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

88 Histopathology of Seed-Borne InfectionsfsgtABCFIGURE 4.4 Artificially inoculated stigma and style of Paspalum dilatatum by ascosporesand conidia of Claviceps paspali. A, Germ tubes from conidia penetrating between cells ofstigma. B, Conidia germinating on surface of style and germ tubes penetrating cells andgrowing downward toward ovary. C, Ts of infected ovary 2 days after inoculation, intercellularmycelium in nucellus (lower) and ovary wall (upper) with hyphal tips emerging between cellsof ovary epidermis. (Abbreviations: fs, fungal spore; gt, germ tube.) (From Luttrell, E.S. 1977.Phytopathology 67: 1461–1468. With permission.)pearl millet by conidial suspension of C. fusiformis, noted that the germ tubes enterthrough the stigma, style, and ovary wall.Neergaard (1989) traced the infection path of Didymella bryoniae, a cause ofinternal fruit rot in cucumber. The spores adhere to stigmatic papillae and germinate,and the germ tubes penetrate the stigma and invade the ovary through the style(Figure 4.5A, B). The preferred route taken by the hyphae is the transmitting tissue.Initially the hyphae grow intercellularly, but subsequently they also become intracellular.Marsh and Payne (1984) artificially inoculated silk of corn at different stages(green, yellow-brown, and brown). Conidia on yellow-brown silks germinated in 4to 8 hours, and hyphae entered directly or indirectly through cracks and intercellulargaps. The hyphae reached inside the parenchyma cells and grew parallel to the silkaxis.Halfon-Meiri and Rylski (1983) reported fruit infection in pepper by Alternariaalternata, following stigmatic infection. In a comparative study to determine featuresassociated with the degree of resistance to tomato fruit rot by F. oxysporum f. sp.lycopersici, Kabayashi et al. (1990) observed germination of fungal conidia on thestigma of both susceptible and resistant cultivars, and the hyphae grew in their stylesfor the first four days. The growth was retarded in the styles of the resistant cultivar,but continued in those of the susceptible cultivar.