Showing papers on "Meloidogyne incognita published in 1991"

Arabidopsis thaliana as a new model host for plant‐parasitic nematodes

Abstract: Summary We have established culture conditions for successful infection and development of several economically important cyst-forming and root-knot nematodes on Arabidopsis thaliana under monoxenic conditions. Complete life cycles were obtained with the sedentary cyst nematodes Heterodera schachtii, H. trifolii, H. cajani and the root-knot nematodes Meloidogyne incognita and M. arenariaas well as with the migratory nematode Pratylenchus penetrans. In contrast, H. goettingiana and Globodera rostochiensis were unable to develop on Arabidopsis roots. Tissue-culture quality agar and medium conditions optimized for hydroponic root culture were essential for successful infections. Detailed in-vivo observations were made inside Arabidopsis roots during the early infection stages of M. incognita and during complete development of H. schachtii. Seventy-four different ecotypes of Arabidopsis were screened for their susceptibility towards H. schachtii resulting in a range of infection rates. None of the ecotypes tested showed complete resistance in vitro. The use of Arabidopsis as a host for plant-parasitic nematodes will provide a new model system for the molecular genetic analysis of this interaction.

Biological control of soil pests by mixed application of entomopathogenic and fungivorous nematodes.

Abstract: In greenhouse experiments, massive application of the fungivorous nematode, Aphelenchus avenae, in summer at 26-33 C (1 x l0⁵ nematodes/500 cm³ autoclaved soil) or in autumn at 18-23 C (5 x 10⁴ nematodes/500 cm³ autoclaved soil) suppressed pre-emergence damping-off of cucumber seedlings due to Rhizoctonia solani AG-4 by 67% or 87%, respectively. Application of 2 x l0⁵ A. avenae to sterilized soil infested with R. solani caused leafminer-like symptom on the cotyledons, which did not occur in mixed inoculations with the entomopathogenic nematode, Steinernema carpocapsae. When 1 x 10⁶ A. avenae were applied 3 days before inoculation with 100 Meloidogyne incognita juveniles, gall numbers on tomato roots were reduced to 50% of controls. Gall numbers also were suppressed by S. carpocapsae (str. All). Reduction in gall numbers was no greater with mixed application of A. avenae and S. carpocapsae than with application of single species, even though twice the number of nematodes were added in the former case. These nematodes were positively attracted to tomato root tips. Aphelenchus avenae suppressed infection of the turnip moth, Agrotis segetum, but not the common cutworm, Spodoptera litura, by S. carpocapsae.

Acquired virulence in the plant parasitic nematode Meloidogyne incognita : 1. Biological analysis of the phenomenon

Abstract: Quatre isolats de l'espece Meloidogyne incognita ont ete analyses pour leur virulence vis-a-vis du gene dominant Mi qui est a l'origine de la resistance chez les tomates cultivees. Un isolat trouve naturellement virulent dans une serre a servi de temoin de reference pour un fort degre de virulence. Deux autres isolats ont ete selectionnes a partir d'une population avirulente et multiplies respectivement pendant 12 et 21 generations sur le cultivar resistant Piersol

Characterisation of Potential Adhesins of the Bacterium Pasteuria Penetrans, and of Putative Receptors on the Cuticle of Meloidogyne Incognita, a Nematode Host

Abstract: Pasteuria penetrans spores were fragmented by glass bead vortexing, producing exosporial membranes and spore fragments, which consisted of fibre bundles. Both exosporia and spore fragments are capable of host-specific attachment to the cuticle of Meloidogyne incognita, a root-knot nematode host. Putative M. incognita receptors appear to be soluble in beta-mercaptoethanol (BME) but not SDS, and are also sensitive to tryptic digestion and deglycosylation by endoglycosidase F. Polyclonal antibodies against intact spores and spore fragments of antispore antibodies produced 100% inhibition. The antibodies, however, did not show preferential staining of particular spore structures in thin section immunolabelling studies. Exposure of Pasteuria penetrans spores to HCl or urea-SDS-dithiothreitol renders them incapable of attachment to their host juveniles and extensively disrupts fibres that surround the spore core. Protein extracts from spore fragments or from exosporial membranes are identical, and urea-BME extracts from either structure, but not SDS extracts, can inhibit the attachment of spores to juveniles by 60–80%. An inhibitory BME extract from spore fragments was analysed by anion-exchange chromatography and adsorption onto host cuticle followed by immunoblotting. It appeared to contain six potential spore adhesins of approximate Mr 24–29, 38–47, 59, 89, 126, and 190 (x10(3)). Lectin affinity blotting with wheat germ agglutinin and concanavalin A showed that all of these proteins bear terminal N-acetylglucosamine residues and the 38–47 kDa band also bears terminal Glc/Man residues.(ABSTRACT TRUNCATED AT 250 WORDS)

Characteristics and Efficacy of a Sterile Hyphomycete (ARF18), a New Biocontrol Agent for Heterodera glycines and Other Nematodes.

Abstract: A filamentous, nonsporulating fungus, designated Arkansas Fungus 18 (ARF18), was isolated from 9 of 95 populations of Heterodera glycines, the soybean cyst nematode, in Arkansas. In petri dishes, ARF18 parasitized 89% of H. glycines eggs in cysts. The fungus also infected eggs of Meloidogyne incognita and eggs in cysts of Cactodera betulae, H. graminophila, H. lespedezae, H. leuceilyma, H. schachtii, and H. trifolii. In pot tests, reproduction of SCN was 70% less in untreated field soil that was naturally infested by ARF18 than in autoclaved field soil. Although ARF18 grew well at 25 C on cornmeal agar over a wide pH range, it did not sporulate on 28 media and thus could not be identified to genus or species.

Host Suitability of Prunus Rootstocks to Four Meloidogyne Species and Pratylenchus vulnus in Spain

Abstract: Ten almond varieties and three experimental peach-almond hybrids were evaluated for their reactions against M. arenaria, M. incognita, M. javanica, M. hapla, and Pratylenchus vulnus. In a first experiment, four almond varieties commonly used as rootstocks in Spain were susceptible to M. incognita, M. arenaria, and M. hapla. In a second experiment, the almond D-3-5, and the hybrids G x N No 9 and Cachirulo showed varying degrees of resistance to M. javanica. The remaining cultivars were susceptible to M. javanica. In a third experiment, all tested materials were good hosts of P vulnus. The peach-almond hybrid G x N No 1, highly resistant to several species of root-knot nematodes, had the highest level of parasitism by P vulnus. In an histological study, P vulnus colonized extensively the cortical parenchyma of the roots of Garrigues, Garfi and G x N No 1 forming large pockets that contained all stages of the nematode as well as cavities.

Nematode population changes and forage yields of six corn and sorghum cultivars.

Abstract: Two temperate corn (Zea mays) hybrids (Pioneer 3320 and Northrup King 508), two tropical corn cultivars (Pioneer X304C hybrid and Florida SYN-1 experimental open pollinated cultivar), the sorghum (Sorghum bicolor) x sudangrass (Sorghum sudanense) hybrid DeKalb SX-17, and the sorghum hybrid DeKalb FS25E were compared for effect on nematode densities and forage yield in three plantings (one single-crop and one double-crop system) in Florida. Final population densities of Meloidogyne incognita in the three plantings ranged from 0 to 13/100 cm³ soil on the two Sorghum spp. and were lower (P = 0.001) than those obtained on the corn cultivars (range 147 to 762/100 cm³ soil). Early planted temperate corn and sorghum generally gave higher forage yields than did tropical corn. As second crops in double-cropping systems, tropical corn cultivars generally produced greater yields than temperate corn hybrids did. At 35% dry matter, double crop forage corn yield ranged from 51.1 to 64.8 ton/ha, and sorghum ranged from 79.8 to 102.2 ton/ ha. Tropical corn, forage sorghum, and sorghum-sudangrass were profitably grown at all planting dates. Late summer planting of temperate corn was unprofitable. DeKalb SX-17 sorghum x sudangrass first crop plus the ratoon double crop gave the highest net return of $1,133/ha. Among the corn cultivars, Florida SYN-1 gave the highest double crop net return of $652/ha. Key words: corn, Criconemella ornata, Criconemella sphaerocephala, cropping systems, double cropping, Meloidogyne incognita, nematode, Paratrichodorus minor, Pratylenchus scribneri, Sorghum bicolor, sorghum-sudangrass, Zea mays.

Isolation of a Repeated DNA Probe Showing Polymorphism among Meloidogyne incognita Populations.

Abstract: Several Meloidogyne incognita geographic populations were characterized by analysis of the restriction fragment length polymorphisms (RFLP) obtained after digestion of their total DNA and hybridization with a [(3)(2)P]-labeled probe. The probe consisted of a 1.7-kb-repeated DNA sequence, isolated from a M. incognita genomic library, that hybridized to multiple BamH I fragments in the genome of each isolate. The patterns showed sufficient polymorphism to enable the accurate differentiation of all the populations tested.

Interaction of Meloidogyne incognita and Water Stress in Two Cotton Cultivars.

Abstract: A series of controlled-environment experiments were conducted to elucidate the effects of Meloidogyne incognita on host physiology and plant-water relations of two cotton (Gossypium hirsutum) cultivars that differed in their susceptibility to nematode infection. Inoculation of M. incognita-resistant cultivar Auburn 634 did not affect growth, stomatal resistance, or components of plant-water potential relative to uninoculated controls. However, nematode infection of the susceptible cultivar Stoneville 506 greatly suppressed water flow through intact roots. This inhibition exceeded 28% on a root-length basis and was similar to that observed as a consequence of severe water stress in a high evaporative demand environment. Nematodes did not affect the components of leaf water potential, stomatal resistance, transpiration, or leaf temperature. However, these factors were affected by the interaction of M. incognita and water stress. Our results indicate that M. incognita infection may alter host-plant water balance and may be a significant factor in early-season stress on cotton seedlings.

Invasion of Tomato Roots and Reproduction of Meloidogyne incognita as Affected by Raw Sewage Sludge.

Abstract: The antagonistic effects of raw sewage sludge on infection of tomato by Meloidogyne incognita were tested in greenhouse pot experiments. Sludge was mixed with the soil or added on its surface before and after inoculation of tomato plants with nematode eggs. Juvenile penetration was determined 1 and 10 days after inoculation, and 6 weeks later root systems were assessed for nematode reproduction. Fewer juveniles penetrated roots in pots with sludge added to the soil than in unamended control pots. In both experiments, roots were severely galled despite a significant reduction in gall ratings in amended relative to unamended soils. Egg production in treated soil was less (P = 0.05) than in control pots, regardless of whether sludge was incorporated or added 1 day before or after inoculation. In treated pots, RF values (final egg number/inoculation egg number) were strongly reduced. The toxic effects observed on the parasite may result from the ammoniacal nitrogen released in the soil within 7 days after treatment, associated with possible poor host suitability of tomatoes grown in amended substrate and short-lasting compound(s) active after root invasion.

Resistance to Root-knot Nematodes in Cucumber and Horned Cucumber

Abstract: Two experiments were conducted in the greenhouse. In one experiment, cucumber (Cucumis sativus) and horned cucumber (C. metuliferus) cultigens were evaluated for resistance to four root-knot nematode species (Meloidogyne arenaria, M. hapla, M. incognita, and M. javanica), and, in a second experiment, a standard (12-week) test was compared with a rapid (6-week) test. In the first experiment, horned cucumber cultigens varied in response to the Meloidogyne species. 'Sumter' cucumber was more susceptible than the horned cucumber to Meloidogyne incognita, M. javanica, and M. arenaria. All cultigens were more resistant to M. hapla than to the other root-knot nematode species. In the second experiment, best results were obtained when the test was run for 12 weeks rather than 6 weeks after planting (or 10 and 4 weeks after inoculation, respectively). All cultigens were more resistant to M. arenaria than to either M. incognita or M. javanica. Cucumber (Cucumis sativus L.) is the sec- ond most important vegetable crop in North Carolina, and root knot (caused by Meloidogyne spp.) is the most important cucumber disease. Annually, root-knot nematodes destroy approximately 12% of the crop in the state (6). Four species of root-knot nematodes can potentially attack cucumber in North Carolina: Meloidogyne incognita (Kofoid & White) Chitwood, M. arenaria (Neal) Chitwood, M. hapla Chit- wood, and M. javanica (Treub) Chitwood; but M. hapla is not important on cucumber in the state. Cucumber cultivars resistant to these species would be valuable for growers. The African horned cucumber (Cucumis metuliferus Naud.) is resistant but not im- mune to M. arenaria, M. javanica, and M. incognita (3). As a result, interspecific hy- bridization to transfer root-knot nematode resistance to the cultivated cucumber has been a goal of many researchers. So far, attempts to hybridize the two species have been unsuccessful (4).

Resistance in Soybean Cultivars from Maturity Groups V-VIII to Soybean Cyst and Root-knot Nematodes

Abstract: One hundred thirty-nine cultivars of soybean (Glycine max) in Maturity Groups V, VI, VII, and VIII were evaluated in a greenhouse for resistance to Heterodera glycines races 3 and 14 and Meloidogyne incognita, M. arenaria, and M. javanica. Of the cultivars tested, 37% had resistance to H. glycines race 3 alone, 12% had resistance to both races 3 and 14, and 69% exhibited a moderate or high level of resistance to one or more of the Meloidogyne spp. However, 24% were susceptible to each race of H. glycines and to all Meloidogyne spp. Whereas 40% of the cultivars were moderately resistant to M. javanica, only 23% were moderately resistant to M. incognita and 24% to M. arenaria. Although 28% of the cultivars had a high level of resistance to M. incognita, only 6 and 3% had this level of resistance to M. javanica and M. arenaria, respectively. Seventeen percent of the cultivars possessed a moderate or high level of resistance to all three Meloidogyne spp., and 37 % had resistance to H. glycines race 3 and M. incognita. With the exception of resistance to H. glycines race 14, resistance in soybean to these nematodes was fairly uniformly distributed across maturity groups. Key words: Heterodera glycines, Glycine max, Meloidogyne incognita, Meloidogyne arenaria, Meloidogyne javanica, nematode resistance, soybean, susceptibility.

Acquired virulence in the plant parasitic nematode Meloidogyne incognita. 2. Two-dimensional analysis of isogenic isolates(')

Abstract: SUMMARY Two lines of Meloidogyne incognita virulent to tomato cultivar carrying the Mi gene were selected from avirulent single egg-mass populations. Each line was obtained from a single juvenile belonging to two wild avirulent populations, one coming from France, the'other from Ivory Coast. For each population, two lines were established one maintained on the susceptible cv. Saint-Pierre and the other on resistant cv. Piersol at 20-25 OC. Females of the two virulent lines were compared for their soluble proteins to each other and to their non virulent homologous parent. Analyses were made on females. Some differences appeared between the females of the two lines of different geographical origin using two-dimensional gel electrophoresis (2-DGE) and a sensitive silver stain. Approximatively 400 spots were resolved but due to technical difficulties of the technique, only a small number of them could be considered in comparing the virulent and avirulent liries. Small differences could be observed between the two lines of each population of different geographical origins and only one spot enables the homologous virulent and avirulent lines to be distinguished.

Penetration of susceptible and resistant tobacco cultivars by meloidogyne juveniles.

Abstract: Rates of penetration of Meloidogyne incognita, M arenaria, and M javanica into tobacco cultivars NC2326 (susceptible to all three species) and K399 (resistant to M incognita) and a breeding line that had been selected for resistance to M incognita were compared Meloidogyne incognita penetrated NC2326 rapidly during the first 24 hours after inoculation Numbers of M incognita continued to increase gradually through the 14-day experiment Higher numbers of M incognita were observed in the roots of K399 during the first 24 hours than were observed in NC2326 The number of M incognita in K399 peaked 4 days after inoculation, then declined rapidly as the nematodes that were unable to establish a feeding site left the root or died Numbers of M incognita in the breeding line followed the same pattern as with K399, but in lower numbers Numbers of M arenaria showed little difference between cultivars until 7 days after inoculation, then numbers increased in NC2326 Numbers of M javanica fluctuated in all cultivars, resulting in patterns of root population different from those observed for M incognita or M arenaria Resistance to M incognita appears to be expressed primarily as an inability to establish a feeding site rather than as a barrier to penetration Some resistance to M arenaria may also be present in K399 and the breeding line

Biomass Partitioning in Tomato Plants Infected with Meloidogyne incognita.

Abstract: Tomato plants were inoculated with Meloidogyne incognita at initial populations (Pi) of 0, 1, 10, 50, 100, and 200 (x 1,000) eggs per plant and maintained in a growth chamber for 40 days. Total fresh biomass (roots + shoots) at harvest was unchanged by nematode inoculation with Pi of 1 x 10 eggs or less. Reductions in fresh shoot weight with increasing Pi coincided with increases in root weight. Total fresh biomass declined with Pi above 1 x 10 eggs, whereas total dry biomass declined at Pi above 1 x 10 eggs. The greatest reduction percentages in fresh shoot biomass induced by root-knot nematodes occurred in the stem tissue, followed by the petiole + rachis; the least weight loss occurred in the leaflets. Although biomass varied among shoot tissues, the relationship between biomass of various shoot tissues and Pi was described by quadratic equations. The linear and quadratic coefficients of the equations (stem, petiole + rachis, or leaflets on Pi) did not differ among tissues when calculations were based on standardized values. Meloidogyne incognita-infected plants had thinner leaves (leaf area/leaf weight) than did uninfected plants. Reductions in leaf weight and leaf area with nematode inoculation occurred at nodes 5-15 and 4, 6-14, respectively. Losses in plant height and mass due to nematodes reflected shorter internodes with less plant mass at each node.

Water transport through tomato roots infected with Meloidogyne incognita.

Abstract: The effect of Meloidogyne incognita on water flow in tomato roots was investigated in rooted split-stem cuttings. Total water flow through infected root parts was significantly lower than through comparable uninfected parts. Total water uptake was correlated with total length of the root system. In a root system severed from its stem and placed under a partial vacuum applied at the stem stump, the infected half transported significantly less water than its corresponding uninfected half. In perfusion chambers, infected apical, but not basal, root segments transported less water than adjacent uninfected segments. Axial resistance to water movement in galls at the root apex, but not at the base, increased. Cross sections of galls at the root base showed little effect on vascular continuity, but in terminal galls the number and diameter of xylem vessels were reduced.

Relationship between inoculum density of the nematophagous fungus Paeeilomyces Zilacinus and control of Meloidogyne arenaria on tomato (l)

Abstract: SUMMARY Five doses (0.01 - 0.1 - 1 - 10 and 100 g/m*) of a commercial product of Paecilowzyces lilacinus isolated from eggs of Meloidogyne incognita were applied in a powder formulation (10” sporedg of product) in a glasshouse pot experiment against large infestations of Meloidogyne arenan‘a. The trial was conducted over eleven months on three successive tomato crops, cv. Saint Pierre. Results showed that the number of fungal propagules in the soil was correlated to the initial dose applied and decreased progressively through the time with increased dose. Populations of M. arenaria were significantly reduced by the fungus at 10 and 100 g of spores/m2 in the second and third nematode generations. The number of colonized egg masses and the number of non-viable eggs increased with fungal inoculum and the fungus was most effective at a density of IO6 sporedg of soil. In.the highest level of control (100 Yo colonized egg masses) only 50 O/O of the eggs were parasitized. Twenty three percent of the larvae remained which constitutes an important residual inoculum potential. This fact and a rapid decrease in fungal density in soil below the acceptable control levels, limit the use of this fungus as a bioIogical control agent.

Stage-specific Differences in Lectin Binding to the Surface of Anguina tritici and Meloidogyne incognita.

Abstract: The occurrence and distribution of several lectin binding sites on the outer surfaces of eggs, preparasitic second-stage juveniles (J2), parasitic second-stage juveniles (PJ2), females, and males of two tylenchid nematodes, Anguina tritici and Meloidogyne incognita race 3, were compared. In both species, a greater variety of lectins bound to the eggs than to other life stages; lectin binding to eggs was also more intense than it was to other life stages. Species-specific differences also occurred. More lectins bound to the amphids or amphidial secretions of M. incognita J2 than to the amphids or amphidial secretions of A. tritici J2. Lectins also bound to the amphids or amphidial secretions of adult male and female A. tritici, but binding to the cuticle occurred only at the head and tail and was not consistent in all specimens. Canavalia ensiformis and Ulex europaeus lectins bound specifically to the outer cuticle of M. incognita. Several other lectins bound nonspecifically. Oxidation of the cuticle with periodate under mild conditions, as well as pretreatment of the nematodes with lipase, markedly increased the binding of lectins to the cuticle of A. tritici J2 but not, in most cases, to M. incognita J2 or eggs of either species.

Embryo Culture of Lycopersicon esculentum × L. peruvianum Hybrid Genotypes Possessing Heat-stable Resistance to Meloidogyne incognita

Abstract: Genotypes of Lycopersicon peruvianum (L.) Mill. and L. peruvianum var. glandulosum (Rick), selected from accessions that possess resistance to Meloidogyne incognita ((Kofoid and White) Chitwood) at high soil temper- ature (30C), were used as male parents in crosses with L. esculentum (Mill.) susceptible cultivars UC82, Lukullus, Tropic, and male-sterile line ms-31, respectively. The incongruity barrier between the two plant species was overcome by embryo callus and embryo cloning techniques. Hybridity of the F, progeny obtained from each cross was confirmed by differences in leaf and flower morphology, plant growth habits, and by acid phosphatase isozyme phenotypes using polyacrylamide gel electrophoresis. In greenhouse inoculation experiments, F 1 plants were highly resistant to M. incognita in soil at 25 and 30C. These results confirmed the successful transfer and expression of heat-stable resistance to M. incognita from L. peruvianum to hybrids with L. esculentum as a preliminary step to introgressing additional root-knot nematode resistance into tomato. The resistance to root-knot nematodes (Meloidogyne spp.), present in all resistant commercial cultivars of tomato (Lyco- persicon esculentum Mill.), is generally considered to be con- ferred by a single dominant gene, designated Mi (Ammati, 1985; Medina Filho and Stevens, 1980; Roberts and Thomason, 1989; Sidhu and Webster, 1981). This resistance was identified in L. peruvianum PI 128657. Using embryo rescue, Smith (1944) obtained one resistant F 1 plant from the cross L. esculentum Michigan State Forcing x PI 128657. Watts (1947) cloned this unique F1 plant and obtained the first two backcrosses to L. esculentum. Additional backcrosses to the cultivated tomato were obtained by Frazier and Dennett (1949). This material was dis- tributed to tomato breeders and led to the release of the first tomato cultivars resistant to Meloidogyne incognita. All culti- vars with gene Mi have been derived from this one F1 resistant plant obtained by Smith (1944). Plants possessing gene Mi are resistant to three of the four economically important species of root-knot nematode (RKN): M. incognita, M. arenaria (Neal) Chitwood, and M. javanica (Treub) Chitwood (Ammati, 1985; Fatunla and Salu, 1977; Medina Filho and Stevens, 1980; Roberts and Thomason, 1989; Sidhu and Webster, 1981). Gene Mi does not confer resistance to M. hapla Chitwood. In addition, the resistance conferred by Mi is not effective in soils above 28C (Ammati, 1985; Ammati et al., 1986; Dropkin, 1969). Nonselected virulent populations

Plant protection with inorganic ions.

Abstract: Gradients of salts of the specific ion repellents for Meloidogyne incognita -- NH[sub4][sup+], K[sup+], Cl[sup-], and NO[sub3][sup-] -- have been demonstrated to shield tomato roots from infestation in soil. The strategy of these greenhouse experiments was to interpose a salt barrier in a soil column between the plant roots and the nematodes. The relative effectiveness of the salts as a barrier to infective second-stage juveniles in a sandy loam was NH[sub4]NO[sub3], NH[sub4]Cl KNO[sub3] KCl. Some of these ions are beneficial to plant growth, and the results suggest that a new environmentally tolerable means of plant protection is possible. Key words: ion, Lycopersicon esculentum, Meloidogyne incognita, nematode, protection, repellent.

Nematode Densities Associated with Corn and Sorghum Cropping Systems in Florida

Abstract: Final densities (Pf) of Meloidogyne incognita and Pratylenchus spp. increased more than ten-fold over initial densities (Pi) on corn (Zea mays) cultivars grown at three sites in north Florida. The Pf of M. incognita following sorghum (Sorghum bicolor) were much lower (P =0.001) than Pf following corn at the two sites in which sorghum was grown. At one of these sites, Pf of M. incognita was = 5/100 cm³ soil, and at the other site Pf Pi. At one site, population densities of Criconemella sphaerocephala increased to higher levels on sorghum than on corn, but Pf of Pratylenchus spp. were greater (P = 0.01) on corn. Few differences in nematode densities were observed among the different corn cultivars tested. Key words: corn, Criconemella ornata, Criconemella sphaerocephala, cropping system, double cropping, Glycine max, Meloidogyne incognita, nematode, Paratrichodorus minor, population density, Pratylenchus brachyurus, Pratylenchus scribneri, Sorghum bicolor, soybean, Zea mays.

Reactions of selected bean pure lines and accessions to Meloidogyne species

Abstract: Over 150 bean (Phasealus vulgaris) pure lines and accessions were evaluated in growth chamber and greenhouse trials for reactions to one or more populations of root-knot nematodes (Meloidogyne spp.) collected from Colombia or the United States. Bean pure lines and accessions were evaluated for root galling severity and nematode egg mass production on a 1-9 scale, where 1=no root galling or no egg mass production and 9=76-100% of root system galled or >100 egg masses per root system

Reaction of Prunus Rootstocks to Meloidogyne incognita and M. arenaria in Spain.

Abstract: Prunus rootstocks were evaluated for their reaction to Meloidogyne incognita and M. arenaria. Most rootstocks were peach-almond hybrids of Spanish origin. In one experiment three selections of Garfi x Nemared (G x N) and Hansen-5 were highly resistant to M. incognita, but four other rootstocks were susceptible showing high galling indices and population increases. In two experiments with M. arenaria, the hybrid selections G x N nos. 1 and 9 were immune, GF-305 and Hansen-5 were resistant, but nine other rootstocks expressed various degrees of susceptibility. All Spanish rootstocks were susceptible to both Meloidogyne species except for the three G x N selections. The root-knot nematode resistant peach Nemared used as a male parent with Garfi was found to transmit a high degree of resistance to M. incognita and immunity to M. arenaria. Progenies of P. davidiana (Ga x D no. 3), a known source of resistance to root-knot nematodes, were susceptible. Key words: Meloidogyne arenaria, M. incognita, nematode, Prunus, resistance, root-knot nematode, rootstock.

Interaction of meloidogyne incognita race-3 and macrophomina phaseolina in a root-rot disease complex of chickpea

Abstract: The growth of chickpeas and nodulation was adversely affected by the presence of both Meloidogyne incognita race-3 and Macrophomina phaseolina. Disease severity increased with increasing inocula and various combinations of M. incognita and M. phaseolina had synergistic effect on plant growth reduction. The rate of nematode multiplication was density dependent. Increase in the inoculum level of M. phaseolina progressively decreased nematode multiplication and root galling while root-rotting increased with the increase in the combined inocula of M. phaseolina and M. incognita.

The effect of population densities of meoidogyne incognita on yield of susceptible and resistant tomato

Abstract: The relationship between initial population densities of Meloidogyne incognita race 1 and yield of susceptible and resistant tomato cultivars was investigated in the field. Microplots were infested with finely chopped nematode infected pepper roots to give a range of population densities of 0, 0.031, 0.062, 0.125, 0.25, 0.5, 1, 2, 4, 8, 16, 32, 64 or 128 eggs and juveniles/cm³ soil. A tolerance limit (T) of 0.55 eggs and juveniles of M. incognita/cm³ soil was calculated for both cultivars of tomato. A minimum relative yield (m) of 0 and 0.7 at initial population densities (Pi) = 32 eggs and juveniles/cm³ soil was also calculated for the susceptible and resistant tomato cultivar, respectively. Fruit size and marketable yield of tomato of the susceptible cultivar were negatively affected by the nematode infestation. Maximum nematode reproduction rate was 1,539 at the lowest Pi on the susceptible tomato but decreased with increasing nematode population density. Reproduction rate was lower that 1 at all initial population densities of M. incognita in microplots planted with the resistant tomato cultivar.

Relationships between Soil and Levels of Meloidogyne incognita and Tobacco Yield and Quality

Abstract: A 2-year study with six soils and four levels of Meloidogyne incognita in microplots was designed to determine the effects of these parameters on nematode activity and tobacco yield and quality. Key components under study were affected by soil, nematode level, and season (year-cultivar). In 1980, low initial nematode numbers (1,250) enhanced tobacco yield in Cecil clay loam, but caused slight to moderate yield losses in the other soils. Yield losses to M. incognita were generally greatest in sandy and muck soils. In 1980, regression analyses of the independent parameters Pi - clay-sand vs. yield gave an R(2) of 0.40. Examples of other coefficients of determination for yield vs. selected factors were root-necrosis index, 0.40; root-gall index, 0.18; root-gall index-cation exchange capacity (CEC), 0.34; root-necrosis index-CEC, 0.56; and root-necrosis index-sand-soil acidity-calcium, 0.62. In contrast, the R(2) for Pi alone versus yield in 1981 was 0.84. Soil also affected nematode reproduction with the greatest increases occurring in the sandy soils. In both years, low nematode numbers enhanced the synthesis of sugar in tobacco, whereas leaves from all other nematode treatments had low sugar levels. A low nicotine content was associated with nematode infection. Tobacco from sandy soils had a higher nicotine content than tobacco from clay soils.

Modification of Resistance Expression of Phaseolus vulgaris to Meloidogyne incognita by Elevated Soil Temperatures.

Abstract: The effect of temperature on the reaction of susceptible (Canario Divex) and resistant (A 211) bean pure lines to Meloidogyne incognita was studied with soil temperature tanks housed in a growth chamber at 22 or 24 C. Soil temperature remained constant at 16, 22, 24, 26, 30, or 32 C in several trials. Bean line A 211 was resistant at 16 and 22 C but was susceptible at 24 C and above. Resistance to root-knot nematode reproduction was affected by a lower temperature (24 C) than was resistance to root galling (26 C) in A 211. Incubation of A 211 at 30 C for 3 and 16 days after inoculation with M. incognita resulted in a significant increase in nematode reproduction and root galling, respectively. The resistant reactions of A 211 to nematode reproduction and root galling were retained when inoculated plants were incubated at 21 C for a minimum of 16 and 23 days, respectively, prior to high temperature treatment. Key words: bean, host resistance, Meloidogyne incognita, Phaseolus vulgaris, reproduction, root galling.