Introgression of Drought Tolerance into Elite Basmati Rice Variety through Marker-Assisted Backcrossing

Drought is one of the major abiotic threat to rice production in the context of climate change. Super Basmati is an elite, fine grain basmati rice variety grown in Punjab, Pakistan. Due to drought sensitive in nature, its yield has been facing an alarming situation in production because of gradual decrease in irrigated water for a couple of years. Three reported novel QTLs for drought tolerance were selected for incorporation into Super Basmati by employing marker assisted selection strategy. IR55419-04 with novel QTLs was used as a donor parent. Foreground selection was performed by applying PCR based QTL linked SSR markers followed by recombinant selection by using 2–4 flanking markers. Background selection was exercised by using polymorphic SSR markers for maximum genome recovery of the Super Basmati. The individuals homozygous at the target QTLs and with maximum background of Super Basmati at the rest of the non-target genome was selected for evaluation of drought tolerance. Under drought stress conditions, the yields of all introgressed lines (ILs) were 44.2%–125.7% higher than recurrent parent. Six superior ILs that are drought tolerant and very similar to Super Basmati in terms of agronomic and grain quality traits are marked for release as drought-tolerant varieties in arid regions or for use in breeding programs of high grain quality and drought-tolerant parents.     

Identification of RAPD and ISSR markers for drought tolerance in wheat (Triticum aestivum L.)

Drought tolerance is the essential trait that needs to be incorporated in cereal crops, particularly those grown under the rainfed cultivation. Drought tolerance being contributed by several regions of the genome requires identification of these regions, using suitable molecular markers. Therefore, present investigation was aimed at analyzing the genetic diversity present among the cultivars of rainfed and the irrigated areas with respect to the drought tolerant trait. In all, 14 RAPD and 90 ISSR markers were used to identify these genomic regions. Out of 14 RAPD markers, one RAPD primer exhibited polymorphic banding pattern with 18.6 % polymorphism, clearly separating drought tolerant and drought susceptible genotypes. Out of 90 ISSR primers, only 3 ISSR primers revealed polymorphism in relation to the drought tolerance trait exhibiting 21.38 % polymorphism.     

Molecular Assortment of Lens Species with Different Adaptations to Drought Conditions Using SSR Markers

The success of drought tolerance breeding programs can be enhanced through molecular assortment of germplasm. This study was designed to characterize molecular diversity within and between Lens species with different adaptations to drought stress conditions using SSR markers. Drought stress was applied at seedling stage to study the effects on morpho-physiological traits under controlled condition, where tolerant cultivars and wilds showed 12.8–27.6% and 9.5–23.2% reduction in seed yield per plant respectively. When juxtaposed to field conditions, the tolerant cultivars (PDL-1 and PDL-2) and wild (ILWL-314 and ILWL-436) accessions showed 10.5–26.5% and 7.5%–15.6% reduction in seed yield per plant, respectively under rain-fed conditions. The reductions in seed yield in the two tolerant cultivars and wilds under severe drought condition were 48–49% and 30.5–45.3% respectively. A set of 258 alleles were identified among 278 genotypes using 35 SSR markers. Genetic diversity and polymorphism information contents varied between 0.321–0.854 and 0.299–0.836, with mean value of 0.682 and 0.643, respectively. All the genotypes were clustered into 11 groups based on SSR markers. Tolerant genotypes were grouped in cluster 6 while sensitive ones were mainly grouped into cluster 7. Wild accessions were separated from cultivars on the basis of both population structure and cluster analysis. Cluster analysis has further grouped the wild accessions on the basis of species and sub-species into 5 clusters. Physiological and morphological characters under drought stress were significantly (P = 0.05) different among microsatellite clusters. These findings suggest that drought adaptation is variable among wild and cultivated genotypes. Also, genotypes from contrasting clusters can be selected for hybridization which could help in evolution of better segregants for improving drought tolerance in lentil.     

Wheat flag leaf epicuticular wax morphology and composition in response to moderate drought stress are revealed by SEM,FTIR‐ATR and synchrotron X‐ray spectroscopy

Wheat (Triticum aestivum L.) is the largest cereal crop grown in Western Canada where drought during late vegetative and seed filling stages affects plant development and yield. To identify new physiochemical markers associated with drought tolerance, epidermal characteristics of the flag leaf of two wheat cultivars with contrasting drought tolerance were investigated. The drought resistant ‘Stettler’ had a lower drought susceptibility index, greater harvest index and water‐use efficiency than the susceptible ‘Superb’. Furthermore, flag leaf width, relative water content and leaf roll were significantly greater in Stettler than in Superb at moderate drought stress (MdS). Visible differences in epicuticular wax density on the adaxial flag leaf surfaces and larger bulliform cells were identified in Stettler as opposed to Superb. Mid‐infrared attenuated total internal reflectance spectra revealed that Stettler flag leaves had increased asymmetric and symmetric CH₂ but reduced carbonyl esters on its adaxial leaf surface compared to Superb under MdS. X‐ray fluorescence spectra revealed a significant increase in total flag leaf Zn concentrations in Stettler in response to MdS. Such information on the microstructural and chemical features of flag leaf may have potential as markers for drought tolerance and thereby accelerate the selection and release of more drought‐resistant cultivars.     

玉米耐旱功能标记辅助选择初探

干旱是影响玉米生产的主要因素之一,培育耐旱品种可以有效地保持其在干旱环境下的产量稳定性。随着生物信息学数据库的不断完善及基因组学技术的发展,耐旱通用QTL(Quantitative trait locus)的发掘为分子育种提供了新的机遇和方法。本研究在已发掘的耐旱通用QTL基础上,选取相关的18个连锁标记进行开发并且验证在不同种质背景下24份玉米自交系的耐旱性。结果表明,共检测出42个多态性位点,平均多态性信息量为0.4245;通过GGT32(Graphical GenoTypes)图示基因型软件分析SSR位点,得出umc2217、umc2029、phi099、umc1213和phi022这5个连锁标记可用来初步鉴定玉米耐旱性;利用卡方检验,得出phi022和umc2217均达到显著水平,其与耐旱密切相关。因此,这几个连锁标记不仅可被用于相应群体的耐旱分子标记辅助选择,而且为以后的标记辅助选择及抗旱性基因克隆的研究打下基础。     

Using QTL mapping to investigate the relationships between abiotic stress tolerance (drought and salinity) and agronomic and physiological traits

Background

Drought and salinity are two major abiotic stresses that severely limit barley production worldwide. Physiological and genetic complexity of these tolerance traits has significantly slowed the progress of developing stress-tolerant cultivars. Marker-assisted selection (MAS) may potentially overcome this problem. In the current research, seventy two double haploid (DH) lines from a cross between TX9425 (a Chinese landrace variety with superior drought and salinity tolerance) and a sensitive variety, Franklin were used to identify quantitative trait loci (QTL) for drought and salinity tolerance, based on a range of developmental and physiological traits.

Results

Two QTL for drought tolerance (leaf wilting under drought stress) and one QTL for salinity tolerance (plant survival under salt stress) were identified from this population. The QTL on 2H for drought tolerance determined 42% of phenotypic variation, based on three independent experiments. This QTL was closely linked with a gene controlling ear emergency. The QTL on 5H for drought tolerance was less affected by agronomic traits and can be effectively used in breeding programs. A candidate gene for this QTL on 5H was identified based on the draft barley genome sequence. The QTL for proline accumulation, under both drought and salinity stresses, were located on different positions to those for drought and salinity tolerance, indicating no relationship with plant tolerance to either of these stresses.

Conclusions

Using QTL mapping, the relationships between QTL for agronomic and physiological traits and plant drought and salinity tolerance were studied. A new QTL for drought tolerance which was not linked to any of the studied traits was identified. This QTL can be effectively used in breeding programs. It was also shown that proline accumulation under stresses was not necessarily linked with drought or salinity tolerance based on methods of phenotyping used in this experiment. The use of proline content in breeding programs can also be limited by the accuracy of phenotyping.

Electronic supplementary material

The online version of this article (doi:10.1186/s12864-015-1243-8) contains supplementary material, which is available to authorized users.     

Challenges in pea breeding for tolerance to drought: Status and prospects

Drought is increasingly frequent in the context of climate change and is considered a major constraint for crop yield. Water scarcity can impair growth, disturb plant water relations and reduce water use efficiency. Pea (Pisum sativum) is a temperate grain legume rich in protein, fibre, micronutrients and bioactive compounds that can benefit human health. In reducing pea yield because of drought, the intensity and duration of stress are critical. This review describes several drought resistance mechanisms in pea based on morphology, physiology and biochemical changes during/after the water deficit period. Drought tolerance of pea can be managed by adopting strategies such as screening, breeding and marker-assisted selection. Therefore, various biotechnological approaches have led to the development of drought-tolerant pea cultivars. Finally, the main objective of the current research is to point out some useful traits for drought tolerance in peas and also, mention the methods that can be useful for future studies and breeding programmes.     

Impact of drought stress on growth and quality of miscanthus for biofuel production

Miscanthus has a high potential as a biomass feedstock for biofuel production. Drought tolerance is an important breeding goal in miscanthus as water deficit is a common abiotic stress and crop irrigation is in most cases uneconomical. Drought may not only severely reduce biomass yields, but also affect biomass quality for biofuel production as cell wall remodeling is a common plant response to abiotic stresses. The quality and plant weight of 50 diverse miscanthus genotypes were evaluated under control and drought conditions (28 days no water) in a glasshouse experiment. Overall, drought treatment decreased plant weight by 45%. Drought tolerance – as defined by maintenance of plant weight – varied extensively among the tested miscanthus genotypes and ranged from 30% to 110%. Biomass composition was drastically altered due to drought stress, with large reductions in cell wall and cellulose content and a substantial increase in hemicellulosic polysaccharides. Stress had only a small effect on lignin content. Cell wall structural rigidity was also affected by drought conditions; substantially higher cellulose conversion rates were observed upon enzymatic saccharification of drought‐treated samples with respect to controls. Both cell wall composition and the extent of cell wall plasticity under drought varied extensively among all genotypes, but only weak correlations were found with the level of drought tolerance, suggesting their independent genetic control. High drought tolerance and biomass quality can thus potentially be advanced simultaneously. The extensive genotypic variation found for most traits in the evaluated miscanthus germplasm provides ample scope for breeding of drought‐tolerant varieties that are able to produce substantial yields of high‐quality biomass under water deficit conditions. The higher degradability of drought‐treated samples makes miscanthus an interesting crop for the production of second‐generation biofuels in marginal soils.     

Markers associated with a QTL for grain yield in wheat under drought

Drought is a major abiotic stress that adversely affects wheat production in many regions of the world. The objective of this study was to identify quantitative trait loci (QTL) controlling grain yield and yield components under reduced moisture. A cross between common wheat cultivars ‘Dharwar Dry’ (drought tolerant) and ‘Sitta’ was the source of one hundred twenty-seven recombinant inbred lines evaluated for two-seasons in a field under differing soil moisture regimes in Ciudad Obregon, Sonora, Mexico. An SSR/EST-STS marker map was constructed and a grain yield QTL on the proximal region of chromosome 4AL was found to have a significant impact on performance under reduced moisture. This region was associated with QTL for grain yield, grain fill rate, spike density, grains m⁻², biomass production, biomass production rate, and drought susceptibility index (DSI). Molecular markers associated with these traits explained 20, 33, 15, 23, 30, 26, and 41% of phenotypic variation, respectively on chromosome 4A. Microsatellite locus Xwmc89 was associated with all significant QTL covering a 7.7 centiMorgans (cM) region and generally explained the greatest proportion of phenotypic variation. The alleles associated with enhanced performance under drought stress were contributed by Dharwar Dry. Microsatellite marker wmc89 may be useful for marker assisted selection to enhance drought tolerance.     

抗旱相关基因在烟草中的应用研究进展

干旱是影响烟草正常生长、发育、产量和烟叶品质的一个重要逆境因子。在干旱胁迫下,植物体内会通过激发一些抗旱基因的表达来增强植物的抗旱能力。目前,很多抗旱相关的功能蛋白基因和调控蛋白基因已被克隆并在烟草中实现了遗传转化,外源抗旱基因的表达提高了转基因烟草的抗旱能力。抗旱基因的克隆为烟草抗旱新品种的培育奠定了良好的分子基础,系统深入地研究抗旱相关基因在干旱胁迫条件下的表达与调控,可为通过基因工程手段提高烟草的抗旱能力开辟新途径,同时也能为其他农作物的抗旱分子育种和品种改良提供基因资源。     

Quantitative trait loci associated with drought tolerance at reproductive stage in rice

Drought is a major constraint to rice (Oryza sativa) yield and its stability in rainfed and poorly irrigated environments. Identifying genomic regions influencing the response of yield and its components to water deficits will aid in our understanding of the genetics of drought tolerance and development of more drought tolerant cultivars. Quantitative trait loci (QTL) for grain yield and its components and other agronomic traits were identified using a subset of 154 doubled haploid lines derived from a cross between two rice cultivars, CT9993-510 to 1-M and IR62266-42 to 6-2. Drought stress treatments were managed by use of a line source sprinkler irrigation system, which provided a linearly decreasing level of irrigation coinciding with the sensitive reproductive growth stages. The research was conducted at the Ubon Rice Research Center, Ubon, Thailand. A total of 77 QTL were identified for grain yield and its components under varying levels of water stress. Out of the total of 77 QTL, the number of QTL per trait were: 7-grain yield (GY); 8-biological yield (BY); 6-harvest index (HI); 5-d to flowering after initiation of irrigation gradient (DFAIG); 10-total spikelet number (TSN); 7-percent spikelet sterility (PSS); 23-panicle number (PN); and 11-plant height (PH). The phenotypic variation explained by individual QTL ranged from 7.5% to 55.7%. Under well-watered conditions, we observed a high genetic association for BY, HI, DFAIG, PSS, TSN, PH, and GY. However, only BY and HI were found to be significantly associated with GY under drought treatments. QTL flanked by markers RG104 to RM231, EMP2_2 to RM127, and G2132 to RZ598 on chromosomes 3, 4, and 8 were associated with GY, HI, DFAIG, BY, PSS, and PN under drought treatments. The aggregate effects of these QTL on chromosomes 3, 4, and 8 resulted in higher grain yield. These QTL will be useful for rainfed rice improvement, and will also contribute to our understanding of the genetic control of GY under drought conditions at the sensitive reproductive stage. Close linkage or pleiotropy may be responsible for the coincidence of QTL detected in this experiment. Digenic interactions between QTL main effects for GY, BY, HI, and PSS were observed under irrigation treatments. Most (but not all) DH lines have the same response in measure of productivity when the intensity of water deficit was increased, but no QTL by irrigation treatment interaction was detected. The identification of genomic regions associated with GY and its components under drought stress will be useful for marker-based approaches to improve GY and its stability for farmers in drought-prone rice environments.     

The TaDREB3 transgene transferred by conventional crossings to different genetic backgrounds of bread wheat improves drought tolerance

Drought tolerance of the wheat cultivar Bobwhite was previously enhanced by transformation with a construct containing the wheat DREB3 gene driven by the stress‐inducible maize Rab17 promoter. Progeny of a single T₂ transgenic line were used as pollinators in crosses with four elite bread wheat cultivars from Western Australia: Bonnie Rock, IGW‐2971, Magenta and Wyalkatchem, with the aim of evaluating transgene performance in different genetic backgrounds. The selected pollinator line, BW8‐9‐10‐3, contained multiple transgene copies, had significantly improved drought tolerance compared with wild‐type plants and showed no growth and development penalties or abnormalities. A single hybrid plant was selected from each cross‐combination for three rounds of backcrossing with the corresponding maternal wheat cultivar. The transgene was detected in all four F₁BC₃ combinations, but stress‐inducible transgene expression was found in only three of the four combinations. Under well‐watered conditions, the phenotypes and grain yield components of the F₂BC₃ transgene‐expressing lines were similar to those of corresponding recurrent parents and null‐segregants. Under severe drought conditions, the backcross lines demonstrated 12–18% higher survival rates than the corresponding control plants. Two from four F₃BC₃ transgenic lines showed significantly higher yield (18.9% and 21.5%) than control plants under limited water conditions. There was no induction of transgene expression under cold stress, and therefore, no improvement of frost tolerance observed in the progenies of drought‐tolerant F₃BC₃ lines.     

Leaf cuticular waxes and physiological parameters in alfalfa leaves as influenced by drought

Drought significantly constrains higher yield of alfalfa (Medicago sativa L.) in arid and semiarid areas all over the world. This study evaluated the responses of leaf cuticular wax constituents to drought treatment and their relations to gas-exchange indexes across six alfalfa cultivars widely grown in China. Water deficit was imposed by withholding water for 12 d during branching stage. Cuticular waxes on alfalfa leaves were dominated by primary alcohols (41.7?C54.2%), alkanes (13.2?C26.9%) and terpenes (17.5?C28.9%), with small amount of aldehydes (1.4?C3.4%) and unknown constituents (4.5?C18.4%). Compared to total wax contents, the wax constituents were more sensitive to drought treatment. Drought decreased the contents of primary alcohol and increased alkanes in all cultivars. Alkane homologs, C25, C27, and C29, were all negatively correlated with photosynthetic rate, transpiration rate, stomatal conductance, and leaf water potential. Under drought conditions, both stomatal and nonstomatal factors were involved in controlling water loss from alfalfa leaves. No direct relationship was observed between wax contents and drought resistance among alfalfa cultivars. An increase in alkane content might be more important in improving drought tolerance of alfalfa under water deficit, which might be used as an index for selecting and breeding drought resistant cultivars of alfalfa.     

Genome-wide association mapping of yield components and drought tolerance-related traits in cotton

Drought causes serious yield losses in cotton production throughout the world. Association mapping allows identification and localization of the genes controlling drought-related traits which will be helpful in cotton breeding. In the present study, genetic diversity analysis and association mapping of yield and drought traits were performed on a panel of 99 upland cotton genotypes using 177 SSR (simple sequence repeat) markers. Yield parameters and drought tolerance-related traits were evaluated for two seasons under two watering regimes: water-stressed and well-watered. The traits included seed cotton yield (SCY), lint yield (LY), lint percentage (LP), water-use efficiency (WUE), yield potential (YP), yield reduction (YR), yield index (YI), drought sensitivity index (DSI), stress tolerance index (STI), harmonic mean (HM), and geometric mean productivity (GMP). The genotypes with the least change in seed cotton yield under drought stress were Zeta 2, Delcerro, Nazilli 87, and DAK 66/3 which were also the most water-use efficient cultivars. The average genetic diversity of the panel was 0.38. The linkage disequilibrium decayed relatively rapidly at 20–30 cM (r²?≥?0.5). We identified 30 different SSR markers associated with the traits. Fifteen and 23 SSR markers were linked to the traits under well-watered and water-stress conditions, respectively. To our knowledge, most of these quantitative yield and drought tolerance-associated loci were newly identified. The genetic diversity and association mapping results should facilitate the development of drought-tolerant cotton lines with high yield in molecular breeding programs.