玉米大斑病抗性遗传的研究进展

由于大斑病生理小种的变异,致使原来抗大斑病的玉米品种丧失抗性,对玉米生产造成严重危害,至今已经发现大斑病菌生理小种5个。玉米对大斑病的抗性可分为多基因控制的数量性状和显性单基因控制的质量性状,前者涉及玉米的10条染色体;后者包括t1、Ht2、Ht3、HtN等基因。本文对大斑病生理小种变化,玉米大斑病抗性单基因（Ht）的来源、遗传特点、染色体定位以及数量抗性基因的QTL分析等研究进展作了综述。 Abstract:As the rapid variation and mutation of the races of Exserohilum turcicum (Helminthosporium turcicum),maize varieties lost their resistance to northern corn leaf blight (NCLB) disease caused by new races of E.Turcicum.This brought the disaster in maize production.Up to now 5 races have been found.The maize resistance to E.turcicum can be divided into quantitative and qualitative resistance,the former is associated with 10 chromosomes in maize,and the later includes genes of t1、Ht2、Ht3 and HtN.The race variation of E.turcicum,the original gene resources and genetic characteristics of each Ht monogenic resistance,the chromosome location of t1、Ht2、HtN genes,and the QTL analysis of quantitative resistant genes for E.turcicum in maize were reviewed in this paper.     

A green fluorescent protein-engineered haploid inducer line facilitates haploid mutant screens and doubled haploid breeding in maize

Northern corn leaf blight (NCLB) is a prevalent foliar disease in maize. Deployment of resistant cultivars is an effective way to control NCLB. In this study, 207 recombinant inbred lines derived from a K22 × By815 cross were planted in Yangling, China, in 2012 and 2013. NCLB score and lesion size were investigated after artificial inoculation. Significant phenotypic variation in NCLB resistance was observed in both years. Using a genetic map containing high-density single-nucleotide polymorphisms with average genetic distance of 0.74 cM, quantitative trait loci (QTL) for NCLB score and lesion size were analyzed. For NCLB score, four and three QTL were identified in 2012 and 2013, respectively. Two stable QTL were identified in both years. Of these, qNCLB5.04, located on chromosome 5 (bin 5.04), had the largest resistance effect, accounting for 19 and 20 % of the phenotypic variation in 2012 and 2013, respectively. For lesion size, six QTL were identified. Of these, one consensus QTL was associated with both lesion length and width, and the other five were associated only with lesion width. Among all QTL identified, only qNCLB5.04 was associated with both NCLB score and lesion size. Thus, our mapping results suggest that qNCLB5.04 could be a desirable target for marker-assisted selection for NCLB resistance in maize breeding programs.

     

Genetic gain and cost efficiency of marker-assisted selection of maize for improved resistance to multiple foliar pathogens

Northern corn leaf blight (NCLB) caused by Exserohilum turcicum, gray leaf spot (GLS) caused by Cercospora zeae-maydis and maize streak caused by maize streak Mastrevirus (MSV) are the most destructive foliar diseases limiting maize production in sub-Saharan Africa. Most foliar diseases of maize are managed using quantitative (partial) resistance, and previous studies have reported quantitative trait loci associated with host resistance (rQTL). Our objective was to compare the genetic gain and costs resulting from phenotypic, genotypic, and marker-assisted selection of partially inbred lines derived from many families for resistance to infection by three foliar pathogens. We developed a population of 410 F2:3 families by crossing inbred line CML202 with a breeding line designated VP31. These families were planted in nurseries inoculated separately with each pathogen. We conducted one cycle of early generation pedigree selection using three different procedures, phenotypic, genotypic, and marker/phenotypic index, for improvement of resistance to each pathogen. We used simple sequence repeat (SSR) markers flanking six target rQTL associated with partial resistance. Broad- and narrow-sense heritability estimates were also obtained for the F2:3 families, and selected and non-selected F2:4 families. Genetic gains resulting from the selection procedures were determined. Gene action of the candidate rQTL was determined using orthogonal contrasts. Estimates of costs based on lower boundary values indicated that the cost of marker-based selection was lower than that of phenotypic selection. Our results indicate that molecular markers linked to target rQTL can facilitate pyramiding resistance to multiple diseases during early generation pedigree selection.     

Inheritance of resistance against northern leaf blight of maize using conventional breeding methods

Maize (Zea mays L.) is one of the important cereal crops along with wheat and rice worldwide. The purpose of this study was to use classical genetic approaches to assess the resistance of various maize parents and hybrids to the northern corn leaf blight (NCLB) disease in two different locations in Egypt. Eight parents, 28 F1, and 2 check hybrids were evaluated. The analysis of variance showed high significant variations between maize parents and their hybrids for the studied parameters and NCLB disease, besides there are significant variations between both locations. Results of maize parents showed that Sids 63, Giza 602, and Giza 628 cultivars exhibited the highest values and were resistant to NCLB in both locations comparing with Nubaria 39 and Gemmiza 18 that were susceptible to NCLB disease. Concerning the maize hybrids, analysis of variance and mean squares of growth characters in both locations indicated high significant variations between the maize hybrids including the check hybrids. When combined between the two locations for current parameters against NCLB, the data pointed that the Sakha location values for maize hybrids were much closed to the combining data in parents and the hybrids detected high resistance to this disease comparing with Nubaria location. All tested maize lines (38 lines), including parents and hybrids were classified as follows, two lines were rated as 1 (highly resistant), three were rated as 2 (resistant), sixteen were rated as 3 (moderate resistant), eight were rated 4 (moderately susceptible) and nine were rated 5 (susceptible). The data explaining that the crossing between high resistant maize cultivars produced high levels of resistance to NCLB disease. Therefore, our results verified that classical breeding could efficiently increase the resistance levels of maize germplasm against NCLB disease by developing new cultivars with superior performance in terms of grain yield, disease resistance and grain quality.     

Distribution,Etiology, Molecular Genetics and Management Perspectives of Northern Corn Leaf Blight of Maize (<i>Zea mays</i> L.)

Maize is cultivated extensively throughout the world and has the highest production among cereals. However, Northern corn leaf blight (NCLB) disease caused by Exherohilum turcicum, is the most devastating limiting factor of maize production. The disease causes immense losses to corn yield if it develops prior or during the tasseling and silking stages of crop development. It has a worldwide distribution and its development is favoured by cool to moderate temperatures with high relative humidity. The prevalence of the disease has increased in recent years and new races of the pathogen have been reported worldwide. The fungus E. turcicum is highly variable in nature. Though different management strategies have proved effective to reduce economic losses from NCLB, the development of varieties with resistance to E. turcicum is the most efficient and inexpensive way for disease management. Qualitative resistance for NCLB governed by Ht genes is a race-specific resistance which leads to a higher level of resistance. However, some Ht genes can easily become ineffective under the high pressure of virulent strains of the pathogen. Hence, it is imperative to understand and examine the consistency of the genomic locations of quantitative trait loci for resistance to NCLB in diverse maize populations. The breeding approaches for pyramiding resistant genes against E. turcicum in maize can impart NCLB resistance under high disease pressure environments. Furthermore, the genome editing approaches like CRISPR-cas9 and RNAi can also prove vital for developing NCLB resistant maize cultivars. As such this review delivers emphasis on the importance and current status of the disease, racial spectrum of the pathogen, genetic nature and breeding approaches for resistance and management strategies of the disease in a sustainable manner.     

Loci and candidate gene identification for soybean resistance to Phytophthora root rot race 1 in combination with association and linkage mapping

Molecular Breeding - Northern corn leaf blight (NCLB) is one of the main diseases of maize, which greatly reduces production and causes millions of dollars in losses worldwide annually....     

QTLs for resistance to Setosphaeria turcica in an early maturing Dent×Flint maize population

Quantitative trait loci (QTLs) for resistance to the fungal pathogen Setosphaeria turcica, the cause of northern corn leaf blight (NCLB), were mapped in a population of 220 F₃ families derived from a cross between two moderately resistant European inbred lines, D32 (dent) and D145 (flint). The population was genotyped with 87 RFLP and 7 SSR markers. Trials were conducted in the field in Switzerland, and in the greenhouse with selected F₃ families in Germany. The F₃ population segregated widely for resistance with transgression of the parents. By composite interval mapping, a total of 13 QTLs were detected with two disease ratings (0 and 3 weeks after flowering). Together these QTLs explained 48% and 62% of the phenotypic variation. Gene action at most QTLs was partially dominant. Eight out of the 13 QTL alleles for resistance were contributed by the more-resistant parent, D145. On chromosomes 3, 5 and 8, QTLs were located in the same chromosomal regions as QTLs in tropical and U.S. Corn Belt germplasm. Some QTLs affected NCLB, head smut and common rust at the same time, with alleles at these loci acting isodirectionally. Received: 25 January 1999 / Accepted: 20 Februar 1999     

玉米种质资源对六种重要病虫害的抗性鉴定与评价

在2003-2005年间,对604份玉米种质进行了抗弯孢菌叶斑病和玉米螟鉴定,筛选出抗弯孢菌叶斑病的材料93份,抗玉米螟材料22份。2006-2009年间,对836份玉米种质进行了抗大斑病、茎腐病、穗腐病和瘤黑粉病的鉴定与评价,筛选出一批高抗和多抗的资源。在836份资源中,对大斑病1、2和N号3个生理小种具有抗性的材料均为50%左右;抗茎腐病材料为41.3%,高抗和抗性种质分别为264和81份;穗腐病高抗和抗性种质分别为5和171份,占比为21.1%;瘤黑粉病高抗和抗性种质各261和14份,占总鉴定材料的32.9%。上述结果表明抗大斑病、茎腐病和瘤黑粉病的种质资源较为丰富。通过对抗性结果进行对比分析,发现不同生态区玉米种质的抗性强弱以及抗性多样性存在明显差异,黑龙江和内蒙古的种质对病虫害的抗性强弱及多样性程度明显高于四川种质。此外,玉米自交系对病虫害的抗性强弱以及多抗性程度高于农家种。     

Identification and Fine Mapping of rhm1 Locus for Resistance to Southern Corn Leaf Blight in Maize

rhm1 is a major recessive disease resistance locus for Southern corn leaf blight (SCLB).To further narrow down its genetic position,F 2 population and BC 1 F 1 population derived from the cross between resistant (H95 rhm) and susceptible parents (H95) of maize (Zea mays) were constructed.Using newly developed markers,rhm1 was initially delimited within an interval of 2.5 Mb,and then finally mapped to a 8.56 kb interval between InDel marker IDP961-503 and simple sequence repeat (SSR) marker A194149-1.Three polymorphic markers IDP961-504,IDP B2-3 and A194149-2 were shown to be co-segregated with the rhm1 locus.Sequence analysis of the 8.56 kb DNA fragment revealed that it contained only one putative gene with a predicted amino acid sequence identical to lysine histidine transporter 1 (LHT1).Comparative sequence analysis indicated that the LHT1 in H95 rhm harbors a 354 bp insertion in its third exon as compared with that of susceptible alleles in B73,H95 and Mo17.The 354 bp insertion resulted in a truncation of the predicted protein of candidate resistance allele (LHT1-H95 rhm).Our results strongly suggest LHT1 as the candidate gene for rhm1 against SCLB.The tightly linked molecular markers developed in this study can be directly used for molecular breeding of resistance to Southern corn leaf blight in maize.     

Analysis of genetic mapping in a waxy/dent maize RIL population using SSR and SNP markers

A maize genetic linkage map was generated using SSR and SNP markers in a F_7:8 recombinant inbred line (RIL) population derived from a cross of waxy corn (KW7) and dent corn (Mo17). A total of 465 markers, including 459 SSR and 6 SNP markers, were assigned to 10 linkage groups which spanned 2,656.5 cM with an average genetic distance between markers of 5.7 cM, and the number of loci per linkage group ranged from 39 to 55. The SSR (85.4%) and SNP (83.3%) markers showed Mendelian segregation ratios in the RIL population at a 5% significance threshold. In linkage analysis of six SNP loci associated with kernel starch synthesis genes (ae1, bt2, sh1, sh2, su1, and wx1), all six loci were successfully mapped and are closely linked with SSR markers in chromosomes 3 (sh2), 4 (su1 and bt2), 5 (ae1), and 9 (sh1 and wx1). The SSR markers linked with genes in starch synthesis may be utilized in marker assisted breeding programs. The resulting genetic map will be useful in dissection of quantitative traits and the identification of superior QTLs from the waxy hybrid corn. Additionally, these data support further genetic analysis and development of maize breeding programs.     

Interval mapping of genes for quantitative resistance of maize to Setosphaeria turcica,cause of northern leaf blight,in a tropical environment

Quantitative trait loci (QTL) involved in the resistance of maize to Setosphaeria turcica, the causal agent of northern leaf blight, were located by interval mapping analysis of 121 F_2:3 lines derived from a cross between Mo17 (moderately resistant) and B52 (susceptible). A linkage map spanning 112 RFLP loci with 15 cM mean interval length was constructed, based on marker data recorded in a previous study. Field tests with artificial inoculation were conducted at three sites in tropical mid- to high-altitude regions of Kenya, East Africa. Host-plant response was measured in terms of incubation period, disease severity (five scoring dates), and the area under the disease progress curve (AUDPC). Heritability of all traits was high (around 0.75). QTL associated with the incubation period were located on chromosomes 2S and 8L. For disease severity and AUDPC, significant QTL were detected in the putative centromeric region of chromosome 1 and on 2S, 3L, 5S, 6L, 7L, 8L and 9S. On 2S the same marker interval which carried a gene enhancing latent period was also associated with reduced disease severity of juvenile plants. QTL on chromosomes 3L, 5S, 7L and 8L were significant across environments but all other QTL were affected by a large genotype x environment interaction. Partially dominant gene action for resistance as well as for susceptibility was prevailing. Single QTL explained 10 to 38% of the phenotypic variation of the traits. All but the QTL on chromosomes 1, 6 and 9 were contributed by the resistant parent Mo17. On chromosome 8L a QTL mapped to the same region as the major race-specific gene Ht2, supporting the hypothesis that some qualitative and quantitative resistance genes may be allelic.Abbreviations AUDPC area under the disease progress curve - CIMMYT International Maize and Wheat Improvement Center - KARI Kenya Agricultural Research Institute - NCLB northern corn leaf blight - QTL quantitative trait locus/loci     

<Emphasis Type="Italic">qNCLB7.02</Emphasis>, a novel QTL for resistance to northern corn leaf blight in maize

Northern corn leaf blight (NCLB), which is caused by the hemibiotrophic fungal pathogen Setosphaeria turcica, is a devastating foliar disease that results in considerable maize yield losses. In the present study, quantitative trait locus (QTL) analysis was conducted across two environments using an ultra-high-density bin map constructed using recombinant inbred lines (RILs) derived from a cross between Ye478 and Qi319. A total of 11 QTLs, located on chromosomes 1, 4, 5, 6, 7, 8, 9, and 10, were detected that confer resistance to physiological race 0 of NCLB. Each QTL could explain 3.53–15.29% of the total phenotypic variation in disease resistance after artificial inoculation in two environments. Among these QTL, qNCLB7.02, which is located on chromosome 7, had the largest effect, accounting for 10.11 and 15.29% of the phenotypic variation in resistance in two field trials and BLUP. The common confidence interval (CI) for qNCLB7.02 was 1.4 Mb, according to the B73 RefGen_v3 sequence. The resistance effect of qNCLB7.02 was validated in 2016 by using chromosome segment substitution lines (CSSLs) derived from Qi319 as the donor in the genetic background of Ye478. The type 6 CSSL, which harbors introgressed qNCLB7.02, was found to be significantly associated with resistance to NCLB by linked marker bnlg1808 and exhibited greater resistance than the other CSSLs that did not carry this QTL (P?=?0.0008). The combination of linkage mapping in RILs and validation in CSSLs is a powerful approach for the dissection of QTL for disease resistance in maize.     

Selection mapping of loci for quantitative disease resistance in a diverse maize population

The selection response of a complex maize population improved primarily for quantitative disease resistance to northern leaf blight (NLB) and secondarily for common rust resistance and agronomic phenotypes was investigated at the molecular genetic level. A tiered marker analysis with 151 simple sequence repeat (SSR) markers in 90 individuals of the population indicated that on average six alleles per locus were available for selection. An improved test statistic for selection mapping was developed, in which quantitative trait loci (QTL) are identified through the analysis of allele-frequency shifts at mapped multiallelic loci over generations of selection. After correcting for the multiple tests performed, 25 SSR loci showed evidence of selection. Many of the putatively selected loci were unlinked and dispersed across the genome, which was consistent with the diffuse distribution of previously published QTL for NLB resistance. Compelling evidence for selection was found on maize chromosome 8, where several putatively selected loci colocalized with published NLB QTL and a race-specific resistance gene. Analysis of F(2) populations derived from the selection mapping population suggested that multiple linked loci in this chromosomal segment were, in part, responsible for the selection response for quantitative resistance to NLB.     

Efficacy assessment of antifungal metabolites from Chaetomium globosum No.05, a new biocontrol agent,against Setosphaeria turcica

Northern corn leaf blight (NCLB), an important and potentially destructive corn foliar disease, is caused by Setosphaeria turcica. The intent of this study was to evaluate antifungal metabolites from Chaetomium globosum (Cg) strain No.05 to suppress NCLB in maize. This strain significantly suppressed mycelial growth of numerous phytopathogenic fungi especially S. turcica on potato dextrose agar medium. The secondary metabolites of the strain inhibited mycelial growth and conidial germination of S. turcica. When co-inoculated at three droplets (5 μL/droplet) of conidial suspension (5 × 10⁴ conidia/mL) on each 8-cm-long detached leaf, 20% culture filtrates completely suppressed disease incidence of northern corn leaf blight. The application of the culture filtrates at 2 h post-inoculation (hpi) of S. turcica in greenhouse studies showed a 81.9% inhibition of NCLB on the seedlings, while culture filtrates applied before pathogen inoculation showed even higher rates of disease reduction. The application of the culture filtrates had no observed effects on the treated maize leaves or seedlings. Two active compounds, isolated from the extracts, were identified as chaetoglobosin A and chaetoglobosin C based on the spectroscopic analysis. Both in vitro and in planta bioassay experiments showed that chaetoglobosin A displayed potent biocontrol efficiency against S. turcica. To the best of our knowledge, this is the first report of the evaluation of the inhibitory effects of C. globosum and chaetoglobosin A against S. turcica both in vitro and on detached maize leaves.     

Maize FERONIA-like receptor genes are involved in the response of multiple disease resistance in maize

Receptor-like kinases (RLKs) are key modulators of diverse cellular processes such as development and sensing the extracellular environment. FERONIA, a member of the CrRLK1L subfamily, acts as a pleiotropic regulator of plant immune responses, but little is known about how maize FERONIA-like receptors (FLRs) function in responding to the major foliar diseases of maize such as northern corn leaf blight (NLB), northern corn leaf spot (NLS), anthracnose stalk rot (ASR), and southern corn leaf blight (SLB). Here, we identified three ZmFLR homologous proteins that showed cell membrane localization. Transient expression in Nicotiana benthamiana proved that ZmFLRs were capable of inducing cell death. To investigate the role of ZmFLRs in maize, we used virus-induced gene silencing to knock down expression of ZmFLR1/2 and ZmFLR3 resulting in reduced reactive oxygen species production induced by flg22 and chitin. The resistance of maize to NLB, NLS, ASR, and SLB was also reduced in the ZmFLRs knockdown maize plants. These results indicate that ZmFLRs are positively involved in broad-spectrum disease resistance in maize.     

Dynamic gene action at QTLs for resistance to Setosphaeria turcica in maize

 Cultivars with quantitative resistance are widely used to control Setosphaeria turcica (Luttrell) Leonard & Suggs, the causal organism of northern corn leaf blight (NCLB). Here the effectiveness of quantitative trait loci (QTLs) for NCLB resistance was investigated over the course of host plant development in inoculated field trials. A population of 194–256 F_2:3 lines derived from a cross between a susceptible Italian (Lo951) and a highly resistant African inbred line (CML202) was tested in three environments in Kenya. The traits assessed were the incubation period (IP), the percentage disease severity (DS 1 to 5, taken biweekly), and the area under the disease progress curve (AUDPC). Considering all resistance traits and environments, a total of 19 putative QTLs were detected by composite interval mapping using a linkage map with 110 RFLP markers. In the combined analysis across environments, nine QTLs were significant (LOD >3.0) for DS 3, recorded around flowering time, explaining 71% of the genotypic variance. Four of these nine QTLs displayed significant (P<0.05) QTL×environment (QTL×E) interaction. Most QTLs were already significant in the juvenile stage (IP) and became less effective after flowering. Across environments, three QTLs conditioned adult-plant resistance, in the sense that they were only significant after flowering. Six QTL alleles on chromosomes 2, 4, 5, 8, and 9 of CML202 should be useful for marker-assisted backcrossing. Received: 24 August 1998 / Accepted: 29 September 1998     

A SNP haplotype associated with a gene resistant to Xanthomonas axonopodis pv. malvacearum in upland cotton (Gossypium hirsutum L.)

An F_4:5 population of 285 families with each tracing back to a different F₂ plant, derived from a cotton bacterial blight resistant line ‘DeltaOpal’ and a susceptible line ‘DP388’, was artificially inoculated with bacterial blight race 18 (Xanthomonas axonopodis pv. malvacearum) to assay their resistance or susceptibility to the disease. The segregation in the F_4:5 population indicates that the resistance was conditioned by a single dominant gene designated B _12. Simple sequence repeat (SSR) markers identified as putatively linked to the resistance gene by bulked segregant analysis were confirmed on the entire F_4:5 population. Three SSR markers, CIR246, BNL3545 and BNL3644 on chromosome 14, were found closely linked to B ₁₂ . The association between CIR246 and B ₁₂ was validated among 354 plants of 16 diverse varieties. Based on Monsanto SSR/single nucleotide polymorphism (SNP) consensus map, SNP markers closely linked to CIR246 were used to screen ‘DeltaOpal’ and ‘DP388’ for polymorphism. The polymorphic SNP markers were run on the F_4:5 population and the four SNP markers spanning 3.4 cM were found to flank the resistance gene on chromosome 14. The linkage between B ₁₂ and the 4-SNP marker haplotype was validated using 18 elite cotton lines. This 4-SNP marker haplotype can be used for marker assisted selection for bacterial blight resistance breeding programs or for screening germplasm collections for this locus rapidly.     

Mapping of HtNB, a gene conferring non-lesion resistance before heading to Exserohilum turcicum (Pass.), in a maize inbred line derived from the Indonesian variety Bramadi

The gene HtNB confers non-lesion resistance to the fungal pathogen Exserohilum turcicum in maize. To map this gene, we developed two F(2) populations, P111 (resistant line) x HuangZao 4 (susceptible line) and P111 x B73 (susceptible). HtNB was located on chromosome 8.07 bin, flanked by MAC216826-4 and umc2218 at distances of 3.3 and 3.4 cM, respectively. HtNB appears to be a new gene responsible for resistance to northern corn leaf blight. Functions of the genes in the region between umc1384 and umc2218 were predicted. In addition, several genes were found to be related to disease resistance, such as the genes encoding Ser/Thr protein kinase and protein-like leaf senescence.