Functional mapping of N deficiency‐induced response in wheat yield‐component traits by implementing high‐throughput phenotyping

As overfertilization leads to environmental concerns and the cost of N fertilizer increases, the issue of how to select crop cultivars that can produce high yields on N‐deficient soils has become crucially important. However, little information is known about the genetic mechanisms by which crops respond to environmental changes induced by N signaling. Here, we dissected the genetic architecture of N‐induced phenotypic plasticity in bread wheat (Triticum aestivum L.) by integrating functional mapping and semiautomatic high‐throughput phenotyping data of yield‐related canopy architecture. We identified a set of quantitative trait loci (QTLs) that determined the pattern and magnitude of how wheat cultivars responded to low N stress from normal N supply throughout the wheat life cycle. This analysis highlighted the phenological landscape of genetic effects exerted by individual QTLs, as well as their interactions with N‐induced signals and with canopy measurement angles. This information may shed light on our mechanistic understanding of plant adaptation and provide valuable information for the breeding of N‐deficiency tolerant wheat varieties.     

Genome-wide mapping and prediction suggests presence of local epistasis in a vast elite winter wheat populations adapted to Central Europe

Key message

Genome-wide association mapping as well as marker- and haplotype-based genome-wide selection unraveled a complex genetic architecture of grain yield with absence of large effect QTL and presence of local epistatic effects.

Abstract

The genetic architecture of grain yield determines to a large extent the optimum design of genomic-assisted wheat breeding programs. The main goal of our study was to examine the potential and limitations to dissect the genetic architecture of grain yield in wheat using a large experimental data set. Our study was based on phenotypic information and genomic data of 13,901 SNPs of a diverse set of 3816 elite wheat lines adapted to Central Europe. We applied genome-wide association mapping based on experimental and simulated data sets and performed marker- and haplotype-based genomic prediction. Computer simulations revealed for our mapping population a high power to detect QTL, even if they individually explained only 2.5% of the genetic variation. Despite this, we found no stable marker–trait associations when validating in independent subsets. A two-dimensional scan for marker–marker interactions indicated presence of local epistasis which was further supported by improved prediction abilities when shifting from marker- to haplotype-based genome-wide prediction approaches. We observed that marker effects estimated using genome-wide prediction approaches strongly varied across years albeit resulting in high prediction abilities. Thus, our results suggested that the prediction accuracy of genomic selection in wheat is mainly driven by relatedness rather than by exploiting knowledge of the genetic architecture.

     

Abiotic stress and control of grain number in cereals

Grain number is the only yield component that is directly associated with increased grain yield in important cereal crops like wheat. Historical yield studies show that increases in grain yield are always accompanied by an increase in grain number. Adverse weather conditions can cause severe fluctuations in grain yield and substantial yield losses in cereal crops. The problem is global and despite its impact on world food production breeding and selection approaches have only met with limited success. A specific period during early reproductive development, the young microspore stage of pollen development, is extremely vulnerable to abiotic stress in self-fertilising cereals (wheat, rice, barley, sorghum). A better understanding of the physiological and molecular processes that lead to stress-induced pollen abortion may provide us with the key to finding solutions for maintaining grain number under abiotic stress conditions. Due to the complexity of the problem, stress-proofing our main cereal crops will be a challenging task and will require joint input from different research disciplines.     

Simultaneous improvement of grain yield and protein content in durum wheat by different phenotypic indices and genomic selection

Key message

Simultaneous improvement of protein content and grain yield by index selection is possible but its efficiency largely depends on the weighting of the single traits. The genetic architecture of these indices is similar to that of the primary traits.

Abstract

Grain yield and protein content are of major importance in durum wheat breeding, but their negative correlation has hampered their simultaneous improvement. To account for this in wheat breeding, the grain protein deviation (GPD) and the protein yield were proposed as targets for selection. The aim of this work was to investigate the potential of different indices to simultaneously improve grain yield and protein content in durum wheat and to evaluate their genetic architecture towards genomics-assisted breeding. To this end, we investigated two different durum wheat panels comprising 159 and 189 genotypes, which were tested in multiple field locations across Europe and genotyped by a genotyping-by-sequencing approach. The phenotypic analyses revealed significant genetic variances for all traits and heritabilities of the phenotypic indices that were in a similar range as those of grain yield and protein content. The GPD showed a high and positive correlation with protein content, whereas protein yield was highly and positively correlated with grain yield. Thus, selecting for a high GPD would mainly increase the protein content whereas a selection based on protein yield would mainly improve grain yield, but a combination of both indices allows to balance this selection. The genome-wide association mapping revealed a complex genetic architecture for all traits with most QTL having small effects and being detected only in one germplasm set, thus limiting the potential of marker-assisted selection for trait improvement. By contrast, genome-wide prediction appeared promising but its performance strongly depends on the relatedness between training and prediction sets.

     

Anthesis date mainly explained correlations between post-anthesis leaf senescence, grain yield, and grain protein concentration in a winter wheat population segregating for flowering time QTLs

The genetic variability of the duration of leaf senescence during grain filling has been shown to affect both carbon and nitrogen acquisition. In particular, maintaining green leaves during grain filling possibly leads to increased grain yield, but its associated effect on grain protein concentration has not been studied. The aim of this study was to dissect the genetic factors contributing to correlations observed at the phenotypic level between leaf senescence during grain filling, grain protein concentration, and grain yield in winter wheat. With this aim in view, an analysis of quantitative trait locus (QTL) co-locations for these traits was carried out on a doubled haploid mapping population grown in a large multienvironment trial network. Pleiotropic QTLs affecting leaf senescence and grain yield and/or grain protein concentration were identified on chromosomes 2D, 2A, and 7D. These were associated with QTLs for anthesis date, showing that the phenotypic correlations with leaf senescence were mainly explained by flowering time in this wheat population. Study of the allelic effects of these pleiotropic QTLs showed that delaying leaf senescence was associated with increased grain yield or grain protein concentration depending on the environments considered. It is proposed that this differential effect of delaying leaf senescence on grain yield and grain protein concentration might be related to the nitrogen availability during the post-anthesis period. It is concluded that the benefit of using leaf senescence as a selection criterion to improve grain protein concentration in wheat cultivars may be limited and would largely depend on the targeted environments, particularly on their nitrogen availability during the post-anthesis period.     

Evaluation of Wheat Chromosome Translocation Lines for High Temperature Stress Tolerance at Grain Filling Stage

High temperature (HT, heat) stress is detrimental to wheat (Triticum aestivum L.) production. Wild relatives of bread wheat may offer sources of HT stress tolerance genes because they grow in stressed habitats. Wheat chromosome translocation lines, produced by introgressing small segments of chromosome from wild relatives to bread wheat, were evaluated for tolerance to HT stress during the grain filling stage. Sixteen translocation lines and four wheat cultivars were grown at optimum temperature (OT) of 22/14°C (day/night). Ten days after anthesis, half of the plants were exposed to HT stress of 34/26°C for 16 d, and other half remained at OT. Results showed that HT stress decreased grain yield by 43% compared with OT. Decrease in individual grain weight (by 44%) was the main reason for yield decline at HT. High temperature stress had adverse effects on leaf chlorophyll content and Fv/Fm; and a significant decrease in Fv/Fm was associated with a decline in individual grain weight. Based on the heat response (heat susceptibility indices, HSIs) of physiological and yield traits to each other and to yield HSI, TA5594, TA5617, and TA5088 were highly tolerant and TA5637 and TA5640 were highly susceptible to HT stress. Our results suggest that change in Fv/Fm is a highly useful trait in screening genotypes for HT stress tolerance. This study showed that there is genetic variability among wheat chromosome translocation lines for HT stress tolerance at the grain filling stage and we suggest further screening of a larger set of translocation lines.     

Variation in phosphorus and sulfur content shapes the genetic architecture and phenotypic associations within the wheat grain ionome

Dissection of the genetic basis of wheat ionome is crucial for understanding the physiological and biochemical processes underlying mineral accumulation in seeds, as well as for efficient crop breeding. Most of the elements essential for plants are metals stored in seeds as chelate complexes with phytic acid or sulfur‐containing compounds. We assume that the involvement of phosphorus and sulfur in metal chelation is the reason for strong phenotypic correlations within ionome. Adjustment of element concentrations for the effect of variation in phosphorus and sulfur seed content resulted in drastic change of phenotypic correlations between the elements. The genetic architecture of wheat grain ionome was characterized by quantitative trait loci (QTL) analysis using a cross between durum and wild emmer wheat. QTL analysis of the adjusted traits and two‐trait analysis of the initial traits paired with either P or S considerably improved QTL detection power and accuracy, resulting in the identification of 105 QTLs and 617 QTL effects for 11 elements. Candidate gene search revealed some potential functional associations between QTLs and corresponding genes within their intervals. Thus, we have shown that accounting for variation in P and S is crucial for understanding of the physiological and genetic regulation of mineral composition of wheat grain ionome and can be implemented for other plants.     

Genome mapping of kernel characteristics in hard red spring wheat breeding lines

Kernel characteristics, particularly kernel weight, kernel size, and grain protein content, are important components of grain yield and quality in wheat. Development of high performing wheat cultivars, with high grain yield and quality, is a major focus in wheat breeding programs worldwide. Here, we report chromosome regions harboring genes that influence kernel weight, kernel diameter, kernel size distribution, grain protein content, and grain yield in hard red spring wheat breeding lines adapted to the Upper Midwest region of the United States. A genetic linkage map composed of 531 SSR and DArT marker loci spanned a distance of 2,505 cM, covering all 21 chromosomes of wheat. Stable QTL clusters influencing kernel weight, kernel diameter, and kernel size distribution were identified on chromosomes 2A, 5B, and 7A. Phenotypic variation explained by individual QTL at these clusters varied from 5 to 20% depending on the trait. A QTL region on chromosome 2B confers an undesirable pleiotropic effect or a repulsion linkage between grain yield (LOD = 6.7; R ² = 18%) and grain protein content (LOD = 6.2; R ² = 13.3%). However, several grain protein and grain yield QTL independent of each other were also identified. Because some of the QTL identified in this study were consistent across environments, DNA markers will provide an opportunity for increasing the frequency of desirable alleles through marker-assisted selection.     

A Genetic Framework for Grain Size and Shape Variation in Wheat

Grain morphology in wheat (Triticum aestivum) has been selected and manipulated even in very early agrarian societies and remains a major breeding target. We undertook a large-scale quantitative analysis to determine the genetic basis of the phenotypic diversity in wheat grain morphology. A high-throughput method was used to capture grain size and shape variation in multiple mapping populations, elite varieties, and a broad collection of ancestral wheat species. This analysis reveals that grain size and shape are largely independent traits in both primitive wheat and in modern varieties. This phenotypic structure was retained across the mapping populations studied, suggesting that these traits are under the control of a limited number of discrete genetic components. We identified the underlying genes as quantitative trait loci that are distinct for grain size and shape and are largely shared between the different mapping populations. Moreover, our results show a significant reduction of phenotypic variation in grain shape in the modern germplasm pool compared with the ancestral wheat species, probably as a result of a relatively recent bottleneck. Therefore, this study provides the genetic underpinnings of an emerging phenotypic model where wheat domestication has transformed a long thin primitive grain to a wider and shorter modern grain.     

Crop traits and the tolerance of wheat and barley to foliar disease

The relationship between yield loss and disease severity can differ widely between crops. This has given rise to the concept of disease tolerance, with some crops exhibiting a smaller yield loss under a given severity of disease than others. Genetic improvement to minimise yield loss under disease is an attractive goal, as it exerts little or no selection pressure on pathogen populations, and could form a useful component of durable disease management programmes. However, progress towards this end requires a thorough understanding of the phenotypic traits that influence the response of yield to disease, their genetic control and the possible trade-offs involved with other desirable agronomic characteristics. This paper examines the candidate crop traits that may confer tolerance of foliar disease in wheat and barley and reviews evidence of genetic variation in their expression. In wheat grown under the relatively low light conditions of North-West Europe, post-anthesis source (assimilate supply) and grain sink capacity (capacity for dry matter accumulation) appear to be closely balanced. Traits associated with maintaining post-anthesis radiation interception and radiation use efficiency in spite of disease may confer tolerance. The most promising traits include a larger flag leaf and compensatory increases in photosynthetic rate in non-infected parts of leaves. In barley, yield is often more strongly sink limited, and early-season disease management is required to protect the formation of potential grain sites. A wider range of potential traits may influence tolerance including compensatory adjustments in leaf growth and morphology, and differences in the sensitivity of tiller and spikelet mortality to photoassimilate supply. Different methods for quantifying tolerance are suggested depending on the trait of interest.     

Genetic dissection of grain yield and physical grain quality in bread wheat (Triticum aestivum L.) under water-limited environments

In the water-limited bread wheat production environment of southern Australia, large advances in grain yield have previously been achieved through the introduction and improved understanding of agronomic traits controlled by major genes, such as the semi-dwarf plant stature and photoperiod insensitivity. However, more recent yield increases have been achieved through incremental genetic advances, of which, breeders and researchers do not fully understand the underlying mechanism(s). A doubled haploid population was utilised, derived from a cross between RAC875, a relatively drought-tolerant breeders' line and Kukri, a locally adapted variety more intolerant of drought. Experiments were performed in 16 environments over four seasons in southern Australia, to physiologically dissect grain yield and to detect quantitative trait loci (QTL) for these traits. Two stage multi-environment trial analysis identified three main clusters of experiments (forming distinctive environments, ENVs), each with a distinctive growing season rainfall patterns. Kernels per square metre were positively correlated with grain yield and influenced by kernels per spikelet, a measure of fertility. QTL analysis detected nine loci for grain yield across these ENVs, individually accounting for between 3 and 18% of genetic variance within their respective ENVs, with the RAC875 allele conferring increased grain yield at seven of these loci. These loci were partially dissected by the detection of co-located QTL for other traits, namely kernels per square metre. While most loci for grain yield have previously been reported, their deployment and effect within local germplasm are now better understood. A number of novel loci can be further exploited to aid breeders' efforts in improving grain yield in the southern Australian environment.     

Deciphering genetic basis of developmental and agronomic traits by integrating high-throughput optical phenotyping and genome-wide association studies in wheat

Dissecting the genetic basis of complex traits such as dynamic growth and yield potential is a major challenge in crops. Monitoring the growth throughout growing season in a large wheat population to uncover the temporal genetic controls for plant growth and yield-related traits has so far not been explored. In this study, a diverse wheat panel composed of 288 lines was monitored by a non-invasive and high-throughput phenotyping platform to collect growth traits from seedling to grain filling stage and their relationship with yield-related traits was further explored. Whole genome re-sequencing of the panel provided 12.64 million markers for a high-resolution genome-wide association analysis using 190 image-based traits and 17 agronomic traits. A total of 8327 marker-trait associations were detected and clustered into 1605 quantitative trait loci (QTLs) including a number of known genes or QTLs. We identified 277 pleiotropic QTLs controlling multiple traits at different growth stages which revealed temporal dynamics of QTLs action on plant development and yield production in wheat. A candidate gene related to plant growth that was detected by image traits was further validated. Particularly, our study demonstrated that the yield-related traits are largely predictable using models developed based on i-traits and provide possibility for high-throughput early selection, thus to accelerate breeding process. Our study explored the genetic architecture of growth and yield-related traits by combining high-throughput phenotyping and genotyping, which further unravelled the complex and stage-specific contributions of genetic loci to optimize growth and yield in wheat.     

Hybrid wheat: quantitative genetic parameters and consequences for the design of breeding programs

Key message

Commercial heterosis for grain yield is present in hybrid wheat but long-term competiveness of hybrid versus line breeding depends on the development of heterotic groups to improve hybrid prediction.

Abstract

Detailed knowledge of the amount of heterosis and quantitative genetic parameters are of paramount importance to assess the potential of hybrid breeding. Our objectives were to (1) examine the extent of midparent, better-parent and commercial heterosis in a vast population of 1,604 wheat (Triticum aestivum L.) hybrids and their parental elite inbred lines and (2) discuss the consequences of relevant quantitative parameters for the design of hybrid wheat breeding programs. Fifteen male lines were crossed in a factorial mating design with 120 female lines, resulting in 1,604 of the 1,800 potential single-cross hybrid combinations. The hybrids, their parents, and ten commercial wheat varieties were evaluated in multi-location field experiments for grain yield, plant height, heading time and susceptibility to frost, lodging, septoria tritici blotch, yellow rust, leaf rust, and powdery mildew at up to five locations. We observed that hybrids were superior to the mean of their parents for grain yield (10.7 %) and susceptibility to frost (?7.2 %), leaf rust (?8.4 %) and septoria tritici blotch (?9.3 %). Moreover, 69 hybrids significantly (P < 0.05) outyielded the best commercial inbred line variety underlining the potential of hybrid wheat breeding. The estimated quantitative genetic parameters suggest that the establishment of reciprocal recurrent selection programs is pivotal for a successful long-term hybrid wheat breeding.     

The effect of seaweed concentrate on the growth and yield of potassium stressed wheat

The effects of the seaweed concentrate “Kelpak’ on the growth and yield of wheat grown under conditions of varying K supply were investigated. Kelpak had no significant effect on the yield of wheat receiving an adequate K supply, but significantly increased the yield of K stressed plants. The increase in yield was caused by an increase in both grain number and individual grain weight. Although the beneficial effects of seaweed concentrates have often been attributed to their cytokinin content, several lines of evidence suggested that this group of plant growth regulators may not be solely responsible for the observed effects of Kelpak on wheat. Irrespective of the physiological mechanism of action, Kelpak would appear to have considerable potential for increasing yield in K stressed wheat and may therefore reduce the requirement of wheat for K fertilization.     

Mechanical stimulation in wheat triggers age- and dose-dependent alterations in growth,development and grain characteristics

Background and AimsWheat crops are exposed to a range of mechanical stimulations in their natural environment, yet we know very little about their response to such conditions. The aim of this study was to better understand the effect of mechanical stimulation on wheat growth and development, stem mechanical properties and grain measures. We focused on the following questions: (1) Does plant age affect the response to mechanical stimulation? (2) Is there a minimum threshold for the perception of mechanical stimuli? (3) Is the effect of manual brushing different to natural wind stimulation?MethodsFor age– and dose–response experiments, wheat plants were grown under controlled glasshouse conditions with brushing treatments applied using a purpose-built rig. The results of the controlled experiments are compared with those from an outside experiment where wheat plants were exposed to natural wind, with or without additional brushing. Detailed phenotypic measurements were conducted and treatment effects on grain characteristics were determined using micro-computed tomography imaging.Key ResultsTwo-week-old wheat plants were particularly sensitive to mechanical stimulation by controlled brushing treatments. Amongst others, plants exhibited a large reduction in height and grain yield, and an increase in tillers, above-ground biomass and stiffness of stem segments. Plants responded significantly to doses as small as one daily brushstroke. Outdoor experiments by and large confirmed results from controlled environment experiments.ConclusionsThe morphological and developmental response to mechanical brushing treatment, in relation to vegetative above-ground biomass and grain yield, is dependent on plant age as well as the dose of the treatments. This study shows that mechanical stimulation of wheat impacts on a multitude of agriculturally relevant traits and provides a much needed advancement of our understanding of wheat thigmomorphogenesis and the potential applications of mechanical conditioning to control relevant traits.     

Exploration of Genetic Pattern of Phenological Traits in Wheat (<i>Triticum aestivum</i> L.) under Drought Stress

Drought is the major detrimental environmental factor for wheat (Triticum aestivum L.) production. The exploration of genetic patterns underlying drought tolerance is of great significance. Here we report the gene actions controlling the phenological traits using the line × tester model studying 27 crosses and 12 parents under normal irrigation and drought conditions. The results interpreted via multiple analysis (mean performance, correlations, principal component, genetic analysis, heterotic and heterobeltiotic potential) disclosed highly significant differences among germplasm. The phenological waxiness traits (glume, boom, and sheath) were strongly interlinked. Flag leaf area exhibits a positive association with peduncle and spike length under drought. The growing degree days (heat-units) greatly influence spikelets and grains per spike, however, the grain yield/plant was significantly reduced (17.44 g to 13.25 g) under drought. The principal components based on eigenvalue indicated significant PCs (first-seven) accounted for 79.9% and 73.9% of total variability under normal irrigation and drought, respectively. The investigated yield traits showed complex genetic behaviour. The genetic advance confronted a moderate to high heritability for spikelets/spike and grain yield/plant. The traits conditioned by dominant genetic effects in normal irrigation were inversely controlled by additive genetic effects under drought and vice versa. The magnitude of dominance effects for phenological and yield traits, i.e., leaf twist, auricle hairiness, grain yield/plant, spikelets, and grains/spike suggests that selection by the pedigree method is appropriate for improving these traits under normal irrigation conditions and could serve as an indirect selection index for improving yield-oriented traits in wheat populations for drought tolerance. However, the phenotypic selection could be more than effective for traits conditioned by additive genetic effects under drought. We suggest five significant cross combinations based on heterotic and heterobeltiotic potential of wheat genotypes for improved yield and enhanced biological production of wheat in advanced generations under drought.     

Grain zinc, iron and protein concentrations and zinc-efficiency in wild emmer wheat under contrasting irrigation regimes

Micronutrient malnutrition, and particularly deficiency in zinc (Zn) and iron (Fe), afflicts over three billion people worldwide, and nearly half of the world’s cereal-growing area is affected by soil Zn deficiency. Wild emmer wheat [Triticum turgidum ssp. dicoccoides (Körn.) Thell.], the progenitor of domesticated durum wheat and bread wheat, offers a valuable source of economically important genetic diversity including grain mineral concentrations. Twenty two wild emmer wheat accessions, representing a wide range of drought resistance capacity, as well as two durum wheat cultivars were examined under two contrasting irrigation regimes (well-watered control and water-limited), for grain yield, total biomass production and grain Zn, Fe and protein concentrations. The wild emmer accessions exhibited high genetic diversity for yield and grain Zn, Fe and protein concentrations under both irrigation regimes, with a considerable potential for improvement of the cultivated wheat. Grain Zn, Fe and protein concentrations were positively correlated with one another. Although irrigation regime significantly affected ranking of genotypes, a few wild emmer accessions were identified for their advantage over durum wheat, having consistently higher grain Zn (e.g., 125 mg kg^?1), Fe (85 mg kg^?1) and protein (250 g kg^?1) concentrations and high yield capacity. Plants grown from seeds originated from both irrigation regimes were also examined for Zn efficiency (Zn deficiency tolerance) on a Zn-deficient calcareous soil. Zinc efficiency, expressed as the ratio of shoot dry matter production under Zn deficiency to Zn fertilization, showed large genetic variation among the genotypes tested. The source of seeds from maternal plants grown under both irrigation regimes had very little effect on Zn efficiency. Several wild emmer accessions revealed combination of high Zn efficiency and drought stress resistance. The results indicate high genetic potential of wild emmer wheat to improve grain Zn, Fe and protein concentrations, Zn deficiency tolerance and drought resistance in cultivated wheat.     

Genetic analysis of grain protein-content,grain yield and thousand-kernel weight in bread wheat

Grain yield and grain protein content are two very important traits in bread wheat. They are controlled by genetic factors, but environmental conditions considerably affect their expression. The aim of this study was to determine the genetic basis of these two traits by analysis of a segregating population of 194 F(7) recombinant inbred lines derived from a cross between two wheat varieties, grown at six locations in France in 1999. A genetic map of 254 loci was constructed, covering about 75% of the bread wheat genome. QTLs were detected for grain protein-content (GPC), yield and thousand-kernel weight (TKW). 'Stable' QTLs (i.e. detected in at least four of the six locations) were identified for grain protein-content on chromosomes 2A, 3A, 4D and 7D, each explaining about 10% of the phenotypic variation of GPC. For yield, only one important QTL was found on chromosome 7D, explaining up to 15.7% of the phenotypic variation. For TKW, three QTLs were detected on chromosomes 2B, 5B and 7A for all environments. No negative relationships between QTLs for yield and GPC were observed. Factorial Regression on GxE interaction allowed determination of some genetic regions involved in the differential reaction of genotypes to specific climatic factors, such as mean temperature and the number of days with a maximum temperature above 25 degrees C during grain filling.     

Wheat endophytes and their potential role in managing abiotic stress under changing climate

Wheat (Triticum aestivum L.) cultivation differs considerably in respect of soil type, temperature, pH, organic matter, moisture regime, etc. Among these, rising atmospheric temperature due to global warming is most important as it affects grain yield drastically. Studies have shown that for every 1°C rise in temperature above wheat's optimal growing temperature range of 20–25°C, there is a decrease in 2.8 days and 1.5 mg in the grain filling period and kernel weight, respectively, resulting in wheat yield reduction by 4–6 quintal per hectare. Growing demand for food and multidimensional issues of global warming may further push wheat crop to heat stress environments that can substantially affect heading duration, percent grain setting, maturity duration, grain growth rate and ultimately total grain yield. Considerable genetic variation exists in wheat gene pool with respect to various attributes associated with high temperature and stress tolerance; however, only about 15% of the genetic variability could be incorporated into cultivated wheat so far. Thus, alternative strategies have to be explored and implemented for sustainable, more productive and environment friendly agriculture. One of the feasible and environment friendly option is to look at micro-organisms that reside inside the plant without adversely affecting its growth, known as ‘endophytes’, and these colonize virtually all plant organs such as roots, stems, leaves, flowers and grains. The relationship between plant and endophytes is vital to the plant health, productivity and overall survival under abiotic stress conditions. Thus, it becomes imperative to enlist the endophytes (bacterial and fungal) isolated till date from wheat cultivars, their mechanism of ingression and establishment inside plant organs, genes involved in ingression, the survival advantages they confer to the plant under abiotic stress conditions and the potential benefits of their use in sustainable wheat cultivation.     

小麦地方品种繁殖更新过程中的遗传多样性变化分析

采用分别保存于长期库及中期库的3个小麦地方品种的6份材料,进行了9项农艺性状及35个与农艺性状相关的微卫星标记检测,每份材料选取30个单株进行遗传多样性与遗传结构分析。结果表明:(1)更新前,3个小麦地方品种均为遗传异质性群体,在SSR位点上的异质度分别为57.14%、48.57%和5.71%。(2)在农艺性状表现上,只有温泉小麦3在株高和穗粒数上更新后比更新前显著增加,其他材料无显著差异。(3)在SSR位点多态性表现上,3个品种在更新后均发生了遗传多样性变化,8个与粒重、产量、生育期性状相关位点存在等位位点丢失现象,其中2个与粒重、生育期相关位点频率变化显著。(4)综合农艺性状调查与SSR分子标记检测结果发现,3个品种更新前后在多样性指数上无显著差异,遗传分化系数Gst分别为0.0269、0.0324和0.0380,即更新前后遗传差异分别为2.69%、3.24%和3.80%。上述结果建议,经繁殖更新的小麦种质资源能够比较完好地保持其遗传多样性和遗传结构。对于遗传异质性小麦地方品种在繁殖更新后存在遗传多样性丢失的危险,为了保证更新前后的遗传完整性,建议在繁殖更新过程中每个品种至少应保持300个单株的群体。