Current options in integrated management of plant-parasitic nematodes

Efficient management of plant-parasitic nematodes requires the carefully integrated combination of several methods. Although each individual method of management has a limited use, together, they help in reducing the nematode populations in agricultural soils or in plants. A public desire for methods of managing plant pests in ways that do not pollute or otherwise degrade the environment has increased concomitantly with progress in research. Integrated pest management (IPM) provides a working methodology for pest management in sustainable agriculutural systems. In this paper, current methods for the management of plant-parasitic nematodes are discussed within the guidelines of IPM. The emphasis is on the methods by which decisions are made to manage nematode problems with the most effective and widely used management strategies. The advantages and difficulties associated with nematicidal chemicals (i.e. cost, reinfestation of soil after harvest, contamination of ground water and residues in fruits and vegetables), biological control (by predatory or parasitic fungi and nematodes) and management with cultural methods (including the use of uncontaminated plants or seeds, crop rotation, modification of sowing and/or harvesting times, trap crops and resistant varieties etc.) are considered     

Rice nematode problems in Nigeria: Their occurrence,distribution and pathogenesis

Abstract

In a survey of plant parasitic nematodes associated with or affecting rice throughout Nigeria, some important nematode pests, especially the white tip disease nematode, Aphelenchoides besseyi and the rice root nematodes Hirschmanniella spinicaudata and H. oryzae were identified from seed, soil and root samples from swamp rice fields respectively. The sugarcane cyst nematode, Heterodera sacchari occurred in swamp rice fields only around the major sugarcane estates in Nigeria. The root‐knot Meloidogyne incognita and the root lesion nematode, Pratylenchus brachyurus were also encountered in upland (rainfed) rice fields. The white tip disease nematode, A. besseyi occurred at low levels in soils and rice seeds throughout the country. High population levels of H. spinicaudata and H. oryzae were encountered especially in areas where monoculture of rice is practised. General chlorosis, poor tillering and significantly reduced yield have been observed due to H. spinicaudata. Rice plants attacked by H. sacchari also showed intense chlorosis, delayed and reduced tillering and reduced grain yield. The roots of attacked plants were twiggy, very necrotic and blackened. The root‐knot M. incognita and the root lesion nematodes P. brachyurus have both been observed to reduce rice yields. Rice cultivars screened for reactions to the nematodes showed varying degrees of susceptibilities. Some varieties were however resistant to the root‐knot nematode, M. incognita.     

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.     

植物抗线虫基因与抗性机理研究进展

植物寄生线虫是严重危害农业生产的一类重要病原生物,对全球作物产量造成重大损失.抗线虫基因在植物抗线虫反应中发挥重要作用,发掘抗线虫基因并培育抗线虫品种是防治线虫病害的一条有效途径.抗线虫基因的定位与克隆对解析植物抗线虫性的分子机理做出了巨大贡献,明确线虫与寄主植物之间的互作关系及抗线虫机制,可以为制定和采取更加有效的防控策略提供借鉴.     

Control of root-knot nematodes (Meloidogyne spp.) in Hungary1

Under Hungarian climatic conditions, root-knot nematodes, and other phytoparasitic nematodes, generally cause damage in certain plant growing areas. These pests are present in glasshouses throughout the country. In the field the nematodes occur in sandy soil in the vegetable-growing areas of southern and central Hungary. The following species of root-knot nematodes have so far been reported to occur in Hungary: Meloidogyne incognita, M. arenaria, M. hapla, M. javanica, M. incognita acrita, M. thamesi and M. naasi. There are 10 specific nematicides registered for nematode control in the country. These chemicals are mainly applied in glasshouses where their use produces most economic return. Nematoderesistant cultivars are only available in the case of tomato. The nematodes cause the heaviest damage on glasshouse cucumber.     

Root‐knot nematodes do not affect black root rot disease severity on watermelon and bottle gourd

The effects of root‐knot nematodes on black root rot of watermelon and bottle gourd were studied using field surveys and co‐inoculation tests with Meloidogyne incognita (southern root‐knot nematode) and Diaporthe sclerotioides. The results of the field survey suggested that root‐knot nematodes had little effect on either the severity of black root rot or infection with D. sclerotioides. None of the three fields showed a significant positive correlation between disease severity and nematode gall index, with low correlation coefficients. Co‐inoculation experiments under controlled conditions found no significant effect of root‐knot nematodes on black root rot of watermelon and bottle gourd based on area under disease progress curves (AUDPC). These results were supported by the quantities of DNA of the two agents in root tissues because no significant difference was found between dual‐ and single‐inoculation treatments with M. incognita and/or D. sclerotioides. These findings suggest that root‐knot nematodes probably do not affect the infection of watermelon or bottle gourd roots by D. sclerotioides or the incidence of black root rot in these crops caused by this fungus.     

西南部分地区荞麦根结线虫种类与地理分布

近年来,随着我国荞麦面积的迅速增加,根结线虫病呈逐年加重趋势,严重影响了荞麦的产量与品质。本研究于2014年对西南10个地区17个乡镇秋播苦荞麦根结线虫的分布、发生种类以及危害程度进行了调查。结果表明,西南地区危害荞麦的根结线虫种类有南方根结线虫(Meloidogyne incognita)、爪哇根结线虫(M.javanica)和花生根结线虫(M.arenaria)3种,其中南方根结线虫为优势种群。田间根结线虫种群大多数为单一种群,23.5%的样品为南方根结线虫与爪哇根结线虫(或花生根结线虫)组成的混合种群。调查发现前作为烟草或马铃薯的地块,荞麦根结线虫发生危害严重,平均被害株率为6.0%~77.5%,病情指数为1.4~26.1,而前作为玉米的荞麦根结线虫则较轻,被害株率最高为16.0%,相应病情指数为2.3。     

Root-lesion nematodes of potato: Current status of diagnostics,pathogenicity and management

Root-lesion nematodes of the genus Pratylenchus are migratory endoparasites with worldwide economic impact on several important crops including potato, where certain species like P. penetrans, P. neglectus, and P. scribneri reduce the yield and quality of potato tubers. Morphological identification of Pratylenchus spp. is challenging, and recent advancements in molecular techniques provide robust and rapid diagnostics to differentiate species without the need of specialist skills. However, the fact that molecular diagnostics are not available for all Pratylenchus species means that there are limitations in worldwide application. In general, root-lesion nematodes are difficult to manage once introduced into agricultural land and damage can be related to pathogenicity and population densities. In addition, root-lesion nematodes interact with fungi such as Verticillium dahliae, resulting in disease complexes that enhance the damage inflicted on the potato crop. Management interventions are often focused on limiting nematode reproduction before planting crops and include the application of nematicides, and cultural practices such as crop rotation, cover crops, biofumigation, and biological control. Understanding the limitations of the available crop protection strategies is important and there are many gaps for further study. This review discusses the status of the diagnosis, distribution, pathogenicity, and management of the main species of root-lesion nematodes, reported to infect potatoes worldwide, and highlights areas for potential future research.     

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。     

Host suitability of Vitis rootstocks to root‐knot nematodes (Meloidogyne spp.) and the dagger nematode Xiphinema index,and plant damage caused by infections

The host suitability of commercial Vitis rootstocks commonly used in Spain (161‐49C, 41B, 1103P, 110R, 140Ru and SO4) to root‐knot nematodes (Meloidogyne arenaria, M. incognita, M. javanica) and Xiphinema index, and damage caused by nematode infection were determined under controlled conditions. The three root‐knot nematodes reproduced with a rate higher than one in all rootstocks, indicating that they are suitable hosts for these nematodes. Growth of rootstocks infected with the root‐knot nematodes was less vigorous than that of nematode‐uninfected controls in the majority of the rootstocks studied. Root infection resulted in moderate to severe root galling in all rootstocks. The shoot and main stem diameters appeared to be the most sensitive variables of damage caused by infection by Meloidogyne spp., with reduction rates from 36% and 53% in 161‐49C to 57% and 66% in 140Ru, respectively. The shoot height was not significantly affected by the root‐knot nematodes and the root fresh weight generally increased as a consequence of intensive galling. The nematode X. index caused significant root damage with a reproduction factor higher than one in all rootstocks. However, reproduction factor was significantly influenced by the rootstock and significantly decreased by about 12‐fold (5·7 to 18·1‐fold) with the increase in inoculum density from 100 to 1000 nematodes per plant. The root dry weight was reduced by X. index infections, and was the plant growth variable most affected by the nematode infection in all rootstocks at both inoculum densities. Meloidogyne arenaria, M. incognita, M. javanica and X. index, prevalent in many world vineyards, are all shown to have a damaging effect on the six tested rootstocks.     

Biological control of Meloidogyne spp. with Pasteuria penetrans1

Pasteuria penetrans, an endospore-forming obligate parasite of root-knot nematodes, can be an effective biological control agent, particularly when used in pots, small plots or container-grown crops. The absence of adequate mass-production techniques prevents its deployment on a field scale. The spores are not mobile and their concentration and distribution influence parasitism since attachment of spores to free-living juvenile root-knot nematodes depends upon chance contact. Efficacy can also be influenced by the specificity of the population of P. penetrans to the root-knot nematode population. If these problems can be overcome, the use of P. penetrans in integrated management systems developed over several crop cycles would appear to have good prospects for decreasing root-knot nematodes in intensively cultivated soils.     

Enkele waarnemingen over populatieschommelingen bij het havercystenaaltje,Heterodera avenae (= H. major) onder invloed van enige gewassen op zandgrond

Summary In the course of a survey of the occurrence of cereal root eelworm made in the province of Limburg in 1955, some observations were made on the population density of the nematodes before and after various crops, for although it was well known that non-host crops decreased the population, little information was available on the effect of different cereals and graminaceous crops on the eelworm numbers.In 54 fields of farms at IJsselstein (Limburg) the pre- and postcropping nematode population was estimated by examining samples of 200 ml of soil in March and November 1955. Each sample consisted of 60 rods well distributed over the field. The results are summarized in table 1. Oats is an efficient host plant, but rye, some grasses and leys decrease the eelworm population and these may therefore be considered to be suitable crops to precede oats on infested land. Some rotations are suggested which may be suitable for infested fields, and which may help to avoid damage to oats in Limburg province.     

蔬菜肾形线虫的寄主范围和侵染特点

 肾形线虫Reniforme nematode是为害蔬菜重要病原线虫之一,寄主范围广泛^[1-4],分布普遍.通过在广州地区连续三年调查和室内接种试验得知,可寄生于11科29种蔬菜,寄生率高的有豆科、茄科和葫芦科中的各种蔬菜,其中苦瓜、节瓜、生菜、西洋菜、葱、蒜、姜等8种为首次报道。肾形线虫以年青雌虫从寄主植物幼根的伸长区侵入为害,一个侵染点常只有一条线虫侵染,侵染点周围细胞褐变。线虫在土壤中的垂直分布,主要在0—20cm耕作层。     

Parasitism of the root-lesion nematode Pratylenchus thornei on chickpea

Pratylenchus thornei -chickpea interactions were investigated under controlled and fluctuating environmental conditions in the growth chamber, greenhouse and shadehouse. Under controlled conditions, P. thornei infected chickpea lines 12071/10054 and P2245 and cultivars Andoum 1, JG62 and UC27. Line P 2245 and cv. JG 62 were the most susceptible genotypes on the basis of root damage and nematode reproduction, but nematode infection did not significantly reduce root and shoot weights. Cultivars Andoum 1 and UC27 and line 12071/10054 showed the least root damage and nematode reproduction. Inoculation of cv. Andoum 1 with 2500, 5000 or 10000 nematodes per plant in pots did not affect shoot weight, regardless of the conditions of water stress of the plants. However, root weight was significantly reduced by nematode infection in plants grown under water stress and fluctuating temperature conditions in the greenhouse, but was not affected by any other treatment. The nematode reproduction index was not affected by soil water content under shadehouse conditions, but was greater on plants watered to soil water-holding capacity than in water-stressed plants under greenhouse conditions. For both environments, the nematode reproduction index decreased when inoculum density was greater than 5000 nematodes per plant.     

Specificity oflongidorus cohni as a pathogen of oats

In a host study of the ectoparasitic nematodeLongidorus cohni, involving six field crops, only oats were found to afford rapid nematode population build-up and to suffer severe damage. No increase in nematode population, plant damage or root symptoms was observed on wheat, barley, purple vetch, field pea or berseem clover.     

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。     

The Basis of Predictive Modelling for Estimating Yield Loss and Planning Potato Cyst Nematode Management

The basis of modelling yield loss and population dynamics relations of potato cyst nematodes is that both are strongly density-dependent. Potato cyst nematodes (PCN; Globodera pallida and G. rostochiensis) are particularly suitable for analysing such relationships because they have only one generation per year, potato is their only field host, the juvenile nematodes within the egg are very durable (up to 20 years persistence), and they hatch mainly in response to specific chemicals exuded from host roots. Small populations increase the most, up to 50-fold, when a potato crop is grown. Multiplication rates decrease as the population density increases because damage decreases root system size and increases competition so that very large populations may actually be decreased when potatoes are grown. The newly formed eggs have a ‘half-life’ of c.two years when non-host, rotational crops are being grown. Control is achieved largely by the use of rotation, the application of nematicidal chemicals, and growing resistant cultivars. As rotations are shortened, so PCN populations will be increased, and crop damage becomes more likely. Thresholds for damage vary with both soil type (greatest on sandy soils) and potato cultivar. Cultivars differ in their tolerance of PCN damage depending on how vigorously they grow, on their root sensitivity to damage from the PCN juveniles which invade close to root tips, on cultivar resistance which decreases the parasitic effect by reducing the numbers of developing PCN females, and on various environmental factors such as the amounts of fertiliser applied. The dependence of the yield-loss relationship on population density, soil type and cultivar effects has been described in a simple equation and assessed using field-trial data. Effects on yield are described in proportion to the PCN-free yield but the addition of information on expected yield (in tonnes ha⁻¹) in the absence of PCN renders this equation predictive. Nematicides are widely applied to infestations of potato cyst nematodes, both to prevent the crop from being damaged and to prevent population increase which could hazard the next potato crop in the rotation, but they are generally more effective at preventing the former than the latter. A complex equation has also been developed to model the population dynamics of PCN. This equation incorporates a factor for host-crop growth and tolerance (from the yield-loss equation) and also the effects of host resistance. This latter is particularly relevant to G. pallida, where all the resistance currently available is determined by minor genes and hence is ‘quantitative’ or ‘partial’. Effects of rotation and of nematicides can also be incorporated into this model. To provide a realistic prediction also requires accurate information on PCN population densities, species composition and distributions, and rates of PCN population decline between potato crops.     

杀线虫植物以及植物源杀线虫活性化合物研究与应用进展

植物寄生线虫现已成为危害农业生产的第二大类病害,其防治迫在眉睫。线虫的生物防治是一种新型的线虫防治策略,主要是利用动植物和微生物及其次级代谢产物对线虫进行防治。植物源次级代谢产物即植物源化合物,源于自然,是植物源农药的核心。相比于化学杀线虫剂,植物源杀线虫剂对环境影响较小、靶向性强且不易使线虫产生抗药性。因此,从植物中获得结构新颖且杀线虫活性好的小分子化合物并将其开发成绿色农药,对于线虫病的防治具有重要意义。本文对杀线虫植物、具有杀线虫活性的植物源化合物及其杀虫机理、植物源杀线虫农药的应用情况展开综述,并对该研究领域进行了展望,希望能为植物寄生线虫病的防治与植物源杀线虫农药的开发利用提供参考和帮助。     

Viruses transmitted by nematodes1

The transmission of plant viruses by nematodes is remarkable in involving only two distinct groups of viruses, nepo viruses and tobraviruses, and being limited to longidorid, Paratrichodorus and Trichodorus nematodes respectively. Tobraviruses and their associated vector nematodes are not discussed here. Only 11 of the 36 described nepoviruses are transmitted by nematodes, and 6 of these 11 viruses are present in Europe naturally associated with 8 virus-vector longidorids. Specific relationships exist between the serologically distinct viruses and their vector nematode species. Specificity is largely determined by the virus coat protein and by an inherited ability of the nematode to retain virus particles at specific sites within its oesophagus. This specific relationship can be quite subtle, extending to populations of vector nematodes and also to virus isolates which apparently are serologically indistinguishable. Several serological and/or symptomatological variants of nepoviruses may be present at a field site in association with one or more vector nematode species. The exposure of different crops and new cultivars to these virus and vector combinations will probably result in the occurrence of further nematode-transmitted virus diseases. New methods for suppressing damage to crops caused by these diseases are required including the likely use of transgenic resistant cultivars.     

Integrated pest management of coffee for small-scale farmers in East Africa: needs and limitations

Coffee in East Africa (Kenya, Tanzania and Uganda) is an important cash and export crop for small-scale farmers. The crop suffers heavy yield losses due to damage caused by a wide range of indigenous pests (insects, diseases, nematodes and weeds). Current recommended pest control measures include a combination of cultural, resistant/tolerant cultivars and the use of broad spectrum chemical pesticides. Chemical pesticides are far more popular at the farm level than any of the other recommended pest control measures. Coffee pest control strategies are often aimed at individual pests with little consideration of the implications for the total coffee pest complex and its agro-ecosystem. This unilateral approach has resulted in increased pest pressure on coffee and some of its companion crops, outbreak of new pests of coffee, development of pest strains resistant to the cheap and commonly available chemical pesticides, increased environmental problems, increased health risks to man and livestock and an overall increase in the costs of coffee production, thus forcing many farmers to neglect their coffee plantations. Measures to alleviate the above problems, particularly the high production costs, are needed to improve coffee production and increase the cash return to the small-scale farmer. Integrated pest management (IPM) offers the best prospects for solving the above problems. However, lack of national IPM policies, poor extension systems, inefficient research-extension-farmer linkage and the lack of a holistic approach will delay the development and implementation of appropriate, acceptable and sustainable IPM practices.