Enhanced resistance to Helicoverpa zea in tobacco expressing an activated form of maize ribosome- inactivating protein

Progeny of two transgenic tobacco (Nicotiana tabacum L.) lines that expressed an activated form of maize (Zea mays L.) ribosome-inactivating protein (RIP) had varying resistance to the insect species tested. A subset of R(2) plants from the two lines appeared to be more resistant to larvae of the cigarette beetle, Lasioderma serricorne (F.), and the tobacco hornworm, Manduca sexta (L.) than the wild type plants. Progeny (R(3)) of the more resistant R(2) plants were tested more extensively for insect resistance. Resistance to the corn earworm, Helicoverpa zea (Boddie), was most consistent, with significantly decreased feeding often accompanied by increased mortality and reduced weights of survivors fed on leaf disks of the two transgenic lines compared to the wild type. The amount of damage by H. zea was significantly inversely correlated with levels of RIP. Resistance of RIP-producing plants to H. zea was greater than expected on the basis of prior in vitro results using diet-incorporated maize RIP. The R(3) transgenic plant leaf disks were also often more resistant to feeding by larvae of L. serricorne compared to wild type plants. Although reduced feeding by M. sexta was noted when they were fed leaf disks from transgenic compared to wild type plants the first day of exposure, differences were not significant. This information provides further support for maize RIP having a role in resistance to maize-feeding insects.     

Relative activity of a tobacco hybrid expressing high levels of a tobacco anionic peroxidase and maize ribosome-inactivating protein against Helicoverpa zea and Lasioderma serricorne

Tobacco (Nicotiana tabacum) plants grown from seed obtained by crossing a tobacco line that expressed an activated maize ribosome-inactivating protein (RIP) with a line that overexpressed tobacco anionic peroxidase were tested for their effects on corn earworm Helicoverpa zea and cigarette beetle Lasioderma serricorne larvae as compared to the wild-type plant cross. Significant feeding reductions were noted for transgenic plants expressing both resistance proteins as compared to wild-type plants for both H. zea and L. serricorne. Significant increases in mortality were also noted for those insects fed on the transgenic cross as compared to wild-type plants in some cases. Levels of both peroxidase and maize RIP were significantly higher in transgenic as compared to wild-type plants (which did not produce maize RIP). The degree of feeding was significantly negatively correlated with the level of RIP or peroxidase individually.     

Long chain alkanes in silk extracts of maize genotypes with varying resistance to Fusarium graminearum

The alkane content of the silks of nine maize genotypes was analyzed to investigate the role of silk wax in resistance to Fusarium graminearum. Silk samples were collected 2, 4, 6, and 8 days after silk emergence and divided into three sections: exposed silk, silk channel silk, and silk that is under the husk and overlying the kernels. Four major unbranched alkanes (C(25), C(27), C(29), and C(31)) and three isoalkanes (C(27i), C(29i), and C(31i)) were identified. Total alkane contents were highest in the exposed silk followed by the silk channel silk, with the lowest in the youngest silk closest to the kernels. In the silk channel and overlying kernel silks, the moderately resistant inbred CO272 consistently had the highest alkane content. None of the other inbreds with improved resistance had as high a level of alkanes as CO272, indicating that alkane content is not a major mechanism of resistance.     

Identification and effects of maize silk volatiles on cultures of Aspergillus flavus

Volatiles generated from corn silks of individual genotypes of maize were found to exhibit differences in biological activities when the volatiles were exposed to 5-day solid cultures of Aspergillus flavus. In inverted potato dextrose-agar Petri plate bioassays, it was found that volatiles emitted from silks of the different maize genotypes had a profound effect on the growth of the fungus and, consequently, aflatoxin production. To determine the underlying cause for this bioactivity, volatiles emitted from the maize silks were trapped on Tenax glass columns and were analyzed by GC-MS. Aflatoxin field-resistant maize genotypes exhibited a larger relative concentration of the antifungal aldehyde, furfural (2-furancarboxaldehyde), when compared to the relative concentrations of the field-susceptible varieties tested. In a closed-container 5-day study, it was observed that fresh 1- and 4-day-old corn silk samples of aflatoxin-resistant maize genotypes emitted higher concentrations of furfural compared to those from susceptible genotypes. This observation probably explains the reason for the bioactivity observed in the in vitro bioassays, and the presence of furfural appears to contribute to a defense mechanism for protecting the developing maize kernel from fungal attack.     

Fungal growth and fusarium mycotoxin content in isogenic traditional maize and genetically modified maize grown in France and Spain

Fungi of the genus Fusarium are common fungal contaminants of maize and are also known to produce mycotoxins. Maize that has been genetically modified to express a Bt endotoxin has been used to study the effect of insect resistance on fungal infection of maize grains by Fusarium species and their related mycotoxins. Maize grain from Bt hybrids and near-isogenic traditional hybrids was collected in France and Spain from the 1999 crop, which was grown under natural conditions. According to the ergosterol level, the fungal biomass formed on Bt maize grain was 4-18 times lower than that on isogenic maize. Fumonisin B(1) grain concentrations ranged from 0.05 to 0.3 ppm for Bt maize and from 0.4 to 9 ppm for isogenic maize. Moderate to low concentrations of trichothecenes and zearalenone were measured on transgenic as well as on non-transgenic maize. Nevertheless, significant differences were obtained in certain regions. The protection of maize plants against insect damage (European corn borer and pink stem borer) through the use of Bt technology seems to be a way to reduce the contamination of maize by Fusarium species and the resultant fumonisins in maize grain grown in France and Spain.     

Oral toxicity of beta-N-acetyl hexosaminidase to insects

Insect chitin is a potential target for resistance plant proteins, but plant-derived chitin-degrading enzymes active against insects are virtually unknown. Commercial beta-N-acetylhexosaminidase (NAHA), a chitin-degrading enzyme from jack bean Canavalia ensiformis, caused significant mortality of fall armyworm Spodoptera frugiperda larvae at 75 microg/gm, but no significant mortality was noted with Aspergillus niger NAHA. Maize Zea mays callus transformed to express an Arabidopsis thaliana clone that putatively codes for NAHA caused significantly higher mortality of cigarette beetle Lasioderma serricorne larvae and significantly reduced growth rates (as reflected by survivor weights) of S. frugiperda as compared to callus that expressed control cDNAs. Tassels from model line Hi-II maize (Z. mays) plants transformed with the NAHA gene fed to S. frugiperda caused significantly higher mortality than tassels transformed to express glucuronidase; mortality was significantly correlated with NAHA expression levels detected histochemically. Leaf disks from inbred Oh43 maize plants transformed with the NAHA gene on average had significantly less feeding by caterpillars than null transformants. Leaf disks of Oh43 transformants caused significant mortality of both S. frugiperda and corn earworm Helicoverpa zea larvae, which was associated with higher expression levels of NAHA detected by isoelectric focusing, histochemically, or with antibody. Overall, these results suggest that plant NAHA has a role in insect resistance. Introduction of NAHA genes or enhancement of activity through breeding or genetic engineering has the potential to significantly reduce insect damage and thereby indirectly reduce mycotoxins that are harmful to animals and people.     

Sources of resistance to aflatoxin production in maize

Drought-tolerant maize genotypes (Huffman, Z08-004, Tuxpan, PH 9, NRC 5348, Chunco, Saint Croix, and Arizona) were compared in the field and laboratory to toxin-resistant GT-MAS:gk and Yellow Creole. SDS-PAGE, scanning electron microscopy of kernel cuticle, amount of kernel wax, Aspergillus flavus kernel colonization, Aspergillus ear rot, insect damage, aflatoxin production, and their relationships were examined. SDS-PAGE showed the presence of a 14 kDa trypsin inhibitor in the kernels of all genotypes except Chunco, which contains a protein of a larger molecular weight. The 14 kDa trypsin inhibitor protein content in these genotypes was higher than in GT-MAS:gk and Yellow Creole. Scanning electron microscopy revealed that Arizona, Huffman, and Chunco genotypes had abundant wax deposits on kernel surfaces and the amount of pericarp wax was equal to or above that from GT-MAS:gk and Yellow Creole. Differences in Aspergillus ear rot ratings, fungal colonization, and insect damage by corn earworm were observed in all drought-tolerant maize genotypes as well as in the controls. Kernel screening assays showed that aflatoxin B(1) levels in inoculated drought-tolerant genotypes differed significantly from those in GT-MAS:gk and Yellow Creole (LSD = 576). Aflatoxin B(1) levels in the inoculated genotypes differed significantly from those of GT-MAS:gk or Yellow Creole (LSD = 1389) when grown under drought stress conditions. Pearson correlation coefficients were significant between ear rot ratings and insect damage (r = 0.75; P = 0.01) and between Aspergillus ear rot and aflatoxin levels (r = 0.54; P = 0.05). On the basis of the parameters studied, there are indications that these genotypes were potential sources of A. flavus resistance.     

玉米抗玉米蚜种质的鉴定与抗性位点的定位分析

玉米蚜是世界性的玉米害虫,利用玉米自身的抗性是控制玉米蚜虫危害的重要途径。为培育抗蚜新品种,提高玉米的抗性,首先需要鉴定筛选抗性种质,明确其抗性遗传模式,发掘抗性基因。本研究首先对新收集的国内外玉米种质资源进行抗玉米蚜鉴定,然后采用分离群体分组分析与高通量测序技术相结合的方法,对鉴定出的高抗蚜玉米自交系携带的抗性位点进行了定位分析。结果表明,在98份玉米种质资源中有5份表现高抗玉米蚜,其中高抗蚜自交系32t33的抗蚜性受多基因控制,表现数量遗传特征,测序分析在第3、第5染色体上获得了2个与抗蚜性状关联的区域,其大小分别为19.66和6.34 Mb,并在关联区域初步筛选出5个抗蚜候选基因。本研究结果丰富了玉米的抗蚜基因资源,为最终分离出抗性基因、明确抗蚜的遗传机制和培育抗蚜品种奠定了基础。     

Soil organic amendment impacts on corn resistance to Helicoverpa zea: Constitutive or induced?

Earthworm produced compost or vermicompost has been shown to improve plant growth and productivity. Vermicompost amendment to the soil also results in plant resistance to arthropod pests. In the present study we used corn, Zea mays L., and the corn earworm, Helicoverpa zea Boddie (Lepidoptera: Noctuidae) to investigate the effects of two vermicompost sources Oregon (OSC) and Raleigh (Ral) and previous feeding by H. zea larvae on the response and preference of immature and adult stages of the insect to corn plants. Results from our study show that Ral and OSC vermicompost were both effective in inducing corn antixenosis (non preference) and antibiosis (lower performance) resistance to H. zea that is effective against adult (decreased oviposition) and immature insect stages (lower immature weight gain and survival), respectively. We also found that previous conspecific induction appears to have a phagostimulatory effect on larval vermicompost leaf tissue consumption, especially for the Ral treatment. Conspecific induction also buffered the resistance effects of the vermicompost resulting in a stimulatory effect on oviposition by adults. The potential factors leading to the insect responses observed are discussed within the context of previous studies evaluating vermicompost-mediated resistance to pests.     

融合坐标注意力机制的轻量级玉米花丝检测

玉米花丝性状是玉米生长状态的重要表征,也是决定玉米果穗生长进而影响玉米产量的重要因素。为了提升无人巡检机器人视觉系统对玉米花丝的检测精度和速度,该研究提出一种融合坐标注意力机制的轻量级目标检测网络YOLOX-CA。将坐标注意力机制（coordinate attention,CA）模块嵌入到YOLOX-s主干特征网络（Backbone）部分,以加强对关键特征的提取,提升检测精度;在颈部特征加强网络（Neck）部分,将特征金字塔结构中的普通卷积,更改为深度可分离卷积,在降低网络参数量的同时保证精度不丢失;在预测头（Head）部分引入GIoU(generalized intersection over union)改进定位损失函数计算,得到更为精准的预测结果。基于自建玉米花丝数据集训练和测试网络,试验结果表明,YOLOX-CA网络平均检测精确度达到97.69%,参数量低至8.35 M。在同一试验平台下,相较于YOLOX-s、YOLOv3、YOLOv4等目前主流的目标检测网络,平均检测精确度分别提升了2.21、3.22和0.64个百分点;相较于YOLOv3、YOLOv4,每帧推理时间分别缩短4...     

转Bt基因玉米自交系及其杂交种的抗螟性鉴定

采用基因枪法将Bt基因(GFM CrylA)导入东北春玉米自交系铁7922的幼胚中,获得转基因植株。经过连续3年的田间接卵、室内饲喂玉米螟鉴定,获得稳定抗虫转基因系。以此为亲本与常规自交系配制了四密25Bt、通单24Bt、吉单209Bt3个杂交种。转基因自交系和杂交种的抗螟性鉴定结果表明：转基因系间抗虫性差异极显著,同一转基因系单株间和配制的3个杂交种间抗虫性也存在差异;与对照相比,转基因系配制的杂交种抗虫性明显提高,差异显著。农艺性状鉴定结果显示,转基因系配制的杂交种与对照在株高、穗长、穗行数、行粒数、百粒重上无显著差异。本研究认为,GFM CrylA(Bt)基因可用于玉米的抗螟性改良,也为转Bt基因玉米自交系能够直接用于育种提供了依据。     

DCPTA对干旱胁迫下玉米种子萌发影响的无损检测

为探究2-(3,4-二氯苯氧基)乙基二乙胺(2-(3,4-dichlorophenoxy) ethyl triethylamine,DCPTA)在干旱胁迫下对玉米种子萌发的影响,使用聚乙二醇(polyethylene glycol-6 000,PEG-6 000)和浓度为0.5、1.0、1.5 mg/L的DCPTA混合溶液对玉米种子进行浸泡处理,采用种子标准发芽试验总结得出不同浓度的DCPTA对玉米种子发芽情况影响的规律,再结合低场核磁共振(low field nuclear magnetic resonance,LF-NMR)及核磁共振成像(magnetic resonance imaging,MRI)技术,通过研究其内部水分变化情况、水分迁移规律及水分分布特征解释造成该结果的原因。试验结果表明:一定浓度的DCPTA可以提高玉米种子萌发过程中的耐旱性能,加快种子内部水分的存储速率,提供种子萌发所需的水分条件,减轻干旱胁迫对玉米种子造成的损害。DCPTA对玉米种子干旱胁迫的缓解效果随着其浓度的升高呈现先上升后下降的趋势,以1.0 mg/L的DCPTA处理效果最显著(P<0.05)...     

Soil and foliage arthropod communities in conventional,reduced and no-tillage corn (maize,Zea mays L.) systems: A comparison after 20 years of continuous cropping

The influence of long-term (20 years) tillage - moldboard-plowed, reduced- and no-tillage practices - on soil-inhabiting and canopy arthropod communities was examined in corn (maize) systems during a 3-year period. Effects of a soil-applied insecticide (terbufos) on the anrthropod communities were also investigated. Damage by 3 major insect pest species of maize were evaluated: black cutworm, Agrotis ipsilon (Lepidoptera: Noctuidae); European corn borer, Ostrinia nubilalis (Lepidoptera: Pyralidae); corn rootworm beetles, Diabrotica spp. (Coleoptera: Chrysomelidae). Cutworm damage to corn was lowest in the conventional-tillage treatment. Damage by this species was greater in soil-applied insecticide treatments versus no-insecticide treatment. Neither tillage treatment nor insecticide usage had a significant impact on European corn borer damage to corn. Rootworm feeding on corn varied from year to year, with no discernible effect of tillage treatment on damage levels. Total numbers of microarthropods (mites and collembola) were lowest in the conventionally- (moldboard-) plowed treatments and highest in no-tillage treatments. Insecticide treatment significantly increased oribatid mite density, but consistently lowered (although not significantly so) mesostigmatid mite populations. Insecticide application had little if any noticable influence on collembolan (springtail) numbers. With macroarthropod populations, there was a trend toward greater numbers of ground beetles and spiders in the no-tillage systems. Corn rootworm and ladybird beetles (Coccinellidae) accounted for over 95% of the arthropods collected from the corn foliage. With the exception of 2 sampling dates, western corn rootworm beetle density was greater in no-tillage compared with reduced- and conventional-tillage treatments. Ladybird beetle populations were not affected by tillage or insecticide treatments.     

Diferulate content of maize sheaths is associated with resistance to the Mediterranean corn borer Sesamia nonagrioides (Lepidoptera: Noctuidae)

The leaf sheaths of selected inbred lines of maize (Zea mays L.) with variable levels of stem resistance to the Mediterranean corn borer Sesamia nonagrioides (Lefèvbre) were evaluated for antibiotic effect on insect development. Phytochemical analyses of leaf sheaths were conducted for cell wall phenylpropanoid content to gain a better understanding of maize-resistance mechanisms. Laboratory bioassays established that sheath tissues from different genotypes significantly affected the growth of neonate larvae. Three hydroxycinnamates, p-coumaric, trans-ferulic, and cis-ferulic acids, and three isomers of diferulic acid, 8-5', 8-O-4', and 8-5' b (benzofuran form), were identified. Significant negative correlations were found between larvae weight and diferulic acid content for six genotypes. These results are in agreement with previous studies concerning the role of cell wall structural components in stem borer resistance.     

硫肥用量对玉米氮硫吸收分配和产量的影响

为明确硫肥用量在作物增产方面的效应,本研究采用单因素随机区组设计,通过大田试验,设置5个硫肥(硫磺)用量,分别为0 kg(S)·hm~(-2)(S0)、40 kg(S)·hm~(-2)(S1)、80 kg(S)·hm~(-2)(S2)、120 kg(S)·hm~(-2)(S3)和160kg(S)·hm~(-2)(S4),研究不同硫肥用量对玉米产量和氮硫素吸收、分配的影响。结果表明,施用硫肥可使玉米产量增加7.0%~18.1%,S2处理玉米产量最高,为12 978.30 kg·hm~(-2)。施用硫肥能显著提高玉米各生育时期(除大喇叭口期外)植株干物质积累量。成熟期,玉米叶片、叶鞘、籽粒干物质积累量均在S2处理下达最大值,玉米茎秆、苞叶、穗轴干物质积累量均在S1处理下达最大值。整个生育期内,玉米硫素积累量和硫素吸收强度均在S2处理下达最大值,且显著高于不施硫的S0处理。成熟期时,玉米叶片硫素积累量随施硫量的增加而增加,S4处理时达最大值;玉米茎秆、苞叶、穗轴硫素积累量均在S1处理下最大;玉米叶鞘和籽粒硫素积累量则S2处理下最大。从拔节期至抽雄吐丝期,S3处理促进玉米氮素积累效果最佳;灌浆期和成熟期分别以S1和S2处理更有助于玉米氮素积累。施硫量的增加会在一定程度上降低玉米硫肥偏生产力和硫肥利用率;玉米硫肥农学利用率在S2处理下最大。玉米植株的氮素和硫素吸收累积量具有极显著相关关系。因此,适量的硫肥在提高玉米产量和氮硫吸收、分配及利用效率方面发挥着重要作用,施硫量为80 kg(S)·hm~(-2)时,整体效果最佳。     

利用无人机多光谱影像的多品种玉米成熟度监测

基于遥感监测多品种玉米成熟度进而掌握最佳收获时机，对提高其产量和品质至关重要。该研究在玉米成熟阶段获取无人机多光谱影像，同步采集叶片叶绿素含量（chlorophyll content，C）、籽粒含水率（moisture content，M）、乳线占比（proportion of milk line，P）等地面实测数据，以此构建玉米成熟度指数（maize maturity index，MMI），从而定量表征玉米成熟度。通过MMI与植被指数构建回归模型和随机森林模型，验证MMI适用性，并分析无人机遥感对不同品种玉米成熟度的监测精度。结果表明：1）不同品种玉米的叶片叶绿素含量、籽粒含水率、乳线占比的变化速率均存在差异。2）MMI与所选植被指数的相关性均可达到0.01显著水平，其中与归一化植被指数（normalized difference vegetation index，NDVI）、转换叶绿素吸收率（transformed chlorophyll absorbtion ratio index，TCARI）相关性最高，相关系数均为0.87。3）该研究基于不同组合的数据集进行了模型验证，其中随机森林模型对MMI的估测精度最高，测试集决定系数（coefficient of determination，R²）为0.84，均方根误差（root mean squared error，RMSE）为8.77%，标准均方根误差（normalized root mean squared error，nRMSE）为12.05%。此外，随机森林模型对不同品种MMI的估测精度较好，京九青贮16精度最优，其中R²、RMSE、nRMSE为0.76、10.67%、15.88%，模型精度证明了可以利用无人机平台对不同品种玉米成熟度进行监测。研究结果可为多光谱无人机实时监测农田多品种玉米成熟度的动态变化提供参考。     

Composition of forage and grain from second-generation insect-protected corn MON 89034 is equivalent to that of conventional corn (Zea mays L.)

Insect-protected corn hybrids containing Cry insecticidal proteins derived from Bacillus thuringiensis have protection from target pests and provide effective management of insect resistance. MON 89034 hybrids have been developed that produce both the Cry1A.105 and Cry2Ab2 proteins, which provide two independent modes of insecticidal action against the European corn borer ( Ostrinia nubilalis ) and other lepidopteran insect pests of corn. The composition of MON 89034 corn was compared to conventional corn by measuring proximates, fiber, and minerals in forage and by measuring proximates, fiber, amino acids, fatty acids, vitamins, minerals, antinutrients, and secondary metabolites in grain collected from 10 replicated field sites across the United States and Argentina during the 2004-2005 growing seasons. Analyses established that the forage and grain from MON 89034 are compositionally comparable to the control corn hybrid and conventional corn reference hybrids. These findings support the conclusion that MON 89034 is compositionally equivalent to conventional corn hybrids.     

Improving nutritional quality of maize proteins by expressing sense and antisense zein genes

The predominant proteins in maize grain are a family of alcohol-soluble prolamin storage proteins called zeins. They account for >50% of total seed proteins but are deficient in several essential amino acids. As a result, the corn grain is considered to be nutritionally poor for monogastric animals with respect to key essential amino acids, most notably lysine, tryptophan, and methionine. Thus, corn mutants with reduced levels of zeins, such as opaque-2 (o2), have been demonstrated to possess grain with improved nutritional quality characteristics. The o2 mutant has a superior amino acid composition and has been used through conventional breeding to develop Quality Protein Maize (QPM) for human and animal consumption in developing countries. With the understanding of molecular genetics of zeins and progress in biotechnology, an alternative approach to zein reduction is explored here. Through the targeted reduction of the 19-kDa alpha-zeins, increased levels of lysine, tryptophan, and methionine have been engineered in grain of transgenic hybrids. Currently, the agronomic properties and nutritional values of these transgenic lines are being evaluated.     

利用径向生长修复算法检测玉米根系表型

针对根系图像中的断根易导致根系表型信息难以精确获取的问题,该研究提出一种根系径向生长修复算法,并基于此进行不同抗性玉米种子根系表型对比研究。首先,采用自适应对比度增强、直方图灰度查找、椒盐去噪等对采集的根系图像进行预处理,从复杂背景中分离出根系图像;再通过YOLO-V3检测模型进行根系图像中主根根尖识别;最后,自根尖开始进行径向生长,通过分叉点主根提取策略、端点自适应修复策略实现主根图像修复,并提取主根和侧根表型信息。将普通、抗旱、抗涝、抗盐4种不同抗性的玉米种子种植于槽型扁平容器中培养14 d后取出,冲洗得到完整根系并进行图像采集。采用径向生长修复算法进行根系修复后提取根系长度和直径与根系图像修复前相比,根系长度和直径的提取精度分别由83.6%和84.4%提高至97.4%和94.8%,径向生长修复算法提取精度优于区域生长算法,适用于不同胁迫环境下玉米根系表型参数提取。在干旱环境和盐腌环境下,径向生长修复算法精度提升更明显。结果表明,本研究所提算法所提出的根系径向生长修复算法可有效提高根系图像表型信息精度,为根系表型快速提取提供参考。