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.     

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.     

Marker assisted polycross breeding to increase diversity and yield in perennial ryegrass (Lolium perenne L.)

Summary In this study, the application of molecular markers to optimise genetic diversity in a polycross breeding program of perennial ryegrass (Lolium perenne L.) was evaluated. The genetic diversity among 98 potential parental plants from three maturity groups (early, intermediate and late flowering) was investigated using amplified fragment length polymorphism (AFLP) markers. For each maturity group, two polycrosses of six parental plants with contrasting levels of genetic diversity were composed. Average genetic diversity among parents selected for narrow polycrosses was 36% lower than among parents selected for wide polycrosses. Diversity within first generation synthetic progenies (Syn1) was proportional to the diversity within the respective parental polycrosses. However, differences were less pronounced with Syn1 progenies from narrow polycrosses showing 16% reduced diversity when compared to Syn1 progenies from wide polycrosses. Multivariate analyses allowed for a clear separation of the six Syn1 progenies based on AFLP markers and demonstrated their genetic distinctness. Evaluation of dry matter yield, date of ear emergence and stem length of Syn1 and Syn2 progenies showed progenies from wide polycrosses to be constantly higher yielding when compared to progenies from narrow polycrosses. On the other hand, there was no significant difference in variability for the two morphological traits between progenies of narrow- and wide polycrosses. The results presented here provide evidence for an efficient application of molecular markers to select genetically diverse polycross parents which resulted in an average yield increase of 3.8%.     

非生物胁迫对玉米杂交种及其亲本自交系产量性状的影响

以抗逆性较强玉米杂交种郑单958及其亲本(郑58、昌7-2)和抗逆性较差的杂交种陕单902及其亲本(K22、K12)为材料, 在不同种植密度(45 000株 hm^-2和75 000株 hm^-2)、施氮量(112.5 kg hm^-2和337.5 kg hm^-2)和灌水量(正常灌水和前期干旱控水)条件下, 分析了2个杂交种及其亲本产量及相关生理特性的变化规律。结果表明, 在非生物胁迫条件下(高密度、低氮和前期干旱控水), 与陕单902相比, 品种郑单958叶面积指数、SPAD值、花后干物质积累量和产量的中亲优势值分别增加18%、9%、28%和22%; 与陕单902亲本(K22、K12)比, 郑单958亲本(郑58、昌7-2)叶面积指数、SPAD值、花后干物质积累量和产量的中亲值分别增加45%、36%、51%和45%; 郑单958产量的中亲值和中亲优势显著高于陕单902, 且中亲值增幅高于杂种优势值。玉米杂交种郑单958较陕单902增产的同时, 增强了对非生物逆境适应的能力。玉米杂交种的抗逆性来自亲本自交系。玉米杂交种抗逆性强在于增强了花后叶片光合能力(较高的LAI和SPAD值), 促进了花后干物质积累。     

Quantitative trait locus mapping of drought and salt tolerance in an introgressed recombinant inbred line population of Upland cotton under the greenhouse and field conditions

Drought and salt tolerances are complex traits and controlled by multiple genes, environmental factors and their interactions. Drought and salt stresses can result in more than 50% yield loss in Upland cotton (Gossypium hirsutum L.). G. barbadense L. (the source of Pima cotton) carries desirable traits such as tolerance to abiotic and biotic stress along with high fiber quality. However, few studies have been reported on mapping quantitative trait loci (QTL) for abiotic stress tolerance using a permanent bi-parental population in multiple tests. The transfer of drought and salt tolerance from Pima to Upland cotton has been a challenge due to interspecific hybrid breakdown. This issue may be overcome by using introgression lines with genes transferred from Pima to Upland cotton. In this study, four replicated tests were conducted in the greenhouse each for drought and salt tolerance along with another test conducted in a field for drought tolerance using an Upland recombinant inbred line population of TM-1/NM24016 that has a stable introgression from Pima cotton. The objectives of the study were to investigate the genetic basis of drought and salt tolerance and to identify genetic markers associated with the abiotic stress tolerance. A total of 1004 polymorphic DNA marker loci including RGA-AFLP, SSR and GBS-SNP markers were used to construct a genetic map spanning 2221.28 cM. This population together with its two parents was evaluated for morphological, physiological, yield and fiber quality traits. The results showed that drought under greenhouse and field conditions and salt stress in the greenhouse reduced cotton plant growth at the seedling stage, and decreased lint yield and fiber quality traits in the field. A total of 165 QTL for salt and drought tolerance were detected on most of the cotton chromosomes, each explaining 5.98–21.43% of the phenotypic variation. Among these, common QTL for salt and drought tolerance were detected under both the greenhouse and field conditions. This study represents the first study to report consistent abiotic stress tolerance QTL from multiple tests in the greenhouse and the field that will be useful to understand the genetic basis of drought and salt tolerance and to breeding for abiotic stress tolerance using molecular marker-assisted selection in cotton.     

利用回交导入系定位干旱环境下水稻植株水分状况相关QTL

日益严重的水资源危机使水稻的耐旱育种尤为迫切, 干旱环境下较高的植株水分含量有助于提高或维持作物产量的稳定性, 挖掘与耐旱性密切相关的分子标记有助于提高耐旱品种的选育效率。从供体Lemont (粳稻)导入到特青(籼稻)背景的254个高代回交导入系中筛选出覆盖供体全基因组的55个回交导入系, 采用PVC管栽培, 分析了干旱(胁迫)条件下水稻植株水分状况相关性状与籽粒产量、生物量的相关性并定位了相关QTL。研究表明, 植株水分相关性状(相对含水量、叶片水势、渗透势、卷叶度)均与籽粒产量显著相关。检测到7个相对含水量QTL, 7个叶片水势QTL, 5个渗透势QTL及5个卷叶QTL; 另检测到5个产量QTL, 7个生物量QTL。分析发现, 不仅QLwp5、QLr5、QRwc5和QY5同时分布在RM509~RM163区域, 且该区域还分布有对水分环境表现稳定的产量QTL(QGy5), 效应方向一致, 从遗传学角度解释了籽粒产量与水分相关性状之间的显著相关性。另外, QLr5、QRwc5、QY5、QLr2、QLr7、QLr8、QLr9、QRwc3、QRwc4a、QRwc12及QY7 等11个QTL曾在不同遗传背景群体中被检测到, 它们控制相同目标性状。研究认为RM509~RM163区域及QLr2、QLr7、QLr8、QLr9、QRwc3、QRwc4a、QRwc12和QY7所分布的染色体区域对水分环境或者遗传背景相对稳定, 在水稻分子标记辅助选择(MAS)耐旱育种实践中有较重要利用价值。     

Genetic variation, heritability and progeny testing in meadow bromegrass

Meadow bromegrass is a recently introduced pasture grass in western Canada. Its leafy production and rapid regrowth have made it a major grass species for pasturing beef animals in this region. Because relatively little breeding work has been done on this species, there is little information on its breeding behaviour. The main objective of this study was to estimate genetic parameters and assess breeding methodologies for meadow bromegrass. Forty half‐sib (polycross and open‐pollinated) and full‐sib (selfed) progenies were evaluated for dry matter and seed yield, fertility index, harvest index, plant height, plant spread, crude protein, neutral detergent fibre and acid detergent fibre. Genetic variation for seed yield, harvest index, and plant height was significant in the open‐pollinated and selfed tests. Genetic variation estimates for dry matter yield were negative (polycross), not significant (open‐pollinated), or significant (selfed). Estimates of genetic variation for quality traits were not significant, except for acid detergent fibre (selfed). Correlations among characters indicated that it is possible to simultaneously improve seed and forage yield. Rankings of progenies by the half‐sib tests for forage and seed yield were not altered by the use of the synthetic parental value (SV_i), which includes information from selfed progeny. The polycross progeny test did not discriminate parents as well as the open‐pollinated and selfed tests; this may have been a result of non‐random pollination in the polycross. Correlation among the progeny tests, showed that open‐pollinated and selfed progeny tests agreed for all characters, except for harvest index, while correlation between polycross and selfed tests were significant for six characters but not dry matter yield, and acid and neutral detergent fibres. The most dissimilar tests were polycross and open‐pollinated, with significant correlations found only for fertility index, height, spread and neutral detergent fibre. It was concluded that there was significant variation and moderate heritability for most traits in the meadow bromegrass populations evaluated, and that the open‐pollinated progeny test is the method of choice for selecting parents for synthetics of this species.     

Functional mechanisms of drought tolerance in maize through phenotyping and genotyping under well watered and water stressed conditions

Developing tolerant genotypes is crucial for stabilizing maize productivity under drought stress conditions as it is one of the most important abiotic stresses affecting crop yields. Twenty seven genotypes of maize (Zea mays L.) were evaluated for drought tolerance for three seasons under well watered and water stressed conditions to identify interactions amongst various tolerance traits and grain yield as well as their association with SSR markers. The study revealed considerable genetic diversity and significant variations for genotypes, environment and genotype × environment interactions for all the traits. The ranking of genotypes based on drought susceptibility index for morpho-physiological traits was similar to that based on grain yield and principal component analysis. Analysis of trait – trait and trait – yield associations indicated significant positive correlations amongst the water relations traits of relative water content (RWC), leaf water potential and osmotic potential as well as of RWC with grain yield under water stressed condition. Molecular analysis using 40 SSRs revealed 32 as polymorphic and 62 unique alleles were detected across 27 genotypes. Cluster analysis resulted in categorization of the genotypes into five distinct groups which was similar to that using principal component analysis. Based on overall performance across seasons tolerant and susceptible genotypes were identified for eventual utilization in breeding programs as well as for QTL identification. The marker-trait association analysis revealed significant associations between few SSR markers with water relations as well as yield contributing traits under water stressed conditions. These associations highlight the importance of functional mechanisms of intrinsic tolerance and cumulative traits for drought tolerance in maize.     

Mapping the QTLs underlying drought stress at developmental stage of sorghum (Sorghum bicolor (L.) Moench) by association analysis

This study was conducted to identify quantitative trait loci (QTLs) for drought tolerance in sorghum (Sorghum bicolor (L.) Moench) by association mapping using a simple sequence repeat (SSR)-marker-based diversity research set. Genotypic data for 98 SSR marker loci on ten chromosomes were used for the association analysis. The experiment was conducted under control (well-watered) and drought stress conditions, and the phenotypic values of 23 morphological traits were recorded. Drought tolerance was assessed by using a leaf drying score as a parameter of the tolerance/susceptibility: scores were assigned on a scale from 1 (most tolerant) to 9 (most susceptible). Under the control conditions, 17 QTLs associated with 12 traits were identified on chromosomes 1, 2, 4, 8, 9, and 10, with ?Log₁₀ (P) ranging from 2.5 to 7.6 and explaining 9.5–57.5 % of the total phenotypic variance for the traits. Under the drought stress conditions, nine QTLs associated with 8 traits were identified on chromosomes 1, 2, 3, and 10 that explained 9–61.2 % of the total phenotypic variance for the traits, with ?Log₁₀ (P) ranging from 2.5 to 3.5. QTLs for some traits were detected only under the drought stress condition, suggesting that these traits are important in drought tolerance. These QTLs could be used to further dissect the genetic and physiological basis of drought tolerance in sorghum.     

Genetic analysis of drought tolerance in adapted × exotic crosses of maize inbred lines under managed stress conditions

Introduced maize (Zea mays L.) germplasm can serve as sources of favorable alleles to enhance performance in new maize varieties and hybrids under drought stress conditions. In the present study, the combining abilities of 12 exotic maize inbred lines from CIMMYT and 12 adapted maize inbred lines from IITA were studied for grain yield and other traits under controlled drought stress. The inbred lines from each institution were separated into groups using SSR-based genetic diversity and were intercrossed using a factorial mating scheme to generate 96 hybrids. These hybrids were evaluated under both controlled drought stress and well-watered conditions at Ikenne in Nigeria in 2010 and 2011. Average mean yields of hybrids under drought stress represented 23 % of the average yield of hybrids under full irrigation. General combining ability (GCA) effects accounted for 49–85 % of the observed variation for several traits recorded under both well-watered and drought stress conditions. Specific combining ability effects for grain yield, though positive in most hybrids, were not significant under drought stress conditions. All the twelve exotic and nine adapted lines had positive GCA effects (female, male, or both) for grain yield under either drought stress or full irrigation, or both environments. EXL03 and EXL15 that had positive and significant female and male GCA effects for grain yield under both environments can be used to improve their adapted counterparts for grain yield and drought tolerance. Normalized difference vegetation index had weak but significant correlation with grain yield.     

Genetic analysis and phenotypic associations for drought tolerance in Hordeum spontaneum introgression lines using SSR and SNP markers

Associations between markers and drought related traits were investigated on a set of 57 advanced barley breeding lines, carrying various levels of introgression from Hordeum spontaneum lines 41-1 and 41-5, the best sources of drought tolerance in the ICARDA barley breeding program, using 74 simple sequences repeats (SSR) and 20 single nucleotide polymorphism markers. The 57 lines were evaluated for grain yield and drought related traits for three years (2003/04, 2004/05, 2005/06) in nine Mediterranean low rainfall environments. A high level of polymorphism was found with SSR markers, and the mean polymorphism information content and gene diversity values were 0.67 and 0.71, respectively. The number of alleles per locus varied from 2 to 11, with an average of 5.8 alleles per marker. Considering all the 57 lines, the linkage disequilibrium (LD) analysis was significant at a comparison-wise P?<?0.01 level in nearly 9 % of the SSR marker pairs used and a decay of LD was observed to a value of r ²?<?0.2 at a genetic distance of 40?cM. The association analysis revealed a total of 147 significant marker?Ctrait associations for grain yield and drought related traits. A total of 72 (49 %) marker?Ctrait associations showed favorable effects of the exotic germplasm where the H. spontaneum lines contributed to an improvement of the trait under drought stress conditions. The number of significant marker?Ctrait associations per trait were: 12 for growth habit; 2 for growth vigor; 11 for peduncle extrusion; 5 for number of grains per spike; 20 for peduncle length; 16 for days to heading; 20 for plant height; 8 for spike length; 17 for thousand kernel weight; 30 for grain yield; 4 for harvest index and 2 for biological yield. The phenotypic variation explained by individual marker?Ctrait associations ranged from 7.6 % to 36.2 %. The identification of genomic regions associated with grain yield and drought related traits is useful for the genetic improvement of cultivars better adapted to drought stress environments. Thus, the present study is encouraging in identifying significant marker?Ctrait associations through LD based association mapping analysis, which could complement and augment previous quantitative trait loci information for the potential use of Marker Assisted Selection for drought.     

Comparisons of genetic and morphological distance with heterosis between Medicago sativa subsp. sativa and subsp. falcata

Biomass yield heterosis has been shown to exist between Medicago sativasubsp. sativa and Medica gosativa subsp. falcata. The objective of this study was to gain a better understanding of what morphological and genetic factors were most highly correlated with total biomass yield heterosis. We calculated genetic distances among nine sativa and five falcate genotypes based on amplified fragment length polymorphism (AFLP) and simple sequence repeat (SSR) DNA markers. Genetic distance did not correlate with specific combining ability (SCA) or mid-parent heterosis. In contrast, a morphological distance matrix based on seventeen agronomic and forage quality traits was significantly correlated with heterosis; the agronomic traits of maturity, midseason regrowth, and autumn regrowth showed strong association with heterosis. Heterosis was also correlated with subspecies. We suggest that in many cases progeny heterosis can be accounted for by the interaction of genes controlling morphologically divergent traits between the parents. In other cases, progeny heterosis could also be due to divergence between the parents at particular genetic loci that do not control field-level phenotypic differences. Genetic distanceper se between parental genotypes, based on neutral molecular markers, however, does not reflect the potential of individual genotypes to produce heterosis in their progeny. This revised version was published online in August 2006 with corrections to the Cover Date.     

陆地棉种质资源抗旱性状的关联分析

干旱是导致全世界棉花严重减产、纤维品质下降的重要因素,因此获得高产、优质、耐旱的棉花新品种一直是棉花的育种目标。本研究选取217份陆地棉栽培种组成的自然群体为研究对象,采用全生育期处理组灌水量为对照组50%的干旱胁迫处理,并在处理后期对217份材料的株高、衣分、单铃重等18个性状进行2年2点的表型鉴定,干旱胁迫后,群体间响应差异明显,多个表型性状在对照和处理间表现显著差异。通过BLUP分析表型数据并计算各性状的抗旱系数;全基因组范围选取的214对多态性SSR分子标记扫描群体,共检测到393个多态性位点,基因多样性系数平均值为0.402,范围为0.072～0.631, PIC值平均为0.329,范围为0.070～0.560;群体结构分析表明,该群体可分为2个亚群。用上述SSR标记分别对18个性状的抗旱系数进行关联分析,共关联到76个极显著位点(P<0.01),表型变异解释率为2.930%～7.218%,其中共有14个标记位点能同时被2种或以上性状检测到。研究结果可为后期棉花杂交育种亲本选择及抗旱分子标记辅助育种提供理论基础及参考依据。     

Direct and indirect selection for drought tolerance in alien tetraploid wheat x durum wheat crosses

After the evaluation of numerous accessions of primitive wheats for yield components and morphophysiological traits related to drought tolerance (e.g., maintenance of high relative water content, RWC; photochemical quenching of chlorophyll fluorescence, qQ; and chlorophyll loss, chl, under moisture stress conditions), several accessions belonging to three species (Triticum dicoccum, T. polonicum, and T. carthlicum) were crossed with the improved durum wheat varieties Cham 1 and Om Rabi 5. A direct selection (F₂ progeny) for yield and an indirect physiological trait were applied on interspecific T. durum x T. dicoccum, T. durum x T. polonicum, and T. durum x T. carthlicum populations. Divergent selection was applied to validate the possible use of morphophysiological traits (root parameters, RWC, photochemical quenching, proline content, and carbon isotope discrimination) in selection, and to evaluate the resulting effects on yield. Heritability and selection response of these traits has been evaluated, and the impact of divergent selection for morphological and agronomic characters was studied under field conditions. The divergent populations were evaluated under different environmental conditions in France, Syria, and Yemen. Selection for morphophysiological traits related to moisture stress, such as root parameters, RWC and carbon isotope discrimination was possible due to high h² values and effective, resulting in high genetic gains. However, the effect of selection for these traits on yield stability needs to be further studied. Furthermore, a modified bulk method (F₂ 'progeny method') was developed. Direct selection for grain yield per plant in F₂ was carried out and yield per line in F₃ was evaluated under contrasting environmental conditions in France, Syria, and Tunisia. Results revealed that some F₃ lines were higher yielding than the improved durum wheat varieties Cham 1 and Om Rabi 5 under both stressed (Aleppo) and favourable (Montpellier) environmental conditions. Lines were evaluated in preliminary yield trials at Montpellier (France), Aleppo (Syria), and Constantine (Algeria). Results indicated that the use of related species combined with the use of the modified bulk breeding method is promising not only for increasing durum wheat yield in drought prone environments, but also for improving durum wheat yield stability across contrasting environments. Results of both breeding strategies are presented, and the potential advantages of using related tetraploid species in durum wheat breeding for drought tolerance are discussed. This revised version was published online in August 2006 with corrections to the Cover Date.     

The variation of relative water content,SPAD chlorophyll meter reading,stomatal conductance,leaf area,and specific leaf area of Jerusalem artichoke genotypes under different durations of terminal drought in tropical region

This work assessed the responses of Jerusalem artichoke (JA) genotypes experienced to different durations of terminal drought for relative water content (RWC), SPAD chlorophyll meter reading (SCMR), stomatal conductance (SC), leaf area (LA) and specific leaf area (SLA), investigated the significant contributor of physiological traits to yield and yield reduction and diversity of physiological traits in terminal drought tolerance genotypes. Field research was conducted during the late-rainy season for 2 years using a split-plot design with four replications. The three irrigation treatments involved no-drought (SD0), short (SD1) and long (SD2) durations of terminal drought were arranged as main plots, and sub-plots were six genotypes of JA. The current study revealed that RWC, SC, LA, and SLA, were drastically reduced whilst SCMR values slightly increased under SD1 and SD2 compared to SD0. According to multiple linear regression indicated that SLA (SD0), and RWC (SD1 and SD2) had high contributions to tuber fresh weight (TFW), whereas SC had a high contribution to TFW reduction under terminal drought. Principal component analysis also confirmed that the diversity of LA, RWC, and SLA had maximized contributing traits, followed by HI, SCMR and SC in these breeding materials of JA under three irrigation treatments. Our finding emphasized that JA125 (low SLA), HEL256 and JA37 (high SLA) lead to the high performance of TFW under SD0, and they exhibited high TFW under SD1 by performing medium RWC. Likewise, JA4 and JA37 had high TFW under SD2 caused by medium RWC. HEL253 and JA60 were identified as terminal drought-tolerant genotypes because of performed medium SC, which contributed to a low reduction in TFW. Our promising results are the basis for further studies, SLA, RWC and SC are an important keys for screening drought tolerance (low economic yield reduction) and these genotypes studied could be used for parental lines to improved drought tolerance progenies through breeding programs under different durations of terminal drought-prone areas.     

Two Soybean Plant Introductions Display Slow Leaf Wilting and Reduced Yield Loss under Drought

Due to high costs of irrigation, limited availability of irrigation water in many locations and/or lack of irrigation capabilities, genetic improvement for drought tolerance is an effective method to reduce yield loss in soybean [Glycine max (L.) Merr.]. Slow wilting and minimal yield reduction under drought are important traits in evaluating drought tolerance. Two maturity group III soybean plant introductions (PIs, PI 567690 and PI 567731) and two elite cultivars (DKB38‐52 and Pana) were evaluated with and without irrigation on a sandy soil. Drought was imposed by withholding irrigation at full bloom and continued until moderate wilting was shown by the fast leaf wilting in the check cultivar, Pana. Then, irrigation was resumed until maturity. Genotypes were scored for leaf wilting during the stress period, and yields were assessed at the end of the growing season and used to calculate a drought index. Yields of the exotic PIs were lower than those of the checks under both drought and well‐watered conditions. However, the PIs exhibited significantly lower wilting and less yield loss under drought (higher drought index) than check cultivars. The two PIs may have useful genes to develop drought‐tolerant germplasm and cultivars and maybe useful in genetic and physiological studies to decipher mechanisms responsible for improving yield under limited water availability.     

QTL analysis for thousand-grain weight under terminal drought stress in bread wheat (<Emphasis Type="Italic">Triticum</Emphasis><Emphasis Type="Italic">aestivum</Emphasis> L.)

Grain yield under post-anthesis drought stress is one of the most complex traits, which is inherited quantitatively. The present study was conducted to identify genes determining post-anthesis drought stress tolerance in bread wheat through Quantitative Trait Loci (QTLs) analysis. Two cultivated bread wheat accessions were selected as parental lines. Population phenotyping was carried out on 133 F_2:3 families. Two field experiments and two experiments in the greenhouse were conducted at IPK-Gatersleben, Germany with control and post-anthesis stress conditions in each experiment. Thousand-grain weight was recorded as the main wheat yield component, which is reduced by post-anthesis drought stress. Chemical desiccation was applied in three experiments as simulator of post-anthesis drought stress whereas water stress was applied in one greenhouse experiment. Analysis of variance showed significant differences among the F_2:3 families. The molecular genetic linkage map including 293 marker loci associated to 19 wheat chromosomes was applied for QTL analysis. The present study revealed four and six QTLs for thousand-grain weight under control and stress conditions, respectively. Only one QTL on chromosome 4BL was common for both conditions. Five QTLs on chromosomes 1AL, 4AL, 7AS, and 7DS were found to be specific to the stress condition. Both parents contributed alleles for drought tolerance. Taking the known reciprocal translocation of chromosomes 4AL/7BS into account, the importance of the short arms of homoeologous group 7 is confirmed for drought stress.     

Drought stress‐induced changes in starch yield and physiological traits in potato

Drought stress is an important limitation for potato (Solanum tuberosum L.) production as potato depends on appropriate water availability for high yields of good quality. Therefore, especially in the background of climate change, it is an important goal in potato breeding to improve drought stress tolerance. In this study, 34 European starch potato cultivars were evaluated for drought stress tolerance by growing under well‐watered and long‐term drought stress conditions in rainout shelters in 2 years’ pot trials. Besides yield, six physiological traits, that is free proline content, osmolality, total soluble sugar content, chlorophyll content (SPAD), cell membrane stability and crude protein content, were determined in leaves sampled during vegetative growth and during flowering to investigate their association with drought tolerance. ANOVA revealed significant treatment effects for all physiological traits and increased genotypic effects at flowering. The sensitivity of physiological traits to drought was significantly higher during flowering than during vegetative growth. Drought stress decreased starch yield significantly (p < .001), on average by 55%. Starch yield was significantly influenced by genotype and genotype × treatment interactions. Stress tolerance index (STI) calculated from starch yield ranged from 0.26 (sensitive) to 0.76 (tolerant) with significant genotype effects (p ≤ .001). STI correlated positively with cell membrane stability (r = .59) and crude protein content (r = .38) and negatively with osmolality (r = ?.57) and total soluble sugar content (r = ?.71). These contrary correlations suggest a dual adaptation strategy in potato under long‐term drought stress conditions including increased membrane stability combined with an increased osmolality due to an increased soluble sugar content.     

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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Genetic variation in drought tolerance at seedling stage and grain yield in low rainfall environments in wheat (<Emphasis Type="Italic">Triticum aestivum</Emphasis> L.)

Genetic architecture of seedling drought tolerance is complex and needs to be better understood. To address this challenge, we developed a protocol to identify the most promising drought-tolerant genotypes at the seedling stage in winter wheat. A population of 146 recombinant inbred lines (F₉) derived from a cross between wheat cultivars, ‘Harry’ (seedling drought tolerant) and ‘Wesley’ (seedling drought susceptible) were used in this study. All genotypes were sown in three replications in a randomized complete block design under controlled conditions in a greenhouse. Seven traits were scored and grouped into tolerance traits; days to wilting, leaf wilting, and stay green and survival traits; days to regrowth, regrowth, drought survival rate, and recovery after irrigation. Three selection indices were calculated (1) tolerance index, (2) survival index, and (3) drought tolerance index (DTI). The same set of genotypes were also tested for grain yield in two low rainfall environments for two seasons. High genetic variation was found among all genotypes for all seedling traits scored in this study. Correlations between tolerance and survival traits were weak or did not exist. Heritability estimates ranged from 0.53 to 0.88. DTI had significant phenotypic and genotypic correlations with all seedling traits. Genotypes were identified with a high drought tolerance at the seedling stage combined with high grain yield in low rainfall. Breeding for tolerance and survival traits should be taken into account for improving winter wheat drought tolerance at seedling stage. The selected genotypes can be used for to further improve drought tolerance in high yielding wheat for Nebraska.