Alternaria porri (Ellis).Ciffen causes serious problems in onion plants. It is transmitted with naturally infected seeds and bulbs from the previous crop to infect the new flower stalk of the next crop. Also, onion bulb infection decreases seed vitality. Infected sample were collected from four locations; Giza, Sharkia, Kalubia and Menofia governorates to measure disease severity. Experiments have been done on naturally infected seeds and bulbs from the previous year by cultivating infected bulbs. Infection was classified into five categories based on the percentage of disease severity. Pathogen transmission by the onion seed was investigated, either as internal or external infection type, Five different ratios of blub infection was determined as;14.2%, 25.2%, 41.5%, 61.1%, 87.5%. Also, trials were carried out in the current study to evaluate the efficiency of some botanical, biological and chemical as seed dressing treatments for infected seeds before sowing it, i.e. (Achook, Bougainvillea sp., Bacillus sp., Trichoderma sp. and Score). Results showed that disease severity was increased in the blub produced from previous crop, the number of flower stalk was reduced, and its disease severity was increased. Seeds produced from infected blub showed reduction in germination percentage.The most effective seed dressing treatment on seed germination were obtained by using score & Achook treatment compared with other seed dressing treatments. All treatments including Score, Achook, Bacillus sp., Bougainvillea sp., and Trichoderma sp.; respectively showed variable seed stimulation of germination compared with plants in the control treatment.Alternaria porri (Ellis).Ciffen causes serious problems in onion plants. It is transmitted with naturally infected seeds and bulbs from the previous crop to infect the new flower stalk of the next crop. Also, onion bulb infection decreases seed vitality. Infected sample were collected from four locations; Giza, Sharkia, Kalubia and Menofia governorates to measure disease severity.Experiments have been done on naturally infected seeds and bulbs from the previous year by cultivating infected bulbs.