with effects on specific traits related to drought tolerance. Others have studied the relationship of the drought response and yield components, morphological traits and physiological parameters. To our knowledge, QTLs with effects on drought tolerance have not yet been identified in cowpea. The main reason is that very few researchers are working on drought tolerance in cowpea. Some other reasons might be related to the complex nature of the drought stress response, and partly to the difficulties associated with reliable and reproducible measurements of a single trait linked to specific molecular markers to be used for marker assisted breeding. Despite the fact that extensive research has been conducted on the screening aspects for drought tolerance in cowpea only very few—like the ‘wooden box’ technique—have been successfully used to select parental genotypes exhibiting different mechanisms of drought tolerance. Field and pot testing of these genotypes demonstrated a close correspondence between drought tolerance at seedling and reproductive stages. Some researchers selected a variety of candidate genes and used differential screening methods to identify cDNAs from genes that may underlie different drought tolerance pathways in cowpea. Reverse genetic analysis still needs to be done to confirm the functions of these genes in cowpea. Understanding the genetics of drought tolerance and identification of DNA markers linked to QTLs, with a clear path towards localizing chromosomal regions or candidate genes involved in drought tolerance will help cowpea breeders to develop improved varieties that combine drought tolerance with other desired traits using marker assisted selection.

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Marker-assisted characterization of frost tolerance in barley (Hordeum vulgare L.)

Five molecular markers associated to two frost tolerance QTLs ( Fr-H1 and Fr-H2 ) were tested both on nine Turkish accessions, classified by breeders as highly frost-tolerant, and on a previously described sample of 26 barleys, winter, facultative and spring. Accessions were characterized in terms of frost tolerance under both field conditions and artificial freezing test at −12°C. The Turkish lines resulted to be equal or superior to the most tolerant European genotypes tested, showing that they can be used to improve the frost tolerance of the EU barley germplasm. The marker Hv BM5A ( Vrn-H1 and Fr-H1 ) resulted to be the best predictor for assisted selection within this germplasm, because of its high correlation between allelic variation and phenotypic traits. Only Hv CBF4 of the three Hv CBF markers tested at Fr-H2 was associated to the trait, but at lower significance than HvBM5A . The PCR-based molecular marker of Vrn-H1 can thus be used in barley breeding not only for selection of facultative and winter types, but also for fast routine selection of frost tolerant genotypes.     

Genotypic variability among cotton cultivars for heat and drought tolerance using reproductive and physiological traits

Development of rapid and inexpensive screening tools for heat and drought stress tolerance is needed and will be helpful in cotton breeding programs and selecting cultivars for a niche environment. In this study, several pollen-based traits at optimum and high temperatures and physiological parameters measured during the boll-filling period were used to evaluate variability among the cultivars for heat and drought stresses. Principal component analysis and drought stress response index methods were used to categorize cotton cultivars into three heat and drought tolerant clusters. Based on the combined analysis, PX532211WRF has been identified as heat- and drought-tolerant, and would be expected to perform better under both heat- and drought-stressed environments. A poor correlation between reproductive and physiological indices indicates that screening breeders have to use different traits to screen cultivars for reproductive and vegetative tolerance. Identified traits could serve as valuable screening tools in cotton breeding programs aimed at developing genotypes to a changing climate. Moreover, cultivar-dependent relative scores will aid in the identification of cultivars best suited to niche environments to alleviate the influences of abiotic stresses at both vegetative and reproductive stages.     

Stability of soil plant analytical development (SPAD) chlorophyll meter reading (SCMR) and specific leaf area (SLA) and their association across varying soil moisture stress conditions in groundnut (<Emphasis Type="Italic">Arachis hypogaea</Emphasis> L.)

The complex nature of physiological traits associated with drought tolerance and the difficulties associated with their measurements in segregating populations and large number of genotypes inhibited their use in the past in developing water-use efficient genotypes in breeding programmes. With new knowledge of easily measurable surrogates of transpiration efficiency (TE), a trait associated with drought tolerance—specific leaf area (SLA) and soil plant analytical development (SPAD) chlorophyll meter reading (SCMR), it is now possible to integrate TE through the surrogates in breeding and selection schemes in groundnut (Arachis hypogaea L.). As a noninvasive surrogate of TE, SCMR is easy to operate, reliable, fairly stable and low cost. However, in a large-scale breeding program, it is difficult to complete SCMR observations within a specified time. The present study addressed the issue as to what extent the SCMR measurements can be spread over time by evaluating 18 diverse groundnut genotypes for two physiological traits, SCMR and SLA in two postrainy (Nov–Apr) seasons (2002/2003 and 2003/2004) in India. Observations were recorded at different times during and after the release of moisture deficit stress. There was general agreement in genotype and trait performance in both the seasons. Interaction between SCMR and time of observation was significant in only one season (2002/2003) but its variance relative to genotypes and time of observation was very small. ICGV 99029 and ICR 48, which recorded higher SCMR and lower SLA values in both the seasons, will make good parents for water-use efficiency trait in breeding programmes. Other good parents include ICGS 76, TCGS 647 and TCGP 6. SCMR recorded at three different times under differing soil moisture deficit in each season showed highly significant correlation with each other. Similarly, SLA at different times also correlated significantly with each other. SCMR and SLA were significantly negatively correlated with each other and the relationship was insensitive to time of observation. The results of the present study indicated that SCMR/SLA observations can be recorded at any time after 60 days of crop growth, preferably under moisture deficit conditions. This gives groundnut breeders a large flexibility to record these observations in a large number of segregating populations and breeding lines in the field. Thus, making it easy to incorporate these physiological traits associated with drought tolerance in breeding and selection scheme in groundnut.     

Contrasting rice backcross inbred lines (BILs) for grain yield and heading under lowland reproductive stage moisture stress

Identification and understanding the role of physio-morphological drought responsive mechanisms leading to grain yield enhancement under water stress is a critical insight for designing appropriate strategies to breed drought-tolerant cultivars for any drought prone ecology. In this study, three pairs of contrasting BILs with varied maturity were characterized for several agronomical, physiological and morphological traits across a wide range of moisture stress environments at reproductive stage during 2012–2014. Within each group, BILs differ significantly for grain yield, heading, biomass and harvest index under drought stress, but showed similar yield potential, phenology and other traits under control condition. The most tolerant BIL, S-15 out yielded all BILs and standard checks under both conditions. Apart from superior agronomic performance, drought tolerant BILs maintained significantly higher assimilation rate, transpiration rate and transpiration efficiency compared to susceptible BILs under stress in all three groups. In addition, most tolerant BIL (S-15) showed significantly higher stomatal conductance than susceptible BIL (S-55) in early group. Among root traits, significant differences under stress was observed for root dry weight between contrasting BILs in each group, even though tolerant BILs had higher root length and root volume compared to susceptible BILs, which is non-significant. Hence, consideration of root traits an important strategy for drought avoidance in case of rice may not always contributes to significant yield improvement under moisture stress condition. Further, tolerant BILs also recorded significantly higher shoot dry weight and drought recovery score at seedling stage under stress. Our findings suggest that genotypes with higher photosynthetic efficiency and better plant water status are able to produce higher grain yield under drought stress environments.     

Tolerance to paraquat is correlated with the traits associated with water stress tolerance in segregating F2 populations of barley and wheat

To identify scorable marker traits that can be used in cereal breeding programs for selecting drought tolerant individuals, we investigated the correlation among the drought-associated traits in two F₂ populations derived from the crosses made between drought tolerant and sensitive barley and wheat parental genotypes. The parental genotypes of these crosses also differed by at least three other traits – paraquat tolerance, leaf size, and the relative water content. These three traits were scored in two F₂populations of 80 individuals for each barley and wheat cross. Analysis of results indicated that the enhanced tolerance to paraquat was correlated with reduced leaf size and increased relative water content, two traits associated with water stress phenotypes of the drought tolerant barley and wheat parents. Our results suggested that the selection based on paraquat tolerance istechnically less demanding and thus useful for rapid screening of individuals for enhanced drought tolerance in segregating populations. This revised version was published online in August 2006 with corrections to the Cover Date.     

Glycinebetaine Accumulation, Physiological Characterizations and Growth Efficiency in Salt-tolerant and Salt-sensitive Lines of Indica Rice (Oryza sativa L. ssp. indica) in Response to Salt Stress

The aim of this research was to investigate betaine aldehyde dehydrogenase (BADH) and glycinebetaine (Glybet) biosynthesis in photoautotrophic rice seedlings. The role of Glybet on physiological and growth responses to salt stress in both salt‐tolerant and salt‐sensitive lines is to be investigated. The BADH activity in salt‐tolerant seedlings cultured under extreme salt stress (342 mm NaCl) progressively increased during the first few hours until it peaked after 72 h. This was about 2.5 times greater than in salt‐sensitive plants. Similarly, the amount of Glybet detected in salt‐tolerant lines was 1.3 times more than in salt‐sensitive lines at 96 h salt exposure. The BADH activities were positively related to Glybet accumulation in both salt‐tolerant and salt‐sensitive lines. The accumulation of Glybet in salt‐tolerant lines was directly correlated with pigment stabilization. Relative water content in the salt‐tolerant lines was closely related to water oxidation in photosystem II (PSII), defined by maximum quantum yield of PSII (F_v/F_m). In addition, a high concentration of total chlorophyll is more efficient in capturing light energy, defined by photochemical quenching. The concentrations of chlorophyll a and total carotenoid were positively related to the quantum efficiency of PSII (Φ_PSII) and non‐photochemical quenching, respectively, resulting in a high net‐photosynthetic rate (NPR) and the promotion of growth. The high level of Glybet in salt‐tolerant lines plays a role as a salt defensive response mechanism in terms of pigment stabilization and water oxidation in PSII, resulting in high NPR and growth efficiency.