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.     

Use of real-time quantitative PCR to investigate root and gall colonisation by co-inoculated isolates of the nematophagous fungus Pochonia chlamydosporia

The fungus Pochonia chlamydosporia is a potential biological control agent for plant parasitic nematodes, but to date, there has been little investigation of interactions (competitive, antagonistic or synergistic) between different isolates that occur together on roots and nematode galls. Real-time quantitative PCR (qPCR) has greatly improved the study of many fungi in situ on plant and nematode hosts, but distinguishing closely related isolates remains difficult. In this study, primers to discriminate P. chlamydosporia var. chlamydosporia and P. chlamydosporia var. catenulata were used to measure the relative abundance of isolates of the two varieties when inoculated singly or together on tomato plants. Also, sequence-characterised amplified polymorphic regions were identified to distinguish two different isolates of P. chlamydosporia var. chlamydosporia . Individual 1-cm root segments and nematode galls were excised, DNA extracted and subjected to real-time qPCR with the discriminatory primers. The qPCR method proved sensitive and reproducible and demonstrated that roots and nematode galls were not uniformly colonised by the fungi. Results indicated that the P. chalmydosporia var. catenulata isolate was more abundant on roots and eggs than P. chlamydosporia var. chlamydosporia , but all the isolates infected a similar proportion of nematode eggs. There was an indication that the abundance of each fungal isolate was reduced in co-inoculation experiments compared with single inoculations, but the number of root segments and galls colonised was not statistically significantly different.     

Relationship between saprotrophic growth in soil of different biotypes of Pochonia chlamydosporia and the infection of nematode eggs

The ecology of Pochonia chlamydosporia in soil and its interaction with both plant and nematode hosts are important for the successful exploitation of the fungus as a biological control agent. Differences in saprotrophism and parasitism were assessed for biotypes of P. chlamydosporia, which had originated from the eggs of cyst or root‐knot nematodes. Colonisation in soils of different textures (compost, sandy loam and loamy sand) measured by the numbers of colony‐forming units, differed greatly. Most biotypes were more abundant in sterilised soil of the different textures compared with non‐sterilised soils. The proportion of nematode eggs parasitised in a baiting technique demonstrated that biotypes had host preferences. Those biotypes that originated from root‐knot nematodes (RKN‐biotypes) infected significantly more Meloidogyne hapla eggs than Globodera pallida eggs, whereas biotypes from cyst nematodes (CN‐biotypes) parasitised more G. pallida eggs than M. hapla eggs. Differences in virulence between biotypes in an in vitro assay in which the fungi were placed directly onto the egg masses of M. hapla and those differences observed in the baiting technique showed similar trends. There was a negative linear correlation between the growth of the eight biotypes in soil and the proportion of eggs they infected in compatible interactions (i.e. fungal biotype originated from the same nematode genus as the target eggs). Those biotypes that infected most nematode eggs colonised soil the least extensively, suggesting that virulence may have a fitness cost. However, the relationship between saprotrophic growth and virulence is complex. The relative abundance of the different biotypes in soil in Petri dish assays was similar to that under glasshouse conditions using potato but not tomato as the plant host. Chlamydospores of some biotypes applied to soil significantly reduced (>50%) the population densities of M. hapla on tomato and of G. pallida on potato plants. Some biotypes that were both effective and virulent are good candidates for biological control of specific nematode pests. Data presented here and elsewhere indicate that RKN‐biotypes have different host preferences to CN‐biotypes; the specific primers based on the vcp1 gene from P. chlamydosporia rapidly confirmed the host origin of seven of the eight biotypes.     

Parasitism of Heterodera schachtii and Meloidogyne javanica by Hirsutella rhossiliensis in Microplots over Two Growing Seasons

Numbers of cyst and root-knot nematodes and percentage parasitism by the nematophagous fungus Hirsutella rhossiliensis were quantified in microplots over 2 years. The microplots contained either sugarbeets in loam infested with Heterodera schachtii or tomatoes in sand infested with Meloidogyne javanica. The fungus was added to half of the microplots for each crop. Although H. rhossiliensis established in both microplot soils, the percentage of nematodes parasitized did not increase with nematode density and nematode numbers were not affected by the fungus. The results indicate that long-term interactions between populations of the fungus and cyst or root-knot nematodes will not result in biological control.     

Synergistic effects of antagonistic fungi and a plant growth promoting rhizobacterium, an arbuscular mycorrhizal fungus, or composted cow manure on populations of Meloidogyne incognita and growth of tomato

Effects of four antagonistic fungi (Paecilomyces lilacinus, Pochonia chlamydosporia, Trichoderma harzianum and Gliocladium virens) alone and together with a plant growth promoting rhizobacterium Pseudomonas putida, an arbuscular mycorrhizal fungus Glomus intraradices or with composted cow manure (CCM) were assessed on the growth of tomato and on the reproduction of Meloidogyne incognita in glasshouse experiments. Application of all antagonistic fungi (except G. virens), P. putida, G. intraradices or CCM caused a significant increase in the growth of plants without nematodes. However, use of either of these fungi, P. putida, G. intraradices and CCM against plants with nematodes caused a significant increase in tomato growth. Paecilomyces lilacinus caused a 42% increase in the growth of nematode-inoculated plants followed by P. chlamydosporia (36%), T. harzianum (18%) and G. virens (15%). CCM caused about 57% increase in the growth of nematode-inoculated plants followed by P. putida (37%) and G. intraradices (31%). Maximum increase (71%) in the growth of nematode-inoculated plants was observed when CCM was used with P. lilacinus. Moreover, P. lilacinus caused a high reduction (55%) in galling and nematode multiplication, while G. virens the least (25%). Use of P. putida also caused a 39% reduction in galling and nematode multiplication followed by CCM (34%) and G. intraradices (32%). Combined use of CCM with P. lilacinus caused maximum reduction (79%) in galling and nematode multiplication. Re-isolation of antagonistic fungi from nematodes revealed that P. lilacinus parasitised more females and eggs than other antagonistic fungi. Root colonisation by P. putida was increased with P. lilacinus, while colonisation by G. intraradices was reduced in the presence of antagonistic fungi.     

Managing Nematode Population Densities on Tomato Transplants Using Crop Rotation and a Nematicide

Millet, milo, soybean, crotalaria, and Norman pigeon pea were used in conjunction with clean fallow and a nematicide (fensulfothion) for managing nematode populations in the production of tomato transplants (Lycopersicon esculentum Mill.). Glean fallow was the most effective treatment in suppressing nematode numbers. After 2 years in tomato, root-knot nematodes increased in numbers to damaging levels, and fallow was no longer effective for complete control even in conjunction with fensulfothion. After 4 years in tomato, none of the crops used as summer cover crops alone or in conjunction with fensulfothion reduced numbers of root-knot nematodes in harvested tomato transplants sufficiently to meet Georgia certification regulations. Milo supported large numbers of Macroposthonia ornata and Pratylenchus spp. and crotalaria supported large numbers of Pratylenchus spp. Millet, milo, soybean, crotalaria, and pigeon pea are poor choices for summer cover crops in sites used to produce tomato transplants, because they support large populations of root-knot and other potentially destructive nematodes.     

Interaction of vesicular-arbuscular mycorrhizal fungi and root knot nematode on cultivars of tomato and white clover susceptible to Meloidogyne hapla

The interactive effects of vesicular-arbuscular mycorrhizal (VAM) fungi and root-knot nematode (Meloidogyne hapla) were studied on nematode-susceptible cultivars of tomato (cv. Scoresby) and white clover (cv. Huia) at four levels of applied phosphate. The relative merits of simultaneous inoculation with mycorrhizal fungi and nematodes and of inoculation with mycorrhizal fungi prior to nematode inoculation were evaluated. Mycorrhizal plants were more resistant than non-mycorrhizal plants to root-knot nematode at all phosphate levels and growth benefits were generally greater in plants preinfected with mycorrhizal fungi. Nematode numbers increased with increasing levels of applied phosphate. In mycorrhizal root systems, nematode numbers increased in the lower phosphate soils; at higher phosphate levels nematode numbers were either unaffected or reduced. The numbers of juveniles and adults per gram of root were always lower in mycorrhizal treatments. Mycorrhizal root length remained unaffected by nematode inoculation. Mycorrhizal inoculation thus increased the plants' resistance to infection by M. hapla. This was probably due to some alteration in the physiology of the root system but was not entirely a result of better host nutrition and improved phosphorus uptake by mycorrhizal plants.     

The effects of pesticides on the diversity of culturable soil bacteria

The numbers of culturable soil bacteria in plots that had received either no pesticides or the full combination (aldicarb, chlorfenvinphos, benomyl, glyphosate, plus chlorotoluron or triadimefon) over a 20 year period were compared. Differences were very small although there were consistently higher numbers on the treated plot, possibly reflecting the greater crop yields which had been reported previously. There was no significant difference in numbers of bacterial colonies with homology to a nif gene probe in soils from the two plots. Genetic fingerprinting of Pseudomonas fluorescens isolates from the plots, using ERIC-PCR, showed that the dominant strains in the two populations were not the same although there was no obvious difference in the degree of diversity. Substrate utilization by microbial populations from the two plots was compared using Biolog plates. The population from the pesticide-treated plot showed a higher rate of substrate utilization which could reflect a slightly higher inoculum of heterotrophic bacteria, but could also indicate greater metabolic diversity in the population.     

Rapid and reliable DNA extraction and PCR fingerprinting methods to discriminate multiple biotypes of the nematophagous fungus Pochonia chlamydosporia isolated from plant rhizospheres

Aims:  To develop a simple, rapid, reliable protocol producing consistent polymerase chain reaction (PCR) fingerprints of Pochonia chlamydosporia var. chlamydosporia biotypes for analysing different fungal isolates during co-infection of plants and nematodes.
Methods and Results:  DNA extracted from different P. chlamydosporia biotypes was fingerprinted using enterobacterial repetitive intragenic consensus (ERIC)-PCR. Four extraction methods (rapid alkaline lysis; microLYSIS^®-PLUS; DNeasy^®; FTA^® cards) gave consistent results within each protocol but these varied between protocols. Reproducible fingerprints were obtained only if DNA was extracted from fresh fungal cultures that were free of agar. Some DNA degradation occurred during storage, except with the FTA^® cards, used with this fungus for the first time, which provide a method for long-term archiving. Rapid alkaline lysis and ERIC-PCR identified fungal isolates from root and nematode egg surfaces when plants were treated with different combinations of fungal biotypes; the dominant biotype isolated from the rhizosphere was not always the most abundant in eggs.
Conclusions:  ERIC-PCR fingerprinting can reliably detect and identify different P. chlamydosporia biotypes. It is important to use fresh mycelium and the same DNA isolation method throughout each study.
Significance and Impact of the Study:  This evaluation of methods to assess genetic diversity and identify specific P. chlamydosporia biotypes is relevant to other mycelial fungi.     

Effects of arbuscular mycorrhizal fungi and a non-pathogenic<Emphasis Type="Italic"> Fusarium oxysporum</Emphasis> on<Emphasis Type="Italic"> Meloidogyne incognita</Emphasis> infestation of tomato

Arbuscular mycorrhizal (AM) fungi and non-pathogenic strains of soil-borne pathogens have been shown to control plant parasitic nematodes. As AM fungi and non-pathogenic fungi improve plant health by different mechanisms, combination of two such partners with complementary mechanisms might increase overall control efficacy and, therefore, provide an environmentally safe alternative to nematicide application. Experiments were conducted to study possible interactions between the AM fungus Glomus coronatum and the non-pathogenic Fusarium oxysporum strain Fo162 in the control of Meloidogyne incognita on tomato. Pre-inoculation of tomato plants with G. coronatum or Fo162 stimulated plant growth and reduced M. incognita infestation. Combined application of the AM fungus and Fo162 enhanced mycorrhization of tomato roots but did not increase overall nematode control or plant growth. A higher number of nematodes per gall was found for mycorrhizal than non-mycorrhizal plants. In synergisms between biocontrol agents, differences in their antagonistic mechanisms seem to be less important than their effects on different growth stages of the pathogen.     

番茄根际微生物种群动态变化及多样性

采用盆栽试验的方法对番茄根际主要微生物种群在不同生育期的动态变化进行了跟踪研究.结果表明,在番茄整个生育期内,可培养细菌数量在初花期和初果期时最多;放线菌数量从苗期到末期逐渐减少;真菌数量逐渐增多.番茄对细菌根际效应明显.DGGE图谱显示不同生育期番茄根际均具有较高的细菌多样性.根际细菌种类和数量在初花期发生较为显著的变化,初果期根际群落多样性指数(H)和物种丰度(S)值都达到最高,微生物最丰富,是筛选拮抗菌的较好时期.     

Fungal egg-parasites of plant-parasitic nematodes from Spanish soils

We have investigated the presence of fungal egg-parasites in Spanish soils with plant endoparasitic nematodes. Nine out of 68 samples (13%) yielded fungal parasites. The most common (seven strains) was Pochonia chlamydosporia var. chlamydosporia (= Verticillium chlamydosporium var. chlamydosporium), but Lecanicillium lecanii (= Verticillium lecanii) and Paecilomyces lilacinus were also found. Most strains were from cyst nematodes (Heterodera avenae or Heterodera schachtii). Biological factors related with the development and performance of these fungi as biocontrol agents were assessed in laboratory tetsts. Germination for most strains was around 90-100%. Higher biomass values were obtained, for most fungal strains, with complete or yeast extract peptone-glucose liquid media. P. lilacinus and L. lecanii showed the highest sporulation rates (1.0 x 10(9); and 1.5 x 10(10); conidia/g mycelium). All strains had optimum growth at 25 degrees C. High temperature (40 degrees C) was lethal to all fungi but low temperature (5 degrees C) allowed growth of L. lecanii. Most strains showed best growth close to pH 7. Several P. chlamydosporia strains produced diffusible pigments close to pH 3. Lack of moisture (aw = 0.887) in growth medium reduced but never arrested fungus growth. Proteolytic activity was, for all strains, the earliest and highest enzymatic activity. Amylolytic and pectinolytic activities showed the lowest values and the latter was undetectable for most strains. Pathogenicity (70-100percnt; egg infection) and severity (35-40 penetrating hyphae/egg) on Meloidogyne javanica were high for most strains tested. Our results show that agricultural soils in Spain contain fungal parasites susceptible to be biocontrol agents for plant-parasitic nematodes.     

Trophic interactions between bacterial-feeding nematodes in plant rhizospheres and the nematophagous fungus Hirsutella rhossiliensis to suppress Heterodera schachtii

Trophic exchanges in soil food webs may suppress populations of pest organisms. We hypothesize that the suppressive condition of soils might be enhanced by manipulating components of the food web. Specifically, by enhancing populations of bacterial-feeding nematodes, propagule density of the nematophagous fungus Hirsutella rhossiliensis should increase and constrain populations of Heterodera schachtii, a plant-parasitic nematode. The rhizospheres of Crotalaria juncea and Vicia villosa stimulated population growth of the bacterial-feeding nematode, Acrobeloides bodenheimeri, but not of the nematodes Caenorhabditis elegans or Rhabditis cucumeris. The rhizospheres of Tagetes patula, Eragrostis curvula, and Sesamum indicum had no effect on any of the bacterial-feeding nematodes investigated. Acrobeloides bodenheimeri was most susceptible to parasitism by the nematophagous fungus H. rhossiliensis with 35% of individuals being parasitized in a laboratory assay. In three separate trials, parasitism of H. schachtii by H. rhossiliensis was not enhanced when populations of A. bodenheimeri were amplified in a suitable rhizosphere.     

Suppression of the Root-knot Nematode Meloidogyne javanica by Alginate Pellets Containing the Nematophagous Fungi Hirsutella rhossiliensis , Monacrosporium cionopagum and M. ellipsosporum

The endoparasitic fungus Hirsutella rhossiliensis and the nematode-trapping fungi Monacrosporium cionopagum and M. ellipsosporum were formulated as hyphae in alginate pellets. In a soil microcosm experiment, dried pellets of all three fungi decreased the invasion of cabbage seedlings by the root-knot nematode Meloidogyne javanica when juvenile nematodes were placed 2 cm from roots; M. cionopagum was more effective than the other two fungi, reducing nematode invasion by 40-95% with 0.24-0.94 pellets cm - 3 of soil. In a field microplot experiment, in which neither H. rhossiliensis nor M. ellipsosporum suppressed nematodes, 0.5 pellets of M. cionopagum cm - 3 of soil suppressed M. javanica invasion of tomato seedlings by 73%. In a second microplot experiment with only M. cionopagum , again at 0.5 pellets cm - 3 of soil, the fungus suppressed the invasion of tomato seedlings whether the pellets were added 0, 5 or 14 days before planting; the population density of M. cionopagum increased to nearly 3000 propagules g - 1 of soil by day 8 and then declined to less than 300 by day 22. Enchytraeid worms were observed in and around damaged and apparently destroyed pellets in both microplot experiments. Whether enchytraeids consumed the fungi or otherwise affected biological control requires additional research.     

Phenotypic characterization of microbes in the rhizosphere of Alyssum murale

Metal hyperaccumulator plants like Alyssum murale are used for phytoremediation of Ni contaminated soils. Soil microorganisms are known to play an important role in nutrient acquisition for plants, however, little is known about the rhizosphere microorganisms of hyperaccumulators. Fresh and dry weight, and Ni and Fe concentrations in plant shoots were higher when A. murale was grown in non-sterilized compared to sterilized soils. The analysis of microbial populations in the rhizosphere of A. murale and in bulk soils demonstrated that microbial numbers were affected by the presence of the plant. Significantly higher numbers of culturable actinomycetes, bacteria and fungi were found in the rhizosphere compared to bulk soil. A higher percent of Ni-resistant bacteria were also found in the rhizosphere compared to bulk soil. Percentage of acid producing bacteria was higher among the rhizosphere isolates compared to isolates from bulk soil. However, proportions of siderophore producing and phosphate solubilizing bacteria were not affected by the presence of the plant. We hypothesize that microbes in the rhizosphere of A. murale were capable of reducing soil pH leading to an increase in metal uptake by this hyperaccumulator.     

新疆绿洲农田不同连作年限棉花根际土壤微生物群落多样性

以南北疆不同连作年限棉花根际土壤为研究对象,采用Biolog技术,并结合传统平板培养法和土壤酶的测定,研究连作对棉花根际土壤微生物群落多样性的影响。Biolog分析结果表明,不同连作年限棉花根际土壤微生物碳源利用和功能多样性差异显著。荒地土壤微生物活性较低;在连作年限较短时(5—10a),根际土壤微生物群落的平均颜色变化率(AWCD)和Shannon指数较高;长期连作(15—20a),则呈明显下降趋势。主成分分析表明,不同连作年限的棉花根际土壤微生物碳源利用特征有明显不同。第一、二组开垦与未开垦土壤分别在PC1和PC2上出现差异,未开垦土壤得分均为负值,开垦土壤均为正值;而正茬与连作多年的棉花土壤在PC1上差异显著。其中在PC1上起分异作用的碳源主要是羧酸类和聚合物类,这两类碳源可能是影响连作棉花根际土壤微生物的主要碳源。可培养微生物数量的测定结果表明,荒地细菌数量最少;在连作年限较低时(5—10a左右),细菌数量呈上升趋势;而长期连作(>15a)后,细菌数量呈现下降趋势。真菌数量在连作多年后(10—15a)也开始增加。放线菌变化趋势不明显。四种土壤酶活性在连作的初中期(5—15a),连作障碍表现明显,土壤酶活性呈下降(过氧化氢酶和磷酸酶)或先升高后下降(脲酶和蔗糖酶)趋势,但随着连作年限的延长(15—20a),这4种土壤酶活性均表现出增高趋势。综上所述,棉花长期连作使棉花根际土壤微生物群落多样性降低,发生连作障碍,进而导致棉花产量降低。     

Detection and biocontrol potential of <Emphasis Type="Italic">Verticillium leptobactrum</Emphasis> parasitizing <Emphasis Type="Italic">Meloidogyne</Emphasis> spp.

Three isolates of Verticillium leptobactrum proceeding from egg masses of root-knot nematodes (RKN) Meloidogyne spp. and soil samples collected in Tunisia were evaluated against second-stage juveniles (J2) and eggs of M. incognita, to determine the fungus biocontrol potential. In vitro tests showed that V. leptobactrum is an efficient nematode parasite. The fungus also colonized egg masses and parasitized hatching J2. In a greenhouse assay with tomato plants parasitized by M. incognita and M. javanica, V. leptobactrum was compared with isolates of Pochonia chlamydosporia and Monacrosporium sp., introducing the propagules into nematode-free or naturally infested soils. The V. leptobactrum isolates were active in RKN biocontrol, improving plants growth with a significant increase of tomato roots length, lower J2 numbers in soil or egg masses, as well as higher egg mortalities. In a second assay with M. javanica, treatments with three V. leptobactrum isolates reduced egg masses on roots as well as the density of J2 and the number of galls. To evaluate the fungus capability to colonize egg masses a nested Real-time polymerase chain reaction (PCR) assay, based on a molecular beacon probe was used to assess its presence. The probe was designed on a V. leptobactrum ITS region, previously sequenced. This method allowed detection of V. leptobactrum from egg masses, allowing quantitative DNA and fungal biomass estimations.     

Suppression of Meloidogyne hapla populations by Hirsutella minnesotensis

The effects of the endoparasitic fungus Hirsutella minnesotensis on populations of Meloidogyne hapla from Michigan (MI), Rhode Island (RI), Connecticut (CT), Lyndonville, New York (NYL), Geneva, New York (NYG), and Wisconsin (WI) were studied in the greenhouse. Twenty-day-old tomato (cv. Rutgers) seedlings were inoculated with either 0 or 600 eggs of each nematode population mixed with either 0, 0.02, or 0.1 g of fresh H. minnesotensis mycelium 0.1 L^-1 of soil in pots containing 0.5 L of soil, and maintained at 25±2°C for 2 months. No effect of the fungal treatments and nematode treatments on tomato plant heights and shoot dry weights was observed. While all M. hapla populations were suppressed by H. minnesotensis, the degree to which each population was affected varied slightly. Across fungal treatments and nematode populations, the fungus reduced total number of nematodes in roots by 61-98%, with the highest for NYG and RI, intermediate for NYL and CT, and lowest for MI and WI populations. The study demonstrated that H. minnesotensis may be used as a potential suppressor of M. hapla in vegetable production systems in the Great Lakes Region.     

Potential of Leguminous Cover Crops in Management of a Mixed Population of Root-knot Nematodes (Meloidogyne spp.)

Root-knot nematode is an important pest in agricultural production worldwide. Crop rotation is the only management strategy in some production systems, especially for resource poor farmers in developing countries. A series of experiments was conducted in the laboratory with several leguminous cover crops to investigate their potential for managing a mixture of root-knot nematodes (Meloidogyne arenaria, M. incognita, M. javanica). The root-knot nematode mixture failed to multiply on Mucuna pruriens and Crotalaria spectabilis but on Dolichos lablab the population increased more than 2- fold when inoculated with 500 and 1,000 nematodes per plant. There was no root-galling on M. pruriens and C. spectabilis but the gall rating was noted on D. lablab. Greater mortality of juvenile root-knot nematodes occurred when exposed to eluants of roots and leaves of leguminous crops than those of tomato; 48.7% of juveniles died after 72 h exposure to root eluant of C. spectabilis. The leaf eluant of D. lablab was toxic to nematodes but the root eluant was not. Thus, different parts of a botanical contain different active ingredients or different concentrations of the same active ingredient. The numbers of root-knot nematode eggs that hatched in root exudates of M. pruriens and C. spectabilis were significantly lower (20% and 26%) than in distilled water, tomato and P. vulgaris root exudates (83%, 72% and 89%) respectively. Tomato lacks nematotoxic compounds found in M. pruriens and C. spectabilis. Three months after inoculating plants with 1,000 root-knot nematode juveniles the populations in pots with M. pruriens, C. spectabilis and C. retusa had been reduced by approximately 79%, 85% and 86% respectively; compared with an increase of 262% nematodes in pots with Phaseolus vulgaris. There was significant reduction of 90% nematodes in fallow pots with no growing plant. The results from this study demonstrate that some leguminous species contain compounds that either kill root-knot nematodes or interfere with hatching and affect their capacity to invade and develop within their roots. M. pruriens, C. spectabilis and C. retusa could be used with effect to decrease a mixed field populations of root-knot nematodes.     

Interaction of Population Levels of Fusarium oxysporum f. sp. vasinfectum and Meloidogyne incognita on Cotton

In autoclaved greenhouse soil without Fusarium oxysporum f. sp. vasinfectum, Meloidogyne incognita did not cause leaf or vascular discoloration of 59-day-old cotton plants. Plants had root galls with as few as 50 Meloidogyne larvae per plant. Root galling was directly proportional to the initial nematode population level. Fusarium wilt symptoms occurred without nematodes with 77,000 fungus propagules or more per gram of soil. As few as 50 Meloidogyne larvae accompanying 650 fungus propagules caused Fusarium wilt. With few exceptions, leaf symptoms appeared sooner as numbers of either or both organisms increased. In soils infested with both organisms, the extent of fungal invasion and colonization was well correlated with the extent of nematode galling and other indications of the Fusarium wilt syndrome.