Response of Resistant and Susceptible Bell Pepper (Capsicum annuum) to a Southern California Meloidogyne incognita Population from a Commercial Bell Pepper Field

To determine the presence and level of root-knot nematode (Meloidogyne spp.) infestation in Southern California bell pepper (Capsicum annuum) fields, soil and root samples were collected in April and May 2012 and analyzed for the presence of root-knot nematodes. The earlier samples were virtually free of root-knot nematodes, but the later samples all contained, sometimes very high numbers, of root-knot nematodes. Nematodes were all identified as M. incognita. A nematode population from one of these fields was multiplied in a greenhouse and used as inoculum for two repeated pot experiments with three susceptible and two resistant bell pepper varieties. Fruit yields of the resistant peppers were not affected by the nematodes, whereas yields of two of the three susceptible pepper cultivars decreased as a result of nematode inoculation. Nematode-induced root galling and nematode multiplication was low but different between the two resistant cultivars. Root galling and nematode reproduction was much higher on the three susceptible cultivars. One of these susceptible cultivars exhibited tolerance, as yields were not affected by the nematodes, but nematode multiplication was high. It is concluded that M. incognita is common in Southern California bell pepper production, and that resistant cultivars may provide a useful tool in a nonchemical management strategy.     

Progression of Root-knot Nematode Symptoms and Infection on Resistant and Susceptible Cottons

Progressive development in cotton root morphology of resistant A623 and susceptible M-8 cotton (Gossypium hirsutum L.) lines following infection by the root-knot nematode Meloidogyne incognita was studied in glass front boxes. Symptom development and radicle growth were observed; degree of galling, gall and egg mass diameter, and number of eggs per egg mass were recorded; and root segments were examined histologically. Small cracks caused by M. incognita appeared in the root epidermis and cortex soon after the cotyledons expanded on day 4. The cracks were longer and wider and extended through the cortex when the first true leaf became visible at day 8. Galls had formed on taproots by this time. When exposed to M. incognita, A623 had faster radicle growth (22%), fewer and smaller cracks in the root epidermis and cortex, fewer and smaller root galls, one-twelfth as many egg masses, and one-fourth as many eggs per egg mass as M-8. Root cracking, galling, and giant cell formation are major effects of M. incognita that may predispose cotton roots to pathogens resulting in synergistic interactions and diseases.     

Growth and Energy Demand of Meloidogyne incognita on Susceptible and Resistant Vitis vinifera Cultivars

Food (energy) consumption rates ofMeloidogyne incognita were calculated on Vitis vinifera cv. French Colombard (highly susceptible) and cv. Thompson Seedless (moderately resistant). One-month-old grape seedlings in styrofoam cups were inoculated with 2,000 or 8,000 M. incognita second-stage juveniles (J2) and maintained at 17.5 degree days (DD - base 10 C)/day until maximum adult female growth and (or) the end of oviposition. At 70 DD intervals, nematode fresh biomass was calculated on the basis of volumes of 15-20 nematodes per plant obtained with a digitizer and computer algorithm. Egg production was measured at 50-80 DD intervals by weighing 7-10 egg masses and counting the number of eggs. Nematode growth and food (energy) consumption rates were calculated up to 1,000 DD based on biomass increase, respiratory requirements, and an assumption of 60 % assimilation efficiency. The growth rate of a single root-knot nematode, excluding egg production, was similar in both cultivars and had a logistic form. The maximum fresh weight of a mature female nematode was ca. 29-32 μg. The total biomass increase, including egg production, also had a logistic form. Maximum biomass (mature adult female and egg mass) was 211 μg on French Colombard and 127 μg on Thompson Seedless. The calculated total cost to the host for the development of a single J2 from root penetration to the end of oviposition for body growth and total biomass was 0.535 and 0.486 calories with a total energy demand of 1.176 and 0.834 calories in French Colombard and Thompson Seedless, respectively.     

Effect of Mowing Cotton Stalks and Preventing Plant Re-Growth on Post-Harvest Reproduction of Meloidogyne incognita

The southern root-knot nematode (Meloidogyne incognita) is a major parasite of cotton in the U.S., and management tactics for this nematode attempt to minimize population levels. We compared three post-harvest practices for their ability to reduce nematode population levels in the field, thereby reducing initial nematode population for the next year's crop. The three practices tested were: 1) chemical defoliation before harvest plus cutting cotton stalks after harvest, 2) chemical defoliation plus applying a herbicide to kill plants prior to cutting the stalks, and 3) chemical defoliation without cutting stalks. Experiments were conducted in both the greenhouse and in the field. The greenhouse experiments demonstrated that M. incognita reproduction (measured as egg counts and root gall rating indices) was significantly greater when stalks were not cut. Cutting stalks plus applying herbicide to kill cotton roots did not significantly reduce nematode reproduction compared to cutting stalks alone. In field experiments, cutting stalks reduced egg populations and root galling compared to defoliation without stalk cutting. In a greenhouse bioassay which used soil from the field plots, plants grown in soil from the defoliation only treatment had greater root gall ratings and egg counts than in the stalk cutting plus herbicide treatment. Therefore, we conclude that cutting cotton stalks immediately after harvest effectively reduces M. incognita reproduction, and may lead to a lower initial population density of this nematode in the following year.     

Management of root-knot nematode (Meloidogyne spp.) on sweet pepper (Capsicum annuum L.) with moringa (Moringa oleifera Lam.) leaf powder

A major constraint facing sweet pepper production is infestation by nematodes leading to reduced yields. Field studies were conducted during the 2012 cropping season at the Experimental Farms of the University for Development Studies, Nyankpala, Northern region, Ghana, to determine efficacy of various levels of moringa leaf powder for the control of root-knot nematodes in sweet pepper (Capsicum annuum L.) in the savanna ecology of Ghana. Treatments consisted of three levels of moringa leaf powder (40, 60 and 80?g/L) per plot and 0?g/L (control). The experiment was laid out in a randomised complete block design with each treatment replicated four times. The infestations of root-knot nematodes were significantly lower in the moringa leaf powder-treated plots than the control. Although significant differences were not observed in all the parameters evaluated among the moringa leaf powder treatments, sweet pepper plants treated with 80?g/L of moringa leaf powder per plot recorded the highest mean value of plant height, number of leaves, number of fruits per plant, fruit weight per plant total yield per plot and the thickest plant girth. Similarly, the sweet pepper plants treated with 80?g/L of moringa leaf powder had the lowest infection index (root gall) and nematode population. Application of moringa leaf powder at 40, 60 and 80?g/L increased sweet pepper yield and decreased nematode population confirming their potential in management of root-knot nematodes.     

Characterization of Root-Knot Nematode Resistance in Medicago truncatula

Root knot (Meloidogyne spp.) and cyst (Heterodera and Globodera spp.) nematodes infect all important crop species, and the annual economic loss due to these pathogens exceeds $90 billion. We screened the worldwide accession collection with the root-knot nematodes Meloidogyne incognita, M. arenaria and M. hapla, soybean cyst nematode (SCN-Heterodera glycines), sugar beet cyst nematode (SBCN-Heterodera schachtii) and clover cyst nematode (CLCN-Heterodera trifolii), revealing resistant and susceptible accessions. In the over 100 accessions evaluated, we observed a range of responses to the root-knot nematode species, and a non-host response was observed for SCN and SBCN infection. However, variation was observed with respect to infection by CLCN. While many cultivars including Jemalong A17 were resistant to H. trifolii, cultivar Paraggio was highly susceptible. Identification of M. truncatula as a host for root-knot nematodes and H. trifolii and the differential host response to both RKN and CLCN provide the opportunity to genetically and molecularly characterize genes involved in plant-nematode interaction. Accession DZA045, obtained from an Algerian population, was resistant to all three root-knot nematode species and was used for further studies. The mechanism of resistance in DZA045 appears different from Mi-mediated root-knot nematode resistance in tomato. Temporal analysis of nematode infection showed that there is no difference in nematode penetration between the resistant and susceptible accessions, and no hypersensitive response was observed in the resistant accession even several days after infection. However, less than 5% of the nematode population completed the life cycle as females in the resistant accession. The remainder emigrated from the roots, developed as males, or died inside the roots as undeveloped larvae. Genetic analyses carried out by crossing DZA045 with a susceptible French accession, {"type":"entrez-protein","attrs":{"text":"F83005","term_id":"11352626","term_text":"pir||F83005"}}F83005, suggest that one gene controls resistance in DZA045.     

Functionality of resistance gene Hero, which controls plant root-infecting potato cyst nematodes, in leaves of tomato

The expression of host genomes is modified locally by root endoparasitic nematode secretions to induce the development of complex cellular structures referred as feeding sites. In compatible interactions, the feeding sites provide the environment and nutrients for the completion of the nematode's life cycle, whereas in an incompatible (resistant) interaction, the host immune system triggers a plant cell death programme, often in the form of a hypersensitive reaction, which restricts nematode reproduction. These processes have been studied in great detail in organ tissues normally infected by these nematodes: the roots. Here we show that host leaves can support a similar set of programmed developmental events in the potato cyst nematode Globodera rostochiensis life cycle that are typical of the root-invading nematodes. We also show that a gene-for-gene type specific disease resistance that is effective against potato cyst nematodes (PCN) in roots also operates in leaves: the expression of the resistance (R) gene Hero and members of its gene family in leaves correlates with the elicitation of a hypersensitive response only during the incompatible interaction. These findings, and the ability to isolate RNA from relevant parasitic stages of the nematode, may have significant implications for the identification of nematode factors involved in incompatible interactions.     

Gall-forming root-knot nematodes hijack key plant cellular functions to induce multinucleate and hypertrophied feeding cells

Among plant-parasitic nematodes, the root-knot nematodes (RKNs) of the Meloidogyne spp. are the most economically important genus. RKN are root parasitic worms able to infect nearly all crop species and have a wide geographic distribution. During infection, RKNs establish and maintain an intimate relationship with the host plant. This includes the creation of a specialized nutritional structure composed of multinucleate and hypertrophied giant cells, which result from the redifferentiation of vascular root cells. Giant cells constitute the sole source of nutrients for the nematode and are essential for growth and reproduction. Hyperplasia of surrounding root cells leads to the formation of the gall or root-knot, an easily recognized symptom of plant infection by RKNs. Secreted effectors produced in nematode salivary glands and injected into plant cells through a specialized feeding structure called the stylet play a critical role in the formation of giant cells. Here, we describe the complex interactions between RKNs and their host plants. We highlight progress in understanding host plant responses, focusing on how RKNs manipulate key plant processes and functions, including cell cycle, defence, hormones, cellular scaffold, metabolism and transport.     

Host Plant Resistance as an Alternative to Methyl Bromide for Managing Meloidogyne incognita in Pepper

Pre-plant soil fumigation with methyl bromide and host resistance were compared for managing the southern root-knot nematode (Meloidogyne incognita) in pepper. Three pepper cultivars (Carolina Cayenne, Keystone Resistant Giant, and California Wonder) that differed in resistance to M. incognita were grown in field plots that had been fumigated with methyl bromide (98% CH₃Br : 2% CCl₃NO₂ [w/w]) before planting or left untreated. Carolina Cayenne is a well-adapted cayenne-type pepper that is highly resistant to M. incognita. The bell-type peppers Keystone Resistant Giant and California Wonder are intermediate to susceptible and susceptible, respectively. None of the cultivars exhibited root galling in the methyl bromide fumigated plots and nematode reproduction was minimal (<250 eggs/g fresh root), indicating that the fumigation treatment was highly effective in controlling M. incognita. Root galling of Carolina Cayenne and nematode reproduction were minimal, and fruit yields were not reduced in the untreated plots. The root-galling reaction for Keystone Resistant Giant was intermediate (gall index = 2.9, on a scale of 1 to 5), and nematode reproduction was moderately high. However, yields of Keystone Resistant Giant were not reduced in untreated plots. Root galling was severe (gall index = 4.3) on susceptible California Wonder, nematode reproduction was high, and fruit yields were reduced (P ≤ 0.05) in untreated plots. The resistance exhibited by Carolina Cayenne and Keystone Resistant Giant provides an alternative to methyl bromide for reducing yield losses by southern root-knot nematodes in pepper. The high level of resistance of Carolina Cayenne also suppresses population densities of M. incognita.     

The Importance of the Host Plant on the Interaction Between Root-knot Nematodes Meloidogyne spp. and the Nematophagous Fungus, Verticillium chlamydosporium Goddard

The effect of the host plant on the efficacy of Verticillium chlamydosporium as a biological control agent for root-knot nematodes was investigated in four experiments. The growth of the fungus in the rhizosphere differed significantly with different plant species, the brassicas kale and cabbage supporting the most extensive colonization. The presence of nematodes in roots increased the growth of the fungus on most plants, and this effect was associated with the emergence of egg masses on the root surface; the presence of Meloidogyne incognita did not stimulate growth of the fungus in the rhizosphere until 5 weeks after the addition of infective juveniles to soil. The susceptibility of the plant host to M. incognita attack influenced the numbers of nematode eggs parasitized by the fungus. The control of the nematode was less effective on tomato roots, which produced large galls as a result of nematode infection compared with control on potato roots where galls were smaller, despite the greater abundance of the fungus in the rhizosphere of tomato plants. In large galls, a significant proportion of the egg masses remained embedded in the roots and was isolated from the fungus which was confined to the rhizosphere. Hence, the plant species has a marked effect on the efficacy of V. chlamydosporium as a biological control agent.     

Inheritance of Resistance to Pratylenchus penetrans in Alfalfa

Fifty-two alfalfa (Medicago sativa L.) clones, randomly selected from the cultivar Baker and the experimental line MNGRN-4, were evaluated for resistance (based on nematode reproduction) to Pratylenchus penetrans in growth chamber tests (25 C). Twenty-five clones, representing the range of nematodes and eggs per plant, were selected and retested. Four moderately resistant and two susceptible alfalfa clones were identified. Inheritance of resistance to P. penetrans was studied in these six clones using a diallel mating design. The S₁, Fl, and reciprocal progenies differed for numbers of nematodes and eggs per g dry root and for shoot and root weights (P < 0.05). Resistance, measured as numbers of nematodes in roots, was correlated between parental clones and their S₁ families (r = 0.94), parental clones and their half-sib families (r = 0.81), and S₁ and half-sib families (r = 0.88). General combining ability (GCA) effects were significant for nematode resistance traits. Both GCA and specific combining ability (SCA) effects were significant for plant size traits, but SCA was more important than GCA in predicting progeny plant size. Reciprocal effects were significant for both nematode resistance and plant size traits, which may slow selection progress in long-term selection programs. However, the GCA effects are large enough that breeding procedures that capitalize on additive effects should be effective in developing alfalfa cultivars with resistance to P. penetrans.     

Host-Parasite Relationships of Meloidogyne trifoliophila Isolates from New Zealand

Root-infecting nematodes are commonly found on white clover in New Zealand pasture where they reduce yield, nitrogen fixation, and persistence. The dominant root-knot nematode on white clover in New Zealand is confirmed in this study as Meloidogyne trifoliophila by isozyme phenotype comparison with the type population from Tennessee. Results from a host differential test differed in the host ranges of M. trifoliophila and M. hapla from New Zealand locations, with M. trifoliophila failing to reproduce on the standard host plants of the test. The size and character of white clover root galls differ between species as M. trifoliophila galls are large, elongate, and smooth compared to the M. hapla galls, which are small, round, inconspicuous, and generally have adventitious, lateral roots. Culture and identification of root-knot nematode populations from sites in the North Island of New Zealand showed that M. trifoliophila is more widespread and abundant than M. hapla. Similar differential resistant and susceptible galling responses among half-sib families of white clover from a breeding program indicated that all M. trifoliophila populations tested were of the same pathotype. This resistant material was not effective in reducing reproduction of M. hapla. Meloidogyne trifoliophila did not develop to maturity on six grasses tested, but galls were formed on some species.     

In-vitro Assays of Meloidogyne incognita and Heterodera glycines for Detection of Nematode-antagonistic Fungal Compounds

In-vitro methods were developed to test fungi for production of metabolites affecting nematode egg hatch and mobility of second-stage juveniles. Separate assays were developed for two nematodes: root-knot nematode (Meloidogyne incognita) and soybean cyst nematode (Heterodera glycines). For egg hatch to be successfully assayed, eggs must first be surface-disinfested to avoid the confounding effects of incidental microbial growth facilitated by the fungal culture medium. Sodium hypochlorite was more effective than chlorhexidine diacetate or formaldehyde solutions at surface-disinfesting soybean cyst nematode eggs from greenhouse cultures. Subsequent rinsing with sodium thiosulfate to remove residual chlorine from disinfested eggs did not improve either soybean cyst nematode hatch or juvenile mobility. Soybean cyst nematode hatch in all culture media was lower than in water. Sodium hypochlorite was also used to surface-disinfest root-knot nematode eggs. In contrast to soybean cyst nematode hatch, root-knot nematode hatch was higher in potato dextrose broth medium than in water. Broth of the fungus Fusarium equiseti inhibited root-knot nematode egg hatch and was investigated in more detail. Broth extract and its chemical fractions not only inhibited egg hatch but also immobilized second-stage juveniles that did hatch, confirming that the fungus secretes nematode-antagonistic metabolites.     

Effect of Meloidogyne incognita and Importance of the Inoculum on the Yield of Eggplant

The relationship between population densities of race 1 of Meloidogyne incognita and yield of eggplant was studied. Microplots were infested with finely chopped nematode-infected pepper roots to give population densities of 0, 0.062, 0.125, 0.25, 0.50, 1, 2, 4, 8, 16, 32, 64, and 128 eggs and juveniles/cm³ soil. Both plant growth and yield were suppressed by the nematode. A tolerance limit of 0.054 eggs and juveniles/cm³ soil and a minimum relative yield of 0.05 at four or more eggs and juveniles/cm³ soil were derived by fitting the data with the equation y = m + (1 - m)z^P⁻T. Maximum nematode reproduction rate was 12,300. Hatch of eggs from egg masses in water or from sodium hypochlorite dissolved egg masses was similar (41% and 39%), but egg viability was significantly greater from egg masses in water (58%) than from sodium hypochlorite dissolved egg masses (12%) after 4 weeks. Greater numbers of nematodes were collected from roots of tomatoes from soil infested with entire egg masses than from tomato roots from soil infested with egg masses dissolved by sodium hypochlorite.     

Energetics of Meloidogyne incognita on Resistant and Susceptible Alyceclover Genotypes

To determine the energy cost of a population of Meloidogyne incognita on the roots of alyceclover, nematode biomass was estimated and equations in the literature were used to calculate energy budgets. Amounts of energy consumed, respired, or used in production of nematode biomass were calculated. Results suggested that severe infestations of root-knot nematodes can remove significant quantities of energy from their hosts. Over a 36-day period, a population of 2.6 females of M. incognita per root system removed less than 0.4 calories of energy from a resistant alyceclover plant but over 11 calories were removed by 28 females from a susceptible alyceclover. The calculations indicate that on the resistant alyceclover line, 53% of the energy assimilated by the root-knot population was allocated to respiration, with only 47% allocated to production, whereas on the susceptible line, 65% of the assimilated energy was allocated to production. Such energy demands by the parasite could result in significant reductions in yield quantity and quality at a field production level.     

Influence of Six Varieties of Cynodon on Four Meloidogyne spp.

Two years of giant star grass, Cynodon nlemluensis var. nlemfuensis, in a field plot markedly reduced the incidence of the root-knot nematodes. Tomato planted following the grass showed very little or no root galling and the yield was thrice that of tomato planted on an adjacent field plot previously cropped to tomato. Replicated greenhouse experiments indicated that six varieties of Cynodon were resistant to root-knot nematode but it took up to 6 months of grass growth to appreciably lower the nematode population. The nematodes were eliminated from the soil by all the six grass varieties after 18 months.     

Relationships between initial population densities of Meloidogyne incognita race 2 and nematode population development in terms of variable soybean resistance

The effect of increasing initial population density levels (Pi) of Meloidogyne incognita race 2 on nematode population development and yield of a susceptible (Prima2000) and resistant (LS5995) soybean cultivar was investigated. Two experiments, one in a hail net cage and one in microplots, were conducted one each during two consecutive growing seasons at Potchefstroom in the North West Province of South Africa. Nematode reproduction was assessed by determining the number of eggs and second-stage juveniles (J2) in the rhizosphere and roots, egg masses, egg-laying females (ELF) and reproduction factor (Rf) values per root system at harvesting 110 days after planting. Percentage yield reduction in the two cultivars was also calculated. Strong non-linear relationships existed between all nematode variables as well as between Pi and percentage yield loss in both cultivars for both experiments in this study. Significantly higher numbers of eggs and J2, egg masses and ELF were maintained in the roots of the nematode-susceptible Prima2000 than in the resistant LS5995 from Pi = 100 and higher in both experiments. Rf values were inversely related to Pi for both cultivars and were lowest on LS5995, with Prima2000 maintaining significantly higher Rf values in both experiments. Yield loss in LS5995 was at least six times higher than that of Prima2000. The difference in monetary terms is demonstrated, although it is suggested that host plant resistance to plant-parasitic nematodes may not be sufficient as the only management tool in highly infested soils or in rotation systems including nematode susceptible crops.     

Reproduction and Development of Meloidogyne incognita and M. javanica on Guardian Peach Rootstock

Guardian peach rootstock was evaluated for susceptibility to Meloidogyne incognita race 3 (Georgia-peach isolate) and M. javanica in the greenhouse. Both commercial Guardian seed sources produced plants that were poor hosts of M. incognita and M. javanica. Reproduction as measured by number of egg masses and eggs per plant, eggs per egg mass, and eggs per gram of root were a better measure of host resistance than number of root galls per plant. Penetration, development, and reproduction of M. incognita in Guardian (resistant) and Lovell (susceptible) peach were also studied in the greenhouse. Differences in susceptibility were not attributed to differential penetration by the infectivestage juveniles (J2) or the number of root galls per plant. Results indicated that M. incognita J2 penetrated Guardian roots and formed galls, but that the majority of the nematodes failed to mature and reproduce.     

Effects of chicken manure and summer ploughing on root-knot nematode (Meloidogyne javanica) management in cantaloupe (Cucumis melo var. cantalupensis)

Abstract

A 2-year trial was performed in two regions of Ardestan (Iran, Isfahan province) to investigate effects of chicken manure and summer ploughing on root-knot nematode (Meloidogyne javanica) in two infested cantaloupe fields. Before planting cantaloupe, summer ploughing and chicken manure (3, 6 and 9?T/ha) separately and combination of these treatments were applied in nematode-infested fields. At the harvest time, the number of galls, egg masses, gall and egg mass indices and multiplication rate were determined. Also, quantitative and qualitative parameters of cantaloupes in different treatments were evaluated. The results revealed that double summer ploughing in combination with 6?T/ha chicken manure treatments had the best effects on the control of M. javanica. By applying this treatment, reduction of the egg mass number, gall number, total population in root and soil and reproduction factor were observed 17, 6.75, 8591?g/root and 3.37?g/root, respectively (compared to control: 132.5, 36.87, 45037?g/root and 23.13, respectively). It also had positive effect on fruit weigh (28 vs. 18.25?kg) and root dry weight (3.8 vs. 2.08?g). According to the results, it seems that decrease in growth parameters and yield reduction due to root-knot nematode could be overcome by incorporation of summer ploughing and applying the chicken manure with the most efficacy in increasing the quantity and quality of the yield.