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.     

Studies on the Australian Pathotype of Heterodera avenae1

Australian studies on populations of Heterodera avenae have been conducted in Victoria, Western Australia. South Australia, and New South Wales. Only one pathotype has been identified so far, and it is distinct from those recorded elsewhere. Few recognised sources of resistance in barley and oats are useable in Australian breeding programmes. The first commercially acceptable cultivars of wheat, barley, and oats resistant to cereal cyst nematode will be released in Victoria within the next year or two. Their resistances are derived from spring wheat(AUS 10894), Marocaine 079 (CI 8334), and Arena sterilis (Cc 4658) respectively.     

小麦对小麦孢囊线虫抗病性研究进展

由小麦孢囊线虫引起的小麦孢囊线虫病发生分布范围广,防治困难,严重危害我国小麦生产.在我国危害小麦的孢囊线虫主要包括禾谷孢囊线虫(Heterodera avenae)和菲利普孢囊线虫(H.filipjevi).种植抗病小麦品种是防治小麦孢囊线虫病最经济有效的措施,近10年来,我国科学家制定了小麦孢囊线虫抗性评价标准,测试...     

禾谷孢囊线虫(Heterodera avenae)的分子鉴定及抗性基因研究进展

禾谷孢囊线虫是温带禾谷类作物上的世界性重要病原线虫。本文回顾关于禾谷孢囊线虫的分子鉴定和亲缘分析等方面的研究,以及对国内外小麦品种抗性基因的筛选和应用等结果。根据上述方面的结果拟定更为合理的防治策略。     

Breeding cereals for rust resistance in Australia

Rust diseases have caused significant losses to Australian cereal crops, and continue to pose a serious threat. Because Australian cereal crop yields are generally low, genetic resistance remains the most economical means of rust control. Resistant cultivars also contribute significantly to reducing over-summer rust survival. A policy of releasing only rust resistant wheats in northern New South Wales and Queensland has resulted in industry-wide protection from rust in this region for the past 40 years. The Australian Cereal Rust Control Program conducts annual pathogenicity surveys for all cereal rust pathogens, undertakes genetic research to identify and characterize new sources of resistance, and provides a germplasm screening and enhancement service to all Australian cereal breeding groups. These three activities are interdependent, and are closely integrated with particular emphasis on linking pathology and genetics to ensure breeding outcomes. Recent changes in the wheat rust pathogens, including the development of virulences for Yr17 , Lr24 , Lr37 and Sr38 resistance genes, and the introduction of a new pathotype of the wheat stripe rust pathogen, have provided new and significant challenges for wheat rust resistance breeding. Similar challenges exist in breeding barley and oats for rust resistance. Examples are discussed to illustrate the ways in which rust isolates are providing information that can be used in breeding for rust resistance. In future, as more markers linked to durable rust resistance sources become available, it is likely that the use of marker-assisted selection will become more common-place in rust resistance breeding.     

Cereal and Grass Hosts of Some Gramineous Cyst Nematodes1

The host ranges of some British populations of cyst nematodes from cereals and grasses have been studied. The nematodes were isolated from agricultural and natural habitats. Their morphology corresponded to the Heterodera avenaeImani type, to ≪ pathotype 3 ≫, or to the H. hordecalisIlatipons type. The host series included barley, oats and wheat, some of which were known to be resistant to H. avenae pathotypes, and agricultural and wild grasses. Many of the H. avenae-resistant cereals were susceptible to pathotype 3 and to a population resembling H. avenae I mani, which had a very wide host range including grasses. The population of H. hordecalis, collected from grasses, also overcame the resistance of gene Rha2. Two populations of H. mani reproduced to a limited extent on cereals, and showed a clear preference for grass hosts. A third H. mani population reproduced only on grasses. The results draw attention to some problems in conducting and interpreting tests with many different hosts and nematodes. They reinforce the view that these gramineous cyst nematodes are a species complex, with variations in host range, as well as in morphology and biology.     

Inducible Flavone in Oats (Avena sativa) Is a Novel Defense Against Plant-Parasitic Nematodes

ABSTRACT The induction of defense compounds in oats (Avena sativa) in response to invasion by parasitic nematodes and to application of the wound hormone methyl jasmonate was examined. Oats cv. Quoll seedlings were challenged with Pratylenchus neglectus, Heterodera avenae, and Ditylenchus dipsaci and treated with 1 x 10(-4) M methyl jasmonate. Three compounds, isolated in methanolic root and shoot extracts of oats, exhibiting an absorbance spectrum typical of flavone glycosides, were induced by nematode invasion and methyl jasmonate. These were identified as flavone-C-glycosides by mass spectrometry. The effect of the flavone-C-glycosides on the invasion by and development of cereal cyst nematode H. avenae was assessed using methanolic extracts of shoots and roots from methyl jasmonate-treated plants. Both extracts impaired nematode invasion and development. When the extracts were fractionated by high voltage paper electrophoresis, only one flavone-C-glycoside, O-methyl-apigenin-C-deoxyhexoside-O-hexoside, inhibited nematode invasion. The protective effect of the induction of flavone-C-glycosides in oats by methyl jasmonate was evaluated against H. avenae and P. neglectus. Treatment with methyl jasmonate reduced invasion of both nematodes and increased plant mass, compensating for damage caused by the nematodes, and is attributed to the active flavone-C-glycoside. The active compound, O-methyl-apigenin-C-deoxyhexoside-O-hexoside, has not been implicated previously in plant defense against any pest or pathogen, and appears to provide protection against the major cereal nematodes Heterodera and Pratylenchus.     

Population Dynamics and Control of Heterodera avenae -A Review with some Original Results1

Control of Heterodera avenae should largely aim to keep densities below tolerance limits at sowing-time (in spring oats < 1 egg/g soil, in susceptible barley < 3 eggs/g soil; spring wheat is only slightly less sensitive than oats, autumn-sown cereals are more tolerant than spring-sown ones). To obtain this, knowledge of population dynamics is important. Essential items in population dynamics are the host properties of different plants (characterized by two factors which do not always covary: maximum rate of multiplication and equilibrium density of the nematode), population decline of the nematode under fallow and non-hosts and the external factors influencing these characteristics. For cereals the following host efficiency order is found: winter oats (best), spring oats, spring wheat, spring barley, winter wheat, rye. Winter barley may be close to spring barley, and maize is a bad host. Grasses are generally less good hosts than cereals and usually cause high and moderate densities of H. avenae to decline. However, especially in first-year leys, rather high equilibrium densities may sometimes be maintained. Host properties of plants vary between sites and years and also relations between hosts may change. Populations decline under fallow, non-hosts and resistant cereals, usually in the order of 70–85 96 annually. H. avenae populations are favoured by lighter soils and heavier soils with a proper structure and also by good plant nutrient conditions. Soil moisture in interaction with temperature influences population dynamics in a complex way, in which natural enemies of the nematodes may also be involved, not least certain fungi. In many fields these may keep nematode populations at harmless levels. Traditional control measures like proper crop rotations can only be used to a limited extent. The most promising approach for controlling H. avenae is an appropriate use of resistant cultivars, of which barley cultivars are also tolerant, while oat cultivars are usually very sensitive. Biological control has hitherto not been used actively. Chemical control is profitable in Australia but not under European conditions. Farmers should check the need for control through soil sample investigations or by other means.     

Assessment of the pest status of Pratylenchus curvicauda and ultrastructural changes in roots of infected wheat and barley

Pratylenchus curvicauda, which was first described in metropolitan Perth in 1991, was recently identified in grain-growing areas in Western Australia. The biology of this root-lesion nematode, and especially its pest status, is unknown. We investigated its life cycle and interaction with host plants, because such information is essential for its management. The life cycle took 45 days to complete in a wheat cultivar maintained at 23°C. Over 10 weeks, the nematode multiplied in 26 of 61 genotypes; these host plants were all cereals and included widely grown cultivars of wheat and barley. Eighteen other cereal genotypes and 13 cultivars including canola, chickpea, ryegrass, lupin, soybean, and tomato, sustained the nematodes to different degrees without multiplication. Four cover crops were not suitable hosts. The patterns of attraction of the nematodes and penetration into roots of the host and tolerant plants were similar. The nonhosts attracted fewer nematodes, none of which penetrated the roots. Browning of infected roots was atypical—it occurred late in some roots, 55 days after inoculation, and in the presence of a fungus. The nematodes were confined to, and fed from, cortical cells. The ultrastructure of infected wheat and barley cells showed typical signs of damage caused by Pratylenchus spp. and included cell disorganization and lack of membrane integrity, disintegration of cytoplasm, hypertrophy of some nuclei, and deposition of tannin-like granules. This detailed characterization of P. curvicauda–host interaction indicates the nematode is likely to be a pest of major crops, and attention should be given to its management.     

Characterization of virulence reactions for Heterodera avenae populations from two localities in Algeria

Heterodera avenae is widely distributed in areas where most cereal crops are produced in Algeria. However, the virulence of the Algerian populations of this nematode on individual cereal species and cultivars has not been well documented. The virulence of H. avenae populations from Tiaret and from Oued Smar were tested under natural outdoor conditions and in an in vitro test to determine reactions of nine barley, oat and wheat cultivars selected from the International differential assortment for identifying pathotypes of H. avenae. All nine cereal differentials expressed the same reactions to both populations. The nematodes reproduced well on the barley cultivar ‘Emir’ and the wheat cultivar ‘Capa’. Resistant entries included the barley cultivars ‘Siri’, ‘Ortolan’ and ‘Morocco’, the oat cultivars ‘Nidar II’ and ‘A. sterilis I.376’, and the wheat cultivars ‘Loros’ and ‘AUS10894’. This matrix of reactions indicated that H. avenae populations from both locations were characterized as H. avenae Group 1 pathotypes but did not conclusively distinguish among pathotypes Ha21, Ha31 or Ha81. The Cre1 gene was identified as a potentially valuable source of resistance when developing wheat cultivars intended for release into these localities.     

植物寄生线虫滞育机制研究进展

植物寄生线虫防治困难与其在土壤中存活时间和抗逆能力有直接关系。休眠或滞育是其度过逆境条件或缺乏寄主时的主要策略。根据植物寄生线虫休眠或滞育的特点和规律可确定防治的关键时期。本文就植物寄生线虫休眠或滞育的影响因素和不同寄生线虫的滞育特点, 以及一些植物寄生线虫休眠或滞育生理生化机制的研究进展进行综述, 以期为植物寄生线虫的综合防治提供新的思路。     

The classification of isolates of Gaeumannomyces graminis from wheat, rye and oats using restriction fragment length polymorphisms in families of repeated DNA sequences

Isolates of the take-all fungus, Gaeumannomyces graminis var. avenae , which affects oats, wheat and other grasses, and of G.g. var. tritici , which preferentially affects wheat, rye and barley, contain a high proportion of repeated sequences. Total DNA from 57 fungal isolates collected from many locations and different cereal hosts, and scored for virulence on wheat, rye and oats, revealed many restriction fragment length polymorphisms. These RFLP s were observed either by staining the DNA directly, by hybridization to radioactively labelled total fungal DNA , or by hybridization with labelled wheat ribosomal DNA . With only a few exceptions, the isolates with the same preferred cereal hosts showed more similar patterns of restriction fragments than isolates that had different pathogenicity properties on cereal hosts, irrespective of the geographical origins of the isolates. This was even the case for R isolates of G.g. var. tritici that were virulent on wheat and rye compared with N isolates that were virulent only on wheat. Isolates were identified by hybridizing DNA from infected root samples with ³²P-labelled total fungal DNA . The restriction fragment polymorphisms involving families of repeated sequence can therefore be used as a predictive assay for host preference of an isolate, and have probably arisen by host selection of fungal lineages. The variation between isolates in different pathogenicity groups suggests that there is little gene flow between isolates that can infect different hosts, even though they can coexist in the same field.     

Effect of invasion by cereal cyst nematode (Heterodera avenue) on the growth and development of the seminal roots of oats and barley

The effect of juvenile cereal cyst nematodes (Heterodera avenae) on the root growth of oat and barley seedlings was tested in three pot experiments. Invasion by juveniles hindered the extension of the seminal root axes of both cereals; after invasion, axes took 2–3 days to attain normal rates of extension. This response was found in susceptible and resistant cultivars. When oats and barley were exposed to continued invasion over 9 days, barley produced a larger root system than oats and was less stunted by nematode invasion. The density of nematodes per unit of root was less in barley than in oats. The effects on root growth were similar to reported responses of roots to mechanical damage.     

小麦叶内杀菌剂含量对条锈病组分的定量影响

来源于澳大利亚的２５份麦类作物抗笥材料及中国８个省市的２２个小麦品种对禾谷胞囊线虫太谷群体的抗病性测定表明,６个由硬粒小麦的品种“Ｌａｎｇｄｏｎ”与节节麦的抗性材料为亲本合成的异源六倍体小麦均表现高抗;一些含有抗病基因Ｃｃｎ－１的品种,如Ｆｅｓｔｉｇｕａｙ和Ａｕｓ１０８９４等表现感病;其它来源于澳大利亚的６份燕麦及５份大麦材料也均高抗。     

The Effects of Cultural Measures on Cereal Pests and Their Role in Integrated Pest Management

The influences of cultural control measures on invertebrate pests and their natural enemies in cereals (wheat, barley and oats) are described and discussed, with emphasis on the major pests in north-west Europe. Possibilities for additive and synergistic combinations of cultural measures are identified, together with opportunities for integrating cultural measures with chemical and biological control where appropriate. Recent studies confirm the central role of cultural control measures in integrated pest management and integrated production of cereal crops. However, cultural measures often have opposing effects on different pests as well as diseases and weeds, so that appropriate measures must be selected on the basis of an assessment of the risks from key pests, diseases and weeds. Crop rotation is not an important means of controlling cereal pests, but its use is recommended for control of cereal diseases and weeds, as well as pests of crops grown in rotation with cereals. Diversification of crops and non-crop habitats in predominantly cereal growing areas is thought to increase numbers of certain parasitoids and polyphagous predators of cereal pests. The presence of weeds or an intercrop in a field together with cereals may reduce the severity of aphid and slug damage to cereals. Trap cropping has not yet been adequately tested in wheat, barley or oats. Cover crops reduce damage by wheat bulb fly in a following wheat crop, but increase the risk of slug damage. Resistance to a wide range of cereal aphid species has been identified in wheat and barley, but in Europe, more emphasis is placed on selecting cultivars with resistance to cereal diseases rather than pest resistance. Resistance in wheat to wheat bulb fly and wheat blossom midge is recorded, and resistance to slug damage has been reported in some laboratory studies. Early sowing of winter cereals results in more damage by certain dipterous pests and increased numbers of the aphid vectors of barley yellow dwarf virus (BYDV), but early sowing results in less damage by wheat bulb fly and slugs in autumn/winter and by late infestations of aphids in summer. Avoidance of ploughing results in reduced incidence of wheat bulb fly, yellow cereal fly and aphids, but increased numbers of slugs, wheat blossom midge and bibionid larvae. Avoidance of ploughing can result in greater numbers of certain polyphagous predators, particularly in the first weeks following crop establishment. The presence of straw residues results in increased slug populations, but reduced incidence of yellow cereal fly and wheat blossom midge. Preparation of fine, firm seedbeds discourages attack by slugs and wheat bulb fly on cereals. Drilling at slightly greater depth in rough cloddy seedbeds helps to protect wheat seeds from slug damage. Nitrogen fertiliser applied in spring can help cereal plants compensate for losses by wheat bulb fly or slugs. However, nitrogen applications tend to result in increased summer infestations of aphids.     

Co-evolution of potato cyst nematodes and their hosts: implications for pathotypes and resistance1

The co-evolutionary process is believed to have resulted, through interaction of wild populations of potato cyst nematodes and their hosts in geological time, in the resistant hosts now utilized in plant breeding programmes and in nematode populations with genes for resistance-breaking or virulence. It is argued that all such interactions between highly adapted, truly parasitic plant nematodes and their hosts are likely to be governed by gene-for-gene interrelationships. Practical implications of this hypothesis are that only pathotypes (resistance-breaking races) defined against identified resistance genes are scientifically sound and of practical value; that, in the case of potato cyst nematodes, other pathotypes (Ro2, Ro3, Ro5 and Pa2 and Pa3) should be abandoned; and that oligogenically based resistance to potato cyst nematodes, especially important in providing resistance to Globodera pallida, is non-durable. Working definitions of the terms ‘pathotype’, ‘host-race’ and ‘virulence’ are provided.     

Models of incomplete selection for virulence of potato cyst nematodes caused by sex determination that depends on host resistance

Sex determination of potato cyst nematodes (Globodera rostochiensis andG. pallida) is strongly affected by host resistance. Larvae may develop more frequently into males in case of poorly compatible host parasite combinations than in case of fully compatible combinations. As a consequence, the number of males on a resistant host may be higher in case of a virulence than in case of virulence. To development into females, in contrast, virulence is more advantageous. According to logical reasoning, these conflicting interests of the two sexes may give rise to an equilibrium frequency of virulent nematodes, and therewith to incomplete selection for virulence when a resistant host is grown during a long period. This incomplete selection would manifests itself as durable partial resistance of the host.This new idea was studied theoretically for a host that is completely resistant to avirulent females on the basis of a gene-for-gene relationship. One calculation route to the equilibrium frequency of virulent nematodes was a numerical approach, by means of computer simulation, and the other route was an analytical approach, i.e. algebraic derivation.In case of excess of virulence allele a, the resistant host may even select for avirulence, according to the models. The equilibrium frequency of virulent nematodes equals 0.5/(1-α), where α represents the proportion of eggs that develop into males in case of virulence (aa) divided by that proportion in case of avirulence (Aa). If α≥0.5, then selection for virulence becomes complete. Consequences for purification of potato cyst nematodes to complete virulence are discussed.     

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.     

The Status of Heterodera avenae on Cereals in New Zealand1

The cereal cyst nematode (Heterodera avenae) was discovered in New Zealand in 1975 on wheat and oats. It was not at that time causing appreciable economic losses in yield, presumably because usual management practice incorporated a good crop rotation with lucerne. However, now that the growing of cereals has become more profitable, farmers are tending to grow consecutive cereal crops and more damage from H. avenae is being experienced. On one farm, up to 9 % of an oat crop was lost due to this nematode. The biotype has not yet been determined.     

小麦禾谷孢囊线虫湖北群体活动期特性

小麦播种时定量接种禾谷孢囊线虫（ＣＣＮ）（Ｈｅｔｅｒｏｄｅｒａａｖｅｎａｅ）的孢囊,发芽生根后进行系统观察,结果表明,该线虫在小麦生长季节中完成１代,小麦播种后２５～３５ｄ是２龄幼虫入侵幼根的高峰期,１００～１２０ｄ根内出现３龄幼虫,１１０～１３０ｄ发育成４龄幼虫,１３０～１５０ｄ根表露出白色孢囊（雌虫）。受感染的麦根,侵染点首先变褐,进而肿大,常见分叉增多,形成须根团,ＣＣＮ多居于自然含磷,钾元