الفهرس 
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Abstract
Potato (Solanum tuberosum, L.) crop is the fourth main food crop in the world. The present work was planned to isolation and identification of causal organism, study effect of some plant extracts oils on the growth of pathogenic bacterium (Pectobacterium atrosepticum) and on severity of bacterial soft rot disease, In vitro and effect of some organic matters and mineral fertilizers individually and/or interaction on population of pathogenic bacterium, antagonistic microorganisms population, frequency of antagonistic microorganisms, severity of black-leg disease of potato and potato yield, under artificial inoculation conditions. The obtained data indicated that all bacterial isolates were identified as Pectobacterium atrosepticum according to their morphological, cultural, physiological and biochemical characters. In vitro, examined plant extracts oils (camphor, garlic and marjoram) were inhibited the growth of P. atrosepticum bacterium and decreased severity of soft rot disease compared with the control, Also, garlic extract was the most effective against the growth of pathogenic bacterium and disease severity compared with other extracts. Application of organic matters (ground leaves of cabbage, camphor and garlic) and mineral fertilizers (ammonium nitrate, ammonium super-phosphate, potassium sulfate and urea) as soil amendments individually and/or interaction led to decrease population of P. atrosepticum bacterium and severity of black-leg disease of potato compared with the control. While, these treatments led to increase population of antagonistic microorganism and potato yield compared with the control. Meanwhile, ground leaves of garlic as organic matters and urea as mineral fertilizer individually and/or interaction were the most effective to reduce pathogenic bacterium population and disease severity compared with other treatments. But, ground leaves of camphor as organic matters and ammonium nitrate and/or potassium sulfate individually and/or interaction were the most effective to increase population of antagonistic microorganism and potato yield compared with other treatments. Meantime, Bacillus spp. was the most frequency followed by actinomycetes species and Pseudomonas fluorescents species with all treatments. Interaction treatments were more effectively than individually treatments against pathogenic bacterium population, antagonistic microorganism population, frequency of antagonistic microorganism, severity of black-leg disease and yield of potato.