Uromyces Viciae-fabae Haustorium Formation in Susceptible and Resistant Faba Bean Lines

Haustorium formation by the faba bean rust (Uromyces viciae-fabae) was studied on susceptible and resistant faba bean lines. The resistant lines showed incomplete resistance, based on late acting hypersensitivity or on non-hypersensitive resistance acting before haustorium formation. Histological observations on infected leaves showed that both the number of haustoria per infection unit and their developmental stage was reduced in both resistant lines. Isolation of haustoria confirmed that both the number and the size of haustoria were reduced in resistant lines, irrespective of whether the resistance was associated with hypersensitivity. Plant age had no detectable effect on both parameters.     

Role of Aeciospores in Outbreaks of Pea (Pisum sativum) Rust (Uromyces fabae)

Aeciospores in Uromyces fabae were found to be repeating spores and play an important role in pea rust outbreaks in the North Eastern Plain Zone (NEPZ) of India. Experiments conducted on pea rust from 2001 to 2004 revealed the dominance of aeciospores at all growth stages of pea in this region. Urediospore production was erratic and was only observed in a few samples of stems and tendrils (5–10%). Inoculation of pea plants either by aeciospores or urediospores resulted in the production of aeciospores. Production of aeciospores was observed at a temperature range of 10–25 °C, with a maximum at 25 ± 2 °C. Among the different growth stages of pea, the pod formation stage was highly susceptible and produced the maximum number (744) of aecidia/leaf at 20–25 °C. Significant effects of growth stages and temperature were also noticed for pustule number. Urediospore production mainly coincided with the senescence of the pea plants. Maximum germination (2%) of aeciospores was observed at 25 °C, whereas maximum urediospore germination (3.5%) was at 15 °C. Temperatures > 15 °C decreased urediospore germination. A relative humidity (RH) of 100% was favourable for aeciospore germination while 98% RH favoured urediospore germination. Typical histo-pathological behaviour of the aeciospores was observed.     

Field Resistance to Willow Leaf Rust Melampsora epitea in Inter- and Intraspecific Hybrids of Salix viminalis and S. dasyclados

Families of interspecific hybrids between Salix dasyclados and S. viminalis, and intraspecific hybrids of the two species, were monitored for rust infection caused by Melampsora epitea during the years 1997–1999. The resistance of interspecific hybrids was compared to intraspecific pure species halfsibs. In addition, uredospores were sampled from the most infected interspecific hybrids to determine whether rust from interspecific hybrids differed from the rust spores that infected the pure species. The results from 1997 and 1999 showed that interspecific hybrids were more resistant than the intraspecific pure species, thus exhibiting a pattern of hybrid resistance. In 1998 the interspecific hybrids showed intermediate resistance compared to intraspecific pure species hybrids, i.e., an additive pattern of resistance. The rust sampled from the interspecific hybrids consisted of the same types of rust that infect the pure species. Comparisons of weather conditions prevailing during the three growing seasons indicated that these conditions might play a role in the infection pattern, in addition to the level of sensitivity to infection shown by the plants.     

菜豆锈菌侵染过程的显微和超微观察

 本文报道了通过微分干涉衬显微镜、荧光显微镜及扫描电镜和透射电镜所观察到的菜豆锈菌的侵入和扩展过程。菜豆锈菌夏孢子萌发多产生1个芽管,偶尔也产生双芽管。芽管以气孔侵入为主,也可从表皮直接侵入。侵入前形成或不形成明显的附着胞。气孔侵入的芽管首先在气孔腔内形成气孔下囊,再进一步分化出圆形的膨大体,由膨大体产生1~2支初生菌丝。初生菌丝与叶肉细胞壁接触后分化出吸器母细胞,吸器母细胞进入叶肉细胞内部形成吸器。初生侵染菌丝在产生吸器母细胞的部位的后部产生分枝,形成次生侵染菌丝在叶肉细胞间蔓延。     

进境美国苜蓿草携带的真菌种类鉴定

为明确美国苜蓿草携带的真菌有害生物种类并为评估其风险奠定基础,从广东和江苏口岸进境的美国苜蓿草中挑拣出茎杆上有明显褐色至黑色斑点的可疑病害样品635份,经分离培养,获得菌株1382株。经鉴定,共有真菌37属52种,其中鞭毛菌1种,接合菌1种,子囊菌3种,担子菌1种,半知菌46种。     

豌豆蚜为害下CO2浓度升高对两种不同固氮能力蒺藜苜蓿间接防御的影响

大气CO_2浓度升高增加了豆科植物的光合作用和生物固氮能力,从而改变植物对初生和次生代谢产物的资源配置,进而影响植物与昆虫互作。为了明确CO_2浓度升高条件下豆科植物对蚜虫间接防御的影响,利用蒺藜苜蓿Medicago truncatula固氮突变体dnf1和野生型植株Jemalong研究CO_2浓度升高对不同固氮能力蒺藜苜蓿挥发物释放的影响,从而改变蒺藜苜蓿对豌豆蚜Acyrthosiphon pisum的间接防御。结果表明,豌豆蚜为害显著诱导蒺藜苜蓿野生型和固氮突变体中单萜类化合物4-蒈烯、倍半萜类挥发物(E)-β-法呢烯以及绿叶挥发物顺式-3-己烯-1-醇的释放。CO_2浓度升高降低了野生型Jemalong受害植株上2-蒈烯和柠檬烯以及绿叶挥发物顺式-3-己烯-1-醇的释放量,却没有改变固氮突变体dnf1上这几种单萜类及绿叶挥发物的释放。正常CO_2浓度下,固氮突变体dnf1受害植株上2-蒈烯、4-蒈烯、柠檬烯的释放量与野生型Jemalong受害植株无显著差异,而CO_2浓度升高条件下固氮突变体dnf1受害植株上2-蒈烯、4-蒈烯、柠檬烯的释放量显著高于野生型Jemalong受害植株。表明CO_2浓度升高条件下豆科植物对蚜虫的间接防御降低。     

The use of host resistance in disease management of rust in common bean

Bean rust, caused by Uramyces appendiculatus, is one of the major diseases in dry and snap bean production world-wide. Numerous advancements in disease management have been made to reduce rust losses. Host resistance is an important component of rust management. However, durability of disease resistance has often been short due to the use of single genes for resistance interacting with extremely high virulence diversity of the bean rust fungus. The challenge to increase durability of resistance has led to strategies such as gene pyramiding of race-specific resistance, selection and use of partial resistance, and investigation and discovery of leaf morphological features that may slow the rust epidemic. Germplasm with multiple sources of rust resistance has been developed in specific bean seed classes and released for public and commercial use in intensive production systems such as those in the United States. However, progress to develop rust resistant germplasm for the subsistence agriculture of Latin America and Africa where intercropping and mixed cultivars dominate the production system has been slow. Incorporation of high yielding, disease-resistant components as partial replacement in farmer's mixtures has the potential to reduce severity in the crop and increase yield in the presence of rust. This strategy would not erode the genetic diversity that is historically known to enhance resistance durability and for many years has given stability in production in the subsistent agriculture systems.     

43个中国小麦品种(系)抗叶锈性研究

 选用12个墨西哥叶锈菌生理小种对43个中国小麦品种(系)所携带的抗叶锈病基因进行了推导,在25个品种(系)中推导出6个抗叶锈基因Lr1,Lr10,Lr13,Lr14a,Lr16和Lr26,9个品种(系)对本试验所使有的12个叶锈菌生理小种都表现感病反应,另有9个品种(系)携带未知的抗叶锈基因。在墨西哥2个地点进行的田间成株期抗叶锈性试验表明,12个品种(系)表现慢叶锈性,在将来的抗病育种中有一定的应用价值。     

Resistance to acylalanine fungicides in Phytophthora megasperma f.sp. medicaginis

Isolates ofPhytophthora megasperma f. sp.medicaginis resistant to the systemic fungicide metalaxyl were obtained by mycelial adaptation and by mass selection from zoospores either untreated or treated with UV irradiation or with the chemical mutagenN-methyl-N-nitro-N-nitrosoguanidine. In an assay with one-week-old lucerne seedlings all of 19 spontaneously obtained isolates showed a relatively low degree of resistance and were less virulent than the original isolate. Only one of these isolates showed resistance in vivo in this test. From 176 highly resistant isolates obtained after mutagenic treatment, 81 were as virulent as the orginal isolate and 33 of the latter displayed a considerable degree of resistance in vivo.Metalaxyl at a concentration of a.i. in soil of 20 mg.l^–1 failed to control root rot of 7–8 week old lucerne plants inoculated with mycelial fragments of virulent resistant isolates. Under similar conditions root rot caused by the original isolate was completely prevented even at a concentration of a.i. of 2.5 mg.l^–1.The resistance to metalaxyl appeared to be highly stable since virulent and resistant strains did not loose their resistance after 12 infection cycles in a seedling assay in the absence of the fungicide, neither did mixed populations of a resistant and a sensitive isolate under similar conditions.The likelihood of development of resistance to acylalanine fungicides under practical conditions is discussed.Samenvatting VanPhytophthora megasperma f. sp.medicagninis, een wortelpathogeen van luzerne, konden tegen metalaxyl resistente isolaten worden verkregen na adaptatie van mycelium en selectie uit, zoösporen die al dan niet behandeld waren met het chemisch mutagensN-methyl-N-nitro-N-nitrosoguanidine. Alle 19 spontaan verkregen isolaten vertoonden een lage graad van resistentie en hun virulentie in een zaailingentest was lager dan van het oorspronkelijke isolaat. Slechts één van deze isolaten vertoonde resistentie in vivo. Bij toetsing van 176 isolaten met een hoge graad van resistentie die na een mutagene behandeling waren verkregen bleek dat 81 isolaten even virulent waren als het oorspronkelijke isolaat en dat er 33 een aanzienlijke graad van resistentie in vivo te zien gaven.Metalaxyl in een a.i. concentratie van 20 mg.l^–1 grond kon het optreden van wortelrot bij 7–8 weken oude luzerne planten niet verhinderen, wanneer deze werden geinoculeerd met gefragmenteerd mycelium van resistente isolaten. Onder dezelfde omstandigheden kon het oorspronkelijke isolaat reeds volledig worden bestreden bij een a.i.-dosering van 2.5 mg.l^–1.Resistentie tegen metalaxyl bleek een zeer stabiele eigenschap te zijn omdat bij een viertal getoetste stammen de resistentie niet verdween na 12 infectiecycli in een zaalingentest bij afwezigheid van het fungicide.Onder deze omstandigheden bleek ook dat de resistente stammen niet verdwenen uit mengpopulaties van een gevoelige en een resistente stam hetgeen erop wijst dat de virulentie van de resistente isolaten van hetzelfde niveau is als dat van het oorspronkelijke isolaat.Op grond van de gevonden resultaten mag de mogelijkhei tot resistentieontwikkeling tegen acylalanine fungiciden in de praktijk aanwezig worden geacht.     

谷子抗病基因同源序列的克隆与分析

谷子锈病是谷子上的一种流行性强、毁灭性大的病害,严重影响谷子生产.种植抗病品种是防治锈病最经济有效的方法,但谷子抗锈病种质资源非 常贫乏,而且高抗锈病的材料其农艺性状又很差.很难通过传统育种方法培育抗锈病品种,因此克隆谷子抗锈病基因尤为重要.目前克隆到的许多植 物抗病基因编码的氨基酸序列都有一定的保守结构域.根据抗病基因保守结构域,已克隆的抗病基因主要分为5类,其中最主要的是NBS-LRR(nu- leotide-binding site leucine-rich epeat)和STK(Se-rine／Threonine protein kinase)类.因而根据抗病基因保守结构域设计引物,从植物的DNA中扩增植物的抗病基因同源序列RGA(resistance geneanalogs)更加快捷有效,目前通过RGA方法克隆植物抗病基因已有报道[1,2].     

Induction of Systemic Acquired Resistance in Pepper Plants by Acibenzolar-S-methyl against Bacterial Spot Disease

The ability of acibenzolar-S-methyl to induce resistance in pepper plants against Xanthomonas campestris pv. vesicatoria was investigated in both growth chamber and open field conditions. Growth chamber experiments showed that acibenzolar-S-methyl (300M) treatment protects pepper plants systemically and locally against X. campestris pv. vesicatoria. Evidence for this was a reduction in the number and diameter of bacterial spots and bacterial growth in planta. Systemic protection was also exerted by the acibenzolar-S-methyl acid derivative, CGA 210007, which may be produced by hydrolysis in the plant. The efficacy of acibenzolar-S-methyl was also found in open field conditions, where both leaves and fruit were protected from the disease. The highest efficacy (about 67%) was obtained by spraying the plants 6–7 times every 8–12 days with a mixture of acibenzolar-S-methyl and copper hydroxide (2.5 + 40ghl^–1 active ingredient). Persistence and translocation data obtained from the growth chamber experiments revealed a persistence of acibenzolar-S-methyl lasting five days after treatment with rapid translocation and negligible levels of acid derivative formation. Since the protection exerted by acibenzolar-S-methyl against bacterial spot disease was observed when the inducer was completely degraded, it would appear to be due to SAR activation.     

蚕豆和豌豆锈病病原菌的分子鉴定

为明确我国热带和亚热带地区蚕豆Vicia faba和豌豆Pisum sativum锈病的病原菌种类,通过致病性测定和ITS序列系统发育分析对来自我国云南省玉溪市的4份豌豆锈菌分离物及云南、广西、重庆和四川省(区、市)的5份蚕豆锈菌分离物进行系统鉴定。结果显示,分离自豌豆的锈菌WX1分离物对蚕豆和豌豆均具有高致病性,在侵染叶片上产生大量锈子器;分离自蚕豆的锈菌CX3分离物仅对蚕豆具有高致病性,能在叶片上产生大量夏孢子,而对豌豆的致病性相对较低,仅产生少量的夏孢子堆;分离物WX1和CX3对小扁豆和鹰嘴豆不具有致病性。基于ITS序列系统发育分析表明,所有不同寄主来源的蚕豆单胞锈菌分离物均聚类于一个系统发育组,但分离自蚕豆和豌豆的分离物分别聚类在不同的亚组。表明分离自云南省玉溪市豌豆上的蚕豆单胞锈菌Uromyces viciae-fabae应为豌豆专化型,定名为U. viciae-fabae ex P. sativaum,而来源于云南、广西、重庆和四川省(区、市)的蚕豆锈病病原菌为蚕豆专化型U. viciae-fabae ex V. faba。     

北京地区粘虫对5种杀虫剂的抗药性

采用浸叶法测定了北京地区6个粘虫Mythimna separata(Walker)田间种群对5种不同类型杀虫剂的抗药性。结果表明:与相对敏感品系相比,6个田间种群对5种杀虫剂均表现出不同程度的抗性水平。其中,对氯虫苯甲酰胺(抗性倍数为1.314~4.213)、甲氨基阿维菌素苯甲酸盐(抗性倍数为1.000~4.385)和毒死蜱(抗性倍数为1.083~5.936)表现为敏感至低水平抗性;对虫螨腈(抗性倍数为1.355~20.80)和氯氟氰菊酯(抗性倍数为1.748~13.98)表现为敏感至中等水平抗性。因此,北京地区的粘虫防治应注重将氯虫苯甲酰胺、甲氨基阿维菌素苯甲酸盐和毒死蜱与虫螨腈或氯氟氰菊酯交替或轮换使用,以延缓抗药性的产生与发展。     

Resistance toLeveillula Taurica mildew (=Oidiopsis taurica) inCapsicum annuum

Several studies ofLeveillula taurica have been carried out in India, France, Israel and the USA. This report describes a promising source ofL. taurica resistance that can be incorporated into Mediterranean pepper cultivars. The present data suggest that full resistance depends on three pairs of genes.     

A Greenhouse Test for Screening Sugar Beet (Beta Vulgaris) for Resistance to Rhizoctonia Solani

Rhizoctonia solani Kühn is a serious plant pathogenic fungus, causing various types of damage to sugar beet (Beta vulgaris L.). In Europe, the disease is spreading and becoming a threat for the growing of this crop. Plant resistance seems to be the most practical and economical way to control the disease. Experiments were carried out to optimise a greenhouse procedure to screen plants of sugar beet for resistance to R. solani. In the first experiment, two susceptible accessions were evaluated for root and leaf symptoms, after being grown in seven different soil mixtures and inoculated with R. solani. The fungus infected all plants. It was concluded that leaf symptoms were not reliable for the rating of disease severity. Statistically significant differences between the soil mixtures were observed, and there were no significant differences between the two accessions. The two soil mixtures, showing the most severe disease symptoms, were selected for a second experiment, including both resistant and susceptible accessions. As in the first experiment, root symptoms were recorded using a 1–7 scale, and a significant expression of resistance was observed. The average severity of the disease in the greenhouse experiment generally was comparable with the infection in field experiments, and the ranking of the accessions was the same in the two types of experiments. It was concluded that evaluation procedures in the greenhouse could be used as a rapid assay to screen sugar beet plants for resistance to R. solani.     

Study of Resistance to Orobanche ramosa in Host (Oilseed Rape and Carrot) and Non-host (Maize) Plants

Orobanche ramosa is a parasitic Angiosperm responsible for severe yield losses in several economical crops. It is a serious threat in oilseed rape in France and Morocco and is appearing in carrot crops in Morocco. In this study, several varieties of oilseed rape and carrot were screened in order to identify resistant cultivars and to characterize the resistance mechanisms involved. All the 15 oilseed rape varieties tested were susceptible. In carrot, the varieties 'Colmar à coeur rouge' and 'Nantaise demi-longue' were susceptible, whereas 'Palaiseau' and 'Buror' were resistant. In the susceptible 'Colmar à coeur rouge' carrot no defence reactions were found and the development of the parasite inhibited carrot tap root formation. In the resistant carrot varieties, the parasite germinated, became attached to the host root but became necrotic before emergence. In 'Buror' carrot, formation of a mechanical barrier was associated with the restriction to the cortex of the parasite. In maize cv. 'Vigni', a non-host of O. ramosa, thickening of xylem vessels, cell divisions in the central cylinder and formation of an encapsulation layer were observed in association with restricted development of Orobanche haustoria.     

Evidence that a Leaf-Disk Test Allows Assessment of Isolate-Specific Resistance in Brassica oleracea Crops Against Downy Mildew (Peronospora parasitica)

A rapid resistance/susceptibility test for Peronospora parasitica (downy mildew) was established by inoculating leaf-disks of four Brassica oleracea accessions. Several conditions were tested: disk disinfection or not, agar medium with or without nutrients and with 50 or 100 ppm of benzimidazole. Using disinfected disks placed on agar (no nutrient and benzimidazole at 50 or 100 ppm), the responses of leaf-disks to four isolates were similar to those obtained using the classical cotyledon test, whereas undesired contaminations occurred in all other conditions. The possible effect of the particular leaf used for obtaining the disks was also studied. In each incompatible interaction tested, disks were resistant whatever the leaf used. In compatible interactions, susceptible phenotypes were observed on disks derived from the six lowest leaves, but disks from upper leaves were resistant. The genetic basis of resistance in a F1 hybrid broccoli was assessed, by testing six isolates on an F2 population derived from this hybrid. The cotyledon test only allows inoculation of two isolates per seedling, whereas many isolates can be tested on each plant by using leaf-disks. The segregation of the resistance to each of the six isolates was analysed: two dominant genes (tightly linked) control resistance to all isolates (one to five isolates; the other to only one isolate).     

Resistance Reaction of Conifer Species (European Larch, Norway Spruce, Scots Pine) to Infection by Selected Necrotrophic Damping-off Pathogens

Three conifer species (European larch, Norway spruce, Scots pine) were investigated for their resistance to five damping-off pathogens (Rhizoctonia solani, Fusarium solani, F. oxysporum, F. culmorum, F. avenaceum). Inoculation of the primary roots of seedlings with these pathogens caused host cell death which did not prevent the invasive growth of these fungi; seedlings that had formed secondary and tertiary roots could overcome the infection to a significant degree. Infections with R. solani caused significant mortality to all the conifer species. In contrast, the tree species expressed different levels of resistance when challenged with the Fusarium isolates, with Norway spruce being the most resistant compared to uninoculated controls. Some of the Fusarium isolates were more pathogenic to certain hosts than others; F. oxysporum for European larch, F. avenaceum for Scots pine, F. solani for European larch; only F. culmorum was significantly pathogenic to Norway spruce. No significant differences in disease severity were observed at different soil pH (4.3–7.5). Disease progression was delayed at lower (10–15°C) rather than higher temperatures (20–25°C).     

Enhancement of Postharvest Disease Resistance in Ya Li Pear (Pyrus bretschneideri) Fruit by Salicylic Acid Sprays on the Trees during Fruit Growth

The Ya Li pear (Pyrus bretschneideri) trees were sprayed three times with 2.5 mM salicylic acid (SA) around 30, 60 and 90 days after full flowering. The fruit were harvested at commercial maturity (about 120 days after full flowering), inoculated with Penicillium expansum, and incubated at 20 °C, 95–100% RH. The results showed that resistance to the pathogen of the mature pear fruit was remarkably enhanced by the SA sprays. Disease incidence in the SA-treated fruit was 58.0% or 26.5%, and lesion diameter on SA-treated fruit was 58.4% or 29.0% lower than that in/on fruit without SA treatment (control) on day 12 or 17 after incubation, respectively. The SA spray applied to the trees around 30 days after full flowering notably enhanced accumulation of hydrogen peroxide in the young fruit. Meanwhile, activities of defense enzymes, including peroxidase, phenylalanine ammonia-lyase (PAL), chitinase or β-1,3-glucanase in the young fruit from SA-treated trees was 29.5%, 60.0%, 24.4% or 35.7% higher than that in the control fruit 4 days after the SA spraying. Furthermore, after harvest, activities of PAL, chitinase and β-1,3-glucanase were still significantly higher in the mature pear fruit from the trees sprayed three times with SA than those of the control fruit. Activities of the antioxidant enzymes including catalase and ascorbate peroxidase in the young fruit were significantly reduced by SA spraying. However, the activity of another antioxidant enzyme, glutathione reductase in the young fruit was significantly enhanced by SA spraying. These results suggest that enzymes exerting their functions in different ways may be coordinately regulated by SA in the pear fruit. Our study indicates that treatment of SA sprays on the trees may provide further protection against postharvest disease of Ya Li pear fruit in practice and could be used as an alternative and economical approach to reduce application of chemical fungicides.