Bursaphelenchus species in conifers in Europe: distribution and morphological relationships

The morphological relationship between European Bursaphelenchus species living in conifers was studied in order to provide key characters for their taxonomic identification. Several species have been newly described or recorded in Europe during the past few years and were morphologically investigated. Among the 28 conifer-inhabiting European species, four groups can be distinguished from each other by the number of lateral incisures, number and position of anal papillae of males and presence and size of a vulval flap of females. Two groups, each containing just one species show two and six lateral lines, respectively, whereas most Bursaphelenchus species belong to two groups, possessing either three or four incisures. Each of the last two groups can be divided into three subgroups, which can be differentiated by spicule shape, number and position of caudal papillae, presence and size of a vulval flap and some other features. A fifth group includes species with unclear group affiliation due to insufficient knowledge of their morphology. The B. xylophilus group ( B. xylophilus, B. mucronatus, B. fraudulentus ) with four lateral lines, unique spicule shape and characteristic position of the caudal papillae can clearly be differentiated from all other groups by morphology, also using only light microscopy. Within this group, B. xylophilus can clearly be differentiated morphologically from the other species, provided that adult specimens of both sexes are found and also provided that the round-tailed form of the species remains the only form present, as in Europe. Figures showing the important identification features of spicule shape and female tail shape are given for 28 species. A table shows the complete range of the most important morphometric measurements of these species. Data on the occurrence, host range and, as far as known, the vectors of these species were collected throughout Europe and references are given for each record.     

Distribution of Cereal and Grass Cyst Nematodes in the Federal Republic of Germany1

A survey of cereal and grass cyst nematodes in the Federal Republic of Germany revealed that Heterodera avenae is the most widely distributed heteroderid species and common mainly in areas with light sandy soils and intensive cereal cultivation. The so-called ≪race 3 ≫ was recovered several times, and other populations differing morphologically from ≪ typical ≫ H. avenae were found. H. hordecalis, H. bifenestra, H. mani, H. iri and Punctodera punctata were also recovered in many parts of the country. In arable soils these species constituted only 7 % of all records of cereal and grass cyst nematodes, whereas they prevailed in grassland, forests and other habitats, where they amounted to almost 80 % of the records. 93 % of all H. avenae records came from agricultural soils, but only 21 % of the records of the five other species. H. hordecalis and H. bifenestra are obviously of no economic importance in FRG.     

Hirschmanniella caudacrenaSher, 1968 intercepted in aquarium plants imported to Poland

Hirschmanniella caudacrena was detected in roots of aquarium plants imported from Thailand and Singapore to Poland. Morphology, morphometrics and diagnostic characters of the species are analyzed. It was shown that the ventral notch near the tail tip is a structure of two small symmetrical cuticular flaps. The significance of the tail tip structure to identify Hirschmanniella spp. pests is emphasized. Such detections indicate that aquarium plants imported from non‐European countries are an important pathway for entry to the EPPO region of the EU quarantine species of Hirschmanniella Luc & Goodey, 1963, other than H. gracilis (De Man, 1880), and deserve special attention from the plant quarantine services of EU member states.     

Winter wheat yield loss in response to Avena fatua competition and effect of reduced herbicide dose rates on seed production of this species

Journal of Plant Diseases and Protection - Avena fatua is one of the most abundant and competitive grass weed species in cereal cropping systems worldwide. Despite its main occurrence in summer...     

The impact of landscape structure and sown grass margin strips on weed assemblages in arable crops and their boundaries

A paired-field study was made in southern England in arable fields, each with or without sown 6-m wide grass margin strips. Seven field pairs were located in each of small, intermediate and open landscapes, which were based on mean field size. Ground cover, plant species diversity and assemblages were assessed in crop centres, crop edges and non-crop field boundaries. The data were used to test for effects of sown grass margins, differences in field location, impacts on rare weed species and for landscape effects on weed assemblages. Significantly higher plant species diversity was found in boundaries protected by buffer strips. Annual weeds associated with field edges, notably Anisantha sterilis , were found at lower cover where perennial grass strips were present. Sown grass strips enhanced boundary plant diversity, particularly by increasing polycarpic species. Margin strips had a small influence on the weed flora of the crop edge, possibly reducing weed cover, but had no influence on floras of field centres. Field size and landscape context did not affect weed assemblages, which show marked field-to-field variability, though crop type was an important influence. Grass margins did not enhance rare arable weed species and may be a threat to them, if margins are sited where such species are known to occur in the seedbank. With this exception, grass strips are a positive influence on boundary flora diversity and reduce margin weeds in arable landscapes.     

Cereal diseases caused by <Emphasis Type="Italic">Fusarium graminearum</Emphasis>: from biology of the pathogen to oxidative burst-related host defense responses

Small grain cereals, such as wheat, barley and oats are considered among the most important food sources. Plant-parasitic nematodes play a considerable role in decreasing cereal yields. The three-major species of cereal cyst nematodes (CCN) Heterodera avenae, H. latipons, and H. filipjevi are distributed worldwide and cause considerable damage. This review provides information regarding the global distribution of these nematode species, yield loss due to CCN, their biology and pathogenic relation to plants, identification and control through agricultural practices, biological agents and resistance breeding. As morphological identification of CCN is difficult and time-consuming, several molecular techniques for the identification of these CCN species have been developed in recent years. The restrictions on the use of nematicides demand for resistance to CCN. Resistance genes in several lines are known and are used in numerous breeding programmes against CCN; pyramiding these resistance genes into high yielding cultivars that could become commercially available for farmers is progressing.     

Long-term stability of distribution of Alopecurus myosuroides Huds. within cereal fields

The incidence of Alopecurus myosuroides seedheads was monitored annually for 10 years in the cereal fields of a 173-ha arable and dairy farm. A. myosuroides persisted at low population densities, despite the use of herbicides and grass breaks in the rotation. The distribution of the weed was irregular, with none occurring on at least 60% of the positions surveyed in the cereal fields. Spatial distributions were compared between years, and some significant correlations were found from year to year in continuous cereals, and in cereal crops separated by a 3-year grass ley.     

Transmission of barley yellow dwarf virus by cereal aphids collected from different habitats on cereal farms

Cereal aphids were collected from cereal crops, from Poa annua within cereal fields, from Lolium perenne pastures and from wild grasses in hedge bottoms and around farm buildings. The frequency of barley yellow dwarf virus (BYDV) transmission was assessed by aphid transmission tests. There were differences in transmission rates between aphid species, between host species and between years. The transmission rates of Rhopalosiphum padi from the different host species were broadly similar whereas for Sitobion avenae, P. annua within cereal fields was significantly better than the other host species. Wild grasses other than P. annua were relatively poor sources of virus. A large percentage of aphids frequently transmitted more than one strain, suggesting that host plants are often infected with more than one BYDV strain.     

植物线虫分子鉴定研究进展

植物线虫可危害农作物和林木,对它们的准确鉴定是防治植物线虫病害的基础。由于植物线虫很小,而且在形态上种间常有覆盖,而种内有较大的变异,仅依据形态特征很难鉴定。分子鉴定技术给植物线虫的检测和鉴定提供了快速、精确、可靠的方法。文章综述了植物线虫分子的DNA提取、分子鉴定靶标序列的选择及分子鉴定方法等方面的研究进展及现状,以促进对植物线虫分子鉴定更深入的研究。     

Virus-vector nematodes in cereals and fruit crops in Spain

Studies on nepoviruses and tobraviruses, and their relationships with their associated vector nematodes, are scarce in Spain. However, virus disease symptoms have often been detected and their nematode vectors are widespread in Peninsular Spain. Nepovirus vector nematodes (Longidorus attenuatus, L. coespiticola, L. elongatus, L. macrosoma, Xiphinema coxi, X. diversicaudatum, X. index, X. italiae, X. pseudocoxi and X. vuittenezi) have been found associated with fruit and cereal crops. All are also widespread in other crops and uncultivated areas, together with X. rivesi, which has not yet been found associated with fruit and cereal crops in Spain. Tobravirus vectors have been less studied in Spain. Of the five recorded species, Paratrichodorus minor and Trichodorus primitivus are present on maize and wheat respectively. The geographical and host distribution of these nematodes are given and their ecological characteristics are discussed.     

Pathogenicity, Mating Ability and DNA Restriction Fragment Length Polymorphisms of Pyricularia Populations Isolated from Gramineae, Bambusideae and Zingiberaceae Plants

Eighty-five Pyricularia isolates were collected from 29 host species of Gramineae, Bambusideae and Zingiberaceae plants sampled in Brazil, Uganda, Ivory Coast, India, Nepal, China, Indonesia and Japan. These isolates were compared on the basis of pathogenicity, mating ability and restriction fragment length polymorphisms with single-copy DNA probes. Based on the pathogenicity to eight differential gramineous plants, these isolates were classified into seven pathotypes: finger millet type, foxtail millet type, common millet type, rice type, crabgrass type, Italian ryegrass/ weeping lovegrass type, and non-cereal/grass type. Genetic variation among these isolates was assessed by RFLP analysis with two restriction enzymes and nine single-copy DNA probes isolated from a finger millet strain. An UPGMA dendrogram based on the RFLPs revealed that the 85 isolates could be classified into seven major groups. Isolates from cereal crops (finger millet, foxtail millet, common millet, wheat and rice) and a grass, Brachiaria plantaginea, were clustered into a single group. They were further divided into six subgroups corresponding to the pathotypes. Among cereal crop isolates only an isolate from pearl millet was located into a different group. The remaining isolates were clustered into five groups designated as the crabgrass group, the buffelgrass and jungle rice group, the rice cutgrass, knotroot bristlegrass and Setaria tomentosa group, the bamboo and bamboo grass group and the Zingiber mioga group. The isolates from cereal crops were generally capable of mating with finger millet strains and constituted a closed mating compatibility group. These results suggested that the isolates from cereal crops form a single group with a common ancestor although they are pathogenic to taxonomically diverse plants. A combined analysis of the pathogenicity and genetic similarity suggested that the transmission of M. grisea isolates occurs in natural agroecosystems between finger millet and Eleusine africana, goosegrass or Bambusa arundinacea, between foxtail millet and green bristlegrass, and between rice and tall fescue, Italian ryegrass, sweet vernalgrass, reed canarygrass or Oryza longistaminata. Received 9 August 1999/ Accepted in revised form 12 November 1999     

Maize–soybean intercropping effect on yield productivity,weed control and diversity in northern Ghana

The cereal–legume cropping system is a common practice across the tropical world. However, there are limited quantitative data on the effect of cereal–legume intercropping on weed species diversity. A study was conducted in the Guinea savanna zone of Ghana to evaluate the effect of maize–soybean intercropping on yield productivity and weed species control. The treatments used include three maize maturity types (extra‐early: Abontem, early: Sammaz 27 and medium: Obatanpa) intercropped with soybean at three intraspacing (10, 20 and 30 cm), and their sole crop treatments were laid in a randomized complete block design with three replications. Results showed that the land equivalent ratio (LER) for the intercrops was above 1, indicating better intercrop productivity than the sole crops. An average of 40% land was saved for the intercrops compared with the sole crops. Intercropping Sammaz 27 maize with soybean significantly increased LER by 9% compared to the other types. Intercropping maize with soybean significantly reduced weed biomass at 6 and 9 weeks after planting (WAP) and at harvest relative to the sole maize. The weed biomass at 6 and 9 WAP and harvest increased (p < .05) with increasing soybean intraspacing. The grass and broadleaf weed species count at 6 WAP and harvest from the sole crops were significantly higher than that of the intercrops. The results suggest that intercropping early maize maturity type with soybean at 10 cm intraspacing could be used to increase grain yield, LER and control of grass and broadleaf weeds in a maize‐based cropping system in the Guinea savanna zones of West Africa.     

无花果树苗中截获的无花果孢囊线虫形态和分子鉴定

上海口岸从旅客携带进境的树苗中分离到1种孢囊线虫属的2龄幼虫,通过形态特征和分子特征分析,鉴定为无花果孢囊线虫(Heterodera fici Kirjanova,1954)。该2龄幼虫的主要形态特征为:体长409.9~454.4μm;唇环3个;口针发达,长22.6~24.0μm,基部球圆形略向前倾斜;侧线4条;尾长圆锥形,末端细圆,尾部透明区长24.7~30.5μm,约占尾长的1/2。序列分析显示其ITS区序列与GenBank中无花果孢囊线虫的序列相似性为99.48%~99.90%,序列差异为1~5 bp。系统发育分析显示该线虫与无花果孢囊线虫处于一个聚类组内。这是我国口岸首次报道截获无花果孢囊线虫。     

The occurrence of Phialophora-like fungi related to Gaeumannomyces graminis under various grass species and some characteristics of these fungi1

Phialophora graminicola and Phialophora sp. (lobed hyphopodia) are weakly or not pathogenic to the cereal and grass roots which they colonize and are also known to restrict the infection of these plants by Gaeumannomyces graminis. The occurrence of these fungi under 15 field-grown grass species has been studied using wheat as the test plant. P. graminicola occurred under all grass species tested but at different population levels. The lowest populations were found under Bromus erectus and B. inermis, and relatively low populations under Agrostis alba, Festuca ovina and Phalaris arundinacea. Festuca pratensis, F. rubra, F. arundinacea, Dactylis glomerata and Arrhenatherum elatius harboured the highest populations of P. graminicola. Phialophora sp. (lobed hyphopodia) was found at low population levels under 7 of the 15 grasses examined. The strains of P. graminicola isolated in these studies differed markedly in growth rate on wheat roots and in restriction of G. graminis on wheat grown in perlite (preliminary results).     

Rapid bidirectional allele-specific PCR identification for triazine resistance in higher plants

Triazine resistance is reported to be due to chloroplast herbicide target insensitivity in most species, and this is most often caused by a Ser(264)-Gly mutation at the D1 protein. In order to ascertain whether this mutation is really predominant amongst resistant plants, and also for gene flow studies, a rapid test is needed that allows the testing of large quantities of plants. Here a bidirectional allele-specific PCR (polymerase chain reaction) identification is proposed. The designed primers were shown to be universal in the three grass and three broadleaf species examined.     

Nematode pests of some major cereals in Nigeria: Need for integration of morphological/morphometrical,biochemical, and molecular diagnostic approaches for accurate identification

Plant-parasitic nematodes pose a major threat to crop production in Nigeria. Comprehensive data on yield losses for most cereal crops are not readily available. Research on maize (Zea mays), rice (Oryza sativa), and sorghum (Sorghum bicolor) has shown an 18%–67% reduction in yield linked to the destructiveness of parasitic nematodes, particularly root-knot and root-lesion nematodes. Continuous monoculture and a conservative approach to agriculture increase the incidence and population density of nematodes, leading to higher levels of damage and losses in most cultivated cereal crops. These losses affect the food security of the growing population of Nigeria and many African countries that are heavily dependent on cereals. The accurate identification of nematodes is fundamental for effective management strategies. Nematode taxonomy based on morphology has been difficult due to intraspecific character variations coupled with the limited expertise of indigenous nematologists. Biochemical and molecular marker-based tools and approaches have allowed efficient diagnosis of most nematode species affecting cereal production globally. These approaches have proved useful due to their practicality, rapidness, accuracy, and cost-effectiveness. This review describes the important economic effects of these parasitic nematodes on cereal production and highlights the need for integrative approaches to taxonomy for accurate species identification that will improve nematode diagnosis, thereby contributing to the increase of food production in Nigeria.     

An identification guide to common whitefly pest species of the world (Homopt Aleyrodidae)

Abstract

A key is presented to aid the identification of pupal cases of 46 species of whitefly often found infesting economic plants around the world. The general pupal case morphology of each species is illustrated, together with more detailed figures of some key characters. The key is designed for use with slide‐mounted specimens, and techniques for their preparation are described. The synonymy of Bemisia hancocki with B. afer is discussed.     

The Present Position in the Systematics of Meloidogyne

The genus Meloidogyne includes 32 species. The main character used for differentiation is the posterior cuticular pattern of the female. This is difficult to define and often variable but in most species it is characteristic. The body length and length and shape of the tails of the larvae, and the head characters of males, can also be used in identification of some species. The morphological and physiological variability in the commonest species is so great as to suggest that they may be species complexes or that evolution may be proceeding at an observable rate. This results in some uncertainty in the systematics.     

Hymenoscyphus species associated with European ash1

The causative agent of dieback on European ash (Fraxinus excelsior) was first described as Chalara fraxinea based on cultural morphology because no sexual stage of the fungus was known. Later, based on culturing of ascospores of a candidate teleomorph, morphological comparison and nuclear ribosomal internal transcribed spacer sequencing, the sexual stage of C. fraxinea was assigned as Hymenoscyphus albidus, a native and widespread species in Europe. Recently, the morphological species concept of H. albidus was shown to cover two species that cannot be separated from each other based on teleomorph characters, but which can be distinguished by several DNA markers. As a result, the strains causing ash dieback were reassigned as H. pseudoalbidus. The closely related H. albidus is presumably a non‐pathogenic endophyte, but pathogenicity tests to confirm this hypothesis have not yet been performed. Genotyping of herbarium specimens has shown that H. pseudoalbidus was present in Switzerland for at least a decade prior to the epidemic outbreak in Europe. The origin of the ash dieback pathogen, and the general importance of correct pathogen identification to development of effective disease control, are discussed.