Interaction of vesicular arbuscular mycorrhiza with root knot nematodes in tomato

Summary The interaction between the VA mycorrhizal fungus,Glomus fasciculatus and the root-knot nematodes,Meloidogyne incognita andM. javanica, and their effects on the growth and phosphorus nutrition of tomato was studied in a red sandy loam soil of pH 6.0. Inoculation of tomato roots with root-knot nematodes enhanced infection and spore production byG. fasciculatus. Inoculation of tomato plants withG. fasciculatus significantly reduced the number and size of the root-knot galls produced byM. incognita andM. javanica. Inoculation withG. fasciculatus although improved plant growth and its total phosphorus content compared to the uninoculated plants, the difference were not statistically significant.     

Biological Control of Root-Knot Nematode <i>Meloidogyne incognita</i> in <i>Psoralea corylifolia</i> Plant by Enhancing the Biocontrol Efficacy of <i>Trichoderma harzianum</i> Using Press Mud

Meloidogyne incognita is a plant pathogen causing root-knot disease and loss of crop yield. The present study aimed to use Trichoderma harzianum as a biocontrol agent against plant-parasitic nematodes and used press mud, which is a solid waste by-product of sugarcane, as a biocontrol agent and biofertilizer. Therefore, the combined application of T. harzianum and press mud may enhance nematode control and plant growth. Elemental analysis of press mud using scanning electron microscopy (SEM) integrated with an Energy Dispersive X-ray (EDX) analyzer revealed the presence of different elements such as C, O, Mg, Si, P, K, Ca, Cu and Zn. In addition, a greenhouse study was conducted to investigate the combined effects of press mud and T. harzianum on M. incognita reproduction and growth and the biochemical features of Psoralea corylifolia. The results showed that plant length, dry biomass, leaf area, the number of seeds per plant, chlorophyll a, chl b, carotenoid content, nitrate reductase, carbonic anhydrase, and nitrogen content were significantly increased (P ≤ 0.05) in the T2 plants (plants were treated with 100 g of press mud + 50 mL T. harzianum before one week of M. incognita inoculation), over inoculated plants (IC). Antioxidant enzyme activity of ascorbate peroxidase (APX), catalase (CAT), peroxidase (POD), and superoxide dismutase (SOD) in the foliage of P. corylifolia was significantly increased when plants were treated with press mud + T. harzianum. A significant reduction in the number of egg masses, nematode population, and root-knot index (RKI) was found in plants with T2 plants. These results suggest that the combined application of T. harzianum and press mud has the potential to control the M. incognita infection and can be used as an environmentally safe alternative to chemical nematicides and also help in the removal of sugarcane waste that causes environmental pollution.     

Possible utilization of weeds for the management of plant parasitic nematodes infesting some vegetable crops

Leaf extracts of noxious weeds such as Solanum xanthocarpum and Argemone maxicana were used as bare-root dip treatment for the management of three important plant-parasitic nematodes, Meloidogyne incognita, Rotylenchulus reniformis and Tylenchorhynchus brassicae infesting tomato (Lycopersicon esculantum ) and chilli (Capsicum annuum) plants. Significant reduction was observed in the root-knot development caused by M. incognita, multiplication of nematode populations of R. reniformis and T. brassicae on both the test plants. Larval penetration of second stage juveniles of M. incognita was also inhibited at various concentrations of leaf extracts and dip durations. Leaf extract of S. xanthocarpum caused relatively more inhibition in root-knot development in case of root-knot nematode, nematode multiplication of reniform and stunt nematodes than that of A. maxicana. Because of dip treatment in leaf extracts of Argemone maxicana and Solanum xanthocarpum, the plants show better growth and at the same time the populations of nematodes such as M. incognita, R. reniformis and T. brassicae significantly decreased, which naturally improved plant growth. The efficacy of root-dip treatment with respect to improvement in plant weight and reduction in root-knot development and nematode populations, increased with increasing the concentration of leaf extracts and dip durations.     

Histopathology of roots of Glycine max (L.) Merrill induced by root-knot nematode (Meloidogyne incognita)

In Glycine max, the second-stage juveniles of Meloidogyne incognita entered the roots through the apical meristem or elongation zone. The juveniles induced giant cells in the zone of vascular strands. Near the head of the nematode and adjacent to the giant cells, the vascular strands exhibited abnormalities in their shapes and structures; both xylem and phloem were found to be affected. The giant cells had dense and granular cytoplasm, and large nuclei with large nucleoli. Some parenchyma cells exhibited hypertrophy, while others exhibited hyperplasia. The distinctive feature of the study is reporting the occurrence of abnormal xylem, abnormal phloem and abnormal parenchyma.     

Biocontrol of wilt disease complex of pea using Pseudomonas fluorescens and Rhizobium sp.

Biocontrol of wilt disease complex of pea caused by the root-knot nematode Meloidogyne incognita and Fusarium oxysporum f. sp. pisi was studied on pea (Pisum sativum L.) using plant growth-promoting rhizobacterium Pseudomonas fluorescens and root nodule bacterium Rhizobium sp. Inoculation of M. incognita and F.oxysporum alone caused significant reductions in plant growth over un-inoculated control. Reduction in plant growth caused by M. incognita was statistically equal to that caused by F. oxysporum. Inoculation of M. incognita plus F. oxysporum together caused a greater reduction in plant growth than the sum of damage caused by these pathogens singly. Inoculation of P. fluorescens and Rhizobium sp. individually or both together increased plant growth in pathogen inoculated and un-inoculated plants. Inoculation of P. fluorescens to pathogen-inoculated plants caused a greater increase in plant growth than caused by Rhizobium sp. Application of Rhizobium plus P. fluorescens caused a greater increase in plant growth than caused by each of them singly. Inoculation of P.fluorescens caused higher reduction in galling and nematode multiplication than caused by Rhizobium sp. Use of Rhizobium plus P. fluorescens caused higher reduction in galling and nematode multiplication than their individual inoculation. Plants inoculated with both pathogens plus Rhizobium showed less nodulation than plants inoculated with single pathogen plus Rhizobium. Inoculation of Rhizobium plus P. fluorescens resulted in higher root-nodulation than inoculated only with Rhizobium. Wilting indices were 4 and 5, respectively, when plants were inoculated with F. oxysporum and F. oxysporum plus M. incognita. Wilting indices were reduced maximum to 1 and 2, respectively, when plants inoculated with F.oxysporum and plants with both pathogens were treated with P. fluorescens plus Rhizobium.     

Chemical activators: A novel and sustainable management approach for Meloidogyne incognita (Kofoid and White) Chitwood in Chamomilla recutita L

Use of chemical activator for the management of root-knot disease in medicinal and aromatic plants can become an attractive alternative to traditionally used nematicides. Large numbers of chemical molecules are present in the plants and are involved in the induction of different types of proteins. The purpose of our research study is to explore the possibilities of resistance factors that are inherent in the plant by treating them with few chemical activators to activate against root-knot nematode infection. Efforts were made to achieve a satisfactory suppression of root-knot nematode, Meloidogyne incognita, a serious menace to successful cultivation of chamomile, Matricaria recutita L. Rauch (syn. Matricaria chamomilla L. Fain. Asteraceae) causing root-knot disease through use of different chemical activators. Here we examined selected groups of resistance activator viz. Isonicotinamide, 2-chloronicotinic acid, 5-nitrosalicylic acid, 4-chlorosalicylic acid, DL-2 aminobutyric acid, 2-aminobutyric acid, O-acetylsalicylic acid, 4-amino salicylic acid, salicylic acid and these were used as soil drench using 3 week old seedlings transplanted to root-knot nematode infested pots. Maximum reduction in root-knot severity and nematode population occurred with 4-chlorosalicylic acid, O-acetyl salicylic acid, 2-chloronicotinic acid and gave significant flower yield advantages. Present experiment suggests a strong possibility of these activators in integrated management for protection against plant parasitic nematodes.     

Comparative proteomic analysis of the response of fibrous roots of nematode-resistant and -sensitive sweet potato cultivars to root-knot nematode <Emphasis Type="Italic">Meloidogyne incognita</Emphasis>

As a major root-knot nematode (RKN), Meloidogyne incognita causes serious losses in the yield of sweet potato (Ipomoea batatas L.). To successfully colonize the host plant, RKNs elicit changes of dramatic physiological and morphological features in the plants. The expression of several genes is regulated as the nematode establishes its feeding site. Therefore, in this study, we analyzed the proteomes in the fibrous roots of sweet potato plants by an infection of RKN to understand the effect of the infection on the plant root regions. This study revealed differences in proteomes of the RKN-resistant sweet potato cultivar Juhwangmi and RKN-sensitive cultivar Yulmi. During plant growth, Juhwangmi plants were shown to be more resistant to M. incognita than Yulmi plants. No M. incognita egg formation was observed in Juhwangmi plants, whereas 587 egg masses were formed in Yulmi plants. Differentially expressed 64 spots were confirmed by proteomic analysis using 2-D gel electrophoresis with three spots up-regulated in the two cultivars during RKN infection. Of these 64 protein spots, 20 were identified as belonging to such different functional categories as the defense response, cell structure, and energy metabolism. This study provides insight into the molecular and biochemical mechanics of the defense response and metabolism of sweet potato plant during nematode invasion. We anticipate that this study will also provide a molecular basis for useful crop breeding and the development of nematode-tolerant plants.     

Nematicidal effect of an Amaranthus hypochondriacus L. cystatin (AhCPI) on the root-knot nematode Meloidogyne incognita (Kofoid and White) Chitwood

The root-knot nematode Meloidogyne incognita is one of the most damaging plant parasitic nematodes in the world. In this study, the effect of cystatin from Amaranthus hypochondriacus (AhCPI) as a potential control agent for M. incognita was explored. In vitro bioassays demonstrated that AhCPI affects the growth and development of eggs and the infectivity of juveniles (J2) of M. incognita, such as mortality and slower development, showing characteristic tissue damage. Mortality levels were quantified by Probit analysis, estimating LC₅₀s of 1.4 mg/mL for eggs and 0.028 mg/mL for J2. In planta bioassays showed that infected tomato seedlings treated with 0.056 mg/mL of AhCPI showed a 60% reduction in the number of galls, as compared with untreated J2-inoculated seedlings. Under greenhouse conditions, three applications of 10 mL of AhCPI (1.4 mg/mL) in the soil around the stem of M. incognita-infected tomato plants, reduced the number of galls by 93 ± 8%, as compared to the control M. incognita-infected plants. The application of AhCPI to the infected plants increased the yield (10.7%) of harvested tomato fruits, as compared to infected plants. These results show the potential of AhCPI for the control of M. incognita in tomato plants.     

The role of root-knot nematode on the wilt disease of Telfairiaoccidentalis in northern Nigeria

Cultivation of Telfairia occidentalis, an important vegetable grown in central and southern Nigeria, has gradually diffused to northern Nigeria where it has gained an economic importance. Its cultivation is, however, threatened by wilt disease occurring in farmers’ fields. A preliminary survey of farmers’ fields indicated that the disease was severe in fields with high root-knot population compared to the fields with less root-knot. Using Koch's postulate, the wilt causative organism was identified as Fusarium spp. The objective of this study was to determine therole of Meloidogyne incognita and its interaction with Fusarium oxysporum onwilt development in T. occidentalis. Four-week-old seedlings, raised in heat sterilised soil, were inoculated with Fusarium spp. and M. incognita under screenhouse condition. Seedlings were either inoculated with M. incognita and/or F.oxysporum as sole infection and as combined infection in a complex. Combined infection with both pathogens produced wilt symptom on the plant and gave significantly lower vegetative yield (p = 0.05) than sole inoculation with either M.incognita or F. oxysporum, except where the seedlings were mechanically inoculated with F. oxysporum. Results from the screenhouse studies were consistent with the field observations.     

Phenology of Tick weed (Cleome viscosa L.) and its interaction with okra (Abelmoschus esculentus (L.) Moench) and Melodoigyne incognita

Cleome viscosa is an emerging weed with the potential of interfering with okra and influencing pests of okra. Screen house studies were conducted on the phenology of C. viscosa, its interference with okra and its interaction with root-knot nematode-infected okra. Seedlings of C. viscosa were monitored in pots for growth, yield and dry matter accumulation for 14 weeks. C. viscosa was planted with okra at densities 0, 2, 4, 6, 8 and 10 weeds per okra plant and observed for 11 weeks. Data were collected on growth, yield and dry matter of okra. Plants were inoculated with 2,500 M. incognita eggs per pot while control plants were not inoculated. C. viscosa attained 91.7 cm height and accumulated 7.8 g/plant biomass at 14 weeks after planting. The percentage reduction in okra plant height, plant dry weight and fruit yield due to interference at lowest cleome density (2 plants/pot) was 33.7, 83.6 and 82.1%, respectively. Nematode reproductive factor was significantly lower for okra alone (4.9) compared to okra with cleome (7.6). This study shows that C. viscosa is a fast-growing weed that suppressed the performance of okra even at low density, is a good host to M. incognita and increased the population of the nematode in soil.     

Histopathology of Root-knot Nematode (Meloidogyne incognita) Infection on White Yam (Dioscorea rotundata) Tubers

White yam tissues naturally and artificially infected with root-knot nematodes were fixed, sectioned, and examined with a microscope. Infective second-stage juveniles of Meloidogyne incognita penetrated and moved intercellularly within the tuber. Feeding sites were always in the ground tissue layer where the vascular tissues are distributed in the tubers. Giant cells were always associated with xylem tissue. They were thin walled with dense cytoplasm and multinucleated. The nuclei of the giant cells were only half the size of those found in roots of infected tomato plants. Normal nematode growth and development followed giant cell formation. Females deposited eggs into a gelatinous egg mass within the tuber, and a necrotic ring formed around the female after eggs had been produced. Second-stage juveniles hatched, migrated, and re-infected other areas of the tuber. No males were observed from the tuber.     

植物罹病组织中南方、爪哇、花生根结线虫的LAMP快速检测

【目的】建立一种基于环介导等温扩增(loop-mediated isothermal amplification,LAMP)技术,从植物罹病组织中直接检测3种常见的根结线虫,为根结线虫的监测和防治提供技术支持。【方法】分别采用3种根结线虫的种类特异性引物对所选择的根结线虫的DNA片段进行PCR扩增,扩增产物纯化、回收并测序。根据3种根结线虫的测序结果,针对种类特异区段,采用PrimerExplorerV4软件,分别设计3种根结线虫的LAMP引物。设计的引物组人工合成后,以提取的纯化种群线虫DNA为模板,分别进行引物组的特异性测试,筛选出分别针对3种根结线虫的最佳引物组。【结果】研究设计的3种根结线虫的LAMP特异性引物能够直接从植物根结中检测出南方、花生、爪哇3种常见根结线虫,LAMP快速检测体系为:dNTPS浓度为1 mmol·L~(-1),Mg~(2+)的浓度为5 mmol·L~(-1),不添加甜菜碱,反应时间为45 min。【结论】本实验建立的南方、花生、爪哇根结线虫LAMP快速分子检测方法,具有特异性强、灵敏度高、简单、快速、经济等特征,能够从罹病植物组织中快速准确地检测出南方、花生和爪哇根结线虫,具有极高的实践应用价值。     

Interactive effect of root-knot nematode,Meloidogyne incognita and root-rot fungus,Rhizoctonia solani,on okra [Abelmoschus esculentus L.]

The individual, concomitant and sequential inoculation of second stage juveniles (at 2000 J₂/kg soil) of Meloidogyne incognita and Rhizoctonia solani (at 2 g mycelial mat/kg soil) showed significant reduction in plant growth parameters viz. plant length, fresh weight and dry weight as compared to control. The greatest reduction in plant growth parameters was recorded in the plants simultaneously inoculated with M. incognita and R. solani followed by sequential and individual inoculation. In sequential inoculation, plant inoculated with M. incognita 15 days prior to R. solani shows more reduction in comparison to plant inoculated with R. solani 15 days prior to M. incognita. Moreover, the multiplication of nematode and number of galls/root system were significantly reduced in concomitant and sequential inoculation as compared to individual inoculation, whereas the intensity of root-rot/root system caused by R. solani was increased in the presence of root-knot nematode M. incognita as compared to when R. solani was inoculated individually.     

Influence of Glomus intraradices and Soil Phosphorus on Meloidogyne incognita Infecting Cucumis melo

The interaction among Glomus intraradices, Meloidogyne incognita, and cantaloupe was studied at three soil phosphorus (P) levels in a greenhouse. All plants grew poorly in soil not amended with P, regardless of mycorrhizal or nematode status. In soil amended with 50 μg P /g soil, M. incognita suppressed the growth of nonmycorrhizal plants by 84%. In contrast, growth of mycorrhizal plants inoculated with M. incognita was retarded by only 21%. A similar trend occurred in plants grown in soil with 100 μg P /g soil. Mycorrhizal infection had no effect on the degree of root-knot gall formation and did not affect the number of nematode eggs per egg mass. Mineral levels in plant shoots generally declined as soil P levels increased and were not significantly influenced by G. intraradices or M. incognita.     

Physiological Effects of Meloidogyne incognita Infection on Cotton Genotypes with Differing Levels of Resistance in the Greenhouse

Greenhouse tests were conducted to evaluate (i) the effect of Meloidogyne incognita infection in cotton on plant growth and physiology including the height-to-node ratio, chlorophyll content, dark-adapted quantum yield of photosystem II, and leaf area; and (ii) the extent to which moderate or high levels of resistance to M. incognita influenced these effects. Cultivars FiberMax 960 BR (susceptible to M. incognita) and Stoneville 5599 BR (moderately resistant) were tested together in three trials, and PD94042 (germplasm, susceptible) and 120R1B1 (breeding line genetically similar to PD94042, but highly resistant) were paired in two additional trials. Inoculation with M. incognita generally resulted in increases in root gall ratings and egg counts per gram of root compared with the noninoculated control, as well as reductions in plant dry weight, root weight, leaf area, boll number, and boll dry weight, thereby confirming that growth of our greenhouse-grown plants was reduced in the same ways that would be expected in field-grown plants. In all trials, M. incognita caused reductions in height-to-node ratios. Nematode infection consistently reduced the area under the height-to-node ratio curves for all genotypes, and these reductions were similar for resistant and susceptible genotypes (no significant genotype × inoculation interaction). Our study is the first to show that infection by M. incognita is associated with reduced chlorophyll content in cotton leaves, and the reduction in the resistant genotypes was similar to that in the susceptible genotypes (no interaction). The susceptible PD94042 tended to have increased leaf temperature compared with the genetically similar but highly resistant 120R1B1 (P < 0.08), likely attributable to increased water stress associated with M. incognita infection.     

Biological control of root-knot nematode,Meloidogyne incognita infesting tomato

Talc based formulations of two antagonistic fungi, Acremonium strictum W. Gams and Aspergillus terreus Thom were tested separately and together for their ability to suppress the development of root-knot disease of tomato caused by the root-knot nematode, Meloidogyne incognita Kofoid & White in two consecutive trials (2007–08). Tomato seedlings were each inoculated with M. incognita at 2 infective second stage juveniles /g of soil. M. incognita caused up to 48% reduction in plant growth parameters compared to un-inoculated control. Control efficacy achieved by combined soil application of both fungi, in terms of galls/root system and soil population/50 ml of soil, was 66 and 69% respectively at 60 days of inoculation compared to control. Soil application by individual fungus did not achieve as much effectiveness as the biocontrol agents applied together. The combined treatment was found to have antagonistic effect on M. incognita development and increased plant vigor. Incorporation of fine powder of chickpea pod waste with talc powder was beneficial in providing additional nutrients to both plant and biocontrol agents and increased the activity of the nematophagous fungi in soil. A. strictum and A. terreus were successfully established in the rhizosphere of tomato plants up to the termination of the experiment.     

The effects of exotoxin (Thuringiensin) from Bacillus thuringiensis on Meloidogyne incognita and Caenorhabditis elegans

A partially purified preparation as well as two formulations of exotoxin from Bacillus thuringiensis (thuringiensin) were evaluated for nematicidal activity. The methods used in our evaluations included direct contact nematicidal assays, hatching tests, infection tests in seed pouches using the cucumber/root-knot nematode (Meloidogyne incognita) system, and greenhouse test using the root-knot nematode. While contact nematicidal activity was not observed against juveniles of M. incognita, 100% mortality occurred when the free-living nematode, Caenorhabditis elegans, was used as the test organism. Nematode infection evaluations in the seed pouch assay showed reduced root galling at relatively high concentrations (>10 mg kg^-1). Greenhouse assays indicated significant reduction in the soil population. However, the degree of control in relation to the amount of material applied, as measured by the gall numbers, larvae from soil/roots, and plant growth parameters, was not considered adequate. Data on the plant response in relation to treatment with different formulations of the toxin are presented.     

Histological response of resistant tomato cultivars to infection of virulent Tunisian root-knot nematode (Meloidogyne incognita) populations

The response of a susceptible tomato cultivar (Solanum lycopersicum cv. Rio Grande) to infection by three populations of root-knot nematode (Meloidogyne incognita) was compared histologically with that of Lycopersicon esculentum cv. Monita, L. esculentum cv. VFN8 and Solanum lycopersicum cv. Nemador possessing the Mi-1 resistance gene and accession PI126443 of L. peruvianum possessing the Mi-3 gene. The resistant cultivars showed susceptibility to the Tunisian Meloidogyne populations. Feeding sites were characterised by the development of giant cells that contained granular cytoplasm and several hypertrophied nuclei. The cytoplasm of giant cells was aggregated along their thickened cell walls and consequently the vascular tissues within galls appeared disrupted and disorganised. Feeding site formed on resistant L. esculentum lines and susceptible cultivar Rio Grande are similar according to cell and nucleus number, and the nurse superficies. Resistant accession L. peruvianum PI126443, known to possess heat-stable nematode resistance, also showed susceptible reaction to Tunisian Meloidogyne incognita populations; however, nematode development was reduced in comparison with susceptible plants and less developed feeding cells were observed.     

Enhanced tolerance of Mentha arvensis against Meloidogyne incognita (Kofoid and White) Chitwood through mutualistic endophytes and PGPRs

The use of herbs in pharmaceutical preparation is ever increasing, and the demand for pesticides free material by the concern industries is on the rise. Consequently the need to grow disease-free plants using non-chemical fertilizers and pesticides is the need of the hour. Mentha arvensis cv. kosi is highly infested with Meloidogyne incognita (Kofoid and White) Chitwood, and severe oil yield loss occurs due to this nematode pest. Employing ecofriendly ways of nematode management, the mutualistic endophytes (Trichoderma harzianum strain Thu, Glomus intraradices) and plant growth promoting rhizobacteria (Bacillus megaterium and Pseudomonas fluorescens) were assessed individually and in combination on plant biomass, oil yield of menthol mint (M. arvensis cv. kosi), reproduction potential and population development of root knot nematode, M. incognita under glasshouse conditions. These microbes enhanced the plant biomass and percent oil yield both with and without M. incognita inoculation. Dual application of mutualistic fungal endophytes and Plant Growth Promoting Rhizobacteria (PGPRs) may be a wise option for enhancing the oil yield and tolerance of menthol mint against M. incognita infection.