In vitro standardisation of resistance screening methods in cassava against tuber rot disease

Cassava tuber rot caused by Phytophthora palmivora in growing regions of Tamil Nadu and Kerala, is causing yield loss up to 80%. In the present study, resistance reactions of 10 cassava cultivars were analysed on leaf, stem and tuberous roots by artificial inoculation method in search of a suitable in vitro resistant screening method. Leaf and tuber analysis showed positive correlation (0.883) but the stem-based results showed negative correlation with leaf and tuber analysis. The analysis exhibited the susceptibility of the cassava cultivars against P. palmivora. Leaf analysis was superior in discriminating even small variations in resistance reactions than tuber analysis. The cultivar Sree Padmanabha showed higher resistance than other cultivars and the level of resistance in a cultivar is heritable which could be helpful in breeding programme. Based on the results it can be concluded that leaves of cassava could be used for screening resistance in the host and also in analysing the virulence of the isolate. This is the first report on screening the resistance in cassava cultivars against root rot caused by P. palmivora.     

内生真菌印度梨形孢诱导小麦抗根腐病作用研究

【目的】明确印度梨形孢(Piriformospora indica)诱导小麦对根腐病产生抗性的作用机制。【方法】用印度梨形孢悬液浸种,以无菌培养液为对照,用病原菌禾谷镰孢菌(Fusarium graminearum)侵染小麦,对其相关生理生化指标及转录组变化进行分析。【结果】禾谷镰孢菌能诱导小麦产生过氧化氢,降低细胞内水含量,破坏细胞膜的稳定性;根部定殖印度梨形孢的小麦细胞内抗氧化酶活性增强,活性氧自由基含量降低,胞内水含量提高,细胞膜稳定性增强;印度梨形孢定殖能改变由于病原菌引起的mRNA转录组变化,抗性相关基因的表达增强。综合表明印度梨形孢定殖能有效地提高小麦对禾谷镰孢菌的抗性。【结论】研究结果为深入理解植物与微生物互作、开发新型高效环保抗根腐病生物制剂提供理论和实验依据。     

蓖麻根腐病抗性鉴定及其SSR标记的初步建立

蓖麻根腐病是茄腐镰孢菌(Fusarium solani)引起的根部病害,严重影响蓖麻产量。抗源缺乏制约了抗病品种的选育。为寻找抗病种质、建立抗性分子标记,该研究对252份蓖麻材料的抗性进行了表型和分子标记鉴定。结果表明:(1)浓度为1×10⁶个·mL^-1的孢子悬浮液灌根是一种有效的接种方法; 以接种后枯萎天数为基础的5级评价法,可作为鉴定标准。(2)鉴定出130份抗病材料,其中高抗为105份。(3)野生材料中抗病材料比率(66%)远高于栽培材料(35%),建议将野生材料,尤其是中国华南野生材料的研究利用作为今后抗病育种的重要方向。(4)初步建立了8个与抗性关联的SSR标记。该研究结果提供了有效的根腐病抗性鉴定方法和评价标准,筛选出了一批育种迫切需要的抗病基因资源,初步建立了可用于辅助选择的SSR标记,为蓖麻抗根腐病育种奠定了重要基础。     

Screening of certain barley lines for resistance to root rot disease caused by Fusarium graminearum

This investigation was conducted in 2005/2006 and 2006/2007 to test 235 barley lines plus two varieties Giza 127 and Giza 128 for resistance and susceptibility to Fusarium graminearum. All screened barley lines showed varied significant degrees of infestation to root rot pathogen. A screening system is described for identifying barley lines which are effective in controlling resistant or susceptible lines. By detecting small but consistent differences in root rot severity, the bioassay proved effective in large-scale screening for partial resistance: already 335 barley lines and two varieties have been screened. We found five groups (7.12%), 22 barley lines and both varieties are resistant (R) (8.31%); 28 barley lines are moderately resistant (MR) (19.29%); 65 barley lines are moderately susceptible (MS) (27.89%); 94 barley lines are susceptible (S) and (37.39%) 126 barley lines are highly susceptible (HS). The high degree of precision makes this an invaluable tool in the understanding of pathogen aggressiveness, host specialisation and parasitic fitness. Disease scale was strongly negative and had moderate correlation with germination (?0.309?? and ?0.649??) under normal and disease treatment. The correlation between yield and normal and disease treatment during two seasons was strong and negative (?0.834?? and ?0.847??, respectively were detected).     

Disease resistance characterisation of improved cassava genotypes to cassava mosaic disease at different ecozones

Twenty-two cassava genotypes and eight controls were evaluated in two cropping seasons for resistance to cassava mosaic disease (CMD) at the International Institute of Tropical Agriculture (IITA) fields, located at different ecozones of Nigeria. Disease incidence (DI) and index of symptom severity data were obtained monthly at each location and genotype. Symptomatic leaves were also collected during evaluation at each location, and virus was indexed by amplification in polymerase chain reaction. Significant differences within and across locations were observed in the reactions of cassava genotypes to CMD. DI across cassava genotypes was significantly (p = 0.05) highest in the Ibadan (22.6%), followed by Onne (19.3%). Generally, plants of clones 96/0860, 96/1439, 96/0160, 96/1089A, 96/1632, 96/1613, 96/1708, 96/0191, 96/0249 and 96/1565 had significantly lower values of DI in each location. African cassava mosaic virus in single infection was the predominant causal agent of CMD in IITA experimental fields under study.     

Identification of two RAPD markers tightly linked with the Nicotiana debneyi gene for resistance to black root rot of tobacco

Linkage of randomly amplified polymorphic DNA (RAPD) markers with a single dominant gene for resistance to black root rot (Chalara elegans Nag Raj and Kendrick; Syn. Thielaviopsis basicola [Berk. and Broome] Ferraris) of tobacco (Nicotiana tabacum L.), which was transferred from N. debneyi Domin, was investigated in this study. There were 2594 repeatable RAPD fragments generated by 441 primers on DNAs of Delgold tobacco, a BC₅F₈ near isogenic line (NIL) carrying the resistance gene in a Delgold background, and PB19, the donor parent of the resistance gene. Only 7 of these primers produced eight RAPD markers polymorphic between Delgold and PB19, indicating there are few RAPD polymorphisms between them despite relatively dissimilar pedigrees. Five of the eight RAPD markers were not polymorphic between Delgold and the NIL. All of these markers proved to be unlinked with the resistance gene in F₂ linkage tests. Of the remaining three RAPD markers polymorphic between Delgold and the NIL, two were shown to be strongly linked with the resistance gene; one in coupling and the other in repulsion. Application of the two RAPDs in the elimination of linkage drag associated with the N. debneyi resistance gene and marker-assisted selection for the breeding of new tobacco cultivars with the resistance gene is discussed.     

大豆种质对疫霉根腐病抗性特点研究

对1027份中国和国外引进的大豆种质进行了大豆疫霉(Phytophthora sojae)根腐病的抗病性鉴定评价.结果表明,中国大豆种质的抗病性高于国外引进种质;中国南方的大豆种质抗病性较北方种质强,长江流域大豆中抗病种质比率最高,其次为黄淮海流域种质,而东北地区抗病种质较少;不同省份大豆种质的总体抗病性差异明显;育成品系的抗性好于改良品种和农家种,但不同省份来源的农家种、品系和品种抗性存在差异,黑龙江材料抗病性最低,这也是该省大豆疫霉根腐病严重发生的重要原因之一;在大豆籽粒脐色为黄色和褐色的材料中,抗病种质较多.     

云南金铁锁根腐病病原菌的分离及鉴定

金铁锁(Psammosilene tunicoides)是西南地区重要的民族民间药物、云南白药等中成药的主要原料药。为分离并鉴定云南金铁锁根腐病病原菌,该研究采用微生物纯培养方法,分离纯化金铁锁根腐病植株根部的病健交接处组织,获得金铁锁根腐病病原微生物。按照Koch''s法则验证分离得到的病原菌的致病性。结合形态学观察、真菌rDNA-ITS和TEF-1α序列分析以及系统发育树的构建鉴定获得的病原菌的种类。结果表明:(1)从金铁锁根腐病植株组织中分离纯化得到85株真菌,其中PSD-1、PSD-2、PSD-3菌株均能引起金铁锁的根腐病。(2)金铁锁健康植株接种PSD-1、PSD-2、PSD-3菌株后,产生与大田植株根腐病相似的症状,并且发病率分别为60%、61.7%、71.7%。(3)结合形态学观察及基因序列分析,鉴定该三株菌株均为尖孢镰刀菌(Fusarium oxysporum)。该文首次报道了尖孢镰刀菌是引起金铁锁根腐病的主要病原菌之一,为深入探究具有根腐病生物防治功能的内生菌群及其作用机制奠定了基础,也为后续金铁锁病害的防治工作提供了理论依据。     

Screening cassava for resistance to cassava mosaic disease by grafting and whitefly inoculation

Screening for cassava mosaic begomoviruses (CMBs)-resistance using grafting and whitefly inoculation was performed with local and improved cassava. The onset of symptom appearance and the evolution of Cassava mosaic disease (CMD) varied in function of genotypes and virus inoculation techniques used. Grafting position using cassava as scion or rootstock does not affect CMD display and evolution. No relation was established between the number of whiteflies feeding on each genotype and viral inoculation technique tested. Detopping of young leaves induces triggering effect on CMD expression. PCR and ELISA confirmed the EACMV-UG's preferential transmission by whitefly. Hypothesis of virus replication and cultivars's susceptibility were supported by virus increasing particles in infected cassava. Cultivars Mvuazi (TMSI 95/0528) and 96/1089A are suggested field immune to CMBs; Disanka (TMSI 95/0211), Yauma, Timolo, Bangi, Mahungu (TMS 92/297), Mvuama (TMS 83/138), Lueki (TMS 91/377) and Zizila (MV 99/0038) are CMD-resistant; whereas Ponjo, Lofiongi, Ngonga and Mboloko are susceptible. Our results showed that resistant genotypes may express CMD under high inoculum pressure such as grafting.     

Performances of improved cassava (Manihot esculenta Crantz) cultivars against root rot disease and yield in cassava-maize intercropping systems under natural infection

This study examined the performances of 21 cassava cultivars in two cropping seasons on the field against root rot disease and the yield in cassava-maize intercrop. Data were collected on number of root/plant, weight of root (t/ha) and disease severity (DS) on rotted roots at 12 and 16 months after planting (MAP), respectively. There were significant (P ≤ 0.05) differences for DS at 12 and 16 MAP in both seasons with cultivar TMS 97/JW2 having the least DS score. TMS 97/JW2 was resistant to the root rot pathogen, while eleven other cultivars were moderately resistant to the disease at 16 MAP. There was no consistency in the roots weight for the cultivars over the two cropping seasons but higher roots weight was recorded at 16 MAP than 12 MAP with different cultivars having highest roots weight at these periods. Intercropping maize with cassava does not have any management potential on root rot development.     

Effects of the Nicotiana debneyi black root rot resistance factor on agronomic and chemical traits in burley tobacco

Summary Lines isogenic or near isogenic for traits other than resistance to black root rot from Nicotiana debneyi were developed in eight cultivar backgrounds of burley tobacco (N. tabacum L.). For each cultivar background, a resistant and susceptible selection from the seventh backcross generation plus the recurrent parental cultivar were evaluated for ten agronomic and chemical traits. Resistant selections were statistically different from the susceptible entries for days to flower, total nitrogen content, and total alkaloid content. Also, resistant selections were consistently lower in yield, but the differences were statistically nonsignificant. Resistant selections were also taller in three families and in two families the resistant selections had wider leaves. Linkage of genetic material from N. debneyi with the resistance factor was suggested as the possible reason for differences between resistant and susceptible selections.     

In vitro,greenhouse and field assessments of cassava lines for resistance to anthracnose disease caused by Colletotrichum gloeosporioides f.sp. manihotis

Fifty-three cassava lines were selected from breeding populations at the International Institute of Tropical Agriculture (IITA), Ibadan, Nigeria and screened in vitro for resistance to cassava anthracnose disease (CAD). The in vitro inoculation of stem cuttings with the fungus Colletotrichum gloeosporioides f.sp. manihotis showed significant differences (p ± 0.05) in acervuli production and in the sensitivity of the cassava lines to the fungal infection after 7 days of incubation at 25 °C. Cassava lines 88/01084, 91/00595, 91/00475, 91/00344, 91/00684, 91/00313, 91/00422, and 91/00344 were highly resistant, with necrotic lesion sizes less than 7 mm. In contrast pedigree lines 88/02549, 89/0008, 91/00390 and 91/00402 were highly susceptible with the largest necrotic lesion size being greater than 20 mm. Ten cassava lines from the in vitro screening that showed varying levels of resistance to CAD were selected, based on their flowering abilities for diallel hydridization trials, and were further screened in greenhouse and field trials for CAD resistance. The greenhouse and field screening showed significant varietal differences (p ± 0.05) in sensitivity to the fungus. In all cases, the progeny lines showed correlated levels of resistance irrespective of the type of screening or assessments. Correlation analysis of the in vitro, greenhouse and field assessments showed that there was a good correspondence among all three methods of evaluating for CAD. This revised version was published online in June 2006 with corrections to the Cover Date.     

Interaction between zinc nutritional status of cereals and Rhizoctonia root rot severity

An inverse correlation between plant Zn concentration and the severity of Rhizoctonia root rot, described in an earlier paper, was examined in two experiments in a growth chamber. In the first experiment, wheat (Triticum aestivum cv Songlen) was planted in a Zn deficient soil with and without added Zn, and combined factorially with different inoculum densities of Rhizoctonia solani anastomosis group 8. When Zn was added, the percentage of seminal roots infected with R. solani was significantly lower compared to the treatments without added Zn, showing that low Zn potentiated the disease. A subsequent factorial experiment of four inoculum densities and six Zn levels, (0, 0.01, 0.04, 0.1, 0.4 and 6.0 mg Zn kg^–1 soil) was conducted to investigate the Zn effect in more detail. Disease severity was markedly decreased by the higher Zn applications; the disease score dropped sharply between treatments of Zn_0.04 and Zn_0.1, a difference which was reflected in the plant yield response to Zn. For both experiments the Zn concentrations in shoots were significantly different only among Zn treatments, not among the inoculum treatments. This indicated that inoculum density or disease severity did not reduce Zn concentration in the plant. Thus, disease did not exaggerate Zn deficiency, but rather, Zn sufficiency suppressed disease severity. A potentiating link between Zn nutrition and disease severity is thereby established, although this type of experiment did not indicate the mechanism of the Zn effect.     

自然林下与田间根腐三七根际微生物群落特征及比较分析

【背景】三七根际微生物群落特征与其土传根腐病害密切相关,而针对自然林下根腐三七的相关研究鲜见报道。【目的】比较分析自然林下与田间根腐三七根际土壤微生物群落的组成特征,结合土壤理化性质与酶活性分析,为三七根腐病害防治与仿野生栽培提供科学依据。【方法】采集自然林下与田间根腐三七根际土壤,利用高通量测序技术,分析土壤细菌与真菌群落的物种组成与多样性,并测定土壤理化性质和酶活性。【结果】自然林下与田间根腐三七根际土壤中细菌和真菌群落组成具有明显差异,自然林下根腐三七根际土壤中担子菌门(Basidiomycota)、酸杆菌门(Acidobacteria)和疣微菌门(Verrucomicrobia)的相对丰度较高,而田间根腐三七根际土壤中子囊菌门(Ascomycota)、变形菌门(Proteobacteria)和绿弯菌门(Chloroflexi)的相对丰度较高。在属分类水平,镰刀菌属(Fusarium)是自然林下根腐三七根际土壤中的优势菌群,相对丰度为17.30%,而癣囊腔菌属(Plectosphaerella)是田间根腐三七根际土壤中的优势菌群,相对丰度为22.55%;Candidatus Ba...     

Genetics of nonsenescence and charcoal rot resistance in sorghum

Summary Nonsenescence is a delayed leaf and plant death resistance mechanism in sorghum that circumvents the detrimental effects of reduced soil moisture combined with high temperatures during post-anthesis growth. This drought-tolerance mechanism is often equated with charcoal rot resistance, a widespread root and stalk disease of great destructive potential. Therefore, the inheritance of charcoal rot resistance was investigated directly, by exposure of sorghum to Macrophomina phaseolina, the causal organism, and indirectly, by determination of the inheritance of nonsenescence. Sorghum families derived from diallel crosses between two nonsenescent, resistant inbreds (B35, SC599-11E) and two senescent, susceptible inbreds (BTx378, BTx623) were evaluated in 1989 at College Station and at Lubbock, Texas, under controlled and field conditions. We determined that nonsenescence was regulated by dominant and recessive epistatic interactions between two nonsenescence-inducing loci and a third locus with modifying effects. The same conclusion was reached for charcoal rot resistance. The presence of different genetic mechanisms within SC599-11E for nonsenescence and charcoal rot resistance verifies that these two forms of resistance are not different manifestations of a single trait, i.e., they are not to be equated with each other. We conclude that nonsenescence alone cannot account for, and should not be used as the sole breeding criterion for, resistance to charcoal rot in sorghum.     

一种由粉红粘帚霉引起的青稞根腐病

[背景]根腐病在青稞生产中的危害日趋严重,阻碍了青稞根腐病的有效防控及青海省青稞产业的发展。然而人们对青稞根腐病的研究甚少且病原菌不详。[目的]明确青稞根腐病发生的危害、病原及致病性,为青稞根腐病的防控提供理论依据。[方法]采用常规的组织分离法分离青稞根腐病病原,通过形态鉴定与分子鉴定结合的方法对病原进行鉴定,并采用烧杯水琼脂法测定其致病性。[结果]共分离得到4株青稞根腐病病原菌,鉴定为Clonostachys rosea,有较强的致病性且致病性差异显著,经柯赫氏法则验证为青稞根腐病病原菌,并且是一种新的青稞根腐病病原,该类根腐病也是一种新的根腐类病害,在国内外属首次发现。[结论]Clonostachys rosea可引起青稞根腐病且致病性强。     

Assessment of partial resistance to powdery mildew in hexaploid wheat genotypes

In the present study the degree of partial resistance (PR) of eleven hexaploid wheat (Triticum aestivum L.) genotypes was evaluated in laboratory (ratio of infection units in stage of second germ tube elongation versus stage of appressorium formation — ESH/App) and field conditions (calculating area under the disease progress curve — AUDPC). Based on the obtained data, genotypes with high degree of PR (Estica, GK Csornoc and Lívia), middle-resistant genotypes (Sana, Mv Vilma and Folio), genotypes with low portion of PR (Barbara, Torysa and Proteinka), and supersensitive genotypes (Renesansa and Am22/99) were differentiated. Both approaches appeared to be suitable for PR measuring with a good discriminating capability between the given genotypes. The results were equivalent in both instances. In addition, a new statistical approach permitting comparison of the obtained data is described.     

Observations on the teleomorph of the white root rot fungus,Rosellinia necatrix, and a related fungus,Rosellinia aquila

The process of teleomorph development in the white root rot fungusRosellinia necatrix is described on diseased roots of Japanese pear. Stromata were also found on dead plants in nonagricultural lands such as yards and forests. The stroma ofR. aquila is also described. Research based on the program for Promotion of Basic Research Activities for Innovative Biosciences.     

一株花椒根腐病拮抗菌的筛选、发酵条件及其抑菌物质的初步分析

【背景】腐皮镰孢(Fusarium solani)是陇南花椒根腐病的主要病原物,是危害花椒生产的重要原因之一。【目的】筛选拮抗腐皮镰孢的生防菌株,为开发防治花椒根腐病的微生物农药提供新的生物资源。【方法】采用平板对峙法结合16S rRNA基因序列分析等方法从花椒根围中分离具有较强抑菌效果的细菌并进行筛选鉴定;通过Box-Benhnken中心组合设计试验探究该菌最佳发酵条件;采用液质联用(LC-MS)方法对该菌发酵液的有机溶剂提取相进行非靶向代谢组学分析及KEGG、Lipidmaps数据库注释。【结果】分离筛选出一株拮抗菌株贝莱斯芽胞杆菌(Bacillus velezensis) W-1,该菌株对腐皮镰孢的抑菌率为89%,对藤仓赤霉(Gibberella fujikuroi)、禾谷镰孢(Fusarium graminearum)、梅毒镰孢(Fusarium syphilis)、层生镰孢(Fusarium proliferatum)和松针刺盘孢(Colletotrichum fioriniae)的抑制率为57%-90%。优化后W-1的最佳发酵条件为pH值6.5、温度30℃、接种量5%、转速...     

Pink root rot,a revised name of brown root rot of gentian,and the causal fungi,Pyrenochaeta gentianicola sp. nov. andP. terrestris in Japan

Cultivated gentian (Gentiana scabra var.buergeri) has been seriously damaged by pink root rot since the 1970s. Diseased plants finally collapse after wilting and stunting. More than 40 fungal genera were found to be associated with roots of mature and immature diseased plants or seeds. Among these fungi,Pyrenochaeta gentianicola sp. nov. andP. terrestris were almost always associated with the diseased plants. Their morphologies and temperature responses were compared, and their pathogenicity was also demonstrated by artificial inoculation tests.Part of this work was conducted at the National Institute of Agricultural Sciences (presently National Institute of Agro-Environmental Sciences), Tsukuba S.C., Ibaraki 305, Japan by T. Watanabe.