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

Location of Fungal Hyphae in Seeds 1375.5.4.1.5 CercosporaCercospora species cause serious diseases of Arachis hypogaea, Glycine max, andBeta vulgaris. Cercospora kekuchii and C. sojina cause purple seed stain and seeddiscoloration of soybean, respectively. Ilyas et al. (1975) found hyphae of C. kekuchiiconfined to the seed coat, but Singh and Sinclair (1985, 1986) observed theiroccurrence in the seed coat, endosperm, and embryo. Singh and Sinclair (1985),using symptomatic seeds with gray to brown discoloration of the seed coat as wellas cotyledons (collected from uninoculated and artificially inoculated plants byC. sojina), found that the pathogen colonized the seed coat tissues (Figure 5.16A),the space between the seed coat and embryo, and, rarely, the hypocotyl-radicle regionof the embryo. Abundant hyphae occurred in the hilar region including tracheid bar(Figure 5.16B).Rastogi, Singh, and Singh (1998c) found hyphae of C. traversiana in the seedcoat and tissues of the hilar region in moderately infected seeds of Trigonella foenumgraecum.Abundant hyphae occurred in the seed coat, endosperm, and embryo inseverely infected seeds. Singh (1991) has reported the presence of conidia ofC. personata in the shells of groundnut, but there is no histopathological evidencefor this.5.5.4.1.6 BotrytisBotrytis anthophila, which causes anther mold of Trifolium pratense (red clover),reduces pollen fertility and also seed formation. Bondarzew (1914) and Silow (1933)reported systemic infection of plants. The infection originated from intraseminalmycelium, particularly present in the hourglass cells of the seed coat. Using seedsincubated on agar for 3 to 5 days, Bennum (1972) observed predominantly intercellularand rarely intracellular mycelium in the seed coat and hilar region — remnantsof funiculus, tracheid bar, and aerenchyma (stellate parenchyma) — but not in theembryo.Botrytis fabae occurs in the seed coat, cotyledons, and embryonal axis in infectedseeds of Vicia faba. Hyphae are present in the seed coat of all the infected seeds,but these occur in 40% of cotyledons and 20% of embryonic axes (Harrison, 1978).Van der Spek (1965) has reported Botrytis cinerea in the cells of seed coat in flax.5.5.4.1.7 PyriculariaPyricularia oryzae causes the most destructive and widely distributed blast diseasein rice. Chung and Lee (1983) have reported infection of P. oryzae within the tissuesof the glumes, rachilla, pedicel, palea, lemma, and pericarp. In heavily infectedseeds, the mycelium penetrates the aleurone layer and peripheral layers of theendosperm. The affected layers of endosperm turn dark brown. The embryos arefree of infection. Earlier, Suzuki (1930, 1934) had reported that seeds from earsartificially inoculated before, during, and after the flowering period, carried thefungal hyphae in the endosperm and embryo.The seeds of Eleusine coracona infected by Pyricularia grisea are asymptomaticand symptomatic (discolored). The discolored seeds exhibited two to three timeshigher infection than the asymptomatic seeds. Pericarp of all the infected seeds had