Low-Temperature Scanning Electron Microscope Observations of the Meloidogyne incognita Egg Mass: The Gelatinous Matrix and Embryo Development

The root-knot nematode Meloidogyne incognita was cultured monoxenically on excised tomato roots. Galls and egg masses were observed daily using a light microscope. Two phases were distinguished in the gelatinous matrix of the egg mass: a translucent, amorphous material on the surface of the egg mass and a denser, layered phase in which nematode eggs were deposited. Egg masses were also cryofixed, fractured, and observed as frozen, hydrated specimens on a cold stage in a scanning electron microscope (SEM). In the SEM, the layered phase appeared as a meshwork of fibrils that became more loosely associated as the gelatinous matrix aged: Small pearl-like bodies were observed along the fibers of gelatinous matrix. The egg shell surface and several stages of embryo development, including the one-cell stage, initial cleavages, blastula, gastrula, tadpole stage, elongation, and molt of the first-stage juvenile within the egg shell, were observed and photographed with this technique. The developmental events observed were consistent with those described in other nematode species with different techniques.     

Effects of Temperature,Shoot Age,and Medium on Gall Induction by Subanguina picridis in Vitro

The influence of temperature, shoot age, and medium on gall induction by Subanguina picridis on Russian knapweed (Acroptilon repens) was examined in vitro. The optimal temperature for gall formation was 20 C. Gall induction was delayed as the temperature decreased, and decreased as shoot age increased. Bud primordia (0-day-old shoots and 5-day-old shoots) with an average length of 4.2 mm and 7.9 mm were the most suitable tissues for nematode development and gall formation. Gall formation was more effective on B5G medium than on MSG. Young shoots under slow growth were most suitable for mass rearing of S. picridis.     

The applicability of the plant vigor and resource regulation hypotheses in explaining Epiblema gall moth–Parthenium weed interactions

A basic question in insect–plant interactions is whether the insects respond to, or regulate plant traits, or a complex mixture of the two. The relative importance of the directions of the influence in insect–plant interactions has therefore been articulated through both the plant vigor hypothesis (PVH) and the resource regulation hypothesis (RRH). This study tested the applicability of these hypotheses in explaining the interactions between Parthenium hysterophorus L. (Asteraceae) and its stem‐galling moth, Epiblema strenuana Walker (Lepidoptera: Tortricidae). Parthenium plants exposed to galling were sampled at three sites in north Queensland, Australia, over a 2‐year period, and the relationship between gall abundance and plant vigor (plant height, biomass, flowers per plant, and branches per plant) was studied. To test the predictions of PVH and RRH, the vigor of parthenium plants protected from galling using insecticides was compared to galled plants and plants that escaped from galling. The vigor of ungalled plants was less than the vigor of galled plants. The higher plant vigor in galled plants was not due to galling, as was evident from insecticide exclusion trials. The insect seemed to preferentially gall the more vigorous plants. These findings support the predictions of the PVH and are contrary to those of RRH. Since gall abundance is linked to plant vigor, galling may have only a limited impact on the vigor of parthenium. This has implications for weed biological control. If the objective of biological control is to regulate the population of a plant by a galling insect, a preference for more vigorous plants by the insect is likely to limit its ability to regulate plant populations. This may explain the paucity of successes against biocontrol of annual weeds using gall insects.     

THE RELATIONSHIP BETWEEN A FLOWER GALL MIDGE PSEUDAS-PHONDYLIA SP. (DIPTERA: CECIDOMYIIDAE) AND ITS HOST PLANT ACTINIDIA VALVATA*

Abstract Kiwifruit plants, Actinidia sp., are native to subtropical China. The flower-bud gall of A. valvata, which is induced by an undescribed gall midge in the genus Pseud as phond ylia, is valued by the pharmaceutical industry. When studying the biology of the Actinid ia/Pseud as phond ylia interaction in Central-south China we found evidence suggesting that under certain circumstances the gall insect modifies the reproductive mode of the dioecious host plant. Surveys and field experiments in the National Hupingshan Natural Reserve showed a high frequency of galled trees. The density of galled trees varied among valleys and among trees within the valleys. In two valleys, 92% and 75%, respectively, of all trees were attacked, while in a third valley no trees were attacked. When infested, staminate tree only produced galls, whereas pistillate plants produced normal fruits as well as galls. Gall shape differed between male and female trees. Trees with galls tended to produce more fruits than treea without galls. We speculate that this is one of a few documented examples of an insect that induces androdioecy in an otherwise functionally dioecious plant.     

The three-dimensional structure of vascular tissues in Agrobacterium tumefaciens-induced crown galls and in the host stems of Ricinus communis L.

The three-dimensional pattern of phloem and xylem in 10-d-to two-month-old tumors induced by Agrobacterium tumefaciens (C58) and in adjacent Ricinus communis L. stem tissues was studied in thick sections by clearing with lactic acid and by staining with lacmoid. The crown galls contained two types of vascular strands: treelike branched bundles, which developed towards the tumor surface in fast-growing regions, and globular bundles in the slowly developing parts. Both types of vascular bundles contained xylem and phloem and were continuous with the vascular system of the host plant. The tumor bundles were interconnected by a dense net of phloem anastomoses, consisting of sieve tubes but no vessels. These vascular patterns reflect the apparent synthesis sites, concentration gradients and flow pathways of the plant hormones additionally produced in the tumors upon expression of the T-DNA-encoded genes. The A. tumefaciens-induced crown gall affected vascular differentiation in the host stem. In the basipetal direction, the tumor induced more xylem differentiation directly below it, where the crown-gall bundles joined the vascular system of the host. In the centripetal direction, the crown gall caused the development of pathologic xylem characterized by narrow vessels, giant rays and absence of fibers. On the other hand, most probably as a consequence of its gibberellic acid content, the host plant stimulated a local differentiation of regenerative phloem and xylem fibers with unique ramifications, only at the base of the tumor. However, fibers were absent from the main body of the crown gall. The study shows that A. tumefaciens-induced crown galls are characterized by a sophisticated network of vascular tissues in the tumor and are accompanied by a perturbated vessel system in the host. The hormonal mechanisms controlling vascular differentiation in the tumor and neighboring host tissues are discussed. In addition, the gall constriction hypothesis is proposed for explaining the mechanism which gives priority in water supply to the growing gall over the host shoot.We thank Dr. Zs. Koncz (Max-Planck-Institut für Züchtungsforschung, Köln, Germany) for Agrobacterium strains and the Deutsche Forschungsgemeinschaft (SFB 199) for financial support to C.I.U.     

Medfly eradication in California:

The impact of malathion-bait sprays (directed against medfly, Ceratitis capitata [Wiedemann]) on an endemic gall midge (Rhopalomyia californica Felt) and its parasitoids was investigated during 1982–83 in the south San Francisco Bay area of northern California. In a heavily sprayed area (Woodside), a population explosion of the midge was detected following 24 applications of malathion bait. The midge population reached levels ca. 90x greater than those observed in an adjacent unsprayed area (Jasper Ridge). In a moderately sprayed area (Portola Valley), the midge population increased as much as 5x that observed in the adjacent unsprayed area (Jasper Ridge), following 12 applications of malathion bait. In laboratory tests, the malathion bait was toxic to both the midge and its parasitoids. The major parasitoids were Torymus koebelei (Huber), Zatropis capitis Burks, Platygaster californica (Ashmead) and Mesopolobus sp. Population increases of the midge following malathion-bait sprays were attributed to destruction of parasitoids and other natural enemies of the midge. If the environmental impact of malathion-bait sprays is related to the number of applications (as suggested in this study), then it would be worthwhile to determine the appropriate bait-spray strategy for a given situation, so as to minimize adverse effects on nontarget species, yet insure suppression or eradication of medfly.

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Résumé L'impact des pièges tratiés au malathion (destinés à Ceratitis capitata Wiedem) sur Rhopalomyia californica Felt et ses parasitoïdes a été examiné en 1982–1983 dans le sud de la zone de la baie de San Francisco en Californie. Dans une zone fortement traitée (Woodside), une explosion de population a été décelée après 24 traitements. La population de R. californica a atteint des niveaux 90 fois supérieurs à ceux observés dans une zone contiguë non traitée (Jasper Ridge). Dans une zone modérément traitée (Portola Valley), avec 12 traitement, la population de R. californica a atteint jusqu'a 5 fois celle de Jasper Ridge. Au laboratoire, le piège à malathion a été toxique tant pour R. californica que pour ses parasitoïdes, dont les principaux étaient: Torymus koebelei (Huber), Zatropis capitis Burks, Platygaster californica(Ashmead) et Mesopolobus sp. L'accroissement de la population de C. capitata après traitement a été attribué à la destruction de parasitoïdes et d'autres ennemis naturels. Si l'effet su l'environnement du traitement est lié au nombre d'interventions (comme le suggère cette étude), alors cela vaudrait la peine de définir une stratégie de traitement appropriée à une situation donnée, de façon à minimiser les effets négatifs sur des espèces non visées, tout en assurant la suppression ou l'éradication de C. capitata.

     

Silent T-DNA genes in plant lines transformed by Agrobacterium tumefaciens are activated by grafting and by 5-azacytidine treatment

Summary A shooty tumor induced by a shooter mutant of an octopine strain of Agrobacterium tumefaciens was cloned. One clone obtained (TS038) behaved aberrantly in that it grew as a shooty tumor tissue on phytohormone free medium, but did not contain octopine synthase activity. In line TS038 the genes for octopine synthase and for the enzymes involved in agropine and mannopine synthesis were present, but were not transcribed. However, the above genes became active in TS038 tumor shoots after grafting as well as after treatment with the hypomethylating agent 5-azacytidine. After an unusually long incubation period in the growth cabinet shoot cultures appeared to have developed small shoots from the top of the leaves. This unusual form of differentiation was found to be accompanied by the induction of octopine synthase activity.     

Mucin-associated T antigens in benign and malignant epithelium of the gall bladder,extrahepatic bile ducts and ampulla of Vater

The mucin-associated antigens Tn, sialosyl-Tn (STn), T and sialosyl-T (STAg) antigens accumulate through aberrant and incomplete glycosylation in malignant epithelial cells. Their diagnostic and prognostic significance in tumours of the colon and cervix has been described, and a possible role for Tn antigen in cell-to-cell adhesion has been suggested. These antigens have been demonstrated through peanut agglutinin (PNA) lectin binding and more recently using specific monoclonal antisera. Differences between the two methods have been described, which may be due to fixation schedules and/or specificity. We have investigated the effect of fixation on the binding of biotinylated PNA lectin and compared its reactivity with the immunoreactivity of monoclonal antisera to Tn, STn, T and STAg antigens in benign and malignant epithelium of the gall bladder, extrahepatic bile ducts and ampulla of Vater. We found that short-term fixation in formol sublimate resulted in poor PNA binding. All other tested fixation schedules showed strong perinuclear binding, similar to that found on cryostat sections. When compared with monoclonal antisera, PNA binding demonstrated the lowest specificity in benign epithelium. In both benign and malignant epithelium, the two methods cannot substitute for each other. STn and STAg antigens were found to be oncodevelopmental throughout the extrahepatic biliary tract. When used in a panel, they are useful as diagnostic markers of malignancy in gall bladder epithelium.     

Ribosylzeatin and zeatin in tobacco crown gall tissue

Cytokinins were extracted from two cultures of tobacco crown gall tumor tissue: an unorganized tissue and a teratoma which produced leafy shoots. On Sephadex LH-20 column chromatography, extracts of both types of tissue yielded two peaks of cytokinin activity with elution volumes similar to ribosylzeatin and zeatin. Ribosylzeatin and zeatin were detected and quantified by coupled gas chromatography — mass spectrometry selected ion monitoring (GC/MS SIM), comparable quantities being found in the two extracts. Full mass spectral evidence for the presence of ribosylzeatin in both tissues was obtained. No evidence was found for the presence of N⁶-(²-isopentenyl)adenosine (i⁶Ade) or N⁶-(²-isopentenyl)adenine (i⁶Ade) although these compounds have been reported to occur in cytokinin-habituated tobacco callus tissues.Abbreviations BAP 6-benzylaminopurine - GC gas chromatography - GC/MS coupled gas chromatography-mass spectrometry - i⁶ Ade N⁶-(²-isopentenyl)adenine - i⁶ Ado N⁶-(²-isopentenyl)adenosine - RFE rotary film evaporation - SIM selected ion monitoring - TLC thin-layer chromatography - TMS trimethylsilyl     

Distribution of Nothanguina phyllobia and Its Potential as a Biological Control Agent for Silver-leaf Nightshade

The nematode Nothanguina phyllobia Thorne was found within large foliar galls on the perennial weed Solanum elaeagnifolium Cav. in west Texas. A two-year survey of a 6400 sq-km area in west Texas showed extensive distribution of the nematode. No hosts other than S. elaeagnifolium were observed. Densities of juvenile nematodes in the soil were high. N. phyllobia spread rapidly after small numbers of infective juveniles were applied in a foliar spray to an S. elaeagnifolium population. The host plant declined in vigor and frequently died. Artificial inoculation of an S. elaeagnifolium population with large numbers of the nematodes by broadcasting infected plant tissue resulted in high infection incidence.