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.     

Fungal Parasites of the Cereal Cyst Nematode Heterodera avenae in Southern Sweden

Fungal parasites of the cereal cyst nematode Heterodera avenae were isolated from four sites in southern Sweden. In all, 15 different fungi were isolated from different stages of the nematode life cycle. Among the egg parasites, Verticillium chlamydosporium was common in young cysts on roots, whereas an unidentified species of Verticillium (Verticillium sp. 1) was the dominating species in cysts from soil, especially if the soll had been stored for 8-12 months. V. chlamydosporium was frequently isolated from eggs in cysts from soil, when analyzed shortly after sampling. Verticillium sp. 1 is distinct from V. chlamydosporium because it does not produce dichtyo-chlamydospores in the aerial mycelium and because it grows at 6 C where V. chlamydosporium fails to grow. Paecilomyces lilacinus, Microdochium bolleyi, Cylindrocarpon sp., and several nonsporulating fungi were also isolated from eggs in cysts from soil. Between 10 and 20% of the eggs in cysts collected in the field were infected with fungi. In a pot test between < 1 and 29%, with a mean of 13%, of females on roots became infected, always by Nematophthora gynophila. Resting spores of N. gynophila extracted directly from field soil, collected at the four sites, varied from 3 to 49 spores/gram of air dried soil.     

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.     

Extent of disease in populations of Heterodera, with especial reference to H. schachtii

Analysis was made of the extent of disease in 112 populations of Heterodera schachtii, comprising 88 populations of cysts obtained from soil samples and 24 populations of females and cysts taken from host roots. Overall, some 14% of full cysts taken from soil were diseased, although much variation was found. About half of the cysts were substantially and half partially diseased. Where beet monoculture had long been practised, overall disease was approximately doubled. Less than 50% of diseased cysts were parasitised by recognised egg pathogens and nearly the same proportion showed symptoms of lysis, coagulation or decay, the causes of which could not be ascertained. The remainder contained unexamined or miscellaneous fungi and a few showed oily degeneration. Disease in 10 populations of cysts from roots was higher than in cysts from soil. In females from roots it was especially variable, for most diseased females were invaded by one or two specific fungal pathogens in whose absence all were healthy. Examination of six populations of Heterodera avenae indicated the extent and nature of disease was not dissimilar from that in H. schachtii. The pathogens, which were all fungi, and the disease symptoms of uncertain origin found in cysts and females of H. schachtii are briefly summarised.     

Microbial parasites associated with Tylenchulus semipenetrans in citrus orchards of Catalonia,Spain

Citrus orchards in Catalonia, Spain were surveyed to identify microbial parasites of Tylenchulus semipenetrans, and their distribution and density. Of 62 orchards, 48 were positively infested with the citrus nematode. Fungal strains were isolated from single eggs, females or second-stage juveniles of the citrus nematode in 69% of the infested orchards. The fungi identified in order of occurrence were Paecilomyces lilacinus, Fusarium solani, Fusarium spp., Cylindrocarpon cylindroides, Verticillium fungicola, Cladosporium cladosporioides, F. oxysporum, Veronaea botryosa, Sepedonium chrysospermum, Volutella ciliata, Exophiala pisciphila and Acremonium sp. Fungal parasitism was related directly to the number of females g^?1 of root and magnesium in the soil, and inversely, to the number of eggs g^?1 of root and phosphorus in the soil (R ²=0.8654; P<0.0001). Nematode trapping fungi were isolated from soil samples in 29% of the orchards, and Monacrosporium elegans, Arthrobotrys dactyloides, A. javanica, A. superba and A. oligospora var. microspora, were the species present. Endospores of the hyperparasite Pasteuria adhering to vermiform stages of T. semipenetrans were found in 50% of the orchards infested with the citrus nematode.     

Infection of plant-parasitic nematodes by Paecilomyces lilacinus and Monacrosporium lysipagum

Studying the mode of infection of a biocontrol agent is important in order to assess its efficiency. The mode and severity of infection of nematodes by a soil saprophyte Paecilomyces lilacinus (Thom) Samson and a knob-producing nematode trapping fungus Monacrosporium lysipagum (Drechsler) Subram were studied under laboratory conditions using microscopy. Infection of stationary stages of nematodes by P. lilacinus was studied with three plant-parasitic nematodes Meloidogyne javanica (Treub) Chitwood, Heterodera avenae Wollenweber and Radopholus similis (Cobb) Thorne. Paecilomyces lilacinus infected eggs, juveniles and females of M. javanica by direct hyphal penetration. The early developed eggs were more susceptible than the eggs containing fully developed juveniles. As observed by transmission electron microscopy, fungal hypha penetrated the M. javanica female cuticle directly. Paecilomyces lilacinus also infected immature cysts of H. avenae including eggs in the cysts and the eggs of R. similis. Trapping and subsequent killing of mobile stages of nematodes by M. lysipagum were studied with the above three nematodes. In addition, plant-parasitic nematodes Pratylenchus neglectus (Rensch) Chitwood and Oteifa and Ditylenchus dipsaci (Kuhn) Filipjev were tested with M. lysipagum. This fungus was shown to infect mobile stages of all the plant-parasitic nematodes. In general, juveniles except those of P. neglectus, were more susceptible to the attack than adults.     

Effectiveness of Hirsutella minnesotensis and H. rhossiliensis in control of the soybean cyst nematode in four soils with various pH,texture, and organic matter

The parasitism of soybean cyst nematode, Heterodera glycines, by the fungi Hirsutella rhossiliensis and Hirsutella minnesotensis and their biocontrol effectiveness against the nematode were investigated in four soils with various pH, texture, and organic matter. Fungal parasitism was assayed in the soils in 25 mL vials. As expected, percentage of H. glycines second-stage juveniles (J2) parasitized by either fungus increased with increasing number of fungus-colonized J2 initially added into the soils. Parasitism of J2 by the fungi was negatively related with soil pH. Both positive and negative relationships with fungal parasitism were observed for soil sandiness and organic matter. In greenhouse study, both fungi at 0.2–0.8 g fresh mycelium of liquid culture per 0.3 L pot and 1% corn-grits culture effectively reduced nematode population density. The relationship between biocontrol effectiveness and the soil factors depended on fungal species and inoculation levels. In general, percentage reduction of egg population density in the soil was negatively correlated with soil pH and positively correlated with sandiness. There was no or weak correlation between egg reduction and organic matter. The percentage of J2 parasitized by the fungi 2 months after planting did not correlate with the soil factors. Plant growth was better in the two soils with intermediate pH and sand than the soil with high pH and low sand or with low pH and high sand. It appeared that soil pH and/or texture are important in influencing biocontrol effectiveness, but further studies are needed to determine the effect of individual factors because they are correlated.     

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.     

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.     

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.     

Fungi recovered from root-knot nematodes infecting vegetables under protected cultivation

A survey was conducted in root-knot nematode-infested plastic houses to determine the diversity and frequency of occurrence of fungi associated with the nematode. The relationships between percentage fungal parasitism and physicochemical properties of soil were also investigated. Fifty-nine plastic houses were sampled in southeastern Spain, 42 treated with nematicides and 17 left untreated. Eleven fungal genera and unidentified fungi were isolated from nematode eggs or juveniles. Fungal parasitism occurred more frequently in untreated (82.4%) than treated (50%) soils. The species richness in untreated soils ranged from 0 to 5, the Shannon–Wiener diversity index (a measurement of how many different fungi there are in site taking into account how evenly they are distributed among the site) from 0 to 2.01, and the evenness index from 0.46 to 0.99. In treated soils, species richness ranged from 0 to 4, the Shannon–Wiener diversity index from 0 to 1.61, and the evenness index from 0.81 to 1. Of the sites with nematophagous fungi, Arthrobotrys dactyloides (34%), Cylindrocarpon sp., Neosartoria hiratsukae (17%), and Fusarium solani (14%) were the fungi most frequently found. Physicochemical properties of soil were similar in nematicide treated and untreated soils. Percent fungal parasitism in untreated soils correlated positively with lime, silt and carbonate content of soil.     

Untersuchungen über den Befall des Rübenzystennematoden (Heterodera schachtii Schmidt) durch pilzliche Eiparasiten in zwei Zuckerrüben-Getreide-Fruchtfolgen

Abstract Investigations on fungal egg parasites of the sugar beet nematode ( Heterodera schachtii Schmidt) in two sugar beet-cereal-rotations
In two field trials with rotations of sugar beet-cereals-green manure the population dynamics of Heterodera schachtii was investigated as well as the frequency of its fungal egg parasites. During the rotation, highest rates of fungal parasitism (20–48%) were observed after years with sugar beet, independently of the nematode population density. In the interim parasitism decreased to about 10%. A highly significant correlation was found between nematode population density and the amount of parasitized eggs and larvae. The effect of resistant catch crops (oil radish'Pegletta and white mustard'Maxi') on fungal egg parasites was not different from the effect of Phacelia or fallow. There are indications, however, that a high nematode multiplication on a susceptible catch crop promotes antagonistic fungi and, in consequence, a nematode population decrease may occur in the following sugar beet crop.     

Biocontrol: Fungal Parasites of Female Cyst Nematodes

Three species of fungi, Catenaria auxiliarls (Kühn) Tribe, Nematophthora gynophila Kerry and Crump, and a Lagenidiaceous fungus have been found attacking female cyst nematodes. All are zoosporic fungi which parasitize females on the root surface, cause the breakdown of the nematode cuticle, and prevent cyst formation. Their identification and some aspects of their biology are reviewed. N. gynophila is widespread in Britain and reduces populations of the cereal cyst nematode, Heterodera avenae Woll., to nondamaging levels. The potential of these nematophagous fungi as biocontrol agents is discussed.     

PATHOLOGY OF CYST-NEMATODES

1. The cyst-nematodes, which belong to the genus Heterodera Schmidt, are obligate plant parasites. Several species cause crop diseases of economic importance. These nematodes differ greatly in structure from the other, vermiform, plant-parasitic and soil-inhabiting nematodes, for although the migrant larval phase of cyst-nematodes is vermiform, this phase is only transient. The principal phases are the sedentary female, which feeds upon the plant root, and the cyst, which derives from the female and consists of the eggs surrounded by mucilage within the dead female cuticle. The term ‘egg’ includes the contents within the shell, which at maturity is usually a coiled, second stage, larva. 2. The migrant larva may be parasitized by many species of predacious and endozoic fungi which have been much studied, but these do not parasitize the females or cysts. Until 1974 only one parasite of the females was known, and that imperfectly. On the other hand, many fungi have been cited as parasites of eggs inside cysts, notably the species now known as Phialophora malorum and Cylindrocarpon destructans. Insect-pathogenic fungi have also been cited as egg parasites but evidence is now against their pathogenicity to Heterodera. No other classes of organism are known to parasitize the females or cysts, although Collembola have been reported as predators. 3. Studies published since 1973, including the present, show a total of seven (or eight) pathogenic fungi. There are two (or three) pathogens of the females, two major and three minor pathogens of the eggs. The former comprise Catenaria auxiliaris and two Entomophthora-like fungi, possibly the same species but both imperfectly known. The major egg pathogens are Verticillium chlamydosporium and an incompletely known species termed the ‘contortion fungus’ from the symptoms on infected larvae newly hatched from eggs. The minor egg pathogens are a ‘black yeast’ taxonomically fairly similar to but not identical with Phialophora malorum; a sterile ‘crystal-forming fungus’ and Cylindrocarpon destructans. The main features of these pathogens are described and illustrated. 4. Mycorrhizal fungi belonging to Glomus Tulasne & Tulasne are sometimes associated with cysts. They ordinarily sporulate inside empty cysts, but in one remarkable example from Heterodera schachtii growing on tomato host in glasshouse culture a Glomus apparently behaved as a pathogen. Pythium species may invade cysts maintained under unfavourable conditions. Miscellaneous other fungi are also found occasionally in eggs. 5. In addition to undergoing disease caused by fungi, eggs sometimes undergo oily degeneration. This disorder is not of numerical significance, but a high proportion of cysts are diseased through apparently non-specific causes whose symptoms can be summarized as ‘lysed, shrivelled, coagulated or decayed’. Although the majority of diseased females are killed by fungal pathogens, some 25–40% of diseased cysts are destroyed through non-specific causes. Overall disease in ten populations of Heterodera schachtii examined from roots was 9% of females and 26% of young cysts; in 76 populations sieved from soils a mean of 14% of older cysts were diseased. Where the cyst-nematode host had been grown in monoculture for 11 years higher proportions of cysts were diseased although few pathogens of females were present. Heterodera avenue cysts were parasitized to a similar extent. 6. Of the pathogens of females, Catenaria auxiliaris was widespread in H. schachtii and uncommon in H. avenue, whereas Entomophthora-like fungi were widespread in H. avenue and rare in H. schachtii. Of egg pathogens, Verticillium chlamydosporium and the ‘contortion fungus’ were common in H. schachtii and H. avenae, and the ‘contortion fungus’ was also found in H. glycines. The minor egg pathogens were much less common.     

The effects of formalin, nabam, irrigation and nitrogen on Heterodera avenae Woll., Ophiobolus graminis Sacc. and the growth of spring wheat

In 1964, nabam (sodium ethylene bisdithiocarbamate), water and three amounts of nitrogen fertilizer were applied to spring wheat on soil treated and untreated with formalin. The experiment lasted for 3 years during which there were eight different formalin, no–formalin sequences. The nabam and irrigation treatments were discontinued when it was found they did not affect the principal pathogens present, the cereal cyst nematode Heterodera avenae and the take–all fungus Ophiobolus graminis. Formalin increased grain and straw yields in the year in which it was applied but led to increased H. avenae populations which adversely affected the succeeding crop. Formalin controlled O. graminis in the year it was applied except on land treated for the first time in 1966. H. avenae seemed to be the main check to growth until about June, and O. graminis later. At the end of the experiment, total grain yields and nematode soil populations were greatest in the plots treated with formalin each year and least in those never treated with formalin. Yield loss from either O. graminis or H. avenae alone could not be assessed because formalin usually controlled both during the season in which it was applied and both were present in untreated plots. However, in 1965, some comparisons of the effects of each pathogen were possible when one occurred in the presence of differing amounts of the other. A doubling of total grain yield over 3 years was accompanied by an eightfold increase in H. avenae in sequences of continuous formalin or formalin 1964 and 1965, whereas yield increases caused by extra nitrogen were not matched by such a big increase in H. avenae. This suggests that formalin might be affecting H. avenae through factors other than increased plant size and vigour, which in themselves would tend to encourage larger nematode populations. In the absence of formalin, H. avenae soil populations either fell or failed to increase.     

Interactions between Heterodera avenae and Pratylenchus neglectus on Wheat

In a long-term field experiment, differential population densities of Heterodera avenae were produced by frequent cropping with resistant (cv. Panema) or susceptible (cv. Peniarth) oat. The two oat cultivars were equally good hosts of Pratylenchus neglectus in a glass house experiment with field soil. On wheat crops grown after oats in field experiments, P. neglectus population densities in roots were higher in plots where H. avenae had been controlled than in plots with moderate infestations (40 H. avenae eggs/g soil). The field observations indicated that the reduction in population densities of P. neglectus coincided with the development in roots of sedentary stages of the cyst nematode. Evidence for an indirect effect of H. avenae on P. neglectus was found in vitro in a split-root experiment. In the same field, grain yields of two wheat cultivars susceptible or resistant to H. avenae, but both susceptible to P. neglectus, was not reduced by P. neglectus. Alternation of H. avenae resistant and susceptible cultivars is a possible way of exploiting the inverse relationship between these nematodes, whilst controlling cyst nematode -populations in intensive cereal production systems.     

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.     

Natural occurrence of fungal egg parasites of root-knot nematodes, Meloidogyne spp. in organic and integrated vegetable production systems in Spain

A survey was conducted to assess the biodiversity and frequency of infection of fungal egg parasites of Meloidogyne spp. and relate results to soil properties in organic and integrated vegetable production in Spain. Forty sites were sampled at the end of the cropping cycle, 30 under integrated and ten under organic production. Fungal egg parasites were isolated from all organically managed sites and from 73 % sites under integrated production. Species richness and Shannon–Wiener index did not differ between production systems but the percentage of fungal egg parasitism did, as well as soil properties. Percentages of egg parasitism higher than 40 % were found in five and three sites under organic and integrated production, respectively. In all these sites, Pochonia chlamydosporia was present alone or co-occurring with other fungal species. The relative frequency of P. chlamydosporia was positively related to the percentage of parasitism in both production systems.     

Potential for biological control of Heterodera schachtii by Pochonia chlamydosporia var. chlamydosporia on sugar beet

The biological control potential of an isolate of Pochonia chlamydosporia var. chlamydosporia against Heterodera schachtii was examined by assessing the percentage of females and cysts that became infected on water agar, the effect of culture filtrate on juvenile mobility, and the effects of the fungus on the final population of the nematode on sugar beet under greenhouse conditions. After 3 weeks at 20°C, 74 and 95% of the eggs within cysts and females, respectively, were colonised by the fungus on water agar. The full concentration of the fungal filtrate from cultures in malt extract broth killed only 12% of the juveniles after 24 h at 25°C. In the greenhouse experiment, adding 16,000 chlamydospores of the fungus per gram of soil as either colonised barley grains or spores reduced the final number of females on roots of sugar beet by 50 and 66%, respectively, after 3 months. The reproduction factor was reduced to ×2 in spore-treated soil compared with ×5 in the untreated control, and 18% of the eggs in spore-treated soil were colonised by fungal mycelium. Generally, P. chlamydosporia var. chlamydosporia was more efficient at reducing the nematode population when applied as spores without any substrate than when used as colonised barley grains.     

The invasion and development of the cereal cyst-nematode, Heterodera avenae in the roots of autumn-and spring-sown cereals

Observations were made at 2 or 4 wk intervals from December to harvest on all stages of Heterodera avenae in winter oats growing on infested land. Second-stage larvae were present in all soil samples except on 5 and 20 July. Invasion and development of larvae was slow during winter. The nodal and seminal roots of winter oats were both heavily invaded by the nematode; larvae which invaded seminal roots tended to become male whereas those in nodal roots tended to become female. There was a small second invasion in August. Females were first observed on the roots of winter oats on 17 May, 214 days after the crop was sown and 62 days after the first fourth-stage larva was observed. The nodal roots of spring barley contained few H. avenae larvae whereas these roots were heavily invaded in winter wheat and oats. In spring barley the nodal roots were developing in June and July when few second-stage larvae were in the soil whereas in winter oats and wheat the nodal roots were growing rapidly in April when larvae were most numerous, and so were heavily invaded.