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

Location of Fungal Hyphae in Seeds 111mycelium of Sclerospora phillippinensis in the pericarp and endosperm of maizekernels. Arya and Sharma (1962) found dormant mycelium of S. graminicola, thecausal organism of the green ear disease of pearl millet, in seeds collected from theinfected portion of the ears. However, Suryanarayana (1962), who also observedmycelium in seed, did not attribute it to S. graminicola. It was not until recently,during the last two decades, that convincing evidence of the occurrence of hyphaeof S. graminicola in pearl millet seed and its role in disease transmission has beenrevealed. The dormant mycelium of S. graminicola is reported in the pericarp,endosperm, and embryo (Figure 5.5A to C) of infected grains (Safeeulla, 1976;Shetty et al., 1978; Shetty, Mathur, and Neergaard, 1980; and Subramanya, Safeeulla,and Shetty, 1981). The mycelium is coenocytic, thick, and netlike with constrictionsand forked haustoria (Figure 5.5D). In embryos, scutellum alone is infected, and theradicle and plumule are not invaded. This embryal mycelium alone causes systemicinfection of seedlings and plants (Shetty, Mathur, and Neergaard, 1980).Several Sclerospora species have been placed under Peronosclerospora andSclerophthora in recent years. The mycelium and oospores of P. sorghi occur in theglumes and pericarp of seeds from systemically infected sorghum plants (Kaveriappaand Safeeulla, 1975; Safeeulla, 1976). The fungal mycelium occasionally invadesthe endosperm, but neither mycelium nor oospores are found in embryos. Kernelscollected from maize plants systemically infected by Peronosclerospora sorghioospores and mycelium occurred in all parts of infected kernels, i.e., the pericarp,endosperm, and embryo (Muralidhara Rao et al., 1984, 1985). The infected seedsproduced diseased plants in large numbers.In seeds from partially malformed finger millet (Eleusine coracana) earheads,P. sorghi mycelium is reported in the pericarp, endosperm, and embryo. Similarly,Rathore, Siridhana, and Mathur (1987) found mycelium of Peronosclerospora heteropogoniin most parts including the embryo in kernels of Zea mays.Sclerophthora macrospora (Sclerospora macrospora), the cause of crazy top inmaize, is internally seed-borne. Ullstrup (1952) reported coenocytic mycelium incob tissues including seeds. In a few kernels from severely infected plants, themycelium was found in the scutellum and coleorhiza. Singh, Joshi, and Chaube(1968) found the presence of Sclerophthora rayssiae var. zeae mycelium in theplumule and the adjoining part of coleoptile in corn kernels from infected plants.The aseptate mycelium in the embryo was swollen and irregular with prominentvacuoles and granular protoplasm. Thin hyphae extended from the broad swollenmycelium to the adjoining tissues. Ullstrup (1952) reported the transmission ofSclerophthora mycelium to the seedlings and plants, including aerial vegetative andfloral primordia.5.5.1.4 AlbugoAlbugo species cause white blisters (white rust) and hypertrophy of vegetative andfloral parts in crucifers. Alcock (1931) reported minute white spots of A. candida(Cystopus candidus) on turnip seeds. Oospore contamination is common in Brassicaseeds (Petrie, 1975; Verma and Bhowmik, 1988). According to Sharma, Agarwal,and Singh (1997), the white rust-affected seeds may be symptomless or symptomatic