Ultrastructure of the host – pathogen relationship in red leaf disease of lowbush blueberry caused by the fungus Exobasidium vaccinii

1986 ◽  
Vol 64 (7) ◽  
pp. 1338-1343 ◽  
Author(s):  
Charles W. Mims ◽  
Nancy L. Nickerson

Actively growing shoots of Vaccinium angustifolium Ait. infected with Exobasidium vaccinii (Fckl.) Woron. contain slender, septate intercellular hyphae bearing short, typically lobed haustoria. Hyphae and haustoria are also present in the apical meristem, where they often distort the shapes of the host cells they contact. The overall structure of the meristem is, however, not significantly altered and leaf primordia continue to develop from the meristem. A rather sparse hyphal system is present in young leaves, but eventually it becomes more extensive and often fills intercellular spaces in the lower portion of the leaf. Numerous haustoria are present in the leaf and are basically similar in structure to those described previously in E. camelliae var. gracilis. Haustoria contain membranous inclusion bodies, and electron-dense penetration matrices are characteristically associated with each haustorium. Overall there is very little host cell wall response to a developing haustorium and no distinct collar of host wall material is associated with the haustorium.

1992 ◽  
Vol 70 (1) ◽  
pp. 58-72 ◽  
Author(s):  
Jeffrey G. Duckett ◽  
Roberto Ligrone

The ventral epidermal cells of the photosynthetic, surface-living gametophytes of Lycopodium cernuum, collected from moist shaded banks in Peninsular Malaysia, contain an aseptate fungus. In some cells the hyphae are thick walled and form coils encapsulated by a thin layer of host wall material. In others the fungus is thin walled and shows limited differentiation into larger trunk hyphae and arbuscules. The adjacent host cytoplasm, separated from the fungus by a granular interfacial matrix, contains numerous chloroplasts, mitochondria, and microtubules. The hyphae contact the substratum via the ventral walls of the epidermal cells and the rhizoids are free from infection. In the protocorm and root nodules, aseptate hyphae initially colonize mucilage-filled schizogenous intercellular spaces. Subsequent invasion of the host cells is associated with the development of massive overgrowths of host wall material. The fungal associations in L. cernuum share a mixture of attributes otherwise found in different angiosperm mycorrhizae and in mycotrophic relationships in liverworts. Wall ingrowths are present in both the gametophyte and sporophyte cells in the placenta of L. cernuum. The very limited development of the placenta, compared with L. appressum, certain bryophytes and ferns, the diminutive size, and early senescence of the gametophytes of L. cernuum are all linked to the presence of the protocorm. This massive absorptive organ, homologous to a foot, in terms of its position in sporophyte ontogeny, but external to the parent gametophyte, derives its nutrition partly from photosynthesis and partly from its fungal endophyte. Key words: chloroplasts, Lycopodium, mycorrhiza, pteridophytes, root nodules, symbiosis, transfer cells.


2007 ◽  
Vol 85 (2) ◽  
pp. 175-183 ◽  
Author(s):  
C.W. Mims ◽  
E.A. Richardson

Only a very small percentage of the shoots of the numerous Camellia sasanqua Thunb. plants examined in this study were infected by Exobasidium camelliae var. gracilis Shirai, and prior to the onset of new leaf formation in the spring, it was impossible to distinguish these shoots from healthy shoots with the naked eye. However, beginning in early April, an infected shoot gave rise to a group of tightly clustered, pale-green leaves that were significantly larger and thicker than the dark-green healthy leaves. Light and transmission electron microscopic observations revealed the presence of intercellular hyphae of E. camelliae var. gracilis in the apical meristems of shoots that gave rise to enlarged infected leaves. Very slender intercellular hyphae were observed between the tightly packed cells of the apical meristem as well as between the cells of the tunica that covered the meristem. Hyphae also filled many of the intercellular spaces in the stem immediately below the apical meristem. Some hyphae formed distinctive haustoria that protruded for short distances into the invaded host cells. Hyphae also were present in the leaf primordia and proliferated in the intercellular spaces while the primordium differentiated into a leaf. Eventually a distinct pseudoparenchymatous layer of intercellular hyphae developed some four to six cell layers above the lower epidermis. This layer then gave rise to the basidia that made up the hymenium of E. camelliae var. gracilis. As basidia developed, the underlying cell layers of the leaf separated from the overlying hymenium and eventually sloughed away to expose the basidia. Localized infections of random leaves also were observed. In many cases only a small part of a leaf was infected. Localized infections also culminated in successful hymenium development.


Author(s):  
H.M. Mazzone ◽  
W.F. Engler ◽  
G. Wray ◽  
A. Szirmae ◽  
J. Conroy ◽  
...  

Viral inclusion bodies isolated from infected pest insects are being evaluated by the U.S. Dept. of Agriculture as biological insecticides against their hosts. Our research on these inclusion bodies constitutes part of an effort to support their approval by the Environmental Protection Agency as insect control agents. The inclusion bodies in this study are polyhedral in shape and contain rod-shaped viral particles. When ingested by pest insects, the inclusion bodies are broken down in the insect gut and release the viral particles which infect and multiply in the nuclei of host cells. These viruses are termed nucleopolyhedrosis viruses (NPV) and are representatives of the baculoviruses (Wildy, P. 1971 IN J.L. Melnick, ed., Monographs in Virology, vol. 5, S.Karger, New York).


2017 ◽  
Vol 7 (4) ◽  
pp. 281-289 ◽  
Author(s):  
David F. Bridges ◽  
Anna Breard ◽  
Alison Lacombe ◽  
Don C. Valentine ◽  
Shravani Tadepalli ◽  
...  

1988 ◽  
Vol 68 (1) ◽  
pp. 63-75 ◽  
Author(s):  
LEONARD J. EATON ◽  
DAVID G. PATRIQUIN

Soil ammonium and nitrate in the top 15 cm of soil were monitored after application of ammonium nitrate and ammonium sulfate to plots at 14 PF (previously fertilized) and 12 NF (never fertilized) lowbush blueberry (Vaccinium angustifolium Ait.) stands representing a range of soil types and management histories. Overall, nitrate values in unfertilized and ammonium sulfate plots were higher at PF than at NF sites, suggesting greater nitrification at PF sites. In laboratory incubation studies, nitrification proceeded immediately in soil from a PF site, but only after a 4-wk lag in that from an adjacent NF site. Nitrification rates were low compared to that in a garden soil (pH 6.6). N-Serve inhibited nitrification in both soils. In ammonium nitrate plots, "excess" N values (N values in fertilized plots minus values in unfertilized plots) were higher for PF than for NF sites, suggesting greater immobilization, plant uptake or loss of N at NF sites. There was no evidence, in laboratory studies, of immobilization of added N by soil from either type of site. Rhizome N concentration increased significantly in response to fertilization at an NF site, but not at a PF site. Key words: Blueberry (lowbush), fertilizer and soil nitrogen


Botany ◽  
2015 ◽  
Vol 93 (1) ◽  
pp. 41-46 ◽  
Author(s):  
Scott N. White ◽  
Nathan S. Boyd ◽  
Rene C. Van Acker ◽  
Clarence J. Swanton

Red sorrel (Rumex acetosella L.) is a ramet-producing herbaceous creeping perennial species commonly found as a weed in commercially managed lowbush blueberry (Vaccinium angustifolium Aiton) fields in Nova Scotia, Canada. Flowering and seed production occur primarily in overwintering ramets of this species, indicating a potential vernalization requirement for flowering. This study was therefore initiated to examine the role of vernalization, photoperiod, and pre-vernalization stimulus on ramet flowering. Red sorrel ramets propagated from creeping roots and seeds collected from established red sorrel populations in lowbush blueberry had an obligate requirement for vernalization to flower. Ramet populations maintained under pre- and post-vernalization photoperiods of 16 h flowered following 12 weeks of vernalization at 4 ± 0.1 °C, whereas those maintained under constant 16, 14, or 8 h photoperiods without vernalization did not flower. Vernalization for 10 weeks maximized, but did not saturate, the flowering response. Pre-vernalization photoperiod affected flowering response, with increased flowering frequency observed in ramet populations exposed to decreasing, rather than constant, photoperiod prior to vernalization. This study represents the first attempt to determine the combined effects of vernalization and photoperiod on red sorrel flowering, and the results provide a benchmark for the future study of flowering and sexual reproduction in this economically important perennial weed species.


2002 ◽  
Vol 82 (4) ◽  
pp. 781-783 ◽  
Author(s):  
K. I. N. Jensen ◽  
E. G. Specht

Spring application of 1.0 kg ha-1 hexazinone to fruiting-year lowbush blueberry no later than the F3 floral stage, when floral buds separate, but before the corolla tube shows white, controlled some common herbaceous perennial weeds without injury to the crop. Key words: Herbicide injury, growth stages, weed control, hexazinone, Vaccinium angustifolium


1994 ◽  
Vol 74 (2) ◽  
pp. 341-345 ◽  
Author(s):  
Leonard J. Eaton

Effects of herbicide and herbicide-fertilizer combinations on vegetative and reproductive growth of the lowbush blueberry (Vaccinium angustifolium Ait.) were assessed over a 12-yr period (six production cycles). All treatments stimulated stem lengths, fruit buds per stem and fresh fruit yields compared with untreated controls, but only after 3–6 yr. After the second cycle, stem lengths and fruit bud numbers were greater in herbicide + NPK-treated plants than in all others. Fresh fruit yields were variable throughout the study but were higher in herbicide and herbicide + fertilizer plots than in untreated controls after 1982, except in 1988. Nitrogen levels were greater in leaves and rhizomes of plants in all herbicide and herbicide + fertilizer plots than in control plots after 10 yr, whereas phosphorus was higher only in plants fertilized with NPK. These results suggest the lowbush blueberry responds slowly to herbicide and fertilizer applications. Increased vegetative and reproductive development, as well as denser plant stands, resulted from repeated herbicide and fertilizer applications. Fertilizers applied in conjunction with herbicides stimulate vegetative growth (and fruit buds if an NPK fertilizer), but appear to have no consistent effect on fresh fruit yields. Key words:Vaccinium angustifolium, fertilizer, herbicide, fruit buds, yield


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