The Decline of Heterodera avenae Populations1

Populations of the cereal cyst nematode fail to multiply in many soils in Europe and farmers are able to grow susceptible crops intensively on infested land. Similar numbers of females develop on roots in summer in soils where numbers of the nematode increase or decline. Two fungi, Nematophthora gynophila and Verticillium chlamydosporium parasitize females on roots, prevent cyst formation, decrease fecundity, and limit nematode numbers. Formalin (38 % formaldehyde) soil drenches at 3000 1/ha reduce the activity of these fungi and populations of the nematode increase, N. gynophila is an Oomycete which infects by motile zoospores whose activity is decreased when summer rainfall is light whereas V. chlamydosporium is much less affected by soil moisture. The decline of Heterodera avenae populations is associated with large numbers of spores in soil. At present it is not possible to control the nematode by introducing these fungi into soils where they are few or absent.     

Integrated Control of Heterodera avenae1

Cereal cyst nematode is a major pathogen in southern Australia costing $40 to $80 million in lost production each year. Our research has shown that three chemicals applied with the seed in the drill row, viz. Counter (terbufos) granules, Vydate (oxamyl) as a seed dressing and Nemadi (ethylene dibromide), reduced Heterodera avenae damage and gave yield increases which are economical in the Australian wheat farming system. A plant assay of soil has been developed to assess potential damage by H. avenae before employing chemical control. Wheat yields 2 years after growing H. avenae-resistant Festiguay wheat were 0.4 to 1 t/ha higher than after other cultivars. Rotations with legumes alternating with wheat reduced damage from H. avenae. Wheat sown without cultivation (minimum tillage) resulted in less root damage from H. avenae and higher yields than when sown into cultivated soil.     

Characterization of Heterodera avenae in Spain1

Several types of Heterodera spp. belonging to the ≪ avenae ≫ group have been found in Spain on cereal crops and wild Gramineae. The morphological differences between them relate to the colour of the cysts, presence or absence and consistency of the subcrystalline layer, presence or absence and shape of the ≪ underbridge ≫ in the vulvar cone, length of the 2nd-stage larvae and shape of their stylet knobs. The value of these characters in the diagnosis of these species is discussed together with the identity of the types.     

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.     

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.     

Classification of Plants Resistant to Heterodera avenae1

Differentiation of barley plants resistant to Heterodera avenae is simple when they are completely without cysts and the number of cysts is high on a susceptible control cultivar. Problems with classification are discussed.     

Some Problems Posed by the Heterodera avenae Complex1

Cyst nematodes are sedentary parasites with limited host ranges and co-evolution with circumscribed host groups is believed to result in species complexes. A scheme for this process is given. The Heterodera avenae group is such a complex parasitising cereals and grasses. Although the group includes ten nominal species, only H. mani, H. avenae and H. avenae pathotype 3 present taxonomic problems of immediate relevance in agriculture. Application of a multivariate technique, principal co-ordinate analysis, to second-stage juvenile characters indicates that H. avercae pathotype 3 is as distinct from H. avenae as H. arenaria, an accepted species in the H. avenae group. In contrast there are difficulties with juvenile and cyst morphology in distinguishing H. mani from H. avenae.     

Polymorphisme génétique chez Heterodera avenae1

On a étudié par l'électrophorèse la variabilityé de certains enzymes avec l'idée de trouver des caractéres plus commodes pour la distinction des pathotypes. Les premiers resultats font apparaître qu' Heterodera avenae , contrairement à ce qui a été observé chez le genre voisin Meloidogyne , est très polymorphe pour les quatre premiers enzymes déjà analyses, soit: deux estérases, la malate déhydrogénase (MDH) et les phosphatases acides. Les differences d'une population à l'autre semblent pour l'instant plutôt se situer au niveau du nombre d'allèles presents et de leurs fréquences respectives dans chacune d'elles. Différents phénomènes biologiques ont été parallèlement mis en évidence comme l'≪ inbreeding ≫à faible densité de population ou la fécondation effective d'une femelle par plusieurs mâles.     

北京地区小麦禾谷孢囊线虫病发生动态调查

小麦禾谷孢囊线虫病是小麦生产上的重要病害.2010-2011年对北京地区小麦禾谷孢囊线虫的发生规律进行了定期定点调查.结果表明,禾谷孢囊线虫在北京地区全年只发生1代,夏季滞育,卵孵化高峰为4月初;2龄幼虫侵染高峰为4月上旬,3龄幼虫发育高峰为4月下旬至5月初,4龄幼虫发育高峰为5月上旬,白雌虫发育高峰为5月下旬至6月上旬,10月份播种后部分2龄幼虫就可以发生侵染并且冬前发育至3龄幼虫.本研究结果可为北京地区禾谷孢囊线虫的防治提供理论依据.     

Towards a Consistent Laboratory Assay for Resistance to Heterodera avenae1

Causes of variation in numbers of females on a cultivar are examined. These are such that an accurate assessment of resistance in the field is not possible. The method used for a laboratory assay is as follows. Seed is selected for uniformity of size and pre-germinated before sowing, when the seminal roots are about 1 cm long, in tubes of sandy loam. Tubes are opaque (2.5 cm internal diameter by 13 cm long) and are set on a base of potting compost. Seedlings are inoculated immediately with the required number of larvae in 1 mi water - for oats 50 larvae, wheat 75 larvae and barley 100 larvae. They are inoculated at the same density at 3-daily intervals on four further occasions. The aim is to produce 50 females on the most susceptible cultivar; densities have been determined from intolerant cultivars. Plants are grown under 10-h day-length at 15oC and are harvested 2 months after the last inoculation, at which time they are assessed and the valuable plants can be repotted and grown on for seed production.     

青海省小麦孢囊线虫病发生和分布特点

小麦孢囊线虫病是青海省小麦青稞产区的主要病害之一。2007-2010年,采用随机取样方法对青海省小麦孢囊线虫病的发生、分布情况进行了调查。调查结果表明,小麦孢囊线虫病主要分布在青海省西宁、海东、海北、黄南、玉树、海西州6个地区,在不同海拔、不同生态区均有分布,但不同生态区以及同一生态区不同地块间发生量差异较大。垂直分布调查结果表明,同一地块中禾谷孢囊线虫主要分布在20 cm以上的土层中。     

甘肃省小麦禾谷孢囊线虫的发生及分布

为了解甘肃省小麦孢囊线虫病发生程度和分布情况,2009-2012年于小麦抽穗至灌浆期,采用Z字形取样法,取根际0~20cm土壤,用漂浮法分离孢囊,统计100g土样的孢囊数量,用形态学方法鉴定线虫。从甘肃省12个地区50个县区,134个乡镇共采集到463个小麦田间土样。结果表明,孢囊平均检出率为47.9%,其中冬麦区孢囊平均检出率为61.5%,春麦区平均检出率为34.2%,冬麦和春麦混播区为52.3%,冬麦、春麦及冬春麦混播区平均孢囊数分别为3.5、6.8和3.9个/100g土样。其中平凉市灵台县和兰州市永登县孢囊线虫发生最为严重,个别地块每100g土样中孢囊数超过40个。根据孢囊形态学特征的观察,将甘肃省采集到的孢囊线虫鉴定为禾谷孢囊线虫(Heterodera avenae)。研究结果可为有效防治甘肃省麦类孢囊线虫病提供依据。     

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.     

燕麦孢囊线虫在田间的水平和垂直分布

为明确燕麦孢囊线虫在田间的水平和垂直分布,分别在小麦收获后玉米播种前和小麦播种前土壤翻耕后进行水平和垂直取样调查。调查结果表明,燕麦孢囊线虫在田间水平分布主要为聚集分布,翻耕对其水平分布影响不大; 小麦收获后翻耕前燕麦孢囊线虫在田间垂直分布主要分布于5～10cm处,占取样深度土层孢囊总数量的35.8%,翻耕后燕麦孢囊线虫的垂直分布主要在0～15cm的土层发生变化,0～10cm的孢囊数量下降而10～15cm的孢囊数量增加。在0～20cm土壤中,翻耕前与翻耕后孢囊数量分别占孢囊总数量的89.4%和88.6%。     

Variations in Cereal Yield Losses associated with Heterodera avenae in England and Wales1

Many field experiments in England and Wales during the past 20 years have measured cereal yield losses and established regressions of yield on numbers of Heterodera avenae. Yield benefits from soil sterilants were greatest where most H avenae was present. Isogenic selections of barley and oats resistant and susceptible to H. avenae were extensively grown to assess the losses caused by this nematode alone. In some experiments these losses were identical with those measured by nematicide use, but in others (notably where broad spectrum biocides were used) losses were greater than those attributable to H. avenae and could be explained only by the known incidence of accompanying pathogens. Some yield loss may be due to migratory nematodes, e.g. Pratylenchus spp. occurring with H. avenae. Barley and wheat yields in the last 30 years have increased by 63 and 84 % due to improvements in cultivars and farming practice. Smaller percentage loss in a high yielding crop can be as costly as large percentage loss in poor crops grown on dry light soils. Many factors - soil type, rainfall, nutrients, other pathogens etc. - can greatly modify crop responses to similar popuiation levels of H. avenae.     

旱稻孢囊线虫（Heterodera elachista）孵化特性研究

为了解旱稻孢囊线虫的孵化特性,从水稻根系及根系附近土壤分离孢囊,在室内离体条件下研究不同温度及水稻根系分泌物、土壤浸液、水稻根汁等因子对2龄幼虫孵化的影响,并观察不同温度下2龄幼虫的存活能力.结果表明:旱稻孢囊线虫孵化的适宜温度范围为28～32℃,且在该温度范围初孵2龄幼虫的存活率高、存活时间相对较长,35℃下孵化率及初孵2龄幼虫的存活率、存活时间均明显下降,40℃下无线虫孵化,20℃下孢囊线虫孵化率仅为0.9％,4℃下可延长2龄幼虫的存活时间.水稻分泌物、水稻土壤浸液和水稻20倍根汁对旱稻孢囊线虫孵化具有刺激作用,5倍根汁和4 mmol/L氯化锌溶液对线虫的孵化有抑制作用.上述结果可为制定旱稻孢囊线虫防治措施提供依据.     

Cultural Practices and their Effects on Heterodera avenae and Grain Yields of Wheat in Victoria, Australia1

The effects of various cultural practices on cereal cyst nematode (Heterodera avenae) populations, and the subsequent yield of wheat, have been studied over many seasons in Victoria, Australia. Crop rotations which include periods of fallow, or of non-host crop reduce population levels and improve yields. The inclusion of a legume has the additional advantage of improving soil nitrogen levels. Early sown crops (April/May) are less severely damaged, and produce better yields, than late sown crops (June/July). The resowing of damaged wheat crops with either wheat or barley is not effective in improving yields, although cyst numbers are lower on resown crops. Nitrogenous fertilisers are not generally applied to cereals, and although small increases in yield are sometimes obtained, they are rarely economic. Sulphate of ammonia applications increase cyst numbers, especially when applied at seeding, but urea has only a marginal effect on cyst numbers.     

小麦禾谷胞囊线虫(Heterodera avenae)的核糖体基因(rDNA)限制性片段长度多态性研究

 采用PCR技术扩增出中国和摩洛哥禾谷胞囊线虫群体的核糖体基因(rDNA)的内转录间隔区(ITS)片段的长度约为1 060 bp。用11种限制性内切酶(RE)酶切禾谷胞囊线虫ITS扩增产物,共产生27个酶切片段。用AluI和RsaI酶切ITS扩增产物证明中国禾谷胞囊线虫ITS属于"B型",而摩洛哥禾谷胞囊线虫ITS属于"A型"。用HinfI酶切后,7个中国禾谷胞囊线虫群体产生2个RFLP片段(860和200 bp),而摩洛哥群体产生3个RFLP片段(520、340和200 bp),HinfI揭示出中国与摩洛哥禾谷胞囊线虫ITS之间存在差异。AvaI和HindⅢ不能酶切禾谷胞囊线虫ITS。用CfoI、Bsh1236I、MsrFI、ScrFI、HaeⅢ和MvaI 6种RE酶切中国和摩洛哥禾谷胞囊线虫群体的rDNA-ITS,均分别得到相同类型的RFLP分布型,因此这6种RE不能揭示中国与摩洛哥群体的rDNA-ITS的差异。     

禾谷孢囊线虫与不同小麦根系的互作表型特征

为了明确高抗品种‘华麦1号’的抗禾谷孢囊线虫机制,以Pluronic F-127胶体为介质,比较了禾谷孢囊线虫2龄幼虫(J2)侵入根系前对抗病品种‘华麦1号’与感病品种‘豫麦34’和‘矮抗58’的根尖趋性差异,并采用室内人工接种法观察了线虫侵入3个品种后的发育进程。结果表明,J2对3个品种的根尖均表现明显的趋性,对‘矮抗58’的趋性最强,而对‘华麦1号’的最弱,接种4h和6h时‘华麦1号’与‘矮抗58’根尖吸引的线虫总量差异显著(P0.05);组织染色观察到J2对3个品种的根系均有一定数量的侵入,但高抗品种‘华麦1号’根系侵入的幼虫量和后期形成的白雌虫量均显著低于感病品种‘豫麦34’和‘矮抗58’。结果证实,‘华麦1号’的抗性机制主要表现为减少线虫的有效侵入量、抑制侵入后的线虫生长发育。