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

96 Histopathology of Seed-Borne Infections4.6 CONCLUDING REMARKSThe infection course pathogens take and the passages they use to reach the ovuleand seed differ in developing seeds and seeds in storage. They also vary with thenature of pathogens, necrotroph or biotroph, and the course of disease developmentand reinfection of the plant. In flower and fruit, the pathogen may follow predominantlyone path of infection or it may also use alternate routes. After reaching theinterior of the ovary, the nonvascular pathogens may become more opportunisticand enter the ovule and seed through more than one site.The avenues of infection in threshed seeds including one-seeded fruits differfrom those of developing seeds. Field fungi usually remain quiescent. Storage fungi,which may show activity under low available moisture, may cause internal infectionif they are thermotolerant.The penetration of the ovary and fruit and the ovule and seed surfaces may bemechanical or enzymatic, or both. The invasion may be direct or may take placeafter the formation of appressoria, cushions, and pegs. A fungus may invade thesurface using more than one mode of entry. Entry may also differ on surfaces ofdifferent cultivars. If the cuticle or cell wall at the point of entry is depressed inward,the penetration is mechanical and evidence of weakening or digestion of cuticle isconsidered to support an enzymatic penetration. The resistant reactions betweenpathogen and host tissues are seldom described, but the information on specific andquick resistant reactions in tissues forming passages for entry and spread in theovary and fruit and the ovule and seed could be of practical importance in breedingcultivars with inhibitory reactions to the invasion of fungi from the outside.REFERENCESAgarwal, V.K. and Sinclair, J.B. 1997. Principles of Seed Pathology, 2nd ed. CRC Press, BocaRaton, FL.Agrios, G.N. 1988. Plant Pathology, 3rd ed. Academic Press, San Diego.Baker, K.F. 1948. Fusarium wilt of garden stock (Mathiola incana). Phytopathology 38: 399.Bandyopadhyay, R., Mughogho, L.K., Manohar, S.K., and Satyanarayana, M.V. 1990. Stromadevelopment, honeydew formation and conidial production in Claviceps sorghi.Phytopathology 80: 812–818.Bassi, A., More, E.L., and Batson, W.E. 1979. Histopathology of resistant and susceptibletomato fruit infected with Rhizoctonia solani. Phytopathology 69: 556–559.Batts, C.C.V. 1955. Observation on infection of wheat by loose smut (Ustilago tritici [Per.])Rosta). Trans. Br. Mycol. Soc. 38: 465–475.Bennum, A. 1972. Botrytis anthophila Bondarzew, med sacrligt henblik på patologisk anatomi.Ph.D. Thesis, Royal Veterinary and Agricultural University, Copenhagen, Denmark.Binyamini, N. and Schiffman-Nadel, M. 1972. Latent infection in avocado fruit due toColletotrichum gloeosporioides. Phytopathology 62: 592–921.Bonman, J.M. and Gabrielson, R.L. 1981. Localized infections of siliques and seed of cabbageby Phoma lingam. Plant Dis. 65: 868–869.Brefeld, O. 1903. Neue Untersuchungen und Ergebnisse über naturliche Infektion und Verbreitungder Brandkrankheiten des Getreides. Klub Landw. Berlin. Nachr. 466:4224–4234.