玉米是世界上最重要的农作物之一，中国玉米总产量占全国所有谷物产量的38.12%。穗腐病是玉米生产中的重要病害，在降低玉米产量和品质的同时，产生的毒素也危害人畜安全。抗性品种的选育和利用是控制玉米穗腐病的经济、安全和有效措施。目前，国内外对玉米穗腐病的致病菌进行了较为详细的研究，鉴定出40余种病原真菌，其中拟轮枝镰孢、禾谷镰孢和黄曲霉引起的穗腐病发生普遍，危害最为严重。建立了4种玉米抗穗腐病鉴定的方法，即双牙签接种法、花丝喷雾法、花丝通道注射法和针刺果穗注射法，从数千份玉米种质资源中筛选出一批抗拟轮枝镰孢、禾谷镰孢或黄曲霉穗腐病的材料。明确了玉米抗穗腐病的物理与生化机制，主要表现为抗侵染和抗扩散两个方面。对部分材料进行了抗性遗传分析和抗性基因QTL定位研究，在玉米1—8号染色体上检测到60余个抗黄曲霉侵染或抑制黄曲霉毒素积累的QTL；定位了55个抗拟轮枝镰孢穗腐病、29个抗禾谷镰孢穗腐病、16个抗伏马毒素和DON毒素的QTL，并通过meta-QTL分析获得了数个能稳定表达且贡献率较大的QTL位点。创制了10余份抗穗腐病种质，育成了少数对穗腐病具有较好抗性的玉米新品种。尽管如此，抗性研究和抗病育种成果用于生产实践的事例仍很少，生产上缺乏抗穗腐病且高产优质的玉米品种。本文从玉米穗腐病病原类型、抗性种质筛选与评价、抗性遗传及抗性基因的发掘与分子定位、抗性机制、抗病品种的选育等方面对国内外玉米抗穗腐病研究进行了综述，并对今后的相关研究进行了展望，以期对促进玉米抗穗腐病研究有所裨益。

Ear rots caused by Fusarium spp. are among the main fungal diseases that contribute to poor quality and the contamination of maize grains with mycotoxins. This study aimed to determine the visual incidence of fungal-damaged kernels (FDKs), the incidence of two main Gibberella (a teleomorph of Fusarium) complexes (G. fujikuroi and G. zeae) associated with maize using a seed health blotter test, and the fumonisin levels, using high performance liquid chromatography, in samples of maize grains grown across 23 municipalities during the 2008/09 and 2009/10 growing seasons. Additionally, 104 strains that were representative of all of the analysed samples were identified to species using PCR assays. The mean FDK was seven per cent, and only six of the samples had levels greater than six per cent. Fusarium spp. of the G. fujikuroi complex were present in 96% of the samples, and G. zeae was present in 18% of the samples (5/27). The mean incidence of G. fujikuroi was 58%, and the incidence of G. zeae varied from 2 to 6%. FB1 was found in 58.6%, FB2 in 37.9%, and both toxins in 37.9% of the samples. The FB1 and FB2 levels were below the quantification limits for 41.3% of the samples, and the mean FB1 levels (0.66 μg/g) were higher than the mean FB2 levels (0.42 μg/g). The PCR identification separated the 104 isolates into three of the G. fujikuroi complex: F. verticillioides (76%), F. subglutinans (4%) and F. proliferatum (2%); and G. zeae (anamorph = F. graminearum) (18%). Our results confirmed the dominance of F. verticillioides, similar to other regions of Brazil, but they differed due to the relatively higher incidence of F. graminearum. Total fumonisin levels were below the maximum limit determined by current Brazilian regulations.

Maize (Zea mays L.) is a vital crop susceptible to Gibberella ear rot (GER), a disease caused by Fusarium graminearum, resulting in significant yield losses and mycotoxin production. This study aimed to investigate the correlation between ear characteristics and GER resistance in 74 maize inbred lines (42 with non-stiff stalks and 32 stiff stalks) adapted to the northern Italian environment. Mycotoxin analysis was performed to assess the presence of deoxynivalenol (DON) and zearalenone (ZEA). The results showed a positive correlation between the husk traits, like the husk number and husk cover, and GER resistance in both heterotic groups. A positive correlation was also found between the DON and ZEA concentrations. In addition, we conducted a genome-wide association study (GWAS) which identified novel quantitative trait loci (QTLs) associated with the husk number, husk cover, ear attitude, and infection score. These QTLs can be utilized in marker-assisted selection for breeding new GER-resistant maize varieties. Our study provides valuable insights into the genetic basis of ear traits and their relationship with GER resistance, which can contribute to an improvement in the environmental and economical sustainability of the corn growing system.

玉米是我国最重要的农作物之一，腐霉茎腐和镰孢穗腐病是玉米生产上的重要病害。2006－2012年期间，对1647份玉米种质进行了抗肿囊腐霉茎腐病和轮枝镰孢穗腐鉴定，筛选出高抗茎腐病和穗腐病的种质分别为564和27份，占鉴定总材料的32.24%和1.64%；抗性材料分别为209和352份，占比为12.69%和21.37%，表明高抗肿囊腐霉茎腐病的资源较为丰富，高抗镰孢穗腐病的种质相对匮乏。其中，13份种质对2种病害均表现高抗， 207份种质对2种病害均表现抗性或对其中一种表现高抗而另一种表现抗性。自交系中对肿囊腐霉茎腐病和轮枝镰孢穗腐表现抗性以上（含HR和R）的种质分别占总鉴定种质的56.5%和23.6%，在农家种中分别为21.2%和21.4%，表明玉米自交系中的抗性资源较农家种丰富。2009－2013年期间参加国家玉米区试的品种中，对腐霉茎腐病表现高抗、抗性、中抗、感病和高感的品种分别占11.5%、11.9%、40.1%、17.6%和18.9%。2009－2011年间，中抗以上的育成品种所占比例呈现明显上升趋势，但2012－2013年间，中抗以上的品种所占比例呈下降趋势。

玉米是我国第一大粮食作物, 实现玉米的高产稳产对于我国粮食安全、农业稳定有重要意义。穗腐病是一种严重危害全球玉米的真菌性病害, 会造成玉米大幅减产和品质劣变。本研究选用我国玉米穗腐病的优势致病菌拟轮枝镰孢(Fusarium verticillioides), 对241份来源广泛的玉米自交系进行2年田间人工接种抗性鉴定, 同时利用20,586个高质量SNP标记通过全基因组关联分析(genome-wide association study, GWAS), 鉴定拟轮枝镰孢穗腐病抗性显著关联的SNP位点; 在此基础上选取对拟轮枝镰孢穗腐病表现高抗和高感的玉米自交系各1份, 其籽粒在室内接种拟轮枝镰孢, 通过对3个不同侵染时间的籽粒进行转录组测序(RNA-seq), 分析抗感材料差异表达基因(differentially expressed genes, DEGs)及其富集情况; 结合GWAS和RNA-seq结果, 共同定位筛选抗病候选基因。主要研究结果如下: (1) 综合2年田间抗性鉴定结果, 筛选到4份抗拟轮枝镰孢穗腐病的玉米自交系, 其中含有热带血缘的玉米种质对拟轮枝镰孢穗腐病表现出更好的抗性。(2) 2年GWAS分析共检测到26个与拟轮枝镰孢穗腐病抗性显著关联的SNP位点, 其中有18个位点位于前人定位到的QTL范围内。(3) RNA-seq结果表明, 抗感材料对病原菌的响应基因不同。与感病材料相比, 抗病材料均显示出更多的DEGs, 且都有更多的上调基因; 在抗感材料特异性DEGs共同富集的GO条目和KEGG通路中, 抗病材料中富集到的DEGs占比显著多于感病材料; 一些与植物防御病原菌相关的条目和通路也仅在抗病材料中被特异富集。(4) 在GWAS检测到的显著关联位点上下游100 kb范围内筛选与转录组DEGs共同定位到的候选基因, 结果16个基因被GWAS和RNA-seq同时检测到; 根据这些基因的蛋白功能及相关文献报道, 从中预测到6个与拟轮枝镰孢穗腐病抗性相关的候选基因。综上所述, 本研究筛选出4份抗拟轮枝镰孢穗腐病的玉米自交系, 来自热带、亚热带的玉米种质可以作为抗逆性品种选育的研究重点; 对抗感玉米自交系响应拟轮枝镰孢侵染的DEGs及其相关抗病机制进行了初步解析, 联合GWAS和RNA-seq共定位到6个与拟轮枝镰孢穗腐病抗性相关的候选基因, 研究结果为玉米穗腐病抗性基因的克隆验证与抗性品种的培育提供了一定的理论依据。

Fusarium ear rot and fumonisin contamination is a major problem facing maize growers worldwide, and host resistance is the most effective strategy to control the disease, but resistant genotypes have not been identified. In 2003, a total of 103 maize inbred lines were evaluated for Fusarium ear rot caused by Fusarium verticillioides in field trials in Ikenne and Ibadan, Nigeria. Disease was initiated from natural infection in the Ikenne trial and from artificial inoculation in the Ibadan trial. Ear rot severity ranged from 1.0 to 6.0 in both locations in 2003. Fifty-two inbred lines with disease severity ≤3 (i.e., ≤ 10% visible symptoms on ears) were selected and reevaluated in 2004 for ear rot resistance, incidence of discolored kernels, and fumonisin contamination in grain. At both locations, ear rot severity on the selected lines was significantly (P < 0.0020) higher in 2004 than in 2003. The effects of selected inbred lines on disease severity were highly significant at Ikenne (P = 0.0072) and Ibadan (P < 0.0001) in 2004. Inbred lines did not affect incidence of discolored kernels at both locations and across years except at Ikenne (P = 0.0002) in 2004. Similarly, significant effects of inbred lines on fumonisin concentration were observed only at Ikenne (P = 0.0201) in 2004. However, inbred lines 02C14585, 02C14593, 02C14603, 02C14606, 02C14624, and 02C14683 had consistently low disease severity across years and locations. Fumonisin concentration was significantly correlated with ear rot only at Ikenne (R = 0.42, P < 0.0001). Correlation between fumonisin concentration and incidence of discolored kernels was also significant at Ikenne (R = 0.39, P < 0.0001) and Ibadan (R = 0.35, P = 0.0007). At both locations, no significant inbred × year interaction was observed for fumonisin concentration. Five inbred lines, namely 02C14585, 02C14603, 02C14606, 02C14624, and 02C14683, consistently had the lowest fumonisin concentration in both trials. Two of these inbred lines, 02C14624 and 02C14585, had fumonisin levels <5.0 μg/g across years in trials where disease was initiated from both natural infection and artificial inoculation. These lines that had consistently low disease severity are useful for breeding programs to develop fumonisin resistant lines.

Fusarium ear rot (FER) incited by Fusarium verticillioides is a major disease of maize that reduces grain quality globally. Host resistance is the most suitable strategy for managing the disease. We report the results of genome-wide association study (GWAS) to detect alleles associated with increased resistance to FER in a set of 818 tropical maize inbred lines evaluated in three environments. Association tests performed using 43,424 single-nucleotide polymorphic (SNPs) markers identified 45 SNPs and 15 haplotypes that were significantly associated with FER resistance. Each associated SNP locus had relatively small additive effects on disease resistance and accounted for 1–4% of trait variation. These SNPs and haplotypes were located within or adjacent to 38 candidate genes, 21 of which were candidate genes associated with plant tolerance to stresses, including disease resistance. Linkage mapping in four biparental populations to validate GWAS results identified 15 quantitative trait loci (QTL) associated with F. verticillioides resistance. Integration of GWAS and QTL to the maize physical map showed eight colocated loci on chromosomes 2, 3, 4, 5, 9, and 10. QTL on chromosomes 2 and 9 are new. These results reveal that FER resistance is a complex trait that is conditioned by multiple genes with minor effects. The value of selection on identified markers for improving FER resistance is limited; rather, selection to combine small effect resistance alleles combined with genomic selection for polygenic background for both the target and general adaptation traits might be fruitful for increasing FER resistance in maize.

Fusarium verticillioides causes Fusarium ear rot (FER) of maize and produces fumonisins, which affects grain quality. Host-plant resistance can reduce both FER and fumonisins in maize. In this study, 18 maize inbred lines were evaluated for resistance to F. verticillioides and fumonisin accumulation at five localities in South Africa. Additive main effects and multiplicative interaction analyses revealed significant environment × genotype interactions, with inbred lines CML 390, US 2540W, RO 424W, and VO 617y-2 consistently exhibiting low FER severity (≤5.4%), fungal target DNA (≤0.1 ng μl), and fumonisin levels (≤5.6 ppm). Genotype main effect and genotype × environment biplots showed that inbred lines CML 390, US 2540W, and RO 424W were most resistant to FER, fungal colonization, and fumonisin accumulation, respectively, while inbred line RO 424W was most stable in its resistance response over environments. These inbred lines also demonstrated broad adaptability by consistently exhibiting resistance to FER, fungal colonization, and fumonisins across localities. The identified lines could serve as valuable sources of resistance against F. verticillioides and its fumonisins in local breeding programs.

Background: Fusarium verticillioides is a common maize pathogen causing ear rot (FER) and contamination of the grains with the fumonisin B1 (FB1) mycotoxin. Resistance to FER and FB1 contamination are quantitative traits, affected by environmental conditions, and completely resistant maize genotypes to the pathogen are so far unknown. In order to uncover genomic regions associated to reduced FER and FB1 contamination and identify molecular markers for assisted selection, an F-2:3 population of 188 progenies was developed crossing CO441 (resistant) and CO354 (susceptible) genotypes. FER severity and FB1 contamination content were evaluated over 2 years and sowing dates (early and late) in ears artificially inoculated with F. verticillioides by the use of either side-needle or toothpick inoculation techniques.Results: Weather conditions significantly changed in the two phenotyping seasons and FER and FB1 content distribution significantly differed in the F-3 progenies according to the year and the sowing time. Significant positive correlations (P < 0.01) were detected between FER and FB1 contamination, ranging from 0.72 to 0.81. A low positive correlation was determined between FB1 contamination and silking time (DTS). A genetic map was generated for the cross, based on 41 microsatellite markers and 342 single nucleotide polymorphisms (SNPs) derived from Genotyping-by-Sequencing (GBS). QTL analyses revealed 15 QTLs for FER, 17 QTLs for FB1 contamination and nine QTLs for DTS. Eight QTLs located on linkage group (LG) 1, 2, 3, 6, 7 and 9 were in common between FER and FB1, making possible the selection of genotypes with both low disease severity and low fumonisin contamination. Moreover, five QTLs on LGs 1, 2, 4, 5 and 9 located close to previously reported QTLs for resistance to other mycotoxigenic fungi. Finally, 24 candidate genes for resistance to F. verticillioides are proposed combining previous transcriptomic data with QTL mapping.Conclusions: This study identified a set of QTLs and candidate genes that could accelerate breeding for resistance of maize lines showing reduced disease severity and low mycotoxin contamination determined by F. verticillioides.

玉米穗腐病是一种严重危害玉米生产的真菌性病害, 而目前在世界范围内玉米育种上应用的大多数自交系缺少对穗腐病的抗性。玉米穗腐病抗性位点的挖掘和抗病基因的克隆, 对玉米穗腐病的遗传改良至关重要。本研究旨在通过转录组测序和全基因组关联分析的方法进行玉米拟轮枝镰孢菌穗腐病抗性位点的挖掘并初步确定候选基因。抗病自交系法A和感病自交系掖81162的转录组测序结果表明, 人工接种拟轮枝镰孢菌后7 d两个自交系的差异表达基因有10,761个。通过全基因组关联分析共检测到5个与穗腐病抗性显著相关的SNP, 这些SNP分布在1号和9号染色体上。通过比对B73 RefGen_v3并注释, 发现SNP位点附近涉及的基因包括酰基激活酶1过氧化物酶体、蛋白磷酸酶2C 48、镁转运蛋白、受体蛋白激酶CRINKLY4和锌指CCCH域蛋白19。将在转录组测序中获得差异表达基因和全基因组选择中关联到的基因进行比对, 发现全基因组关联分析中关联到的锌指CCCH域蛋白19同时也是转录组测序中获得的差异表达基因, 表明锌指CCCH域蛋白19可能与玉米拟轮枝镰孢菌穗腐病的抗性相关。本研究结果不仅能为抗病基因的克隆和玉米的抗病分子育种提供一定的理论依据和重要的遗传资源, 而且能为玉米和病原菌的相互作用机理的解析奠定基础。

To optimize fitness, plants must efficiently allocate their resources between growth and defense. Although phytohormone crosstalk has emerged as a major player in balancing growth and defense, the genetic basis by which plants manage this balance remains elusive. We previously identified a quantitative disease-resistance locus, qRfg2, in maize (Zea mays) that protects against the fungal disease Gibberella stalk rot. Here, through map-based cloning, we demonstrate that the causal gene at qRfg2 is ZmAuxRP1, which encodes a plastid stroma-localized auxin-regulated protein. ZmAuxRP1 responded quickly to pathogen challenge with a rapid yet transient reduction in expression that led to arrested root growth but enhanced resistance to Gibberella stalk rot and Fusarium ear rot. ZmAuxRP1 was shown to promote the biosynthesis of indole-3-acetic acid (IAA), while suppressing the formation of benzoxazinoid defense compounds. ZmAuxRP1 presumably acts as a resource regulator modulating indole-3-glycerol phosphate and/or indole flux at the branch point between the IAA and benzoxazinoid biosynthetic pathways. The concerted interplay between IAA and benzoxazinoids can regulate the growth-defense balance in a timely and efficient manner to optimize plant fitness.Copyright © 2018 The Author. Published by Elsevier Inc. All rights reserved.