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

Location of Fungal Hyphae in Seeds 1555.8 CONCLUDING REMARKSHistopathology provides information on the exact expanse of mycelium in seed, andthe use of categorized infected seeds has revealed a direct correlation between theseverity of infection and the expanse of mycelium in seed tissues. Most seed infectionsof field fungi occur in the developing ovule and seed in the field. The extentof invasion of seed tissues varies with the stage of development of the host, its nature(susceptibility and degree of resistance), and the environment, particularly humidityand temperature, at the time of infection. Early infections in congenial environmentsusually result in deep internal infections, whereas infections during advanced stagesof seed development generally cause superficial invasion. The nutritional status ofthe fungus, necrotroph or biotroph, seems to have little influence on the invasion oftissues. The effects of invasion on the development of seed and also the degradationof its tissues depend on the harmonic status that exists between the host and thefungus. Necrotrophs cause more damage than biotrophs, and specialized biotrophs,such as loose smuts and endophytes, cause apparently little damage to seed tissues.In mixed fungal infections of seeds, hyphae of different fungi compete forcolonization, showing antagonistic or synergistic behavior.Dermal coatings, cuticula of different components, lignified or suberized cells,and polyphenols or other similar compounds in seed components appear to act asbarriers to fungal invasion; however, the evidence is not wholly conclusive.Deep internal infection remains viable for various durations. This may play animportant role in disease spread over long distances and also in the recurrence ofdisease from one crop season to another.REFERENCESAgarwal, K., Singh, T., Singh, D., and Mathur, S.B. 1985. Studies on glume blotch diseaseof wheat. I. Location of Septoria nodorum in seed. Phytomorphology 35: 87–94.Agarwal, K., Singh, T., Singh, D., and Mathur, S.B. 1986. Studies on glume blotch diseaseof wheat. II. Transference of seed-borne inoculum of Septoria nodorum from seedto seedling. Phytomorphology 36: 291–297.Agarwal, K., Sharma, J., Singh, T., and Singh, D. 1987. Histopathology of Alternaria tenuisinfected black pointed kernels of wheat. Bot. Bull. Academia Sinica 28: 123–130.Agarwal, N.K. and Jain, B.L. 1978. Histopathological studies of ‘Rajma’ infected by Macrophominaphaseolina (Abstr.). J. Mycol. Plant Pathol. 8: 59.Agarwal, S. and Singh, T. 2000. Effect of extra- and intraembryonal infection of Macrophominaphaseolina on disease transmission in okra seeds. J. Mycol. Plant. Pathol. 6:135–139.Agarwal, V.K. and Sinclair, J.B. 1997. Principles of Seed Pathology, 2nd ed. CRC Press, BocaRaton, FL.Alcock, N.L. 1931. Notes on common diseases sometimes seed-borne. Trans. Bot. Soc.Edinburgh 30: 332–337.Alexopoulos, C.J., Mims, C.W., and Blackwell, M. 1996. Introductory Mycology. John Wiley& Sons, New York.