Date of Award


Degree Name

Doctor of Philosophy


Agricultural Sciences

First Advisor

Park, Logan


Fusarium virguliforme is one of the important pathogens on soybeans, and it is a soil borne pathogen. This pathogen causes sudden death syndrome on soybean (SDS). The fungus remains in the soil or on the plant residues for many years in the form of chlamydospores. When the appropriate conditions are available for the infection, the pathogen penetrates the soybean's roots and causes symptoms on the roots that appear in the form of reddish-brown, discoloration and necrosis. On the leaves the symptoms appear in the form of irregular spots shape. In the development of the infection the fall of leaves, abortion of flowers and pods occur. Due to the economic importance of the disease and the fungus that causes it. This study conducted to gain more information and understand the behavior of the pathogen. The results study of the effect of some culture media, pH and nitrogen sources on F. virguliforme growth in vitro showed that the pathogen has able to grow on all culture media that used. on culture media Czapek Dox agar (CDA) and Malt Extract Agar (MEA), the F. virguliforme was grown fast to cover plate in 8 days of incubation. Potato Sucrose Agar (PSA) and Malt Extract Agar (MEA) were the best culture media for fungal sporulation while the lowest number of spores was on Glucose yeast peptone Agar (GYPA). Also, the study showed the best pH for radial growth was 7 at 20, 25 and 30 C. But the radial growth of Fungus was slow at pH 10. The fungal sporulation at pH 6 was good comparing to fungal sporulation at pH 10 which was less. The radial growth of fungus was affected by different nitrogen sources and concentration. In general, the ammonium sulphate was not suitable for fungal radial growth and The best fungal sporulation was on media with peptone 2 g comparing with other nitrogen sources. In the second chapter, the results of histopathology of roots for two soybean varieties infected by F. virguliforme showed that the pathogen uses the same strategy to attack the roots of soybean varieties, penetration and colonization. The pathogen can grow intercellular and intracellular. During infection the pathogen causes damage to the root cells. Accumulating of materials inside root's cells because pathogen invasion. The last chapter in this study is, effect light on F. virguliforme growth. The study showed that the radial growth of the fungus was the maximum under continuous darkness comparing to fungal radial growth under light/dark cycle 12/12 LD, 16/8 LD and 18/6 LD. In addition to that colorful bands were formed when the fungus grew under under light/dark cycle. The results showed the ability of pathogen to cause Lesion on soybean stems under light/dark cycle. Also, using two inoculum 105, 106 of pathogen to test it pathogenicity on soybean roots showed no significant differences.




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