Wheat Growing Regions In China Research Articles

Genomic analysis, trajectory tracking, and field surveys reveal sources and long-distance dispersal routes of wheat stripe rust pathogen in China

Identifying sources of phytopathogen inoculum and determining their contributions to disease outbreaks are essential for predicting disease development and establishing control strategies. Puccinia striiformis f. sp. tritici (Pst), the causal agent of wheat stripe rust, is an airborne fungal pathogen with rapid virulence variation that threatens wheat production through its long-distance migration. Because of wide variation in geographic features, climatic conditions, and wheat production systems, Pst sources and related dispersal routes in China are largely unclear. In the present study, we performed genomic analyses of 154 Pst isolates from all major wheat-growing regions in China to determine Pst population structure and diversity. Through trajectory tracking, historical migration studies, genetic introgression analyses, and field surveys, we investigated Pst sources and their contributions to wheat stripe rust epidemics. We identified Longnan, the Himalayan region, and the Guizhou Plateau, which contain the highest population genetic diversities, as the Pst sources in China. Pst from Longnan disseminates mainly to eastern Liupan Mountain, the Sichuan Basin, and eastern Qinghai; that from the Himalayan region spreads mainly to the Sichuan Basin and eastern Qinghai; and that from the Guizhou Plateau migrates mainly to the Sichuan Basin and the Central Plain. These findings improve our current understanding of wheat stripe rust epidemics in China and emphasize the need for managing stripe rust on a national scale.

Race composition and genetic diversity of a Puccinia striiformis f. sp. tritici population from Yunnan and Guizhou epidemiological regions in China in 2018

Wheat stripe rust, caused by Puccinia striiformis f. sp. tritici (Pst), is an extremely destructive wheat disease worldwide. Yunnan and Guizhou provinces are the main overwintering regions for Pst and inoculum sources for the disease in China. Surveillance of race dynamics of the Pst population is essential for managing the disease in local and other wheat-growing regions of China. However, Pst population dynamics in this region is not monitored yearly. In this study, a Pst population of 113 isolates from Yunnan and Guizhou in 2018 were phenotyped on the two wheat differential sets and analyzed by 12 simple sequence repeat (SSR) markers. As a result, 25 races were identified from the Pst population on Chinese differentials and predominant races was CYR32 with a frequency of 17.70%. None of the isolates was virulent to Yr5 and Yr15. Only a few isolates showed virulence to YrTr1 and differentials Zhong 4. The Kosman index (K) of the Pst population was 0.292 on the Chinese differentials, and 0.274 on single Yr gene lines and additional differentials, respectively. In total, 64 MLGs were detected among 113 isolates and the expected heterozygosity (He) was 0.424. A close genetic relationship was detected between Lufeng (Yunnan) / Nayong (Guizhou), Fuyuan (Yunnan) / Bijie (Guizhou), and Shizong (Yunnan) / Xingyi (Guizhou). This study provided useful information on population structure and virulence to Yr genes in the Yunnan and Guizhou epidemiological regions, and will be used to guide the control of wheat stripe rust and targeted wheat breeding in this region.

Key infection stages defending heat stress in high-temperature-resistant Blumeria graminis f. sp. tritici isolates.

With the increase of temperature in the winter wheat-growing regions in China, the high-temperature-resistant Blumeria graminis f. sp. tritici (Bgt) isolates developed in the fields. To clarify the key infection stages and the roles of heat shock protein (HSP) genes of high-temperature-resistant Bgt isolates defending high temperature, 3 high-temperature-resistant and 3 sensitive Bgt isolates were selected from 55 isolates after determination of temperature sensitivity. And then they were used to investigate the infection stages and the expression levels of HSP genes, including Bgthsp60, Bgthsp70, Bgthsp90, and Bgthsp104, at 18°C and 25°C. The formation frequency of abnormal appressoria and inhibition rate of haustoria formation of high-temperature-resistant isolates at 25°C were lower than those of high-temperature-sensitive isolates, while major axis of microcolonies of high-temperature-resistant isolates was higher than those of high-temperature-sensitive isolates at 25°C. The results indicated that haustoria formation and hyphal expansion were the key infection stages of defense against heat stress in high-temperature-resistant isolates. Further analyses of HSP genes found the expression levels of Bgthsp60 and Bgthsp70c were upregulated at 24 and 72 h post-inoculation in high-temperature-resistant isolates, while no significant difference was observed for Bgthsp90 and Bgthsp104 genes. Taken together, the basis of high-temperature-resistant Bgt isolates is associated with induced expression of Bgthsp60 and Bgthsp70c response to heat stress in haustoria formation and hyphal expansion stages.

Did Wheat Breeding Simultaneously Improve Grain Yield and Quality of Wheat Cultivars Releasing over the Past 20 Years in China?

Grain yield and quality of wheat are both important components for food security. Great effort has been made in the genetic improvement of wheat grain yield in China. However, wheat grain quality (i.e., protein concentration and protein quality) has received much less attention and is often overlooked in efforts to improve grain yield. A timely summary of the recent process of wheat breeding for increasing yield and quality (which can be used to guide future breeding strategies) is essential but still lacking. This study evaluated the breeding efforts on grain yield and grain quality of 1908 wheat varieties in China over the past two decades, from 2001 to 2020. We found wheat yields show a 0.64–1.03% annual growth in the three-dominant wheat-growing regions in China. At the same time, there was no significant decrease in wheat protein concentration. Genetic yield potential was increased, and the genetic yield gap was closed. High grain yields and better quality can likely be achieved simultaneously by genomic selection in future wheat breeding.

Regional differences in the performance of drought mitigation measures in 12 major wheat-growing regions of the world

Drought is considered one of the key barriers influencing wheat production, and various adaptation schemes are practiced globally to mitigate drought impacts. However, it is difficult to precisely assess the performances of drought mitigation measures, especially when multiple measures are implemented simultaneously. Here, a remote sensing-based agricultural drought-affected area change index (ADAC) was applied to assess the performance of drought mitigation schemes, which separates and avoids confusion between performances of drought mitigation and wheat yield improvement. The results revealed the historical performance changes and regional differences under drought mitigation measures in 12 major wheat-growing regions (WGRs) of the world. The drought mitigation efforts have steadily succeeded, with a reduction in the drought-affected area of approximately 14.5 % in the 1980s and 28.5 % in the last decade, relatively 55 % of drought-affected areas are alleviated in the 12 WGRs. However, there are significant regional differences ranging from 28 % to 79 % in the 12 WGRs. The drought mitigation measures implemented in the WGRs of China and India, followed by France and Ukraine, are more effective than other regions, while a few are still declining. By further evaluating the effects of short-term and long-term drought mitigation strategies taken in the WGRs, we found that irrigation is the main drought mitigation measure in dryland, while measures such as conservation tillage are of great value for yield stability for both dry and wet areas. The results of this study improve the understanding of the regional performance of drought mitigation schemes and will help stakeholders to select appropriate measures.

Origin and Phylogeography of Chinese Cereal Cyst Nematode Heterodera avenae Revealed by Mitochondrial COI Sequences.

Heterodera avenae, a globally distributed plant-parasitic nematode, is one of the most significant pests on cereal crops. In China, it is widely distributed in cereal-growing areas of 16 provinces and causes serious yield losses. In the present study, a total of 98 populations of H. avenae were collected from major wheat-growing regions in China and six other countries. The mitochondrial COI genes were amplified and analyzed. Forty-one mitochondrial COI haplotypes were identified, suggesting a high genetic diversity and endemism level of H. avenae in China. Phylogenetic analysis showed that H. avenae populations in China were divided into four clades. Significant evolutionary and genetic differences were found between Chinese (except Hubei) and foreign populations. Hap1, the most widely distributed haplotype, was considered to be a separate evolutionary origin in China. The gene flow of H. avenae from the northwestern region to the north China region and Huang-Huai-Hai region was significant, so as the direction between north China and Huang-Huai-Hai region. We speculate that water flowing from the Yellow River and mechanical harvesters promoted gene exchange among these groups. A distance-based redundancy analysis showed that genetic distances observed among H. avenae populations were explained foremost not only by geographic distance but also by temperature and precipitation. This study provides theoretical support for the origin and spread of H. avenae populations in China and elsewhere in the world.

Pathotype Identification and Virulence Variation in Cochliobolus sativus in China

Spot blotch caused by Cochliobolus sativus has become an important disease in the wheat-growing regions in China that has resulted from changes in the regional climate, agricultural cultivation patterns, and the susceptible wheat varieties that are widely grown. Little information is available about virulence variability and pathogenic specialization of the C. sativus isolates from major wheat-growing regions in China. Here, 12 representative wheat varieties and foundation breeding stocks were selected to characterize the pathotypes of C. sativus isolates from infected wheat plants. Based on the infection phenotypes in the 12 differential genotypes at the seedling stage, 70 Chinese pathotypes were identified from 110 isolates and clustered into three virulence groups. The high virulence isolates were collected from wheat leaves, crowns, and roots, with most (10 of 14) from the Henan province in the Huang-Huai plain. No relationship was evident between virulence variability of C. sativus isolates and their geographic origins or types of diseased wheat tissues. C. sativus showed a significant pathogenic specialization in hosts of wheat and barley. Most of the wheat isolates (50 of 65) were avirulent to all the differential barley genotypes, and a few were virulent only to highly susceptible barley genotypes. These results indicated that C. sativus isolates from the wheat-growing regions in China varied considerably for their virulence in wheat varieties, and showed significant pathogenic specialization to the wheat and barley hosts.

Allelic variation and genetic diversity of HMW glutenin subunits in Chinese wheat (Triticum aestivum L.) landraces and commercial cultivars.

Wheat landraces have abundant genetic variation at the Glu-1 loci, which is desirable germplasms for genetic enhancement of modern wheat varieties, especially for quality improvement. In the current study, we analyzed the allelic variations of the Glu-1 loci of 597 landraces and 926 commercial wheat varieties from the four major wheat-growing regions in China using SDS-PAGE. As results, alleles Null, 7+8, and 2+12 were the dominant HMW-GSs in wheat landraces. Compared to landraces, the commercial varieties contain higher frequencies of high-quality alleles, including 1, 7+9, 14+15 and 5+10. The genetic diversity of the four commercial wheat populations (alleles per locus (A) = 7.33, percent polymorphic loci (P) = 1.00, effective number of alleles per locus (Ae) = 2.347 and expected heterozygosity (He) = 0.563) was significantly higher than that of the landraces population, with the highest genetic diversity found in the Southwestern Winter Wheat Region population. The genetic diversity of HMW-GS is mainly present within the landraces and commercial wheat populations instead of between populations. The landraces were rich in rare subunits or alleles may provide germplasm resources for improving the quality of modern wheat.

Distribution, Genetic Diversity and Population Structure of Aegilops tauschii Coss. in Major Wheat-Growing Regions in China

Aegilops tauschii Coss. is known as a noxious grass weed seriously affecting wheat quality and yield. To investigate its present occurrence in wheat fields and the potential genetic diversity of the grass weed in China, a filed survey covering major wheat production regions was conducted during 2017–2019. Seeds of different Ae. tauschii populations collected from the survey were analyzed with Simple Sequence Repeats (SSRs) technique. Results showed that Ae. tauschii was occurring in each of the provinces surveyed with varied occurrence frequency ranging from 0.91% in Sichuan Province to 92.85% in Henan Provinces. Eighty alleles with size ranging from 98 bp to 277 bp were detected from the 192 collected Ae. tauschii populations with 17 SSR markers. Ae. tauschii, in this study, exhibited a moderately high level of genetic diversity, high differentiation, deficient heterozygosity and limited gene flow. Compared with other provinces, Hubei populations possessed relatively low genetic diversity. Dendrogram analysis showed that genetic distance did not seem to be related to geographic distribution. Additionally, STRUCTURE analysis suggested that Ae. tauschii populations in wheat fields of China can be divided into three groups, which was further supported by cluster analysis. Among the three groups, solely 7% of the total variation was detected, whereas the majority variation (67%) occurred among different populations within same group. Undoubtedly, such information will help us to better understand population relationships and spread of Ae. tauschii in China and will provide a new perspective for its integrated management.

Transcriptomic and anatomic profiling reveal the germination process of different wheat varieties in response to waterlogging stress

BackgroundWaterlogging is one of the most serious abiotic stresses affecting wheat-growing regions in China. Considerable differences in waterlogging tolerance have been found among different wheat varieties, and the mechanisms governing the waterlogging tolerance of wheat seeds during germination have not been elucidated.ResultsThe results showed no significant difference between the germination rate of ‘Bainong 207’ (BN207) (after 72 h of waterlogging treatment) and that of the control seeds. However, the degree of emulsification and the degradation rate of endosperm cells under waterlogging stress were higher than those obtained with the control treatment, and the number of amyloplasts in the endosperm was significantly reduced by waterlogging. Transcriptomic data were obtained from seed samples (a total of 18 samples) of three wheat varieties, ‘Zhoumai 22’ (ZM22), BN207 and ‘Bainong 607’ (BN607), subjected to the waterlogging and control treatments. A comprehensive analysis identified a total of 2775 differentially expressed genes (DEGs). In addition, an analysis of the correlations among the expression difference levels of DEGs and the seed germination rates of the three wheat varieties under waterlogging stress revealed that the relative expression levels of 563 and 398 genes were positively and negatively correlated with the germination rate of the wheat seeds, respectively. Gene Ontology (GO) and Kyoto Encyclopedia of Genes and Genomes (KEGG) analyses showed that the difference in the waterlogging tolerance among the three wheat varieties was related to the abundance of key genes involved in the glycolysis pathway, the starch and sucrose metabolism pathway, and the lactose metabolism pathway. The alcohol dehydrogenase (ADH) gene in the endosperm of BN607 was induced immediately after short-term waterlogging, and the energy provided by the glycolysis pathway enabled the BN607 seeds to germinate as early as possible; in addition, the expression of the AP2/ERF transcription factor was upregulated to further enhance the waterlogging tolerance of this cultivar.ConclusionsTaken together, the results of this study help elucidate the mechanisms through which different wheat varieties respond to waterlogging stress during germination.

Race and Virulence Analysis of Puccinia triticina in China During 2011 to 2013.

Wheat leaf rust, caused by Puccinia triticina, is a common fungal disease of wheat in China. In order to identify races and determine the individual virulence of isolates in different wheat-growing regions in China, leaf rust samples collected from 18 provinces in 2011 to 2013 were tested on 37 Thatcher near-isogenic lines each carrying a different single leaf rust resistance gene. A total of 158 races were identified. Races THTT (19.5%), THTS (16.9%), PHTT (7.7%), THJS (5.0%), THJT (4.2%), and PHTS (4.0%) were the most predominant races in 2011 to 2013. All of these races were avirulent to resistance genes Lr9 and Lr24. The two most frequent races, THTT and THTS, were widely distributed. The frequencies of the isolates with virulence to Lr1, Lr2c, Lr3, Lr16, Lr26, Lr17, LrB, Lr10, Lr14a, Lr3bg, Lr14b, Lr33, Lr37, and Lr50 exceeded 90%. Frequencies of virulence to Lr2a, Lr3ka, Lr11, Lr30, Lr2b, and Lr32 exceeded 70% but were less than 90%. Frequencies of virulence to Lr18, Lr21, Lr15, Lr23, Lr33+34, Lr36, Lr39, and Lr44 were below 70%, whereas the frequency of virulence to Lr25 was less than 1%. All isolates were avirulent to Lr9, Lr19, Lr24, Lr28, Lr42, Lr29, Lr38, and Lr47. The identified races and individual virulence frequencies provide a basis for selection of effective leaf rust resistance genes for use in breeding programs and can also provide information for the study of race evolution of P. triticina.

Genome-Wide Association Mapping of Adult-Plant Resistance to Stripe Rust in Common Wheat (Triticum aestivum).

Stripe rust, caused by Puccinia striiformis f. sp. tritici, is a globally devastating disease of common wheat (Triticum aestivum L.), resulting in substantial economic losses. To identify effective resistance genes, a genome-wide association study was conducted on 120 common wheat lines from different wheat-growing regions of China using the wheat 90K iSelect SNP array. Seventeen loci were identified, explaining 9.5 to 21.8% of the phenotypic variation. Most of these genes were detected in the A (seven) and B (seven) genomes, with only three in the D genome. Among them, 11 loci were colocated with known resistance genes or quantitative trait loci reported previously, whereas the other six are likely new resistance loci. Annotation of flanking sequences of significantly associated SNPs indicated the presence of three important candidate genes, including E3 ubiquitin-protein ligase, F-box repeat protein, and disease resistance RPP13-like protein. This study increased our knowledge in understanding the genetic architecture for stripe rust resistance and identified wheat varieties with multiple resistance alleles, which are useful for improvement of stripe rust resistance in breeding.

Extending a first-principles primary production model to predict wheat yields

Climate exerts a major influence on crop development and yield. Despite extensive modelling efforts, there is still considerable uncertainty about the consequences of a changing climate for the yields of major crops. Existing crop models are complex and rely on many assumptions and parameters, motivating a quest for more parsimonious models with stronger theoretical and empirical foundations. This paper presents a prototype of such a model for wheat, informed by measurements of gross primary production (GPP), biomass and yield at research sites across the wheat-growing regions of China. First, GPP was predicted using a recently developed first-principles model driven only by climate, carbon dioxide (CO2) concentration, and light absorbed by leaves. Modelled GPP was shown to agree well with eddy-covariance measurements. Second, the data were used to show that above-ground biomass (AB) is proportional to time-integrated GPP, and that grain yield shows a saturating relationship with AB. Simple empirical equations based on these findings were combined with modelled GPP to predict yield, including propagated errors due to parameter uncertainty in both the GPP model and the empirical equations. The resulting 'hybrid' model, applied in a variety of climates, successfully predicted measured interannual variations in AB and yield. Third, the model was extended to include a phenology scheme, a mass-balance equation relating mean leaf area index to accumulated GPP over the growth phase, and an independently observed response of leaf mass-per-area to CO2. Sensitivity analyses and scenario runs with this extended model showed a positive but saturating (at ∼600 ppm) response of yield to rising CO2, consistent with experimental evidence. This positive effect was partially counteracted by a net negative response of yield to increasing temperature, caused by increasing photorespiration and an accelerated growth cycle.

Phenotype and Cellular Response of Wheat Lines Carrying Cre Genes to Heterodera avenae Pathotype Ha91.

The cereal cyst nematode (CCN, Heterodera avenae), a major limiting factor for wheat production worldwide, is widespread in most wheat-growing regions in China. Accordingly, screening and characterization of resistant (R) wheat sources against H. avenae are very important. In this study, we screened 51 wheat lines, collected from the International Wheat and Maize Improvement Center (CIMMYT), carrying various Cre genes (Cre1, Cre2, Cre3, Cre5, Cre7, Cre8, CreR, and Pt). From that screen, we identified one immune (M) cultivar (with no adult females produced) and five resistant cultivars (with fewer than five females) to H. avenae pathotype Ha91. The Cre3 gene conferred the most effective resistance against H. avenae pathotype Ha91 in both field and greenhouse assays. Conversely, the Cre1 and CreR genes conferred the poorest effective resistance. Using Pluronic F-127 gel and a staining assay, juvenile nematodes invading wheat roots were observed, and nematode development was analyzed. Compared with R and M roots, those of the susceptible (S) wheat cultivar Wenmai19 were more attractive to H. avenae second-stage juveniles (J2s). We observed the retardation of nematode development in R cultivars and tiny white female cysts protruding from the R cultivar VP1620. Nematodes in M roots either disintegrated or remained J2s or third-stage juveniles (J3s) and failed to complete their life cycle. Molting was also suppressed or delayed in R and M genotypes. For both S and R cultivars, syncytia were characterized by cell wall perforations and dense cytoplasm in hypertrophied syncytium component cells. Syncytial size increased gradually with nematode development in S cultivars. Moreover, an incompatibility reaction occurred in M wheat roots: the syncytium was disorganized, exhibiting disintegration and condensed nuclei. These sources of genetic resistance against CCN can potentially be planted in severely infested fields to reduce economic loss or can be used for introgression in breeding.

Wheat yield functions for analysis of land-use change in China

CERES-Wheat, a dynamic process crop growth model, is specified and validated for eight sites in the major wheat-growing regions of China. Crop model results are then used to test the Mitscherlich-Baule and the quadratic functional forms for yield response to nitrogen fertilizer, irrigation water, temperature, and precipitation. The resulting functions are designed to be used in a linked biophysical-economic model of land-use and land-cover change in China. While both functions predict yield responses adequately, the Mitscherlich-Baule function is preferable to the quadratic function because its parameters are biologically and physically realistic. Variables explaining a significant proportion of simulated yield variance are nitrogen, irrigation water, and precipitation; temperature was a less significant component of yield variation within the range of observed year-to-year variability at the study sites. Crop model simulations with a generic soil with median characteristics of the eight sites compared to simulations with site-specific soils showed that agricultural soils in China have similar and, in general, low-to-moderate water-holding capacities and organic matter contents. The validated crop model is useful for simulating the range of conditions under which wheat is grown in China, and provides the means to estimate production functions when experimental field data are not available.