Histopathology of Seed-Borne Infections - Applied Research Center ...

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Location of Fungal Hyphae in Seeds 143showed drying of leaves from tip to base and died in 2 to 3 weeks. Only 2 to 3%of the plants survived.5.5.4.2.2 AscochytaAscochyta rabiei and A. fabae var. lentis cause chickpea and lentil blight, respectively.Infected seeds show discolored areas. Lesions vary from small to large withmycelium and pycnidia often seen on the seed surface of chickpea (Maden et al.,1975) and occasionally in lentil (Singh, Khare, and Mathur, 1993). In chickpea thelesions are localized, and abundant mycelium occurs in the region of the lesions,but the adjoining clean areas are free of infection. Seeds with small superficial lesionscarry mycelium in the seed coat and on the surface of cotyledons, whereas thosewith deep lesions contain profuse mycelium in the seed coat (Figures 5.18A, B) andcotyledons (Figure 5.18C). Pycnidia are common in the seed coat (Figure 5.18B)and hyphae often become intracellular in vascular elements (Figure 5.18D). Bothsuperficial and deep infections have equal potential to cause seedling infection(Maden et al., 1975; Vishnuawat, Agarwal, and Singh, 1985).The hyphae of A. fabae f. sp. lentis travel vertically as well as horizontally inthe palisade cells, hourglass cells, and parenchymatous cells of the seed coat inmoderately infected seeds. Hyphae are inter- and intracellular in parenchyma. Inheavily infected seeds, the fungal mycelium occurs in the seed coat, the spacebetween the seed coat and the cotyledons, and, rarely, the space between the cotyledonsand the embryonal axis. Heavy accumulation of mycelium also takes placein the hilar tissues (Singh, Khare, and Mathur, 1993).Ascochyta pisi, which causes blight, leaf, and pod spot in pea, is carried asmycelium in the seed coat in infected seeds; 75% of cotyledons and 40% of plumuleare also infected in such seeds. Infection may be caused by mycelium spreading inthe pod cavity or directly by lesions on the pod surface (Dekker, 1957).5.5.4.2.3 BotryodiplodiaBotryodiplodia theobromae is seed-borne in a large number of crops (Kumar andShetty, 1983; Richardson, 1990). It causes stem rot and seed rot in maize. Singh,Singh, and Singh (1986b) found that the seed surface in weak to moderately infectedmaize seeds develops black streaks or pinhead-like microsclerotia, but heavilyinfected seeds are almost black. B. theobromae hyphae are confined to the pericarpand basal cap in weakly infected seeds, but occur in the pericarp, basal cap, closingtissue, aleurone layer, and, rarely, in other layers of the endosperm and placentochalazalregion in moderately infected seeds. It occurs in all tissues, including theembryo in heavily infected kernels (Kumar and Shetty, 1983; Singh, Singh, andSingh, 1986b). Heavy infection causes disintegration of tissues and depletion ofreserve food material.The decoated (woody testa removed) rubber seeds infected with B. theobromaehave brown to black discoloration progressing from micropylar to chalazal end(Varma, Singh, and Singh, 1990). The expanse of mycelium differed quantitativelyin different components in seeds showing different degrees of discoloration. Thefungus colonized the tegmen, perisperm, endosperm, and embryo in all the symptomaticseeds, but it was recorded only rarely in asymptomatic seeds. In moderately
144 Histopathology of Seed-Borne InfectionsepspyccotilsABCDFIGURE 5.18 Ascochyta rabiei in seeds of Cicer arietinum. A, Cleared whole-mount ofinner layers of seed coat showing profuse branched and septate mycelium. B, Ls part of seedwith mycelium aggregated in the layers of seed coat and subepidermal pycnidium. C, Ls partof cotyledon showing inter- and intracellular mycelium (arrow). D, Ts through vascular regionof seed in the position of lesion showing intracellular hyphae (arrows). (Abbreviations: cot,cotyledon; eps, seed epidermis; ils, inner layers of seed coat; pyc, pycnidium.) (FromMaden, S. et al. 1975. Seed Sci. Technol. 3: 667–681. With permission.)
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Histopathology ofSeed-Borne Infecti
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PrefaceThe book deals with only one
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The AuthorsDalbir Singh, Ph.D., for
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ContentsChapter 1 Introduction ....
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4.3.2 Routes for Infection from Ova
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8.4 Survival in Seed ..............
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2 Histopathology of Seed-Borne Infe
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4 Histopathology of Seed-Borne Infe
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2Reproductive Structuresand Seed Fo
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Reproductive Structures and Seed Fo
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14 Histopathology of Seed-Borne Inf
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3Structure of SeedsThe seed habit i
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Structure of Seeds 49(1971) of usin
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Structure of Seeds 51is found in as
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Structure of Seeds 53dry seed of Ly
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Structure of Seeds 553.3.2 SEED COA
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Structure of Seeds 57Endosperm: One
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Structure of Seeds 59scendembepsmuA
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Structure of Seeds 61Endosperm: Sca
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Structure of Seeds 63Chalaza simple
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Structure of Seeds 65stystypmerA Bc
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Structure of Seeds 67epsent endCADB
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Structure of Seeds 69perhscendembpe
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Structure of Seeds 71eposgepi′epo
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Structure of Seeds 73(Zea and Sorgh
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Structure of Seeds 75Baker, D.M. an
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Structure of Seeds 77Maheshwari Dev
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Structure of Seeds 79Vries, M.A. de
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194 Histopathology of Seed-Borne In
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7Seed Infection by VirusesViruses a
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Seed Infection by Viruses 201TABLE
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Seed Infection by Viruses 205Unlike
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Seed Infection by Viruses 2073. The
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Seed Infection by Viruses 209Wilcox
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Seed Infection by Viruses 213floret
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Seed Infection by Viruses 215ptowvv
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Seed Infection by Viruses 2177.4.2
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Seed Infection by Viruses 219seed(s
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Seed Infection by Viruses 221AMV fo
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Seed Infection by Viruses 223REFERE
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Seed Infection by Viruses 225Hunter
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Seed Infection by Viruses 227Wolf,
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