Determining resistance to <Emphasis Type="Italic">Fusarium verticillioides</Emphasis> and fumonisin accumulation in African maize inbred lines resistant to <Emphasis Type="Italic">Aspergillus flavus</Emphasis> and aflatoxins

Fusarium verticillioides and Aspergillus flavus cause Fusarium ear rot (FER) and Aspergillus ear rot (AER) of maize, respectively. Both pathogens are of concern to producers as they reduce grain yield and affect quality. F. verticillioides and A. flavus also contaminate maize grain with the mycotoxins fumonisins and aflatoxins, respectively, which has been associated with mycotoxicosis in humans and animals. The occurrence of common resistance mechanisms to FER and AER has been reported. Hence, ten Kenyan inbred lines resistant to AER and aflatoxin accumulation were evaluated for resistance to FER, F. verticillioides colonisation and fumonisin accumulation; and compared to nine South African lines resistant to FER and fumonisin accumulation. Field trials were conducted at three localities in South Africa and two localities in Kenya. FER severity was determined by visual assessment, while F. verticillioides colonisation and fumonisin content were quantified by real-time PCR and liquid chromatography tandem mass spectrometry, respectively. Significant genotype x environment interactions was determined at each location (P ≤ 0.05). Kenyan inbred CML495 was most resistant to FER and F. verticillioides colonisation, and accumulated the lowest concentration of fumonisins across localities. It was, however, not significantly more resistant than Kenyan lines CML264 and CKL05015, and the South African line RO549 W, which also exhibited low FER severity (≤5%), fungal target DNA (≤0.025 ng μL^?1) and fumonisin levels (≤2.5 mg kg^?1). Inbred lines resistant to AER and aflatoxin accumulation appear to be promising sources of resistance to F. verticillioides and fumonisin contamination.     

花生黄曲霉侵染抗性的AFLP标记

本研究利用抗、感黄曲霉菌侵染的花生品种为亲本配制杂交组合“J11×中花5号”,以其F₂分离群体为研究材料，采用AFLP技术和BSA分析方法，获得了与花生黄曲霉菌侵染抗性连锁的2个分子标记，标记与抗性间的遗传距离分别为8.8 cM和6.6 cM;利用获得的分子标记对抗、感黄曲霉的花生种质资源进行了分子鉴定，实验结果表明分子标记与抗性鉴定结果具有较高的一致性，证实了两标记应用于研究群体之外的育种潜力。该抗侵染分子标记的建立为开展花生抗黄曲霉辅助选择育种提供了有效的筛选技术。     

The role of ear environment in postharvest susceptibility of maize to toxigenic Aspergillus flavus

A kernel screening assay (KSA) was used to assess the genetic and environmental effects on the vulnerability of maize to aflatoxin accumulation. Kernels of 26 inbred lines that had been grown in seven environments, and 190 lines of the Intermated B73xMo17 (IBM) population grown in one location in the United States, were inoculated with a toxigenic strain of A. flavus and incubated in the dark at 30°C for 6 days. Percent kernel colonization (PKC), sporulation and aflatoxin were influenced by the maize genotypes (G), the location (“ear environment” or E) and the GxE interactions. Overall, low broad‐sense heritabilities were observed for PKC, sporulation and aflatoxin. PKC was significantly correlated with sporulation in all environments. Aflatoxin was positively correlated with colonization for two and with sporulation for all ear environments. Higher grain sulphur or magnesium in IBM was associated with less colonization or aflatoxin. Postharvest susceptibility of maize to aflatoxin is thus influenced by factors that are modulated by the ear environment. In a KSA, sporulation could be a proxy test for aflatoxin accumulation.     

Aflatoxin Accumulation and Associated Traits in QPM Maize Inbreds and their Testcrosses

Preharvest aflatoxin (AF) contamination by Aspergillus flavus Link:Fr is one of the main limitations for maize (Zea mays, L.) production in the southern USA, causing enormous economic losses and posing a risk to animal and human health. The objectives of this study were (1) to estimate aflatoxin accumulation and expression of associated traits in quality protein maize (QPM) inbreds and their testcrosses, (2) to compute their repeatabilities and correlations, and (3) to study the relationship between inbred lines and their testcrosses for aflatoxin accumulation. Forty-eight inbreds and their testcrosses plus checks were grown in one and three locations in south and central Texas, respectively. Aflatoxin concentration was evaluated in the plants following inoculation with A. flavus. Average aflatoxin concentration overall for inbreds was 286.3 ng g⁻¹, and for testcrosses 596.5 ng g⁻¹ at Corpus Christi, TX, 325.1 ng g⁻¹ at Weslaco, TX, and 105.1 ng g⁻¹ at College Station, TX. Flinty orange inbreds developed from CIMMYT Population 69 were the least susceptible to aflatoxin accumulation in both inbreds and testcrosses at all locations. Repeatability for aflatoxin was 0.67 in inbreds at Weslaco, TX and 0.54 in testcrosses across locations. Aflatoxin in testcrosses was positively correlated both phenotycally and genotypically with endosperm texture and kernel integrity, and negatively correlated with grain yield and silking date. Less aflatoxin accumulation was associated with flinty endosperm texture, better kernel integrity, and later maturities. Association between the expression of traits in inbreds and aflatoxin in testcrosses was relatively high for endosperm texture (R ² = 0.62), silking date (R ² = 0.44), kernel integrity (R ² = 0.39), and aflatoxin (R ² = 0.60 for log ng g⁻¹). It seems plausible to select for associated traits having high heritabilities and strong correlation with aflatoxin, in addition to low aflatoxin accumulation in inbreds and hybrids to reduce the risk of aflatoxin contamination.     

Flavonoids as Flower Pigments: The Formation of the Natural Spectrum and its Extension by Genetic Engineering

Preharvest aflatoxin contamination of maize (Lea mays L.) gram by Aspergillns spp. is a concern to both producers and consumers of maize. Aflatoxms are carcinogenic to animals and have been linked to liver cancer in humans. The most desirable solution for eliminating or reducing aflatoxin contamination is to identify and/or develop sources of resistance. However, only a few genetic studies, which utilized a limited amount of genetic material, have been conducted. A thorough review and consolidation of information from these studies was deemed necessary. The purpose of this paper is to present a current, critical review on aspects of infection by Aspergillus, role of insects, inoculation techniques, and sources and genetics of resistance as they relate to aflatoxin production in maize. Damage to maize kernels by insects, especially the European corn borer (Ostrinia nubilalis Hübner), fall armyworm (Spodoptera frugiperda J. E. Smith), and corn ear-worm (Helicoverpa zea Boddie), has been associated with high aflatoxin levels. Artificial inoculation techniques that damage maize kernels generally result in the highest and most consistent aflatoxin levels. Although, a relatively large amount of maize germplasm has been screened for resistance and varying levels of resistance have been identified, additional germplasm needs to be systematically evaluated. To date, there are no known genotypes with complete resistance. Results from the few genetic studies indicated that additive genetic effects controlled resist-Preharvest aflatoxin contamination of maize (Zea mays L.) gram by Aspergillns spp. is a concern to both producers and consumers of maize. Aflatoxms are carcinogenic to animals and have been linked to liver cancer in humans. The most desirable solution for eliminating or reducing aflatoxin contamination is to identify and/or develop sources of resistance. However, only a few genetic studies, which utilized a limited amount of genetic material, have been conducted. A thorough review and consolidation of information from these studies was deemed necessary. The purpose of this paper is to present a current, critical review on aspects of infection by Aspergillus, role of insects, inoculation techniques, and sources and genetics of resistance as they relate to aflatoxin production in maize. Damage to maize kernels by insects, especially the European corn borer (Ostrinia nubilalis Hübner), fall armyworm (Spodoptera frugiperda J. E. Smith), and corn ear-worm (Helicoverpa Zea Boddie), has been associated with high aflatoxin levels. Artificial inoculation techniques that damage maize kernels generally result in the highest and most consistent aflatoxin levels. Although, a relatively large amount of maize germ-plasm has been screened for resistance and varying levels of resistance have been identified, additional germplasm needs to be systematically evaluated. To date, there are no known genotypes with complete resistance. Results from the few genetic studies indicated that additive genetic effects controlled resistance to aflatoxin contamination in maize. Aflatoxin production on maize grain appeared to be greatly influence by the environment. Further genetic studies, utilizing additional germplasm, are warranted for a better understanding of the nature of resistance to asflatoxin contamination in maize. Future research needs and plans relative to resistance to aflatoxin contaminaton in maize are presented.     

Control of preharvest aflatoxin contamination in maize by pyramiding QTL involved in resistance to ear-feeding insects and invasion by Aspergillus spp.

Several resistance sources and resistance mechanisms to aflatoxin formation and corn earworm (Helicoverpa zea Boddie) damage to maize (Zea mays L.) have been identified. Based on this knowledge, experiments were initiated toward achievement of the following objectives: (1) to confirm earlier determinations on resistance traits of germplasm sources and to identify quantitative trait loci (QTL) associated with each of the traits, and (2) upon estimation of the degree of QTL effects on each trait, to generate a maize population, with chemical and physical resistance to Aspergillus spp. and ear-feeding insects, for inbred development. A 2-year field experiment to evaluate selected genotypes inoculated with A. flavus and infested with corn earworm revealed that significant variation exists among the genotypes for aflatoxin contamination and corn earworm damage. The protection of maize ears against aflatoxin contamination was primarily dependent on resistance to fungal infection and ear-feeding insects, and excellent husk coverage and tightness. A major QTL (p1) identified on chromosome 1S had effects of 54.0, 42.1, and 28.3% on the phenotypic variability for concentrations of silk maysin, 3′-methoxymaysin+apimaysin, and chlorogenic acid, respectively. Markers/QTLs for husk phenotypic traits and total aflatoxin concentrations have been determined, but more detailed mapping of these chromosomic regions will be necessary to locate precise markers/QTLs for husk traits and aflatoxin production. Realizing the complexity of the Aspergillus–aflatoxin-maize system and the factors affecting aflatoxin contamination, we are directing our program toward marker-assisted breeding to enhance or improve general genetic resistance to ear-feeding insects and invasion by Aspergillus spp.     

Genetics of resistance to kernel infection by Aspergillus flavus in maize *

Although kernel infection by Aspergillus flavus Link ex Fries and subsequent pre-harvest aflatoxin contamination of maize (Zea mays L.) grain are major production problems in the south-eastern United States and elsewhere in the world, limited progress has been made in developing and identifying sources for resistance. Genetics of kernel infection by A. flavus remains poorly understood. A 10-parent diallel experiment was conducted in 1992 and 1994 to study the genetic nature of percentage kernel infection (PKI) by A. flavus. General combining ability (GCA), specific combining ability (SCA), and reciprocal mean squares for PKI were significant. The GCA and SCA sums of squares were about equal. The GCA, SCA, and reciprocal effects varied across years, which implied that percentage kernel infection was greatly influenced by environments. The percentage kernel infection was always greater when Mo 17 was the male parent in a cross than when it was the female parent. The percentage kernel infection mean for female Mo 17 was 38.5% lower than that for male Mol7. Similarly, percentage kernel infection mean for female L668 was 23.7% lower than that for male L668. The use of inbred lines L729 and B73 as female parents should be avoided, as they showed significant, positive maternal reciprocal effects.     

Stability of seed oil quality traits in high and mid-oleic acid sunflower hybrids

Powdery mildew caused by Podosphaera xanthii is an important disease of melon, and race 2F is the predominant race in most areas of China. Resistance to P. xanthii race 2F in melon K7-1 was controlled by a dominant gene, designated Pm-2F, in a 106-member population of recombinant inbred lines derived from K7-1× susceptible K7-2. Using bulked segregant analysis with molecular markers, we have identified two polymorphic simple sequence repeats (SSR) to determine that Pm-2F is located on linkage group II. Comparative genomic analyses using mapped SSR markers and the cucumber genome sequence showed that the melon chromosomal region carrying Pm-2F is homologous to a 288,223 bp genomic region on cucumber chromosome (chr) 1. The SSR markers on chr 1 of cucumber, SSR02734, SSR02733 and CS27 were found linked with Pm-2F. Comparative mapping showed that two SSR markers (SSR02734 and CMBR8) flanked the Pm-2F locus and two nucleotide binding site-leucine-rich repeat resistance genes were identified in the collinear region of cucumber. A cleaved amplified polymorphic sequence (CAPS) marker was developed from the sequence of resistance genes and it delimits the genomic region carrying Pm-2F to 0.8 cM. The evaluation of 165 melon accessions and 13 race differential lines showed that the newly developed CAPS (CAPS-Dde I) marker can be used as a universal marker for effective marker assisted selection in melon powdery mildew resistance breeding. The putative resistance gene cluster provides a potential target site for further fine mapping and cloning of Pm-2F.     

Heterotic affinity and combining ability of exotic maize inbred lines for resistance to aflatoxin accumulation

Aflatoxin accumulation in maize (Zea mays L.) kernels is a serious economic and health problem that reduces grain quality and nutritional values and causes death to livestock and humans. Understanding the genetic parameters and heterotic responses of exotic maize inbred lines can facilitate their use for developing aflatoxin resistant parents of hybrids in Africa. This study was designed to (1) determine the heterotic affinities of aflatoxin resistant exotic lines, (2) identify exotic inbreds with good combining ability, and (3) determine the mode of inheritance of resistance to aflatoxin contamination in these lines. A line?×?tester mating design was used to determine combining ability of 12 yellow and 13 white inbreds and classify them into heterotic groups. The inbreds were crossed to two adapted testers representing two African heterotic groups and the resulting testcrosses along with hybrid checks were evaluated in separate trials at two locations for 2 years in Nigeria. General combining ability (GCA) effects were more important than specific combining ability effects for aflatoxin and grain yield. Among 15 exotic inbred lines having negative GCA effects for aflatoxin and 13 with positive GCA effects for grain yield, six combined the two desired traits. Five white and six yellow endosperm testcrosses were found to be good specific combiners for the two desired traits. The exotic lines with negative GCA effects for aflatoxin accumulation will be used as donor parents to develop backcross populations for generating new inbred lines with much higher levels of resistance to aflatoxin accumulation.     

Mapping antixenosis genes on chromosome 6A of wheat to greenbug and to a new biotype of Russian wheat aphid

Greenbug and Russian wheat aphid (RWA) are two devastating pests of wheat. The first has a long history of new biotype emergence and recently. RWA resistance has just started to break down. Thus, it is necessary to find new sources of resistance that will broaden the genetic base against these pests in wheat. Seventy‐five doubled haploid recombinant (DHR) lines for chromosome 6A from the F₁ of the cross between “Chinese Spring’ and the “Chinese Spring (Synthetic 6A) (Triticum dicoccoides × Aegilops tauschii)” substitution line were used as a mapping population for testing resistance to greenbug biotype C and to a new strain of RWA that appeared in Argentina in 2003. A quantitative trait locus (QTL) (br antixenosis to greenbug was significantly associated with the marker loci Xgwm1009 and Xgwm1185 located in the centromere region of chromosome 6A. Another QTL which accounted for most of the antixenosis against RWA was associated with the marker loci Xgwm1291 and Xiinni1150. both located on the long arm of chromosome 6A. This is the first report of greenbug and RWA resistance genes located on chromosome 6A. It is also the first report of antixenosis against the new strain of RWA. As most of the RWA resistance genes present in released cultivars have been located in [he D‐ genome, it is highly desirable to find new sources in other genomes to combine the existing resistance genes with new sources.     

Resistance to Wheat streak mosaic virus identified in synthetic wheat lines

Wheat streak mosaic virus (WSMV) is an important pathogen in wheat that causes significant yield losses each year. WSMV is typically controlled using cultural practices such as the removal of volunteer wheat. Genetic resistance is limited. Until recently, no varieties have been available with major resistance genes to WSMV. Two resistance genes have been derived from Thinopyrum intermedium through chromosome engineering, while a third gene was transferred from bread wheat through classical breeding. New sources of resistance are needed and synthetic wheat lines provide a means of accessing genetic variability in wheat progenitors. A collection of wheat synthetic lines was screened for WSMV resistance. Four lines, 07-SYN-27, -106, -164, and -383 had significant levels of resistance. Resistance was effective at 18 °C and virus accumulation was similar to the resistant control, WGGRC50 containing Wsm1. At 25 °C, resistance was no longer effective and virus accumulation was similar to the susceptible control, Tomahawk.     

Mapping and candidate gene identification of loci determining tolerance to greenbug (Schizaphis graminum, Rondani) in barley

Greenbug is one of the most aggressive pests of barley and wheat. In Argentina, yield losses of wheat, barley, oat and sorghum crops caused by greenbug are chronic and at times severe. Since Marker Assisted selection for greenbug resistance genes in barley is very limited, the purpose of the current study was to map greenbug resistance genes in doubled haploid (DH) lines and to identify candidate genes. A set of DH lines of the Oregon-Wolfe Barley (OWB) mapping population derived from the cross between OWB_DOM and OWB_REC and both parental lines were screened for tolerance to greenbug. There was significant variation among the DH lines in foliar area (FA), dry weight (DW) and chlorophyll contents (Ch) between infested and control DH lines. Three main QTLs were identified. These QTLs explained 82 % of the FA, 80 % of DW and 58 % of Ch variability of infested plants. The initial and final FA and DW of controls and final DW of infested plants were associated with the same molecular markers on chromosome 2H (Vrs1, BmAc0144f, GBR259, GBS705). The final FA of infested plants was significantly linked to molecular markers on chromosome 5H (GBRO986, GBR518, GBM1483, GBR1082). The positive alleles were provided by OWB_DOM. The content of chlorophyll of infested plants was associated with the marker loci Ris44, GBR1608, GBR1637N and GBS0785 on chromosome 7H, with the positive alleles provided by OWB_REC. Both parents contributed to different tolerance traits. The QTLs found in this population are new greenbug resistance loci. A sequence homology search was performed to derive the putative function of the genes linked to the QTLs.     

QTL mapping of a partial resistance to the corn delphacid‐transmitted viruses in Lepidopteran‐resistant maize line Mp705

A partial resistance to maize mosaic virus (MMV) and maize stripe virus (MStV) was mapped in a RILs population derived from a cross between lines MP705 (resistant) and B73 (susceptible). A genetic map constructed from 131 SSR markers spanned 1399 cM with an average distance of 9.6 cM. A total of 10 QTL were detected for resistance to MMV and MStV, using composite interval mapping. A major QTL explaining 34–41% of the phenotypic variance for early resistance to MMV was detected on chromosome 1. Another major QTL explaining up to 30% of the phenotypic variation for all traits of resistance to MStV was detected in the centromeric region of chromosome 3 (3.05 bin). After adding supplementary SSR markers, this region was found to correspond well to the one where a QTL of resistance to MStV already was located in a previous mapping study using an F₂ population derived from a cross between Rev81 and B73. These results suggested that these QTL of resistance to MStV detected on chromosome 3 could be allelic in maize genome.     

Genetic mapping of bph20(t) and bph21(t) loci conferring brown planthopper resistance to Nilaparvata lugens St?l in rice (Oryza sativa L.)

Brown planthopper(BPH) is one of the most serious and destructive insect pests of rice in most rice growing regions of the world. In this study, two major resistance genes against BPH have been identified in an Oryza rufipogon (Griff.) introgression rice line, RBPH54. Inheritance of the BPH resistance in RBPH54 was studied by screening the resistance in parents, F1, F2 and BC1 generations against BPH biotype 2. A population of BC3F2 lines was developed and SSR markers were employed for the gene mapping, and new markers were designed for fine mapping of the resistance genes, while sequence information of BAC/PAC clones was used to construct physical maps of the genes. The results showed that the BPH resistance in RBPH54 was governed by recessive alleles at two loci, tentatively designated as bph20(t) and bph21(t). The locus bph20(t) was fine mapped to the short arm of chromosome 6 about 2.7 cM to the upper marker RM435 and 2.5 cM to lower marker RM540 and in a 2.5 cM region flanked by two new SSR markers BYL7 and BYL8 which were developed in the present study. The other BPH resistance locus bph21(t) was initially mapped to a region 7.9 cM to upper marker RM222 and 4.0 cM to lower marker RM244 on the short arm of chromosome 10. For physical mapping, the bph20(t)-linked markers were landed on BAC/PAC clones of the reference cv., Nipponbare, released by the International Rice Genome Sequencing Project. The bph20(t) locus was physically defined to an interval of about 75 kb with clone P0514G1. Identification and location of these two genes in the present study have diversified the BPH resistance gene pool, which give benefit to the development of resistant rice cultivars, and the linkage PCR-based SSR markers for the bph20(t) and bph21(t) genes would help realize the application of the genes in rice breeding through marker-assisted selection.     

Detection of quantitative trait loci for leaf rust resistance in wheat––T. timopheevii/T. tauschii introgression lines

Advanced backcross QTL analysis was used to identify QTLs for seedling and adult plant resistance to leaf rust in introgression lines derived from a cross between the spring wheat cultivar ‘Saratovskaya 29’ and a synthetic allopolyploid wheat (T. timopheevii/T. tauschii). F₂ mapping populations involving two backcross selections (‘BC5’ and ‘BC9’ lines) were genotyped with microsatellite markers. Two significant QTL for adult plant resistance were identified in line ‘BC5’: one on chromosome 2B, but originating from chromosome 2G, explained 31% of the trait variance. The other, derived from T. tauschii and mapped to the short arm of chromosome 2D explained 19% of the trait variance. In the second line, one major seedling and adult plant resistance QTL was identified on chromosome 2B. Both QTL co-located to the same marker interval. Such introgression lines, resulting from the reconstruction of common wheat genome, are of interest both as initial material for breeding and improvement of current cultivars, and as a resource for the study of the interaction and transformation of genomes.     

Further QTL mapping for yield component traits using introgression lines in rice (<Emphasis Type="Italic">Oryza sativa</Emphasis> L.) under drought field environments

To better understand the underlying mechanisms of agronomic traits related to drought resistance and discover candidate genes or chromosome segments for drought-tolerant rice breeding, a fundamental introgression population, BC₃, derived from the backcross of local upland rice cv. Haogelao (donor parent) and super yield lowland rice cv. Shennong265 (recurrent parent) had been constructed before 2006. Previous quantitative trait locus (QTL) mapping results using 180 and 94 BC₃F_6,7 rice introgression lines (ILs) with 187 and 130 simple sequence repeat (SSR) markers for agronomy and physiology traits under drought in the field have been reported in 2009 and 2012, respectively. In this report, we conducted further QTL mapping for grain yield component traits under water-stressed (WS) and well-watered (WW) field conditions during 3 years (2012, 2013 and 2014). We used 62 SSR markers, 41 of which were newly screened, and 492 BC₄F_2,4 core lines derived from the fourth backcross between D123, an elite drought-tolerant IL (BC₃F₇), and Shennong265. Under WS conditions, a total of 19 QTLs were detected, all of which were associated with the new SSRs. Each QTL was only identified in 1 year and one site except for qPL-12-1 and qPL-5, which additively increased panicle length under drought stress. qPL-12-1 was detected in 2013 between new marker RM1337 and old marker RM3455 (34.39 cM) and was a major QTL with high reliability and 15.36% phenotypic variance. qPL-5 was a minor QTL detected in 2013 and 2014 between new marker RM5693 and old marker RM3476. Two QTLs for plant height (qPHL-3-1 and qPHP-12) were detected under both WS and WW conditions in 1 year and one site. qPHL-3-1, a major QTL from Shennong265 for decreasing plant height of leaf located on chromosome 3 between two new markers, explained 22.57% of phenotypic variation with high reliability under WS conditions. On the contrary, qPHP-12 was a minor QTL for increasing plant height of panicle from Haogelao on chromosome 12. Except for these two QTLs, all other 17 QTLs mapped under WS conditions were not mapped under WW conditions; thus, they were all related to drought tolerance. Thirteen QTLs mapped from Haogelao under WS conditions showed improved drought tolerance. However, a major QTL for delayed heading date from Shennong265, qDHD-12, enhanced drought tolerance, was located on chromosome 12 between new marker RM1337 and old marker RM3455 (11.11 cM), explained 21.84% of phenotypic variance and showed a negative additive effect (shortening delay days under WS compared with WW). Importantly, chromosome 12 was enriched with seven QTLs, five of which, including major qDHD-12, congregated near new marker RM1337. In addition, four of the seven QTLs improved drought resistance and were located between RM1337 and RM3455, including three minor QTLs from Haogelao for thousand kernel weight, tiller number and panicle length, respectively, and the major QTL qDHD-12 from Shennong265. These results strongly suggested that the newly screened RM1337 marker may be used for marker-assisted selection (MAS) in drought-tolerant rice breeding and that there is a pleiotropic gene or cluster of genes linked to drought tolerance. Another major QTL (qTKW-1-2) for increasing thousand kernel weight from Haogelao was also identified under WW conditions. These results are helpful for MAS in rice breeding and drought-resistant gene cloning.     

Identification of QTL for stalk sugar-related traits in a population of recombinant inbred lines of maize

Increasing sugar content in silage maize stalk improves its forage quality and palatability. The genetic mapping and characterization of quantitative trait loci (QTLs) is considered a valuable tool for trait enhancement, yet little information on QTL for stalk sugar content in maize has been reported. To this end, we investigated QTLs associated with stalk sugar traits including Brix, plant height (PHT), three ear leaves area (TELA), and days to silking (DTS) in two environments using a population of 202 recombinant inbred lines from a cross between YXD053, which has a high stalk sugar content, and Y6-1, which has a low stalk sugar content. A genetic map with 180 SSR and 10 AFLP markers was constructed, which spanned 1,648.6 cM of the maize genome with an average marker distance of 8.68 cM, and QTLs were detected using composite interval mapping. Seven QTLs controlling Brix were mapped on chromosomes 1, 2, 6 and 9 in the combined environments. These QTLs could explain 2.69–13.08 % of the phenotypic variance. One major QTL for Brix on chromosome 2 located between the markers bnlg1909 and umc1635 explained 13.08 % of the phenotypic variance. Y6-1 also contributed QTL allele for increased Brix on chromosome 6. One major QTLs controlling PHT on chromosome 1 and TELA on chromosome 4 were also identified and accounted for 13.68 and 12.49 % of the phenotypic variance, respectively. QTL alleles for increased DTS were located on chromosomes 1 and 5 of YXD053. Significant epistatic effects were identified in four traits, but no significant QTL × environment interactions were observed. The information presented here may be valuable for stalk sugar content improvement via marker-assisted selection in silage maize breeding programs.     

玉米出籽率、籽粒深度和百粒重的QTL分析

为研究玉米出籽率、籽粒深度、百粒重的遗传机制,以豫82×沈137组配的229个F_2:3家系为试验材料,采用复合区间作图法进行QTL定位分析。在3个环境下共检测到10个QTL。其中,控制出籽率、籽粒深度、百粒重相关QTL分别为3个、3个和4个,它们的联合贡献率分别为35.5%、28.1%和39.0%。位于第1染色体上介于标记umc1335与umc2236之间控制出籽率的QTL qKR1b和位于第9染色体上介于标记bnlg1209–umc2095之间控制百粒重QTL q100-KW9b,分别解释18.9%和11.7%的表型变异,且作用方式为加性效应,分析表明这些区域可能包含调控玉米籽粒性状关键基因,对剖析玉米产量形成机制具有重要的参考价值。     

Fine mapping of major QTLs for alkaline tolerance at the seedling stage in maize (<Emphasis Type="Italic">Zea mays</Emphasis> L.) through genetic linkage analysis combined with high-throughput DNA sequencing

Exploiting genes and quantitative trait loci (QTLs) related to maize (Zea mays L.) alkaline tolerance is helpful for improving alkaline resistance. To explore the inheritance of maize alkaline tolerance at the seedling stage, a mapping population comprising 151 F_2:3 lines derived from the maize cross between Zheng58, tolerant to alkaline, and Chang7-2, sensitive to alkaline, was used to establish a genetic linkage map with 200 SSR loci across the 10 maize linkage groups, with an average interval of 6.5 cM between adjacent markers. QTLs for alkaline resistant traits of alkaline tolerance rating (ATR), germination rate (GR), relative conductivity (RC), weight per plant (WPP) and proline content (PC) were detected. The obtained results were as follows: Five QTLs on chromosomes 2, 5 and 6 (GR and WPP: chr. 2; PC and ATR: chr. 5; and RC: chr. 6) were mapped. For precise mapping of the QTLs related to alkaline resistance, two bulked deoxyribonucleic acid (DNA) pools were constructed using individual DNAs from the most tolerant 30 F₂ individuals and the most sensitive 30 F₂ individuals according to the ATR and used to establish a high density map of SLAF markers strongly associated with the ATR by specific locus amplified fragment sequencing (SLAF-Seq) combined with super bulked segregant analysis (superBSA). One marker-intensive region involved three SLAFs at 296,000–6,203,000 bp on chromosome 5 that were closely related to the ATR. Combined with preliminary QTL mapping with superBSA, two major QTLs on chromosome 5 associated with alkaline tolerance at the maize seedling stage were mapped to marker intervals of dCap-SLAF31521 and dCap-SLAF31535 and phi024 and dCap-SLAF31521, respectively. These QTL regions involved 9 and 75 annotated genes, respectively. These results will be helpful for improving maize alkaline tolerance at the seedling stage by marker-assisted selection programs and will be useful for fine mapping QTLs for maize breeding.