الفهرس 
IntroductionOnly 14 pages are availabe for public view
 |  | from | 32 |  |  |
| | | from | 32 | | |
Abstract
Onion rot diseases are the most important diseases and widespread in all onion production areas in Egypt and the world. These diseases are among the limiting factors to onion production in the world wide, which causes yield reduction. Onion is infected with a lot of diseases such as, white rot disease caused by S. cepivorum, black rot caused by A. niger, neck rot caused by B. allii, Fusarium rot caused by F. oxysporum, Penicillium rot caused by P. chrysogenum and Pyrenochaeta rot caused by P. terrestris. So, the present study aimed to: (I) isolate and identify pathogens (II) control the diseases by some biocontrol agents and application of certain plant extracts. The results of this study could be summarized as follows:
1- The isolated fungi were, identified S. cepivorum, A. niger, F. oxysporum, P. chrysogenum, B. allii, and Py. teristris from onion plants and rhizosphere soil of onion plants from different locations of Assiut Governorate. The fungus F. oxysporum showed the highest frequency, mean frequency rate, was 31% followed by S. cepivorum (21%) and A. niger (20%). While, P. teristris had the lowest frequency, mean frequency rate was 5% followed by P. chrysogenum, and B. allii.
2- In vitro, testing the antagonistic capability of T. harzianum, P. fluorescens and B. subtilis against growth of the pathogenic fungi revealed that all the tested antagonists inhibited growth of the tested pathogenic fungi. The highly antagonistic was T. harzianum followed by B. subtilis and P. fluorescens.
3- Under greenhouse conditions, addition of T. harzianum, P. fluorescens and B. subtilis to infested soil with the pathogens exhibited high ability for controlling the disease and reduced the disease severity.
4- Application of mycorrhizal fungus for controlling onion rot diseases (caused by F. oxysporum, P. chrysogenum, B. allii, S. cepivorum, A. niger and P. teristris) had a beneficial effect when added to the soil at all concentrations. Generally, soil treatment with mycorrhiza was effective in decreasing the disease symptoms on onion plants. Application of mycorrhiza to soil not only resulted in reducing disease severity but also enhanced plant growth and increased length, weight plant and increased nitrogen, phosphorus and potassium content in onion plants.
5- In vitro application of plant extracts (garlic cloves, parsley, mint, willow, basil and Lantana camara) at different concentrations of 5, 10 and 20% gave the greatest reduced the mycelial growth of the tested pathogenic fungi with the concentration 20%. Being the best garlic cloves extract showed the lowest effect on reduction of linear growth of the pathogens.
6- Treating onion transplants with certain plant extracts with the concentration 20 % significantly reduced onion rot diseases severity compared with the control. Garlic extract gave the least reduction of disease severity of onion plants.