| 1. |
- Sivan, Pramod, 1984-, et al.
(författare)
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Dieback of Gmelina arborea Trees and Structural Alterations Induced in the Wood Cell Walls by Alternaria alternata
- 2022
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Ingår i: FORESTIST. - : AVES YAYINCILIK A.Ş.. - 2602-4039. ; 72:1, s. 2-9
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Tidskriftsartikel (refereegranskat)abstract
- The death and structural alterations in the secondary xylem of Gmelina arborea trees in response to fungal invasion were investigated by light and electron microscopy methods. In vivo experiments indicate that Alternaria alternata is an aggressive pathogen which invades the deeper part of the wood in the branches-up to 4 cm from the site of infection--within 10 days of inoculation. The mycelial invasion occurred through pits and boreholes formed by the fungus in the vessels, fibers, and axial and ray parenchyma cells. Scanning electron microscopy also revealed the colonization of fungus through pit and vessel elements. In vitro studies showed that ray cells and fibers were more prone to cell wall damage in contrast to vessels during the initial stage of infection. The etiology of infection found in the infected samples collected from the living trees and samples of in vivo and in vitro experiments showed similar patterns of infection and confirmed that A. alternata is responsible for the mortality and decay in Gmelina trees. It causes a typical soft-rot pattern with cell wall alterations such as cavity formation by "L" bending. The separation of fibers at the compound middle lamella region indicated that the fungus is capable of degrading both lignin-rich regions of cell walls. The boreholes in the fiber wall also showed distinct variations in size and shape. The penetration of fungal hyphae through the middle lamella and removal of lignin from the cell walls was also confirmed with transmission electron microscopy studies.
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| 2. |
- Sivan, Pramod, 1984-, et al.
(författare)
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Post infectional alterations caused by Xylaria polymorpha in the secondary xylem of Lannea coromandelica (Houtt.) Merr
- 2021
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Ingår i: Forestist. - : AVES YAYINCILIK A.Ş.. - 2602-4039. ; 71:2, s. 93-101
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Tidskriftsartikel (refereegranskat)abstract
- Xylaria polymorpha is known to cause root rot disease in hardwood trees. In the present study, trees of the species Lannea coromandelica infected with X. polymorpha showed symptoms consistent with root rot disease and also presented with a soft rot decay pattern. Bright-field microscopy, Confocal Microscopy, and Scanning Electron Microscopy revealed that fungal mycelia penetrated the S2 layer of the fiber wall while axial parenchyma was found to be relatively resistant without much visible damage. Occasionally, separation of the parenchyma adjacent to fiber occurred due to the dissolution of the compound middle lamella. Ray parenchyma cells showed several boreholes having irregular shapes and sizes. Enlargement of the pits in axial and ray parenchyma was present in all the samples investigated. Xylem fibers were the most susceptible cell type and developed several tunnels through the S2 layer. Tunnels formed in the S2 layer of the fiber wall by the mycelia showed L- and/or T-bending. The diameter of the tunnels started narrow, increasing in size as the tunnels extended into the S3 layer. In some instances, complete removal of the S3 layer and fusion of the tunnels with the fiber lumen appearing as U-shaped erosion troughs was observed. At the advanced stage of decay, extensive damage was observed in the vessel walls, leaving the middle lamella and wall layer facing the vessel lumen intact. In conclusion the anatomical characteristics observed in the present study suggests that X. polymopha is an aggressive saprobe with strong ligninolytic activity causing soft rot type 2 decay in the wood cell wall of Lannea coromandelica.
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