Observations on the occurrence and inheritance in wheat of resistance to the grain aphid Sitobion avenae

Glasshouse screening tests with the aphid, Sitobion avenae, demonstrated resistance or extreme susceptibility in a minority of winter wheat cultivars. Assessments of some, but not all, resistant cultivars were apparently affected by the conditions of the test, and field observations confirmed some, but not all, of the glasshouse results. Rapier and Galahad were the most resistant of the cultivars currently available to British wheat growers. F₄ lines of spring wheat from crosses of wheat stocks resistant to S. avenae were screened by two methods and on average were resistant. Crosses differed in the amount of variability available for further selection, and wide-ranging segregation among the lines indicated that resistance genes differed among the parent stocks.     

Insecticide toxicity to three strains of green peach aphid (Myzus persicae Sulzer) reared on resistant and susceptible potato cultivars

Three green peach aphid (GPA) strains, Myzus persicae (Sulzer) (Homoptera: Aphididae) obtained from New York, Puerto Rico and Minnesota, were reared on resistant potato hybrid D888-4 and a susceptible cv. Red Pontiac. No significant differences in GPA mortality were observed when aphids were reared on either the resistant or susceptible potato cultivars and later exposed to methamidophos 4EC, pirimicarb 50 WP, azinphos-methyl 2EC or permethrin 2EC. The interaction between the four insecticides × three GPA strains was significant. Of the three aphid strains, those from Minnesota had the lowest susceptibility to permethrin, pirimicarb and azinophos-methyl. No mortality was observed in this GPA strain when tested with azinphosmethyl.     

Genetic analysis and molecular mapping of a stripe rust resistance gene in wheat–Leymus mollis translocation line M8926-2

Stripe rust, caused by Puccinia striiformis f. sp. tritici (Pst), is one of the most widespread and destructive diseases of wheat crop worldwide. Growing resistant cultivars is the preferred method of controlling diseases, but only a few effective genes are available. M8926-2, a translocation line developed from interspecific hybridization between Leymus mollis and a common wheat genotype 7182, is highly resistant to the prevalent Chinese Pst races. In order to identify gene(s) for stripe rust resistance, M8926-2 was crossed with susceptible genotype Mingxian 169, and seedlings of parents and F₁, F₂, and F_2:3 progenies were tested with the most prevalent Pst race CYR32 under controlled greenhouse conditions. M8926-2 has a single dominant gene, designated as YrM8926, conferring all-stage resistance to CYR32. Genetic mapping was used to identify molecular markers linked to YrM8926. A linkage group of seven simple sequence repeat (SSR) markers was constructed for YrM8926 using 191 F_2-2 population plants and the gene was located on wheat chromosome 2DS. The wheat-L. mollis translocation line background of M8926-2 and disease assessments indicated that YrM8926 is originally derived from L. mollis. The stripe rust resistance gene and closely linked molecular markers should be useful for pyramiding with other genes to develop wheat cultivars with high-level and long-term resistance to stripe rust.     

Genetic analysis of field resistance to tan spot in spring wheat

Tan spot, caused by Pyrenophora tritici-repentis (Died.) Drechs., is an important constraint to wheat (Triticum aestivum L.) yield in many countries. Since the inheritance of field resistance to tan spot is poorly understood, this study was conducted to determine the genetic control of resistance in the field. Resistance was measured as disease severity caused by P. tritici-repentis race 1 in four crosses involving five wheat parents: parent 1 (P₁) = catbird; parent 2 (P₂) = Milan/Shanghai-7; parent 3 (P₃) = Alondra/Coc//Ures; parent 4 (P₄) = Bcb//Dundee/Gul/3/Gul); parent 5 (P₅) = ND/VG9144//Kal/BB/3/Yaco/4/Chil. P₁, P₂ and P₃ were resistant and P₄ was moderately resistant, whereas P₅ was susceptible to tan spot. The F₂-derived F₃ families and the parents were field evaluated at El Batán, Mexico, in 1996. When all the plants within a F₃ family expressed low levels of disease severity similar to that of the resistant parent it was classified resistant (R), otherwise the progeny was classified as susceptible (S). The progeny of the three crosses of the susceptible parent with the resistant and moderately resistant parents P₂, P₃, and P₄ segregated as 3R:13S whereas the progeny in the cross with P₁ showed a segregation ratio of 1R:15S. This suggests that each resistant parent possessed two genes conditioning resistance to tan spot severity caused by P. tritici-repentis race 1. Information on the inheritance of resistance measured as disease severity on adult plants under field conditions is of practical importance for wheat breeding programs seeking improvement in tan spot resistance.     

Disease development and PR-protein activity in wheat (Triticum aestivum) seedlings treated with plant extracts prior to leaf rust (Puccinia triticina) infection

The potential to control leaf rust (Puccinia triticina; pathotype UVPt9) in vivo in susceptible (Thatcher) and resistant (Thatcher/Lr15) near-isogenic wheat (Triticum aestivum) lines by foliar applications of crude plant leaf extracts from Tulbaghia violacea and Agapanthus africanus, as well as a commercially available natural product, ComCat^®, and a Lupinus albus seed suspension (SS) was investigated. In vitro activities of the PR-proteins, β-1,3-glucanase, chitinase and peroxidase were quantified in these two wheat lines under both non-infected and infected conditions. Although foliar application of the different plant extracts accelerated the activities of all three enzymes in resistant infected wheat plants, it was only the A. africanus extract that increased the in vitro activities of the three apoplastic pathogenesis-related proteins significantly in both susceptible and resistant wheat cultivars, whether uninfected or infected. The latter resulted in the reduction of pustule and necrotic lesion formation in the susceptible and resistant wheat lines, respectively. Foliar treatment of wheat seedlings with either ComCat^® or SS had no effect on pustule and necrotic lesion formation. The A. africanus crude extract also had a significant in vitro inhibitory effect on both leaf rust spore germination and subsequent germ tube development.     

GWAS for resistance against black point caused by Bipolaris sorokiniana in wheat

Black point is a severe wheat grain disease caused by complex pathogens, of which Bipolaris sorokiniana is dominant. Analysis of effective resistance genes/quantitative trait loci (QTL) is an essential prerequisite for breeding by marker-assisted selection (MAS). In this study, we aimed to identify the loci resistant to black point caused by B. sorokiniana in 10 wheat genotypes by performing a genome-wide association study with an incomplete diallel cross population. Twenty-three major marker-trait associations (MTAs) resistance to B. sorokiniana black point were identified, which could explain more than 11% of the phenotypic variations. They were located on 1B, 1D, 2B (2), 2D, 3A (2), 3B (2), 3D, 4A, 5A (2), 5B (2), 6B (3), 6D, 7A (2), and 7D (2), respectively. The average number of major MTAs in the 10 resistant lines was 20.2, whereas that in the susceptible lines was 9.8. All the major MTAs in the parents were detected in the F₁ hybrids. Three PCR markers were developed for detecting two MTAs using two recombinant inbred line populations. These PCR markers linked to black point resistance and accessions with a larger number of resistance alleles can be used to improve wheat resistance by QTLs pyramiding via MAS.     

Response of selected cucumber cultivars to Meloidogyne incognita

Root-knot nematodes (Meloidogyne spp.) are one of the most destructive pathogens of vegetables. The cultivars resistant to root-knot nematodes have comparatively better crop yield than susceptible varieties and can be employed as a component of integrated nematode management. In the present study, 15 cultivars of cucumber (Cucumis sativus) were tested for their response to Meloidogyne incognita by inoculating with 3000 2nd stage juveniles of the nematode. All cultivars varied significantly in causing reductions in growth parameters over their controls. Likewise, all cultivars behaved differently regarding formation of galls and egg masses and reproductive factor. It was found that none of the tested cultivars was found immune or highly resistant. Long Green was the only cultivar which was found resistant against M. incognita as it showed minimum galls (8.2) and reductions in growth parameters. On the other hand, cultivars Mehran, Mirage, Thamin-II, and Royal Sluis were highly susceptible as evident by maximum galls (>100) on their roots and reductions in growth parameters. Similarly, the cultivars Green Wonder, Cucumber Citriolo and Poinsett were moderately susceptible (31–70 galls) while Babylon, Cobra and Falcon-560 (71–100 galls) were susceptible and reductions in growth parameters of these cultivars were less than those in highly susceptible cultivars. Four cultivars, Marketmore, Dynasty, Pioneer-II, and Summer Green, were rated as moderately resistant (11–30 galls) as these cultivars showed less damage by the nematode than moderately susceptible, susceptible and highly susceptible cultivars.     

Bread wheat cultivar PBW 343 carries residual additive resistance against virulent stripe rust pathotype

With continuous outbreaks of stripe rust (Puccinia striiformis f. sp. tritici) epidemics and rapid breakdown of deployed resistance in bread wheat (Triticum aestivum L.) cultivars in North West Plains Zone (NWPZ) in India warrant knowledge and deployment of new and durable sources of resistance to stripe rust. Bread wheat cultivar PBW 343, until recently the most widely cultivated wheat variety in India, is now highly susceptible to stripe rust (score 9 on a 1–9 scale), whereas PBW 621 (score 5.05–5.65) and HD 2967 (score 5.40–6.20) show low levels of resistance. We conducted an experiment, spanning three crop seasons (2013–2014 to 2015–2016), in which parental lines, F₁ and F₂ populations, F₃ and F₄ families from two bread wheat crosses, PBW 621/PBW 343 and HD 2967/PBW 343 were generated and evaluated for stripe rust resistance against a virulent pathotype. While the F₁ revealed partial dominance, the segregation pattern for stripe rust resistance in F₂ and F₃ showed transgressive segregation for resistance in both crosses. Chi-square analysis indicated that resistant segregants possessed two genes, one contributed by PBW 621 or HD 2967 (depending on the cross) and the other, unexpectedly but obviously, came from the most susceptible cultivar, PBW 343. Possible genetic mechanisms for this residual resistance and implications for breeding programs are discussed.     

Fungicide and cultivar effects on the development and temporal progress of wheat blast under field conditions

The epidemiology of wheat blast, caused by the Triticum pathotype of Pyricularia oryzae, is poorly understood, making it very difficult to manage. We reported on the individual and combined effect of host resistance and fungicide application for managing wheat blast disease on spikes. Two field experiments (Exp. 1 and Exp. 2) were conducted in a region of Brazil where blast is not known to be endemic to evaluate its development as influenced by fungicide and host resistance. Plots of wheat cultivars BR-18 (partially resistant) and Guamirim (susceptible) were either treated with the fungicide epoxiconazole + pyraclostrobin or left non-treated, and then inoculated with a spore suspension of P. oryzae at mid-anthesis. Spike blast incidence and severity, quantified at regular intervals after inoculation, increased over time, and fungicide and cultivar had statistically significant effects (P < 0.005) on both measures of disease and their temporal rates of progress. Relative to Guamirim-non-treated, BR-18-non-treated (resistance alone) led to 44 and 64% control of final incidence and severity, respectively, in Exp. 1, and 3 and 49% control, respectively, in Exp. 2. Guamirim-treated (fungicide alone) led to 65% control of incidence and 77% control of severity in Exp. 1, and 64% control of incidence and 95% control of severity in Exp. 2. For both incidence and severity, fungicide and resistance alone also reduced the temporal rate of progress relative to the susceptible non-treated. However, the greatest overall efficacy was observed when resistance and fungicide were combined, with over 70 and 90% control of final incidence and severity, respectively, and over 75% reduction in the temporal rate of spike blast progress. Based on percent control, the integrated effect of resistance and fungicide was additive for incidence, severity, and their temporal rates of progress, demonstrating the value of combining the two strategies to manage spike blast.     

Field assessment of commercial cotton cultivars for Verticillium wilt resistance and yield

Verticillium wilt is responsible for substantial yield losses in cotton. The use of cultivars with partial resistance to Verticillium wilt is a preferred management strategy. Cotton breeders utilize rating scales based on severity of foliar symptom expression and/or defoliation when making cultivar selections. The objective of this research was to determine the yield relationship with cultivars grouped by both incidence of Verticillium wilt during the boll filling stage, and late season defoliation in fields with a history of Verticillium wilt. Small plot, replicated cultivar trials were conducted over an 11 year period in west Texas. Cultivars were divided into four classes (A–D) based on normalized wilt incidence (NW) and four classes based on normalized defoliation ratings (ND). Classes were determined through a mixed model analysis of cultivars, with T-test comparisons between a partially resistant check (Fibermax 2484B2F) and a susceptible check (Deltapine 0912B2RF). The A and C classes did not differ (P = 0.05) from the partially resistant and susceptible checks, respectively. Classes were used in a mixed model analysis with lint yield. In a model with only NW classes, lint yield decreased significantly as NW increased with least square mean values of 1421, 1385, 1284 and 1204 kg/ha, for classes A, B, C and D, respectively. In a model with both NW and ND classes, the A/A class combination of NW and ND had a significantly (P ≤ 0.05) higher lint yield (1776 kg/ha) than any other combination. NW/ND class combinations of A/B, B/A, B/B, and C/A had intermediate yields, and ND classes of C or D had the lowest yields. Cultivars with both low wilt and defoliation incidences should result in higher yields in fields infested with Verticillium dahliae. Furthermore, these two rating criteria could be used to standardize the process for developing resistant cultivars.     

Evaluation of resistance to root-knot nematode (Meloidogyne incognita) in okra cultivars

The root-knot nematode, Meloidogyne incognita, is one of the major limiting factors affecting plant growth and yield causing an estimated $100 billion loss per year worldwide. Synthetic pesticides, though instantaneously effective, are usually prohibitively expensive, not readily available, may cause hazards to both man and livestock, and inflict injury to the environment. Notable among the alternatives to nematicides is the use of resistant cultivars which are inexpensive and eco-friendly. In the present studies, twelve okra (Abelmoschus esculentus L) cultivars were evaluated for their resistance against M. incognita under field conditions. Ten-day old okra plants of test cultivars were inoculated with 3000 freshly hatched second stage juveniles of M. incognita. The nematode caused reductions in various growth parameters of all the cultivars to varying levels over their respective controls. None of the cultivars was found completely resistant. The cultivar ‘Sharmeeli’ was highly susceptible as >100 galls were recorded on the roots. Sharmeeli also showed maximum reductions in growth among the cultivars evaluated. The cultivars Anmol and Sindha were susceptible with 71–100 galls. The cultivars Sabz Pari, Super Star, PMS-55 and PMS Beauty were moderately susceptible with 31–70 galls and comparatively less reductions in growth. Cultivars Sanam, Dikshah, Arka Anamika, Ikra-1 and Ikra-2 with 11–30 galls were rated as moderately resistant and showed less damage by the nematode as compared to susceptible cultivars and their planting could provide a useful tool to control root-knot nematodes.     

Additive genes in wheat for resistance to stripe (yellow) rust (Puccinia striiformis Westend.)

Forty-nine lines of wheat (F₆ generation) containing minor additive genes conditioning resistance to stripe (yellow) rust (Puccinia striiformis Westend.) were evaluated to several virulence types (physiologic races) of the pathogen obtained from the USA and Europe. All wheat lines showed some level of resistance to all virulence types of P. striiformis but there were differences in level of resistance between crosses and between lines within a particular cross. Generally, all lines expressed the most resistance at the seedling stage when grown at higher temperatures (15°C during the dark period; 25°C during the light period) than at 2°C (dark period) and 20°C (light period). Lines with more resistance genes showed the most resistance, and this resistance was least sensitive to temperature change. Mature plants in the field had levels of resistance equal to, or greater than, those of their seedling counterparts. One parent of each cross evaluated was either a commercial cultivar or an advanced wheat selection, and was rated as susceptible. In many cases, these susceptible parents contributed to resistance in the progeny and thus the progeny showed transgressive segregation for resistance. Some parent cultivars, which were completely susceptible as seedlings and moderately resistant as mature plants, also contributed to seedling resistance in the progeny when combined with parents known to contain minor additive genes for resistance to P. striiformis. The advantages of using minor additive genes are discussed in relation to the control of stripe rust of wheat and to crop protection generally.     

Effectiveness of carbofuran applied to the soil and as a seed treatment for the control of aphids on wheat in Northwestern Mexico

The effectiveness of carbofuran 300 ST and 350 L applied to the soil and as a seed treatment was evaluated with two wheat cultivars ‘Genaro’ and ‘Sonoyta’ in the Valle del Yaqui, Ciudad Obregon, Sonora in Northwestern Mexico. Both the soil and seed treatment significantly (P < 0·05) reduced greenbug, Schizaphis graminum (Rondani) and corn leaf aphid, Rhopalosiphum maidis (Fitch) populations. Infestations of greenbugs and corn leaf aphids were 97·8% and 98·3% less, respectively, with the soil application of carbofuran 350 L in the Genaro wheat plots and 91% less for both aphids in the Sonoyta wheat plots than on the untreated controls. Greenbug and corn leaf aphid infestations in the seed treatment with carbofuran 300 ST on the Genaro wheat plots were 93·4% and 52·5% less, respectively, and in the Sonoyta wheat plots, infestations of greenbugs and corn leaf aphids were 92% and 78·9% less, respectively, than on the untreated controls. The wheat plots where carbofuran 350 L was applied to the soil had yields 18% and 16% greater for the Genaro and Sonoyta cultivars, respectively, than the untreated controls, while those plots where carbofuran 300 ST was applied as a seed treatment had yields 15% and 12% greater for the Genaro and Sonoyta cultivars, respectively, than the untreated controls.     

Effects of Fusarium culmorum and water stress on durum wheat in Tunisia

The effects of water stress on Fusarium foot and root rot in durum wheat were investigated in growth chamber, greenhouse and field tests in Tunisia. In the seedling stage, emergence of six durum wheat cultivars in the growth chamber was significantly reduced by inoculation with Fusarium culmorum and water stress (P<0.0001), with more disease under drier conditions. Additionally, the tiller number per mature plant, the 1000 grain weight and disease severity in mature stage were reduced by inoculation in greenhouse studies. In a field test, inoculation with F. culmorum significantly reduced the yield (P<0.001), by more than 17% for Om Rabiaa and 38% for Karim, the two cultivars tested. Yield was also significantly affected by precipitation and irrigation levels. The severity of the disease, estimated by the percentage of white heads, was separately affected by the cultivar (P<0.001) and inoculation (P = 0.0004). Percentage of white heads was 1.5 and 2 × higher in inoculated plants than non-inoculated for Om Rabiaa and Karim cultivars, respectively. Disease severity was highest in treatments with the greatest water stress. This is the first detailed study of water stress and F. culmorum on durum wheat in Tunisia, and indicates that cultivar resistance and irrigation management may be important in the management of Fusarium foot rot.     

Resistance monitoring and enzyme activity in three field populations of cowpea aphid (Aphis craccivora) from Egypt

The cowpea aphid (Aphis craccivora) is one of the most important sucking insect pests attacking certain legumes in Egypt particularly faba bean, cowpea and pea. In this study we monitored the resistance level of three field populations of A. craccivora to seven insecticides belonging to three different chemical classes (organophosphates, carbamates and neonicotinoids). The three populations were collected from three governorates in Egypt namely Dakahlia, Qalyobia and Beni Suef. Diagnostic concentrations (LC₉₀ values for susceptible strain) for each insecticide were established using a leaf dipping technique. Resistance monitoring showed that the field population from Dakahlia was highly resistant to all the tested insecticides. In a similar manner, the population from Qalyobia was also resistant to all insecticides except for fenitrothion to which only moderate resistance was observed. The field population from Beni Suef exhibited a lower level of resistance to all the seven tested insecticides.Biochemical assay showed that esterase activity in these three field populations was generally higher as the enzyme activity ratio ranged from 4.3 to 7.8 fold more than that for the susceptible strain. The activity of the other measured detoxifying enzymes (glutathione -S- transferase and mixed function oxidases) was moderate in the populations from Qalyobia and Dakahlia. Nevertheless, the enzyme activity in A. craccivora collected from Beni Suef was variable and differed slightly from the activity measured in the susceptible strain. Monitoring insecticide resistance among the three aphid populations was a proactive approach to detect any shift in insecticide efficiency. The possible occurrence of resistance in the cowpea aphid to the tested insecticides may be due to the higher activity of carboxylesterases. Further studies on the resistance mechanism to these insecticides are needed to provide insights in how to manage and delay the onset of the resistance and thus prolong the performance of insecticides against A. craccivora.     

Response of selected okra cultivars to Meloidogyne incognita

Root–knot nematodes (Meloidogyne spp.) are major pests of vegetables especially in the tropics and subtropics. All commercial okra varieties are susceptible to root knot nematodes and cause substantial losses. The objective of this study is to find out resistant germplasm in order to facilitate our breeders for gene manipulation. A greenhouse study was conducted to evaluate 28 okra cultivars against Meloidogyne incognita inoculated with 5000 eggs. Five cultivars (Bamya Yalova, 19,232, 19,236, 1,922,121, and Green Wonder) had significantly fewer root galls and eggs and less reduction in plant growth (shoot weight and root length), than most of the other entries. A positive relationship was demonstrated between root galls and reduction in plant growth parameters measured. These cultivars may improve okra production in fields infested with M. incognita. During our study, none of the cultivars tested were observed to be immune or resistant to nematode infection according to a scale where: good host [susceptible] when Pf/Pi (Pf = Final population of nematodes after harvest and Pi = Initial population of nematodes which was used as inoculum during experiment) > 5.0, fair, better [moderately resistant] if 5.0 ≥ Pf/Pi > 1, poor if 1 > Pf/Pi > 0, and non-host [resistant] when Pf/Pi = 0. The cultivars, including 19,224, 19,235, Pusa Sawami, Ikra-1, Ikra-2 and Sabzperi China Red, were found to be susceptible with Pf/Pi > 5.0, and they were declared as good hosts of M. incognita. While all the other cultivars were moderately resistant, with 0 ≥ Pf/Pi > 1 but still a significant penetration of nematodes was found. The regression studies showed positive and significant relationships between the number of galls and the reduction in shoot weight (r² = 0.95), number of galls and reduction in shoot length (r² = 0.81), and number of galls and decrease in root length (r² = 0.89).     

Simultaneous selection for stem borer resistance and forage related traits in maize (Zea mays ssp. mays L.) × teosinte (Zea mays ssp. mexicana L.) derived populations

Maize spotted stalk borer (Chilo partellus Swinhoe Pyralidae) (MSSB) is a serious pest of the maize (Zea mays ssp. mays L.) crop in Pakistan. This study was conducted to introgress resistance in maize against MSSB by exploring wild sources of resistance for the development of a resistant maize variety. To achieve this, teosinte (‘PI566674’) × maize (‘Sargodha-2002’) crosses were conducted and three populations (F₁, F₂ and F₃) were established. These populations were screened at various locations and in a contrasting artificial insect infestation experiment. Teosinte species ‘PI566674’, following screening, was shown to be highly resistant to MSSB and had the ability to produce a high biomass (5 times higher than susceptible genotypes) under high temperatures (36–40 °C). The biomass of the F₁ hybrid, which was highly susceptible to MSSB, was significantly reduced (P ≤ 0.05) following infestation by MSSB in all experiments. The introgression from teosinte for genes conferring resistance to MSSB was screened in segregating F₂ and F₃ generations. Despite a susceptible F₁ population, F₂ was resistant to MSSB. Twenty new recombinant plants with resistance to MSSB and a high leaf soluble solid (16 °Brix) content were identified. They were selected to grow the F₃ population. Mean values of F₃ progenies showed similar resistance to the F₂ population but a high percentage (60%) of resistant plants was recovered.     

Elastic properties of gluten representing different wheat classes

Traditional instruments used to evaluate dough and/or gluten rheological properties do not provide unambiguous separation of elastic and viscous behaviors. Recovery after shear creep and cyclic large deformation cyclic tensile testing were used here to decouple elastic and viscous effects. A large variation in the recoverable shear strain (∼7.2% to ∼28%) was seen for glutens from 15 U.S. popular common wheat cultivars with varying HMW subunits. Sedimentation values ranged from 29 to 57 ml for 12 hard wheat cultivars and 15 to 22 ml for three soft wheat cultivars. The tensile force at 500% extension ranged from 0.12 to 0.67 N for hard wheat glutens and from 0.10 to 0.20 for soft wheat glutens. However, the recoverable work after large extension was less than 40% of the total work of extension. In addition, recoverable work in tensile testing was highly correlated with the total work of extension (r² = 0.97) and mixograph mix times (r² = 0.81). Good to excellent bread volume was obtained for several cultivars from this sample set. This suggests that optimizing water absorption for mixing doughs to achieve maximal bread volume compensates for the wide range of viscoelastic behaviors of gluten.     

Intra-specific variation of wheat grain quality in response to elevated [CO2] at two sowing times under rain-fed and irrigation treatments

In order to investigate the intra-specific variation of wheat grain quality response to elevated atmospheric CO₂ concentration (e[CO₂]), eight wheat (Triticum aestivum L.)cultivars were grown at two CO₂ concentrations ([CO₂]) (current atmospheric, 389 CO₂ μmol mol⁻¹vs. e[CO₂], FACE (Free-Air CO₂ Enrichment), 550  ±  10% CO₂ μmol mol⁻¹), at two water levels (rain-fed vs. irrigated) and at two times of sowing (TOS₁, vs. TOS₂). The TOS treatment was mainly imposed to understand whether e[CO₂] could modify the effects of timing of higher grain filling temperatures on grain quality. When plants were grown at TOS₁, TKW (thousand kernel weight), grain test weight, hardness index, P, Ca, Na and phytate were not significantly changed under e[CO₂]. On the other hand, e[CO₂] increased TKW (16%), hardness index (9%), kernel diameter (6%), test weight (2%) but decreased grain protein (10%) and grain phytate (11%) at TOS₂. In regard to grain Zn, Mn and Cu concentrations and some flour rheological properties, cultivar specific responses to e[CO₂] were observed at both sowing times. Observed genetic variability in response to e[CO₂] in terms of grain minerals and flour rheological properties could be easily incorporated into future wheat breeding programs to enable adaptation to climate change.     

Investigation and genome-wide association study of grain copper content in Chinese common wheat

Copper is a necessary trace mineral for the human body, and its deficiency threatens human health. Here, a panel of 243 Chinese wheat cultivars from five replications was used to measure the grain copper content (GCC) by atomic absorption spectrometry. Phenotypic analysis results revealed that the averaged GCC of surveyed cultivars ranged from 6.81 to 11.36 mg/kg with an average of 9.23 mg/kg. A genome-wide association study (GWAS) indicated that a total of 489 single-nucleotide polymorphisms (SNPs) were significant, explaining 10.1%–32.6% of the phenotypic variation and were mainly distributed on chromosomes 2A and 5A. Further analysis indicated that GCC_Hap_2A1, GCC_Hap_3B1, and GCC_Hap_5A1 may be important genetic loci that regulate GCC in wheat. Linkage mapping using a bi-parental population detected four QTLs on 1D, 6A, 6B, and 7D, explaining 8.66%, 7.55%, 8.21%, and 4.71% of the phenotypic variation, respectively. Additionally, two of the significant SNPs were located on 1D, as detected by GWAS, and were within the interval of QGCC.hau-1D, suggesting that this locus plays an important role in regulating wheat GCC. This study dissected the genetic mechanism of GCC in wheat and provides useful information for the utilization of high-GCC wheat germplasm by marker-assisted selection in wheat quality breeding.