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.     

Resistance of Cereals to Heterodera avenae: Methods of Investigation, Sources and Inheritance of Resistance1

Techniques used in cereal breeding programmes for selecting for resistance to cereal cyst nematodes are described. Routine screening is done in field nurseries and in pots of infested soil in glasshouse and controlled environments. Other investigations of resistance use a laboratory technique which permits identification of the penetration sites of individual nematodes. Erosion of resistance, as indicated by 1) the development of only one or two females or 2) the occasional development of more females on plants with resistance genes, is discussed in relation to variation in nematode virulence and to environmental, especially temperature effects. Identification of tolerance is more difficult unless the differences are great, or the experimentation carefully controlled and replicated. Direct selection for tolerance in segregating generations is not presently practicable. Indirectly selecting for mechanisms of tolerance may eventually prove possible but has not yet been exploited. Available sources of resistance are described in relation to genetic studies and complementary studies of nematode pathotype and host range. There are three distinct resistances in barley which may have been responsible for selecting present pathotypes. Two, Rha1 and Rha2, are useful in breeding and linkage and allelism at these loci are described. In oats, as in wheat, only one locus has been used by breeders. There are probably additional loci in some of the other resistance sources but polyploidy of the host and different virulence gene frequencies in unselected nematode populations make it more difficult to identify genetic relationships in oats and wheat.     

Phosphite Inhibits Development of the Nematodes Heterodera avenae and Meloidogyne marylandi in Cereals

ABSTRACT Phosphonic acid (H(3)PO(3)) solutions were applied to wheat or to bristle oat as soil drenches before inoculation with juveniles of the sedentary, endoparasitic nematodes Heterodera avenae or Meloidogyne marylandi. All the solutions, which were pH adjusted and added at levels as low as 0.63 mg of phosphite (HPO(3)(2-)) per plant, reduced the numbers of H. avenae females and M. marylandi egg masses. Phosphate (PO(4)(3-)), applied as potassium phosphate at the same concentrations, did not reduce the number of female nematodes on the wheat. Addition of phosphate to the phosphite solutions did not change the inhibitory effect of phosphite on H. avenae, but it reduced phosphite's effect on M. marylandi. Phosphite also reduced the number of H. avenae females when applied as many as 20 days after addition of nematodes. The phosphite treatment did not prevent M. marylandi juveniles from penetrating wheat roots or inducing giant cells. However, phosphite inhibited giant cell development: 14 days after inoculation, the giant cells in the phosphite-treated wheat were almost completely vacuolated, whereas those in untreated wheat contained dense cytoplasm.     

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.     

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.     

Heredity of Heterodera avenae Resistance Originating from two Barley Cultivars and one Spring Wheat Cultivar1

Two spring barley cultivars Bajo Aragon-1-1 and Martin 403-2 from the cyst nematode test assortment were each crossed with a susceptible, a pathotype-11 -resistant, and a pathotype-11 and 12-resistant cultivar, as well as with each other. A spring wheat cultivar, AUS 10894, from the cyst nematode test assortment was crossed with a susceptible and a resistant cultivar. From these crosses F! and F₂ single plants were tested against pathotype 12 and/or pathotype 11 of Heterodera avenae in Denmark. Some plants of the spring barley cultivar Bajo Aragon-1-1 have two resistance genes, which probably are both dominant, but it is not out of the question that one might be recessive. Each gene is inherited independently of the other or with low linkage frequency. Neither gene is the same as or allelic to the resistance gene in the cultivar Ortolan, but one gene is allelic to or the same as the 191 gene in the cultivar Siri. The spring barley cv. Martin 403-2 has one dominant resistance gene which is not allelic to or the same as the resistance gene in Ortolan but is the same as or allelic to the 191 gene in the cultivar Siri. It is possible that there is one more gene, which might be recessive against pathotype 11. The spring wheat cv. AUS 10894 has one dominant resistance gene which might be the same as or allelic to the Loros gene.     

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.     

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。     

The Effect of Environment on Survival and Hatching of Heterodera avenae1

Eggs within cysts of Heterodera avenae are able to survive long periods of desiccation and can be held for several years at 5oC when stored at low relative humidity. While this provides an excellent means of storing the nematode for use in laboratory experiments, field experiments show that desiccated eggs are readily dispersed by wind. Tolerance to desiccation is similar in free and encysted eggs, which hatch at the same rate. When eggs are desiccated, water is withdrawn from the larva within the egg shell. If cysts are exposed to conditions favouring eclosion, subsequent desiccation reduces egg viability and larval emergence. The importance of defining pre-test conditions in survival studies is emphasized, and differences in the physiological state of eggs may explain different observations in Australian and European studies.     

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。     

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.     

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.     

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.     

内蒙古中西部地区小麦禾谷孢囊线虫的发生分布

2005—2008年调查了内蒙古中西部地区7个盟市的20个春小麦种植区,共采集分离并鉴定了255份根际土壤和根系。调查结果表明,禾谷孢囊线虫（Heterodera avenae Woll.）在呼和浩特市、乌兰察布市、包头市、巴彦淖尔市、鄂尔多斯市、锡林郭勒盟等地区都有分布。其中,在乌兰察布市的察哈尔中旗、呼和浩特市的内蒙古农科院和内蒙古农业大学农场禾谷孢囊线虫虫口密度最大,每250 g土壤的孢囊平均含量分别达到了38.4、29.4个和16.4个。     

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。     

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.     

Yield Loss Caused by Heterodera avenae in Cereal Crops Grown in a Mediterranean Climate1

In south-eastern Australia, where large areas of cereal crops are grown in a Mediterranean climate, yield loss caused by Heterodera avenae is generally more severe than in Northern Europe. This appears to be due to differences in seasonal cropping patterns and the stages of crop growth when roots are exposed to larvae. Field observations and laboratory experiments show that, in Australia, crops ≪ sown early ≫, in late autumn, are less damaged than those ≪ sown late ≫. This is explained by the times of emergence and population density of larvae, by the nematode-fungus interaction and by the environmental conditions affecting plant growth, rather than by differences in the nematode or in host tolerance.