Tillage Effects on the Incidence and Severity of Root and Stalk Rot of Maize Caused by Fusarium moniliforme and Macrophomina phaseolina in South-Western Nigeria

Conventional tillage methods were compared with no tillage systems for the control of root and stalk rot disease of maize caused by Macrophomina phaseolina and Fusarium moniliforme in a field with a recent history of high stalk rot incidence in south-western Nigeria. The incidence of stalk rot was significantly less under no-tillage practices than in conventionally tilled plots during the twoseason trial. Application of paraquat or burning of crop residue had no apparent influence ond isease incidence. None of the treatments affected the severity of the diseases.     

Emissions of CH4 and N2O under Different Tillage Systems from Double-Cropped Paddy Fields in Southern China

Understanding greenhouse gases (GHG) emissions is becoming increasingly important with the climate change. Most previous studies have focused on the assessment of soil organic carbon (SOC) sequestration potential and GHG emissions from agriculture. However, specific experiments assessing tillage impacts on GHG emission from double-cropped paddy fields in Southern China are relatively scarce. Therefore, the objective of this study was to assess the effects of tillage systems on methane (CH₄) and nitrous oxide (N₂O) emission in a double rice (Oryza sativa L.) cropping system. The experiment was established in 2005 in Hunan Province, China. Three tillage treatments were laid out in a randomized complete block design: conventional tillage (CT), rotary tillage (RT) and no-till (NT). Fluxes of CH₄ from different tillage treatments followed a similar trend during the two years, with a single peak emission for the early rice season and a double peak emission for the late rice season. Compared with other treatments, NT significantly reduced CH₄ emission among the rice growing seasons (P<0.05). However, much higher variations in N₂O emission were observed across the rice growing seasons due to the vulnerability of N₂O to external influences. The amount of CH₄ emission in paddy fields was much higher relative to N₂O emission. Conversion of CT to NT significantly reduced the cumulative CH₄ emission for both rice seasons compared with other treatments (P<0.05). The mean value of global warming potentials (GWPs) of CH₄ and N₂O emissions over 100 years was in the order of NT<RT<CT, which indicated NT was significantly lower than both CT and RT (P<0.05). This suggests that adoption of NT would be beneficial for GHG mitigation and could be a good option for carbon-smart agriculture in double rice cropped regions.     

Incidence of Fusarium spp. and Levels of Fumonisin B1 in Maize in Western Kenya

Maize kernel samples were collected in 1996 from smallholder farm storages in the districts of Bomet, Bungoma, Kakamega, Kericho, Kisii, Nandi, Siaya, Trans Nzoia, and Vihiga in the tropical highlands of western Kenya. Two-thirds of the samples were good-quality maize, and one-third were poor-quality maize with a high incidence of visibly diseased kernels. One hundred fifty-three maize samples were assessed for Fusarium infection by culturing kernels on a selective medium. The isolates obtained were identified to the species level based on morphology and on formation of the sexual stage in Gibberella fujikuroi mating population tests. Fusarium moniliforme (G. fujikuroi mating population A) was isolated most frequently, but F. subglutinans (G. fujikuroi mating population E), F. graminearum, F. oxysporum, F. solani, and other Fusarium species were also isolated. The high incidence of kernel infection with the fumonisin-producing species F. moniliforme indicated a potential for fumonisin contamination of Kenyan maize. However, analysis of 197 maize kernel samples by high-performance liquid chromatography found little fumonisin B₁ in most of the samples. Forty-seven percent of the samples contained fumonisin B₁ at levels above the detection limit (100 ng/g), but only 5% were above 1,000 ng/g, a proposed level of concern for human consumption. The four most-contaminated samples, with fumonisin B₁ levels ranging from 3,600 to 11,600 ng/g, were from poor-quality maize collected in the Kisii district. Many samples with a high incidence of visibly diseased kernels contained little or no fumonisin B₁, despite the presence of F. moniliforme. This result may be attributable to the inability of F. moniliforme isolates present in Kenyan maize to produce fumonisins, to the presence of other ear rot fungi, and/or to environmental conditions unfavorable for fumonisin production.     

Frequency and Incidence of Pyrenochaeta terrestris in Root Internodes of Different Maize Hybrids

The frequency and incidence of Pyrenochaeta terrestris and symptom type on the roots of each internode of four maize hybrids of different maturity groups were studied 70 days after sowing. The fungus developed in the roots of all developed internodes (from the primary to the sixth or seventh internodes of all tested hybrids). The average frequency and incidence of P. terrestris in the roots of late and medium early maturity hybrids ranged from 29.5 to 55.2% and from 11.8 to 22.7%, respectively. The highest frequency of the fungus was at the 2nd root internode (93.3%), and its greatest incidence was detected in the mesocotyl of the medium early hybrid H‐1 (56.9%). Necrosis predominated in the roots of the medium early (i.e. medium late maturity hybrids, 44.5% and 44.3%, respectively), whereas reddish pink symptoms were recorded in the roots of the late hybrids (51% and 42.5%). Because the fungus always produces a distinctive red pigment on carnation leaf agar (CLA) in a light regime, these conditions can be recommended for the reliable identification of P. terrestris, even if pycnidia are not formed. These are the first reports of the successive distribution of the fungus in each maize root internode of different hybrids, as well as the use of CLA medium in the identification of the P. terrestris.     

Biological Control of Stenocarpella maydis in Maize Seed with Antagonistic Streptomyces sp. Isolates

The effectiveness of two Streptomyces sp. isolates, isolated from maize rhizosphere soil and designated as DAUFPE 11470 and DAUFPE 14632, was evaluated in vitro and under greenhouse conditions for control of Stenocarpella maydis in maize seeds. Stenocarpella maydis incidence was detected in all subsamples of disease‐free maize seeds by in vitro survey test, and ranged from 10.8% to 65.2%. In a filter paper test with surface‐disinfected seeds inoculated with S. maydis, Streptomyces sp. isolates DAUFPE 11470 and DAUFPE 14632 significantly reduced (P ≤ 0.05) the pathogen incidence by 93.2% and 92.3%, respectively. Seed germination in the same treatments was increased by 30.0% and 28.2%, respectively. Treatments of non‐disinfected seeds with the isolates DAUFPE 11470 and DAUFPE 14632, under greenhouse conditions reduced disease incidence in the seedlings by 87.3% and 85.6%, respectively. The reductions in disease incidence in surface‐disinfected seeds were 85.0% and 83.0% for the same isolates. Seedling emergence significantly (P ≤ 0.05) increased in disinfected and non‐disinfected seeds inoculated with the Streptomyces sp. isolates. The results indicate the potential of using Streptomyces sp. isolates as an additional tool to control Stenocarpella ear rot by significantly reducing the incidence of S. maydis in maize seeds and seedlings.     

Time and Site of Inoculation of Maize for Optimum Infection of Ears by Stenocarpella maydis

The optimum inoculation position on the maize plant, and optimum time of inoculation with Stenocarpella maydis for artificial induction of ear rot were determined in field trials. The placement of a conidial suspension on the shank at silking resulted in the highest incidence of S. maydis ear rot.     

Ultrastructural Histopathology of Infection and Colonization of Maize by Stenocarpella maydis (= Diplodia maydis)

The mode of penetration and colonization of stalk, shank and leaf sheath tissues of maize by Stenocarpella maydis (=Diplodia maydis) was determined by Scanning Electron Microscopy (SEM) and Transmission Electron Microscopy (TEM) observations. Detached plant tissues, inoculated with a conidial suspension and examined by SEM at various intervals, showed that S. maydis conidia germinated on all plant material types after 5 h incubation at 30 °C. After 72 h incubation, appressoria had formed at the hyphal tips. Similar observations were recorded on plants inoculated in the glasshouse except that germination was delayed by 7 days after inoculation. TEM studies showed that penetration was affected by a penetration hypha which resulted in the inter- and intracellular colonization of the plant tissues. Colonization was accompanied by degradation of cell walls suggesting that host colonization is facilitated by enzyme activity.     

Epidemiology of Stenocarpella macrospora (Earle) Sutton on Maize in the Mid-altitude Zone of Nigeria

Disease progress of Stenocarpella macrospora (Earle) Sutton (syn. Diplodia macrospora Earle) was monitored on selected maize breeding lines over two seasons at three locations. Tagged plants were assessed at 10 day intervals for foliar lesions on a 1–9 scale and for ear rot on a 1–5 scale. The level of disease at a farm in Jos (West Africa Milk Company farm) was significantly greater than those at the other two locations (UTC Tenti and Saminaka), which had reduced or zero debris from the previous year's cultivation. There was a significant correlation between the leaf severity score and grain weight, where grain weight decreased with increasing leaf disease severity. However, no significant correlation was observed between ear rot and leaf severity. Varieties responded differently throughout the monitoring period. Late planting (1996) resulted in a significantly reduced disease incidence, but also resulted in lower grain weights. Spatial disease progress diagrams indicated that S. macrospora was initiated from random foci from which secondary spread occurred.     

耕作方式对成熟期烤烟质体色素及其降解产物含量的影响

以烤烟(Nicotiana tobacum L.)品种'吉烟9号'为材料,通过田间定位试验研究了6种耕作方式下成熟期烤烟质体色素及降解产物含量的变化规律,以揭示耕作方式影响烤烟品质的原因.结果表明:不同耕作方式之间烤烟叶绿素含量存在显著差异(P<0.05),且均显著低于传统耕作方式(对照),其叶绿素降解产物新植二烯的含量均显著高于对照(P<0.05),并以深耕+前膜后草覆盖处理最高,是对照的153.84%.在不同覆盖条件下各耕作方式的烟叶类胡萝卜素含量与对照相比则呈增加趋势,其类胡萝卜素降解产物总量显著高于对照(P<0.05),并以深耕+前膜后草覆盖处理最高,是传统耕作方式的158.61%;深耕+前膜后草覆盖处理的类胡萝卜素主要降解产物β-大马酮、巨豆三烯酮、香叶基丙酮、二氢猕猴桃内酯、法尼基丙酮的含量均较其他5个耕作方式高,该处理这些降解产物含量分别比对照显著增加47.55%、51.24%、47.54%、21.01%、56.65%(P<0.05).可见,深耕+前膜后草覆盖促进延边烟区烤烟叶片叶绿素的降解,维持较高的类胡萝卜素及其降解产物的含量,有效提高烤烟品质,是该烟区较佳的烤烟耕作模式.     

干旱胁迫和正常灌溉条件下玉米产量性状的QTL分析

产量及其产量因子是衡量玉米耐旱能力的重要性状。本研究利用Lo1067×Y i72的F2∶3家系进行产量性状的数量性状位点(QTL)的分析。结果表明,在正常水分条件和开花期干旱胁迫条件下,分别有14个QTL与产量性状穗重、粒重、轴重、百粒重、穗数、穗粒数有关。此外,还检测到7个与抗旱指数(TI)相关的QTL。各QTL所解释的表型变异在1%~78%;这些QTL以部分显性和超显性为主。不同胁迫条件下检测到的QTL不一致,说明存在显著的QTL与环境互作。     

Comparative Efficacy of Weed Control Practices for Parthenium Weed and Sunflower Crop under Varying Tillage Systems

Parthenium poses serious threat to modern crop production system and necessitate evaluating control practices for its effective management. Efficacy of different weed control practices for controlling parthenium was explored in conventional and deep tillage systems in the field conditions. Hand hoeing (20 and 35 days after emergence), S-Metolachlor (pre-emergence herbicide), sorghum straw mulch @ 5 tons ha^-1 and combination of hand hoeing and sorghum straw mulch (hand hoeing at 20 and straw mulch at 35 days after emergence) were used as weed control practice. Weedy check where no weed control measure was applied was also included in this experiment for comparison. Results concluded that the all weed management treatments significantly reduced parthenium density, its fresh and dry biomass during both the years of study as compared to weedy check. Maximum sunflower achene yield was recorded in hand hoeing (20 and 35 days after emergence) in combination with deep tillage. So, mold bold plough used for the purpose of deep tillage should be encouraged for better control of parthenium and higher achene yield of sunflower crop (3293.3 kg ha^-1 in 2017 and 3221.3 kg ha^-1 in 2018). Moreover, is also inferred that total dose of herbicide might be reduced by using hoeing and mulching in an integrated way.     

Relationship of Cob characters with Grain Morphology in Maize (Zea mays,Poaceae)

Twenty varieties of maize (Zea mays, Poaceae) were studied through 11 attributes in three to seven randomly selected plants of each variety with a view to understanding the effect of cob characters on technologically desirable grain qualities. Canonical discriminant analysis showed thatproductivity (determined by total grain weight/cob, cob diameter and average grain weight) was the most discriminating among varieties followed by round grains fraction (represented by whole top and middle flat grains, number of rows and grain count/surface area), middle flat grains (composed of middle flat grains and grain count/surface area) and shape of the cob (determined by shape index, total grain weight/cob and cob diameter), which accounted for 35.1, 18.3, 12.2, and 9.8% of the total variance, respectively. In the light of these results, tentative norms have been suggested to evolve maize varieties of superior technological properties and yet retain high productivity. A cylindrical cob of large diameter with highest number of grains/area and smallest possible number of rows together constituted an ideal combination to achieve the objectives. Such possibilities in the light of available information are discussed.     

Random Amplified Polymorphic DNA and Polymerase Chain Reaction Markers for the Differentiation and Detection of Stenocarpella maydis in Maize Seeds

The genetic relationship of 34 isolates of Stenocarpella maydis from different geographic regions in South Africa was analysed by random amplified polymorphic DNA (RAPD) and ribosomal DNA markers. Two genetic groups were differentiated by using three RAPD primers and correlated to the cultural morphology of the isolates. Of all the isolates tested, 79.4% were clustered into RAPD group I (RG I), which did not sporulate when cultured on potato dextrose agar (PDA) at 25°C for 10 days. The rest of the isolates designated as RG II sporulated on PDA medium and showed a higher genetic variation. Ribosomal DNA (rDNA) was amplified using polymerase chain reaction (PCR) with the universal primers, internal transcribed spacer (ITS) 1 and ITS 4. Restriction digestion of PCR products displayed three types (RF A, RF B and RF C) of profiles. RF A was in accordance with RG I. RF B was consistent with RG II except for one isolate, U5. However, U5 displayed a unique profile and had no restriction sites for Hpa II and Hae III. The results indicate that two distinct genetic groups exist among S. maydis isolates from maize in S. Africa. The ITS1 and ITS2 regions of rDNA were sequenced and primers were designed. The designed primer pair P1/P2 permitted a sensitive and specific detection of S. maydis .     

水分亏缺条件下玉米根系PIP2-5基因的表达(简报)

在PEG-6000模拟水分亏缺条件下,以微管蛋白基因为内参基因,水通道蛋白基因PIP2—5为检测基因,采用半定量逆转录聚合酶链式反应（RT-PCR）体系检测PIP2—5基因在玉米根系中的表达的结果表明,人工模拟水分亏缺条下PIP2—5基因表达量高于正常水分条件下的。这暗示,水分亏缺条件下细胞-细胞途径对根系吸水的贡献可能增大。     

不同水分条件下玉米株高和穗位高的QTL分析

干旱是影响玉米产量的重要因素.在干旱条件下,玉米株高和穗位高往往受到影响,因此是研究耐旱性的重要指标.本研究利用A188×91黄15的F2∶3家系,进行株高和穗位高的数量性状位点(QTL)分析.结果表明,在水分胁迫条件下,分别各有10个QTL与株高和穗位高有关;在水分充足条件下,则检测到各有6个QTL与株高和穗位高有关.各QTL解释的表型变异在7.3%～53.9%之间.位于第8染色体上的QTL个数占总QTL近50%,LOD值均大于4.6,推测该染色体存在控制玉米株高和穗位高QTL的重要区域.本研究在bnlg1812标记附近检测到在水分胁迫下同时控制株高和穗位高的QTL,解释的表型变异在20%以上,该QTL是值得进一步研究和利用的位点.     

Regulation of Cytoplasmic and Vacuolar pH in Maize Root Tips under Different Experimental Conditions

³¹P-Nuclear magnetic resonance spectra of perfused maize (Zea mays L., hybrid WW x Br 38) root tips, obtained at 10-minute intervals over 12 hours or longer, indicate that no cytoplasmic or vacuolar pH changes occur in these cells in the presence of 25 millimolar K₂SO₄, which induces extrusion of 4 to 5 microequivalents H⁺ per gram per hour. In contrast, hypoxia causes cytoplasmic acidification (0.3-0.6 pH unit) without a detectable change in vacuolar pH. The cytoplasm quickly returns to its original pH on reoxygenation. Dilute NH₄OH increases the vacuolar pH more than it does the cytoplasmic pH; after NH₄OH is removed, the vacuole recovers its original pH more slowly than does the cytoplasm. The results indicate that regulation of cytoplasmic pH and that of vacuolar pH in plant cells are separate processes.     

Morphological and Molecular Characterization of Fusarium Isolated From Maize in Syria

Maize is the third most important cereal after wheat and barley in Syria. Maize plants are attacked by several Fusarium species causing mainly stalk and ear rot of maize which poses a major impact worldwide. Identification of Fusarium species is important for disease control and for assessment of exposure risk to mycotoxines. To identify Fusarium species attacking maize in Syria, a total of 32 Fusarium isolates were recovered from maize ears collected from four different geographical regions, mainly from Ghouta surrounding Damascus. Fusarium isolates were identified based on morphology and on partial DNA sequencing of the TEF1‐α and rDNA/ITS genes. The majority (26 of 32) of these isolates was identified as F. verticillioides (subdivided into four groups), whereas three isolates turned out to be F. thapsinum, F. equiseti and F. andiyazi. The remaining three isolates were close to F. andiyazi, although further investigation is needed to confirm whether they represent a yet undescribed species. Furthermore, our results showed that sequencing the TEF1‐α gene is much more informative than sequencing of the rDNA/ITS region for Fusarium identification at the species level. PCR analysis showed that only F. verticillioides isolates were potentially fumonisin producers and that only the F. equiseti isolate was potentially trichotecene producer. This is the first report on Fusarium thapsinum, F. equiseti and F. andiyazi attacking maize in Syria.     

外引玉米种质对两种穗腐病原镰孢菌抗性鉴定

采用双牙签接种技术,2016-2017年连续2年对从美国、加拿大、罗马尼亚、德国、法国、荷兰等国家引进的177份玉米种质资源抗玉米穗腐病原拟轮枝镰孢(F.verticillioides)和禾谷镰孢(F.graminearum)进行了鉴定。结果表明,鉴定的177份玉米种质资源中,对拟轮枝镰孢表现高抗(HR)的资源2份,占总数的1.13%;抗病(R)38份,占总数的21.47%;中抗(MR)75份,占总数的42.37%;感病(S)48份,占总数的27.12%;高感(HS)14份,占总数的7.91%。177份玉米种质资源中,对禾谷镰孢(F.graminearum)表现抗病(R)12份,占鉴定资源总数的6.78%;中抗(MR)66份,占总数的37.29%;感病(S)64份,占总数的36.16%;高感(HS)35份,占总数的19.77%,未发现对禾谷镰孢菌表现高抗的材料。在177份玉米种质资源中,兼抗两种穗腐病原镰孢菌的种质资源有12份。