الفهرس 
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Abstract
Onion is considered one of the most important vegetable crops in Egypt either for local consumption or for exportation. During the last few years , onion smut disese cased by Urocystis Cepule Frost,is considered one of the most important diseases affecting onion cultivation in many parts of Egypt. This disease attacks onion only dwing the seedling stage and kills some of them.
The aim of this investigation was planned to study the environmental factors affecting spore gennination as a propagules of smut disease pathogen, some agricultural practices
affecting smut incidence, estimation of crop losses resulted from infection and the histological changes in infected tissues.
Results of this work can be summarized as follows :
Artificial inoculation tests showed that highest percentage of infection was obtained when infested seeds were sown in soil inoculated with teliospores. Seeds inoculation with
mycelial growth gave slight infection. Moreover, soil inoculation technique (with teliospores) as well as seed infestation method caused moderate infection.