An improved method for light- and electron microscopial studies of nematode/fungal interactions

A method is presented that enables studies to be made of single nematode-fungal interactions under conditions where fungal growth at the expense of external nutrients is prevented. The nematophagous fungus Arthrobotrys ologospora was used as a model organism in these studies. The method is based on removal of the traps from the vegetative mycelium, immediately after a nematode was captured and transfer of the trap with the captured nematode into a droplet of sterile distilled water placed in a moisture chamber. In the absence of external nutrients, such isolated traps of A. oligospora were fully effective in penetrating and subsequently digesting the captured nematode. Solely vegetative mycelium was formed at the expense of the digested nematode; this developed from the trap that originally had captured the nematode. One advantage of the present method is that studies on various stages of the nematode-fungal interaction can now be performed under conditions that exclude major influences of external nutrients which otherwise could be communicated to the trap cells by way of the vegetative mycelium.     

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.     

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.     

The fungi in Century 21. The XXI Fungal Genetics Conference, Pacific Grove, California, March 13-18, 2001

As an important opportunistic pulmonary pathogen, Pneumocystis carinii has been the focus of extensive research over the decades. The use of laboratory animal models has permitted a detailed understanding of the host-parasite interaction but an understanding of the basic biology of P. carinii has lagged due in large part to the inability of the organism to grow well in culture and to the lack of a tractable genetic system. Molecular techniques have demonstrated extensive heterogeneity among P. carinii organisms isolated from different host species. Characterization of the genes and genomes of the Pneumocystis family has supported the notion that the family comprises different species rather than strains within the genus Pneumocystis and contributed to the understanding of the pathophysiology of infection. Many of the technical obstacles in the study of the organisms have been overcome in the past decade and the pace of research into the basic biology of the organism has accelerated. Biochemical pathways have been inferred from the presence of key enzyme activities or gene sequences, and attempts to dissect cellular pathways have been initiated. The Pneumocystis genome project promises to be a rich source of information with regard to the functional activity of the organism and the presence of specific biochemical pathways. These advances in our understanding of the biology of this organism should provide for future studies leading to the control of this opportunistic pathogen.     

Reproduction of Criconemoides simile, Helicotylenchus pseudorobustus,and Paratylenchus projectus on Soybean

Reproduction of Criconernoides simile, Paratylenchus projectus, and Helicotylenchus pseudorobustus, alone and in certain combinations, was characterized during 50 days on the soybean cultivars Custer and Hood. Custer was the more suitable host for all three nematodes and C. simile was the most vigorous parasite on both cultivars. C. simile and H. pseudorobustus reproduced as well in combination as they did alone; addition of P. projectus to this combination did not alter results. Reproduction by P. projectus was repressed on both cultivars when it was combined with C. simile and H. pseudorobustus. The relative importance of time was assessed, as it relates both to the establishment of parasitism by applied nematodes and to the rate of development of larvae in the various host-parasite combinations. The necessity of characterizing as well as enumerating populations when evaluating population development of ectoparasitic nematodes was demonstrated.     

Behavior of Tethered Meloidogyne incognita

The tethered-nematode technique was adapted for use with second-stage juveniles of Meloidogyne incognita. The data demonstrate that M. incognita exhibits the same patterns of behavior as adults of the free-living nematode, Caenorhabditis elegans. The principal differences are that M. incognita is slower and less regular in its behavior than C. elegans. The frequency of normal waves is about 0.2 Hz; that of reversal waves is about 0.06 Hz. Reversal bouts last about 1 minute. In response to a change in NaCl concentration, M. incognita modulates the probability of initiating a reversal bout in the same manner as C. elegans except that it responds more slowly and is repelled instead of attracted.     

Lipid composition of the entomopathogenic fungus Nomuraea rileyi

The total lipid content, neutral and polar lipid composition, and fatty acid profiles were determined for the different developmental stages of the entomopathogenic fungus, Nomuraea rileyi. In general, the lipid composition of N. rileyi was found to be very similar to that of other Fungi Imperfecti. Triacylglycerides and sterols were the major neutral lipids and phosphatidylethanolamine, phosphatidylinositol, and phosphatidylserine were the major polar lipids. Phosphatidylcholine, resolved in conidial and mycelial samples, was not detected in hyphal body samples. The major fatty acids were palmitic, oleic, and linoleic. Stearic acid was detected as a minor component of hyphal body samples. During conidiogenesis the overall lipid composition was altered in (1) a reduction in total lipid content, (2) an increase in the polar/neutral lipid ratio, and (3) an increase in the degree of fatty acid unsaturation.     

Pathogenicity of Pratylenchus coffeae,Scutellonema bradys,Meloidogyne incognita,and Rotylenchus reniformis on Dioscorea rotundata

Low populations (200 specimens per plant) of Pratylenchus cofl''eae, Scutellonema bradys, Meloidogyne incognita, and Rotylenchulus reniformis stimulated the development of tops, roots, and tubers of Dioscorea rotundata "Guinea" yam. We demonstrated experimentally that P. coffeae was responsible for the deterioration in quality of the yam tuber in Puerto Rico, a condition known as a dry rot of yam. Initial populations of 600 P. coffeae, S. bradys, or M. incognita, and populations of 1,000 P. coffeae or S. bradys per plant were high enough to induce dry rot of the yam tubers. P. coffeae and S. bradys were pathogenic to yam cultivar Guinea, but M. incognita and R. reniformis did not cause necrosis or cracking of the tuber cortex in our experiments.     

真菌菌丝体和发酵液的氨基酸分析比较

<正> 对云芝等7种真菌的菌丝体和发酵液分别测定17种氨基酸的含量,测定结果表明这些菌丝体中含有丰富的人体8种必需氨基酸,支链氨基酸及精氨酸,而芳香族氨基酸和含硫氨基酸却很低。7种真菌的菌丝体和它们的子实体,和三种食用蛋白(α-酪蛋白,卵白蛋白,大豆球蛋白)及4种粮食产品     

Population Development of Pratylenchus hexincisus in Eight Corn Inbreds

Of eight corn inbreds tested in the greenhouse and field, three (H60, H95, and H84) supported lower populations of Pratylenchus hexincisus than other inbreds included in this study. No apparent differences existed among inbreds in nematode invasion or development in the roots, or in population structure. Differences in population were therefore attributed to differential reproduction.     

Association of Macroposthonia xenoplax and Scutellonema brachyurum with the Peach Tree Short Life Syndrome

High populations of both Scutellonema brachyurum and Macroposthonia xenoplax were detected in the root zones of peach trees growing at sites where peach tree short life occurred. Both nematodes responded to changes in tree health, with the highest numbers detected under the most vigorous trees; both populations declined as tree vigor declined. Few of either species were detected 6 months after trees died. The nematode populations were inversely correlated with each other. More M. xenoplax were recovered during cool, wet weather, but moisture seems more important than temperature in influencing population levels. Most S. brachyurum were recovered during hot, dry weather.     

Feeding Habits in Soil Nematode Families and Genera—An Outline for Soil Ecologists

Because research on nematode involvement in trophic interactions, foodweb structure, and biodiversity is constrained by lack of an overview of nematode feeding habits, this outline presents a consensus of current thought on nematode feeding habits. The source of food is fundamental to trophic interactions and provides the basis for our definitions of the essential feeding types: 1) plant feeder, 2) hyphal feeder, 3) bacterial feeder, 4) substrate ingester, 5) predator of animals, 6) unicellular eucaryote feeder, 7) dispersal or infective stage of parasites, and 8) omnivore. Lists of families and genera with their presumed feeding types are given. Major gaps in knowledge of feeding in the smaller tylenchids and many dorylaims are noted.     

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.     

线虫的分子生物学研究

线虫在动物发育的研究及生物防治中起着巨大作用。对20世纪80年代以来有关植物寄生线虫、昆虫寄生线虫的分子生物学研究概况进行了综述。     

Effect of Age of Alfalfa Root on Penetration by Pratylenchus penetrans

Penetration by all migratory life stages of Pratylenchus penetrans into roots of alfalfa (Medicago sativa L. cv. Du Puits) was inversely proportional to tissue age. Two-day-old tissue in the root hair zone was penetrated twice as much as 10- or 20-day-old sections of the tap root. Age-related differences were also observed in branch roots; these differences were not affected by increasing the number of nematodes from 1 to 10 per inoculation site, nor by increasing the length of the incubation period from 6 to 96 h. Age-related differences were only significant with 3-wk-old plants, not with 2- and 1-wk-old seedlings. Nematodes entered roots at temperatures from 5 to 30 C with maximum entry at 20 C and minimum at 5 C. At all temperatures, except 5 C, penetration into young tissue (2 days) was significantly greater than into medium (10 days) and old (20 days) tissue. Females and third-stage larvae entered the different-aged root sections 122% and 83%, respectively, more than did males. Two-day-old seedlings of the alfalfa cultivars Vernal, Saranac, and Du Puits were penetrated equally by P. penetrans. Perhaps the inverse relationship between penetration and age of root is, in part, responsible for the increasing resistance or tolerance of plants to nematode damage as they grow older.     

Interaction of Four Soybean Cultivars with Subsoiling and a Nematicide

Yields of four soybean, Glycine max, cultivars were increased with subsoiling under the row and application of the nematicide, DBCP i 1,2-dibromo-3-chloropropane) in Tiflon sandy loam heavily infested with the root-knot nematode Meloidogyne incognita. These cultivars represent four maturity groups: very early (V), "Essex'', early (VI), "Davis'': medium (VII), ''Ransom''; and late (VIII), '' Hutton ''. The average increase for the four cullivars was about the same for subsoiling or DBCP. When the treatmcnts were used together, the increase was greater than when either was used alone, but the effects were not additive. Increased yields were obtained with subsoiling and DBCP for the most nematode resistant cultivar, Hutton, as well as for the most susccptiblc, Davis. Subsoiling reduced root-knot galling in nonfumigated plots but did not affect it in fumigated plots. On 12 September, M. incognita larvae were most numerous at the 0- to 20 cm depth, intermediate at 20 to 33 cm depth and least numerous at 33 to 46 cm depth, Subsoiling did not affect larval populations at the three levels.