الفهرس 
1. IntroductionOnly 14 pages are availabe for public view
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Abstract
Mushrooms have been known as important food items since the ancient ages because of their high nutritional values and therapeutic properties. Button mushroom ”Agaricus bisporus” (J.E.Lange) is one of the most widely cultivated and consumed mushrooms over the world. Cultivated button mushroom are highly susceptible to a variety of microbial pathogens including bacteria. Blotch usually appears when mushrooms are in the early button stage, but can also appear on mushroom of any age, even on harvested, refrigerated or mushrooms in markets over-wrapped with a water light film. As consumers require high quality plates (completely white), such browning (blotch) in mushroom plates may lead to a huge loss in mushroom marketable appearance where plates become impossible to sell.
Keeping in view the above concerns, this study aimed to highlight on the bacterial brown blotch of button mushroom which either reduce the consumer appeal of mushrooms in markets, or the production quality in farms and markets. Therefore, the main objectives of this thesis were to:
(A) Verify the etiology of the brown blotch of Agaricus bisporus in Egypt, and (B) Evaluate the incidence and spreading of brown blotch in commercial button mushroom in local mushroom markets.
In this study, fresh plates of table mushrooms were collected regularly along three years from four main hypermarkets in Cairo (Egypt). Blotched sporophores were used to isolate P. tolaasi and other bacterial pathogens that may cause damage.
• A total of 39 bacterial isolates were isolated over a period of three years and showed the typical morphology of Pseudomonas on nutritive agar.
• The pathogenicity test was performed on all the isolates. The browning of A. bisporus blocks was caused by 14 isolates out of a total of 39 isolates.
• All the fourteen tested isolates were able to produce either yellow or yellowish-green pigments when cultured on KB media. In addition, these isolates showed the same “LOPAT” profile which is characteristic for the group V of fluorescent pseudomonads.
• In White line assay, Six out of the fourteen isolates were proposed to be P. tolaasii as they were able to form white precipitates when allowed to grow against the reference strain of P.“reactans”. While only two isolates formed a white precipitate when grown near the reference strain of P. tolaasii and therefore proposed to be P. “reactans”.
• Sodium thioglycolate containing substrate affected the bacterial colonies of Pseudomonas tolaasii and P. reactans as following: the addition of sodium thioglycolate to the medium lead to very slow growth and the colonies were actually smaller in diameter.
• Tested isolates of Pseudomonas were able to differently use 23 carbon sources which allowed to group them together. The differences in utilizing such carbon sources by them were examined using the Biolog computerized system. According to the Computerized Biological System Database (Biolog Inc., Hayward, Ca, USA) (6) isolates were identified as P. tolaasii , (2) isolates were P. reactans , (3) isolates were P. fluorescence and (3) isolates were P. marginalis.
• Statistical analysis was conducted to investigate the possible significance correlations between three different criteria of the data gathered along the three years on the incidence of blotch disease as following:
1. The first correlation was between the incidence and the four seasons at which the samples were collected. The spring had the higher blotching percentage (P < 0.05) followed by winter.
2. The second correlation was between the incidence and the sources of fresh mushroom plates. Sources II and III had a higher percentage of blotching over the three years (with P value <0.001).
3. The third correlation was between the incidence and the age. The older age (3-7 days) always had the higher percentage of blotching along the 3 years (with P value <0.001).
In conclusion, the results obtained in the present study showed that P. tolaasii is the main causative agent of the brown blotch disease affecting A. bisporus. P. tolaasii is not an easy pathogen to eliminate because this bacterium has the ability to modify its biochemical pathways for adaptation to many adverse environments. This allows the bacteria to better compete and obtain their nutrients over the other competitors. Moreover, the results of the study revealed that, Bacterial brown blotch of A. bisporus is still an important disease for many growers in Egypt due to brown color and change in texture which reduces product quality. Therefore, it is necessary to find effective strategies to combat this disease to enhance the production and marketing of mushrooms.