Evaluation of Pochonia chlamydosporia var. chlamydosporia as a control agent of Meloidogyne javanica on pistachio

The potential of isolates of Pochonia chlamydosporia var. chlamydosporia as biocontrol agents for root-knot nematodes was investigated in vitro and on pistachio plants. On potato dextrose agar, growth of all isolates started at temperatures above 10°C, reached maximum between 25 and 28°C and slowed down at 33°C. On water agar, all isolates parasitized more than 85% of the eggs of Meloidogyne javanica at 18°C after 3 weeks. Filtrates of isolates grown on malt extract broth did not cause more than 5% mortality on second-stage juveniles of M. javanica after 48 h of incubation. A single application of 10×10³ chlamydospores (produced on sand–barley medium) g^–1 soil, was applied to unsterilised soil planted with pistachio cv. Kalehghochi, and plants were inoculated with 3000 nematode eggs. After 120 days in the glasshouse, nematode multiplication and damage were measured. Ability of fungus isolates to survive in the soil and to grow on roots were estimated by counting colony forming units (cfu) on semi-selective medium. Fungal abundance in soil increased nearly 3-fold and 10×10³ and 20×10³ cfu g^–1 root of pistachio were estimated in pots treated with isolates 40 and 50, respectively. Strain 50 was more abundant in soil and on the roots, infected more eggs (40%) on the roots and controlled 56% of total population of M. javanica on pistachio roots, whereas isolate 40 parasitized 15% of the eggs on the roots and controlled ca. 36% of the final nematode population.     

Evaluation of a Native and Introduced Isolate of Pochonia chlamydosporia against Meloidogyne javanica

Growth chamber and plastic tunnel experiments were conducted to compare the ability of a native and introduced isolate of Pochonia chlamydosporia to colonize the rhizosphere of selected plant species and survive in soil. Effects of the isolates on population density of Meloidogyne javanica and yield of tomato after single or multiple fungal applications were also determined. In growth chamber experiments, both isolates showed a similar ability to colonise the rhizosphere of selected vegetables, except for the introduced isolate, which produced more colony forming units cm^-2 of root surface on tomato and cabbage than the native one. In the tunnel house, both isolates parasitized eggs of M. javanica, and the native but not the introduced isolate increased parasitism after multiple applications. The native isolate was recovered more frequently from soil, and was a better colonizer of tomato roots than the introduced one irrespective of the number of fungal applications. Multiple fungal applications of either isolate reduced the nematode gall rating, and the native isolate also reduced the final egg population in roots. Neither isolates reduced final nematode densities in soil or affected tomato yield when compared to untreated plots.     

Colonisation of barley roots by endophytic Fusarium equiseti and Pochonia chlamydosporia: Effects on plant growth and disease

Colonisation of plant roots by endophytic fungi may confer benefits to the host such as protection against abiotic or biotic stresses or plant growth promotion. The exploitation of these properties is of great relevance at an applied level, either to increase yields of agricultural crops or in reforestation activities. Fusarium equiseti is a naturally occurring endophyte in vegetation under stress in Mediterranean ecosystems. Pochonia chlamydosporia is a nematode egg-parasitic fungus with a worldwide distribution. Both fungi have the capacity to colonise roots of non-host plants endophytically and to protect them against phytopathogenic fungi under laboratory conditions. The aim of this study was to evaluate the root population dynamics of these fungi under non-axenic practical conditions. Both fungal species were inoculated into barley roots. Their presence in roots and effects on plant growth and incidence of disease caused by the pathogen Gaeumannomyces graminis var. tritici were monitored periodically. Both fungi colonised barley roots endophytically over the duration of the experiment and competed with other existing fungal root colonisers. Furthermore, colonisation of roots by P. chlamydosporia promoted plant growth. Although a clear suppressive effect on disease could not be detected, F. equiseti isolates reduced the mean root lesion length caused by the pathogen. Results of this work suggest that both F. equiseti and P. chlamydosporia are long-term root endophytes that confer beneficial effects to the host plant.     

Interaction between Meloidogyne incognita and Pochonia chlamydosporia and their effects on the growth of Phaseolus vulgaris

An experiment was conducted to test the effect of different doses of 2, 4 and 8?g/2?kg of soil of Pochonia chlamydosporia against the root-knot nematode (Meloidogyne incognita) on Phaseolus vulgaris. It was observed that inoculation of plant with the nematode alone, and 15?days prior to fungal inoculation, reduced the plant growth when compared with the plant with fungal application followed by the nematode. Plant length, fresh and dry weight, chlorophyll, carotenoid, protein contents and nitrate reductase activity decreased in nematode-infested plants. Application of higher dose of 8?g/2?kg of soil of P. chlamydosporia increased all the plant growth parameters as well as biochemical parameters. Highest number of galls per root system was recorded on the plants infested with nematode but not treated with the fungus. However, application of fungus prior to nematode inoculation improved the plant growth and reduced the number of galls and the number of egg masses per root system.     

Lack of effect of the nematophagous fungus Duddingtonia flagrans on the development of the dung beetle, Aphodius constans

The nematode-trapping fungus Duddingtonia flagrans may be used as a biological control agent of gastro-intestinal nematode larvae of ruminants by feeding the hosts with fungal spores. This trial was intended to search an eventual detrimental impact of the presence of spores of D. flagrans in high numbers in goat feces on the common dung beetle, Aphodius constans (Coleoptera: Aphodiidae). A. constans eggs were settled in feces derived from grazing goats fed spores at daily dose rates of 0, 0.25 × 10⁶, 0.5 × 10⁶ or 10⁶ spores/kg BW. At the end of the incubation period, the number of adults that have emerged from eggs were counted and compared between dose rates. No difference in emergence rate between treatments can be seen. The presence of D. flagrans spores in goat feces, even in large numbers, did not alter the development of A. constans.     

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.     

Measuring abundance,diversity and parasitic ability in two populations of the nematophagous fungus Pochonia chlamydosporia var. chlamydosporia

Abundance, genetic diversity and parasitic ability in the facultative nematode parasite Pochonia chlamydosporia var. chlamydosporia were compared in soils from two sites in Portugal under long-term tomato cultivation where root-knot nematodes (Meloidogyne sp.) were present. Fungal abundance assessed by selective agar or real-time quantitative PCR with specific primers was similar in both soils. PCR fingerprinting of isolates with ERIC primers indicated that the dominant P. c. var. chlamydosporia biotypes (profiles A and B) in both soils were very closely related, although a second biotype (profile C) was detected in one soil. When tomato plants infected with M. incognita were grown in the two soils, only profiles A and B were recovered from eggs. Primers based on polymorphisms in vcp1 demonstrated that isolates with profiles A and B were likely to prefer root-knot nematodes, whereas profile C preferred cyst nematodes. In the soil containing profiles A, B and C, egg parasitism by P. chlamydosporia was estimated at 1% using water agar plates with antibiotics but fewer than 0.2% of M. incognita eggs were shown to be infected with P. c. var. chlamydosporia when using species-specific β-tubulin-PCR primers. In contrast, the soil containing only profile B showed 22% egg parasitism on water agar plates and more than 2.5% of eggs were confirmed as P. c. var. chlamydosporia by species-specific β-tubulin-PCR primers. The results, which reveal limited diversity within the fungus at the two sites, are discussed in relation to biological control of plant-parasitic nematodes.     

Pathogenicity of Fungi to Eggs of Heterodera glycines

Twenty-one isolates of 18 fungal species were tested on water agar for their pathogenicity to eggs of Heterodera glycines. An egg-parasitic index (EPI) for each of these fungi was recorded on a scale from 0 to 10, and hatch of nematode eggs was determined after exposure to the fungi on water agar for 3 weeks at 24 C. The EPI for Verticillium chlamydosporium was 7.6, and the fungus reduced hatch 74%. Pyrenochaeta terrestris and two sterile fungi also showed a high EPI and reduced hatch 42-73%. Arthrobotrys dactyloides, Fusarium oxysporum, Paecilomyces lilacinus, Stagonospora heteroderae, Neocosmospora vasinfecta, Fusarium solani, and Exophiala pisciphila were moderately pathogenic to eggs (EPI was 2.0-4.5, and hatch was reduced 21-56%). Beauveria bassiana, Hirsutella rhossiliensis, Hirsutella thompsonii, Dictyochaeta heteroderae, Dictyochaeta coffeae, Gliocladium catenulatum, and Cladosporium sp. showed little parasitism of nematode eggs but reduced hatch. A negative correlation was observed between hatch and fungal parasitism of eggs. Fusarium oxysporum, H. rhossiliensis, P. lilacinus, S. heteroderae, V. chlamydosporium, and sterile fungus 1 also were tested in soil in a greenhouse test. After 3 months, the nematode densities were lower in soil treated with H. rhossiliensis and V. chlamydosporium than in untreated soil. The nematode population densities were correlated negatively with the EPI, but not with the percentage of cysts colonized by the fungi. Plant weights and heights generally increased in the soil treated with the fungi.     

Studies of the cereal cyst-nematode, Heterodera avenae under continuous cereals, 1974–1978. I. Plant growth and nematode multiplication

Population changes of Heterodera avenae and crop growth in a sandy loam soil were studied from 1974 until 1978; the nematode decreased plant growth but failed in two of the years to multiply on susceptible hosts. Spring oats were the most heavily invaded cereal and produced the smallest shoots. Second-stage juveniles invaded cereal roots in decreasing numbers: spring oats > autumn oats > spring barley > spring wheat > autumn barley > autumn wheat. Numbers of females developing on the different cultivars were in a similar order. Most females developed on roots in 1976 despite poor crop growth in the severe drought. Numbers of H. avenae in soil treated with oxamyl (Vydate) at 8.8 kg/ha a. i. were less in all years except 1975. In the dry winter and spring of 1975/76 nematode multiplication was prevented in soil treated with oxamyl before drilling in the autumn. In all years large numbers of females were produced on the roots of all cultivars but in 1975 and 1978 nematode populations declined because few females survived to form cysts containing eggs and their fecundity was reduced. Numbers of cysts after harvest were not affected by formalin (38% formaldehyde) applied as a drench at 3000 litres/ha in 1977 but fecundity doubled in treated soil, and nematode multiplication increased from 3.8 × in untreated plots to 18.6 ×. When the plots were irrigated in 1978 numbers of cysts and fecundity increased in formalin treated soil resulting in an increase in multiplication from 0.3 × to 14.6 ×. Fungal parasites attacking H. avenae females and eggs are considered responsible for the poor multiplication of the nematode.     

Identification and molecular characterisation of new Mexican isolates of Pochonia chlamydosporia for the management of Meloidogyne spp.

New Mexican isolates of the nematophagous fungus Pochonia chlamydosporia were obtained from nematode infested fields in the vegetable growing area of Tepeaca Valley, Puebla State, Mexico. Based on macro and microscopic morphology, seven ‘putative’ P. chlamydosporia isolates were selected and the DNA extracted for polymerase chain reaction (PCR). Three new isolates of P. chlamydosporia were identified: Pcp2, Pcp21 and Pcp31. The amplification reaction of the internal transcribed spacer (ITS) region revealed a 650 bp amplicon which was used in a maximum likelihood phylogenetic inference analysis. Three groups were recovered in the tree topology, supported by a > 90% bootstrap value. Nucleotide identity values were > 83.6% between the test sequences and the reference sequence. In addition, using specific primers for two existing varieties of P. chlamydosporia, restriction fragment length polymorphism on the ITS products in conjunction with the phylogenetic inferences and the molecular test for detection of P. chlamydosporia vcp1 gene, it was found that all three isolates belong to a new variety which we have named P. chlamydosporia var. mexicana. We compared the chlamydospore production rate, rhizosphere colonisation and egg parasitism percentages of the three native isolates in Meloidogyne spp. with a reference isolate (Pc10). Native isolates produced > 1×10⁶ chlamydospores/50 g of substrate (of which more than 80% were viable), colonised > 80% of the rhizosphere, and parasitised > 60% of Meloidogyne incognita and Meloidogyne arenaria eggs. Meloidogyne hapla egg parasitism was < 60%. Isolates Pcp2 and Pcp21 were identified as potential biological control agents of Meloidogyne spp. to be tested further in greenhouse and field tests.     

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.     

Effects on plant growth and root-knot nematode infection of an endophytic GFP transformant of the nematophagous fungus Pochonia chlamydosporia

Pochonia chlamydosporia (Pc123) is a fungal parasite of nematode eggs which can colonize endophytically barley and tomato roots. In this paper we use culturing as well as quantitative PCR (qPCR) methods and a stable GFP transformant (Pc123gfp) to analyze the endophytic behavior of the fungus in tomato roots. We found no differences between virulence/root colonization of Pc123 and Pc123gfp on root-knot nematode Meloidogyne javanica eggs and tomato seedlings respectively. Confocal microscopy of Pc123gfp infecting M. javanica eggs revealed details of the process such as penetration hyphae in the egg shell or appressoria and associated post infection hyphae previously unseen. Pc123gfp colonization of tomato roots was low close to the root cap, but increased with the distance to form a patchy hyphal network. Pc123gfp colonized epidermal and cortex tomato root cells and induced plant defenses (papillae). qPCR unlike culturing revealed reduction in fungus root colonization (total and endophytic) with plant development. Pc123gfp was found by qPCR less rhizosphere competent than Pc123. Endophytic colonization by Pc123gfp promoted growth of both roots and shoots of tomato plants vs. uninoculated (control) plants. Tomato roots endophytically colonized by Pc123gfp and inoculated with M. javanica juveniles developed galls and egg masses which were colonized by the fungus. Our results suggest that endophytic colonization of tomato roots by P. chlamydosporia may be relevant for promoting plant growth and perhaps affect managing of root-knot nematode infestations.     

Eggs of Tylenchulus semipenetrans Inhibit Growth of Phytophthora nicotianae and Fusarium solani in vitro

In previous greenhouse and laboratory studies, citrus seedlings infested with the citrus nematode Tylenchulus semipenetrans and later inoculated with the fungus Phylophthora nicotianae grew larger and contained less fungal protein in root tissues than plants infected by only the fungus, demonstrating antagonism of the nematode to the fungus. In this study, we determined whether eggs of the citrus nematode T. semipenetrans and root-knot nematode Meloidogyne arenaria affected mycelial growth of P. nicotianae and Fusarium solani in vitro. Approximately 35,000 live or heat-killed (60°C, 10 minutes) eggs of each nematode species were surface-sterilized with cupric sulfate, mercuric chloride, and streptomycin sulfate and placed in 5-pl drops onto the center of nutrient agar plates. Nutrient agar plugs from actively growing colonies of P. nicotianae or F. solani were placed on top of the eggs for 48 hours after which fungal colony growth was determined. Live citrus nematode eggs suppressed mycelial growth of P. nicotianae and F. solani (P ≤ 0.05) compared to heat-killed eggs and water controls. Reaction of the fungi to heat-killed eggs was variable. Root-knot nematode eggs had no effect on either P. nicotianae or F. solani mycelial growth. The experiment demonstrated a species-specific, direct effect of the eggs of the citrus nematode on P, nicotianae and F. solani.     

Fungal Parasitism of Heterodera glycines Eggs as Influenced by Egg Age and Pre-colonization of Cysts by Other Fungi

The objective of this study was to determine the effect of egg age and pre-colonization of cysts by a saprophytic or parasitic fungus on parasitism of Heterodera glycines eggs by other parasitic fungi. In agar and in soil tests, fungi generally parasitized more eggs in early developmental stages than eggs containing a juvenile. The effect of pre-colonization of cysts by a fungus on parasitism of eggs by other fungi depended on the fungi involved. In most cases, pre-colonization of cysts by an unidentified, saprophytic fungal isolate (A-1-24) did not affect parasitism of eggs in the cysts subsequently treated with other fungi. However, pre-colonization of cysts by A-1-24 reduced fungal parasitism of eggs in cysts subsequently treated with Cylindrocarpon destructans isolate 3. In agar tests, pre-colonization of cysts by Chaetomium cochliodes, a saprophytic or weakly parasitic fungus, reduced parasitism of eggs in cysts subsequently treated with Verticillium chlamydosporium Florida isolate, Fusarium oxysporum, Fusarium solani, ARF18, and another sterile fungus. However, in soil tests, pre-colonization of cysts by C. cochliodes had no effect on parasitism of eggs by subsequent fungal parasites. In another test, parasitism of eggs by V. chlamydosporium in cysts was not affected by pre-colonizing fungi C. destructans, F. oxysporum, and F. solani but was reduced by Mortierella sp., Pyrenochaeta terrestris, and C. cochliodes. Parasitism of eggs in cysts by ARF18 was reduced by pre-colonizing fungi C. destructans, F. oxysporum, F. solani, P. terrestris, and C. cochliodes but not Mortierella sp.     

Observations on the introduction of Verticillium chlamydosporium and other parasitic fungi into soil for control of the cereal cyst-nematode Heterodera avenue

Isolates of Verticillium chlamydosporium and a sterile fungus added to soil on ground oat grain reduced the numbers of Heterodera avenae on wheat by between 26 and 80%. Nematode populations in uninoculated soil increased from 15 eggs/g soil before planting to 218 eggs/g after harvest. V. chlamydosporium was isolated from oat grain that had been air-dried and milled before introduction into soil. Applications of the fungi on attapulgite clay or as suspensions of mycelium and spores in water had no effect on nematode multiplication. The effect of the fungi on numbers of H. avenae eggs was similar in autoclaved and non-sterilised soil. V. chlamydosporium added on attapulgite clay to a calcareous sand and a calcareous silty loam could be re-isolated after at least 6 months. Some isolates colonised the roots of wheat without causing lesions or affecting the dry weights of shoots or roots. These results indicate that V. chlamydosporium may be useful for the biological control of cyst nematode pests.     

Development of Heterodera glycines on Soybean Damaged by Soybean Looper and Stem Canker

Short-term greenhouse studies with soybean (Glycine max cv. Bragg) were used to examine interactions between the soybean cyst nematode (Heterodera glycines) and two other common pests of soybean, the stem canker fungus (Diaporthe phaseolorum var. caulivora) and the soybean looper (Pseudoplusia includens), a lepidopterous defoliator. Numbers of cyst nematode juveniles in roots and numbers of cysts in soil and roots were reduced on plants with stem cankers. Defoliation by soybean looper larvae had the opposite effect; defoliation levels of 22 and 64% caused stepwise increases in numbers of juveniles and cysts in both roots and soil, whereas numbers of females in roots decreased. In two experiments, stem canker length was reduced 40 and 45% when root systems were colonized by the soybean cyst nematode. The absence of significant interactions among these pests indicates that the effects of soybean cyst nematode, stem canker, and soybean looper on plant growth and each other primarily were additive.     

Assessment of three strategies for the management of Meloidogyne arenaria on carrot in Mexico using Pochonia chlamydosporia var. mexicana under greenhouse conditions

Three control strategies for management of Meloidogyne arenaria were evaluated on carrot under greenhouse conditions. The control strategies tested were: i) incorporation of fresh broccoli; ii) carbofuran (Furadan®); and iii) Pochonia chlamydosporia var. mexicana, isolate Pcp21. Each strategy was evaluated separately and in combination (16 treatment combinations), each with three replicates. The experiment was done between February and April 2014 and repeated over the same time period in 2015. Each replicate experimental unit consisted of a 1?kg pot filled with tyndallised soil, to which broccoli, fungus and carbofuran were added according to treatment. Carrot seeds were sown into each pot and inoculated with M. arenaria eggs according to treatment. Pots were then maintained in the glasshouse for 12 weeks at 25?±?5°C. After this time the fresh root weight, root length, percent reduction in root galling, P. chlamydosporia var. mexicana colony forming units (CFU)/g of soil, and CFU/g root were all measured. Results showed that isolate Pcp21 of P. chlamydosporia var. mexicana significantly reduced root galling percentage by 50 and 78% in 2014 and 2015, respectively. Application of the fungus in combination with broccoli or carbofuran also reduced root galling. The number of CFU/ g of soil or root remained the same over the 12 weeks of the experiment. This isolate of P. chlamydosporia significantly reduced damage caused by M. arenaria on carrot and is a promising agent for management of this nematode.     

Studies of the cereal cyst-nematode, Heterodera avenae under continuous cereals, 1975–1978. II. Fungal parasitism of nematode females and eggs

The development and fungal parasitism of Heterodera avenae females and eggs on susceptible cereals was studied from 1975 to 1978 in a sandy loam soil. Despite the production of many females on the roots nematode numbers declined in two years (1975 and 1978), and it is female survival and fecundity and not female numbers which often limit H. avenae multiplication. Fungal parasites may totally destroy females on roots or result in the formation of small cysts which are often empty. Fecundity is reduced and many eggs may became infected. Parasitism of females and eggs was decreased and nematode multiplication was increased in soil treated with formalin (38% formaldehyde) at 3000 litres/ha, but because it is nematicidal and fungicidal interpretation of the effects of the sterilant are difficult. Formalin has a greater effect on H. avenae multiplication in wet summers when fungal parasites, particularly Nematophthora gynophila are more active. Parasitised females which may be destroyed in about 7 days are fragile and difficult to extract from soil. Rates of parasitism tend to be underestimated. Approximately 60% of the females which failed to form cysts containing eggs can be accounted for by N. gynophila and Verticillium chlamydosporium. Fungal parasitism is therefore the major factor in limiting the multiplication of H. avenae.     

Fungi Associated with Females and Cysts of Heterodera glycines in a Florida Soybean Field

Fungal colonization was determined for females and cysts of Heterodera glycines on soybean roots or in rhizosphere soil from a Florida soybean field. A total of 1,620 females and cysts were examined in 1991, and 1,303 were examined in 1992. More than 35 species of fungi were isolated from females and cysts. The frequency of fungi colonizing white and yellow females was low, but a high frequency of fungi was encountered in brown cysts, which increased with time of exposure of the cysts to the soil. No single fungal species predominated in the nematode females or cysts in this field. Rarely was a female or cyst colonized by more than one fungus. The common fungi isolated from the females and cysts were Neocosmospora vasinfecta, Fusarium solani, Fusarium oxysporum, Dictyochaeta coffeae, Dictyochaeta heteroderae, Pyrenochaeta terrestris, Exophiala pisciphila, Gliocladium catenulatum, Stagonospora heteroderae, and a black yeast-like fungus. The communities of common fungal species isolated from cysts in several regions in the southeastern United States appear to be similar.