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.     

Studies on the weed hosts of the rice root nematode, Hirschmanniella spinicaudata Sch. Stek. 1944

Weed hosts of the rice root nematode, Hirschmanniella spinicaudata were surveyed in a swamp rice field at Badeggi, Nigeria. Forty-five weed species, mainly grasses and sedges occurred very frequently and were very good hosts of the nematode. A wild rice, Oryza longistaminata was a preferred host. The importance of the weed hosts is discussed.     

近年水稻主要线虫病害的研究进展

目前,以拟禾谷根结线虫Meloidogyne graminicola、水稻干尖线虫Aphelenchoide besseyi、水稻潜根线虫Hirschmanniella oryzae、水稻茎线虫Ditylenchus angustus和旱稻孢囊线虫Heterodera elachista为主的水稻寄生线虫侵染水稻以及其它禾本科作物引致的线虫病害,已造成了严重的经济损失。近年来,对拟禾谷根结线虫的致病机制和寄主的防御机制等方面的研究已取得了显著进展,但对其它水稻寄生线虫与寄主互作机制的研究还存在较大空白。水稻寄生线虫的防治多依赖化学农药,抗性品种和生物防治等措施的实施存在一定的局限性。本文对上述5种主要水稻寄生线虫病的发生为害、致病机制以及防治方法等进行了综述,并对水稻寄生线虫致病机理的研究以及抗性品种、生物防治和诱导化合物的应用进行了探讨。     

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.     

和田鞘氨醇杆菌AMCC 100218菌株的筛选、鉴定及杀线虫特性

为筛选对南方根结线虫具有致死效果的生防细菌,从山东省10个县市蔬菜主产区番茄根际土壤中分离可培养细菌,采用离体杀线虫试验测定分离菌株对南方根结线虫Meloidogyne incognita的致死活性,结合生理生化特征及分子生物学方法对高效杀线虫菌株进行分类鉴定,同时对其杀线虫特性进行表征,并通过盆栽试验进一步验证其生防潜力。结果显示,从山东省蔬菜主产区番茄根际土中分离到1株高效杀线虫菌株AMCC 100218,结合生理生化试验与16S rRNA序列分析,鉴定此菌株为和田鞘氨醇杆菌Sphingobacterium hotanense;该菌株对南方根结线虫2龄幼虫的致死效果可达88.87%,其杀线虫活性物质具有较好的热稳定性和储存稳定性,且耐碱不耐酸;盆栽试验结果表明,该菌能够显著减少土壤中的虫口密度,降低番茄发病率。表明和田鞘氨醇杆菌AMCC 100218菌株是1株具有防治根结线虫病潜力的生防细菌。     

Heterodera elachista the Japanese cyst nematode parasitizing corn in Northern Italy: integrative diagnosis and bionomics

The Japanese cyst nematode Heterodera elachista was detected parasitizing corn cv Rixxer in Bosco Mesola (Ferrara Province) in Northern Italy. The only previous report of this nematode was in Asia (Japan, China and Iran) attacking upland rice; being this work the first report of this cyst nematode in Europe, and confirmed corn as a new host plant for this species. Integrative morphological and molecular data for this species were obtained using D2-D3 expansion regions of 28S rDNA, ITS1-rDNA, the partial 18S rDNA, the protein-coding mitochondrial gene, cytochrome oxidase c subunit I (COI), and the heat-shock protein 90 (hsp90). Heterodera elachista identified in Northern Italy was morphologically and molecularly clearly separated from other cyst nematodes attacking corn (viz. H. avenae, H. filipjevi, H. delvii, H. oryzae, H. sacchari, H. sorghi, H. zeae, Punctodera chalcoensis, and Vittadera zeaphila) and rice (H. oryzae, H. sacchari). The phylogenetic relationships of H. elachista from Northern Italy with other cyst-nematodes using rDNA and mtDNA showed a separation of the genus Heterodera in various morphospecies groups based on vulval cone structures. The development and parasitic habit of H. elachista on naturally infected corn cv Rixxer confirmed a typical susceptible reaction, including multinucleate syncytial cells in parenchymatic cells. Under greenhouse conditions, H. elachista successfully reproduced on two crops widely used in Northern Italy, such as corn (cv PR 33) and rice (cv Baldo). Considering the limited host-range of this nematode, that include two of the three world’s most important crops, special attention is needed for avoiding the dispersal of this nematode into new areas, by movement of soil on equipment, water, and contaminated containers infested soil, or agricultural practices.     

New sources of resistance to Meloidogyne incognita race 3 in wild cotton accessions and histological characterization of the defence mechanisms

Accessions of Gossypium spp., some of them never previously tested, were evaluated for resistance to a local isolate of Meloidogyne incognita race 3 in greenhouse experiments. Nematode infection was characterized based on the galling and egg mass indexes and the reproduction factors (RF). Root‐knot nematode reproduction among the newly tested accessions varied from highly susceptible (AS0188, AS0189) to moderately resistant (MT123 no. 3), and some accessions showed highly reduced nematode reproduction (CIR1343, CIR1348, Fai Mui). Histological observations of two resistant accessions (G. barbadense CIR1348 and G. hirsutum TX‐25, respectively) showed that resistance occurs through a two‐stage mechanism in the first accession and through a single‐stage mechanism in the second. Parasitism is blocked early after second‐stage juvenile (J2) penetration or during its initial tissue migration (CIR1348) and the development of later‐stage juveniles into female adults is suppressed at a later stage (TX‐25 and CIR1348). Fluorescence and bright light microscopy showed that root cells surrounding nematodes exhibit a hypersensitivity‐like reaction, with the accumulation of presumably phenolic compounds and the presence of necrotic cells that limit the development of nematodes and the formation of giant cells. Underdeveloped giant cells with degenerated cytoplasmic content were found in small numbers in CIR1348 and in large numbers in TX‐25, along with deformed nematodes. The full characterization of the defence mechanisms of novel sources of resistance to the root‐knot nematode in cotton constitutes a first step towards their use in crop improvement.     

Systemic nematicidal activity of fluensulfone against the root-knot nematode Meloidogyne incognita on pepper

BACKGROUND: Fluensulfone, a new nematicide of the fluoroalkenyl group, has proved to be very effective in controlling root‐knot nematodes, Meloidogyne spp., by soil application. The systemic activity of this compound against M. incognita on peppers via soil drenching and foliar spray was evaluated. RESULTS: Root application of fluensulfone via soil drenching showed slight and no nematode control activity when applied 4 and 10 days, respectively, after inoculation. A single foliar spray of peppers with a fluensulfone solution at 3.0 g L^?1 prior to inoculation reduced the galling index by 80% and the number of nematode eggs by 73–82% of controls. The reduction in these parameters by fluensulfone was much higher than that obtained with oxamyl or fenamiphos at the same concentration. This activity was also observed when the plants were sprayed 21 days before inoculation. A series of experiments suggested that foliar spray with fluensulfone prior to inoculation reduces nematode invasion. However, foliar spray after inoculation did not inhibit nematode development inside roots. CONCLUSION: Fluensulfone showed relatively high nematode control activity when sprayed on the foliage before inoculation. Fluensulfone may be used as a foliar application, in addition to soil application, for root‐knot nematode control. Copyright © 2011 Society of Chemical Industry     

Greenhouse and field evaluations of commonly occurring weed species for their host suitability to Meloidogyne species

Since weeds serve as hosts for nematode pests, the host status of 20 weed species (commonly occurring in fields of developing farmers) to Meloidogyne incognita and M. javanica, respectively, were investigated. Greenhouse studies showed that seven weed species had Rf values >1 for both nematode species indicating susceptibility, while 13 had Rf values ≤ 1 indicating resistance. Greenhouse results showed that Hibiscus trionum and Amaranthus tricolor were identified as the most susceptible and Chenopodium carinatum and Datura ferox the poorest hosts for M. incognita and M. javanica. For field experiments at Kuruman, Solanum retroflexum was the most susceptible weed to a M. javanica population, while the same was evident for H. trionum at Nelspruit, where a mixed population of M. incognita and M. javanica occurred and at Potchefstroom, where a population of M. incognita was present. Results from this study indicated that certain weed species are highly susceptible to root-knot nematodes and should be removed timely and effectively to prevent population level increases of root-knot nematode pests in the fields of farmers.     

白僵菌及其伴生菌发酵液对线虫的毒力研究

采用发酵液浸没法,以4种线虫作为靶标,对6株白僵菌、7株伴生菌菌株进行了杀线虫活性筛选,以期获得新的、高效的杀线虫生防菌资源。其中:处理24 h对南方根结线虫Meloidogyne incognita 2龄幼虫及大豆胞囊线虫Heterodera glycines 2龄幼虫校正死亡率均达80%以上的菌株仅有白僵菌Snef2598及伴生菌Snef5;供试菌株对水稻干尖线虫Aphelenchoides besseyi的毒力均较低,其中仅有1株白僵菌校正死亡率达到40%以上。处理48 h对南方根结线虫2龄幼虫校正死亡率达90%以上的菌株有白僵菌4株和伴生菌5株;对大豆胞囊线虫2龄幼虫校正死亡率超过90%的菌株有白僵菌3株和伴生菌1株;供试菌株对水稻干尖线虫毒力均较低,校正死亡率达60%以上的菌株有白僵菌3株和伴生菌2株;几乎所有供试菌株,对小杆线虫Caenorhabditis sp.的毒力均很高,处理24 h及48 h的校正死亡率均达97%以上,且被杀死的小杆线虫体壁以及虫体内部物质均被不同程度地消解。研究表明,球孢白僵菌菌株Snef2598及其伴生菌菌株Snef5对4种靶标线虫的毒力均较好,具有进一步研究的价值。     

Effect of abamectin on root-knot nematodes and tomato yield

BACKGROUND: Tomato growers in Shandong Province, China, commonly face heavy root‐knot nematode infestations. Current methods of control include cadusafos and methyl bromide (MeBr), but alternative methods are required because of the high toxicity of these pesticides and the ecological risk of their use. Therefore, abamectin soil applications were evaluated for their potential to control soil nematodes in a series of laboratory tests, greenhouse pot experiments and field trials. RESULTS: Laboratory tests showed that abamectin exhibited rapid knockdown of Meloidogyne incognita, with LC₅₀ and LC₉₀ values that were superior to those of cadusafos and averaged 7.06 and 21.81 mg L^?1. In the greenhouse pot experiment, soil applications of abamectin provided significant M. incognita control similar to that provided by cadusafos while maintaining excellent plant height and vigour. In the field trials, abamectin exhibited excellent control effects to nematodes while giving a higher tomato yield. There was a 19.3–39.0% yield increase from the various treatments compared with the control, and the best results were obtained from the highest dose of abamectin. CONCLUSION: The results of this study demonstrated that abamectin has the potential to be used as an effective alternative to MeBr and cadusafos for nematode control in tomato production in Shandong Province. Copyright © 2012 Society of Chemical Industry     

First report of the plant‐parasitic nematode Aphelenchoides besseyi (Nematoda: Aphelenchoididae) on rice in Romania

The rice leaf nematode, Aphelenchoides besseyi, was isolated in 2017 from rice seeds cultivated in Romania. Identification was based on morphology and confirmed with a real‐time PCR test. This paper provides the first report of A. besseyi in Romania.     

Population structure and species delimitation of rice white tip nematode,Aphelenchoides besseyi (Nematoda: Aphelenchoididae), in China

Aphelenchoides besseyi is a major nematode pathogen in rice known as the causal agent of white tip disease. In the present study, A. besseyi was recovered from 32 seed samples collected from the major rice-growing regions in China. Nine mitochondrial COI haplotypes and 95 ITS genotypes were identified, suggesting a high genetic diversity and endemism level of A. besseyi in China. Therefore, A. besseyi is likely to have experienced a long history of host–parasite coevolution in China, rather than being recently introduced from other countries. The results of population structure analysis indicated the presence of four clusters within Chinese A. besseyi, but these did not correspond to their geographic distribution. Haplotype H2 was found to be the most widespread. Haplotypes H9 and H13 were most genetically divergent and have been recognized as two cryptic species by molecular species delimitation methods, and with limited support from morphometric measurements. The COI-based phylogeny suggested the ability to parasitize rice has independently evolved at least four times in the genus Aphelenchoides.     

Nematicidal fluorescent pseudomonads for the in vitro and in vivo suppression of root knot (Meloidogyne incognita) of Capsicum annuum L

BACKGROUND: Considerable attention has been paid to plant‐growth‐promoting rhizobacteria (PGPR), especially the fluorescent group of Pseudomonas species, as the best alternatives to chemicals for facilitating ecofriendly biological control of soil‐ and seedborne microorganisms. On the basis of their novel plant‐growth‐promoting attributes, two rhizobacteria Pseudomonas aeruginosa VP1 and VP2 selected out of over 63 isolates from the rhizosphere of chilli (Capsicum annuum) were identified as potential candidates for biocontrol of the root‐knot nematode Meloidogyne incognita on chilli. RESULTS: The nematicidal activity of both strains was evaluated in vitro and in vivo for their efficacy against M. incognita. P. aeruginosa VP2 exhibited strong nematicidal activity in comparison with VP1, based on the in vitro killing of the second‐stage juveniles (J2) of M. incognita. Seed bacterisation with both strains VP1 and VP2 was able to manage root‐knot M. incognita on chilli (C. annuum) in a pot trial study. Increase in root and shoot length and in fresh and dry weight of root and shoot and reduction in the root‐knot index over the control were attained. In overall performance, VP2 was 29.5% more effective than VP1, and about 30% more effective than the control (non‐bacterised). CONCLUSION: The application of P. aeruginosa VP1 and P. aeruginosa VP2 controls the development of M. incognita in C. annuum, and hence they are recommended as efficient plant growth promotors and biocontrolling agents for raising healthy crop of C. annuum that can promote the growth of plants and reduce the nematode (M. incognita) population. Copyright © 2012 Society of Chemical Industry     

宁夏葡萄苗圃根结线虫病发病症状、为害程度及种类

为有效防治葡萄苗圃根结线虫病,采用拔根百分法和直接解剖法调查宁夏永宁县玉泉营镇葡萄苗圃葡萄苗木根结线虫病的发病症状、为害程度,并通过形态学和分子生物学对其种类进行鉴定。结果表明:15个葡萄品种的病害症状之间有一定差异。除抗砧3号外,其余14个葡萄品种均受根结线虫侵染,且不同葡萄品种受根结线虫为害的严重度差异明显,其中西拉、红芭拉蒂、爱神玫瑰、阳光玫瑰、马瑟兰、贝达和黑比诺上根结线虫病较严重,病情指数介于51.67～78.33之间,大青的病情指数最低,为21.67。不同葡萄品种的每根段雌成虫数量之间、每根段根结数量之间差异明显,其中葡萄品种贝达的每根段雌成虫数量和每根段根结数量最多,分别为12.47条和4.27个,葡萄品种黑比诺的每根段雌成虫数量和每根段根结数量较少,分别为3.60条和1.73个;每根段雌成虫数量随着每根段根结数量的增加而增加。根据根结线虫2龄幼虫、雌成虫和会阴花纹的形态学特征及分子生物学鉴定结果确定为害葡萄苗圃的根结线虫主要为南方根结线虫Meloidogyne incognita和花生根结线虫M. arenaria。除抗砧3号外,其它14个葡萄品种均不同程度的感染了南方根结线虫和花生根结线虫,且所有葡萄品种感染南方根结线虫的比例均较高。     

Genetic and Phenotypic Diversity in the Graminaceous Cyst Nematode Complex, Inferred from PCR-RFLP of Ribosomal DNA and Morphometric Analysis

Graminaceous cyst nematodes form a group of eleven valid species including Heterodera avenae, Heterodera filipjevi and Heterodera latipons and constitute major pests to cereals. They are widely spread in circum-mediterranean areas where they are presumed to cause yield losses on bread and durum wheat. The objective was to document the diversity of these cereal cyst nematodes, in particular samples from Mediterranean regions, in comparison to species which develop on cultivated or wild grasses (H. arenaria, H. hordecalis, H. mani) and on rice or sugarcane (H. sacchari). Studies involved PCR-RFLP of ITS and morphometrics of the juvenile and cyst characters. UPGMA analysis of molecular data showed that the isolates segregated in two main clusters which seem to represent different evolutionary lineages. The H. avenae sensu lato cluster (I) contained H. arenaria, H. avenae, H. filipjevi and H. mani. The second cluster (II) contained isolates of H. hordecalis and H. latipons. Within H. avenae sensu lato, H. filipjevi was separated from the other related species with significant bootstrap value. The differentiation of H. arenaria, recognized for the first time based on molecular data, and H. mani with few restriction enzymes were the least significant. Intraspecific polymorphism allowed differentiation of isolates originating from Australia within H. avenae sensu stricto. The group H. hordecalis–H. latipons showed the greatest genetic variability between and within isolates. Two representatives of Heterodera sacchari, taxonomically included in the schachtiigrave group, were genetically as distant to this group as to the other graminaceous species belonging to either H. avenae sensu lato or H. hordecalis–H. latipons group. Results inferred from multivariate analysis applied on morphometrics of the cysts and juveniles showed agreement between genetic and phenotypic classifications. This study demonstrates the utility of combined molecular and classical methods to enhance our knowledge about the diversity within the complex of graminaceous cyst nematodes and to establish robust techniques to identify a wider set of nematode species.     

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.     

Seed treatments associated with resistance inducers for management of <Emphasis Type="Italic">Pratylenchus brachyurus</Emphasis> in soybean

Pratylenchus brachyurus is one of the main limiting factors of soybean yield in Brazil, particularly because of inefficiency of the control methods when used individually. The present study aimed to assess the effect of associated methods, using seed treatment with nematicides (ST) and resistance inducers (RI), on nematode control in soybean plant in both field and greenhouse conditions. A field assay was conducted in an infested field and nematode population was assessed at sowing, 45, 75, and 100 days after sowing and the yield measured at end of crop cycle. The experiment was repeated in greenhouse. In another experiment, that was conducted in two different periods in a greenhouse, seed treatments and resistance inducers, alone or combined, were assessed under two initial populations of P. brachyurus (low IP = 500 specimens and high IP = 2000 specimens). The treatments did not reduce the number of nematodes g^?1 of root in field assay, but all seed treatments effectively controlled nematode population in the greenhouse assay. Most treatments reduced the number of nematodes g^?1 of root when nematode initial population was low (IP = 500) but when initial nematode population was high (IP = 2000) combinations of treatments which includes abamectin inhibited P. brachyurus reproduction. Chemical products did not affect yield but acibenzolar-S-methyl, alone or associated with other products, generally inhibit plant growth.