الفهرس 
Introduction
isolation and identification of soybean rhizoctionia root rot the causal pathogenOnly 14 pages are availabe for public view
 |  | from | 108 |  |  |
| | | from | 108 | | |
Abstract
Rhizoctonia Root rot of soybean is considered to be the most important diseases, that affect seed germination and seedling emergence causing great losses in the yields. It reduced rates of hypocotyl elongation in some soybean cultivars and consequently delayed seedling emergence. The present study aimed to (a) isolate the causal pathogen from different varieties and locations in Assiut (b) identify pathogen isolates by using anastomosis group (AG), electrophoresis and PCR (c) control the disease by untraditional methods such as biocontrol agents, application of compost alone to the soil before sowing and in combination with Trichoderma. The results of this study could be summarized as follows:
1- Seven isolates were isolated from roots and hypocotyls of infected soybean plants, showing symptoms of root rot collected from different counties of Assiut governorate. All isolates were identified as Rhizoctonia solani (Kohn).
2- Pathogenicity tests showed that, all isolates were able to infect soybean (Giza 111cv.) causing root rot with different degrees of severity. The highly pathogenic isolates were isolates no. 1, 2 and 3.
3- Studying the comparison between isolates of Rhizoctonia solani Nos.1, 4 and 6 which varied in their pathogenic capability by using anastomosis group, protein patterns and PCR analysis showed that:
a) Seven isolates of R. solani were tested for their ability to anastomosis with the tester isolate (AG-4) by using the clean slide technique. Microscopic examination showed that all the tested isolates belong to R. solani AG-4.
b) Cluster analysis was used to compare between protein banding patterns obtained by sodium sulfate-polyacrylamide gel electrophoresis (SDS-PAGE) from three R. solani isolates No.1, 4 and 6. It is apparent that cluster divided in two groups with a minimum similarity coefficient of 62.91%. The first group included isolates No. 1. The second group included 2 isolates (4 and 6) with an overall similarity level of 9 0 . 9 1 %.
c) Total 75 RAPD markers bands were obtained by using six primers with molecular weights ranging from 0.1 to 3.6 kd, 74 were polymorphic and one was monomorphic. Five primers (1, 3, 4, 5 and 6) showed high similarity between isolates No.1 and 6 with similarity percentage (82.58, 97.5, 95, 99.2 and 98.27%) respectively.
4- Out of eleven isolates of Trichoderma sp. isolated from rhizosphere and roots of soybean plants, only two isolates were identified as T. harzianum. All isolates exhibited different degrees of reaction against R. solani.
5- Water extract of Animal and Plant compost reduced the mycelial growth of tested isolate of the R. solani. Ratio of growth inhibition increased with increasing in compost extract concentration. Generally, animal and plant compost caused the same effect on mycelial growth of Rhizoctonia solani.
6- Population of Bacillus, fluorescent Pseudomonas and fungi were different in Bio-pianta and Bio-soil CMS. Population of the tested microbs varied in the two tested composts. Bio-soil has the higher population of the recovered microbs than Bio-pianta except in case of Fungi.
7- Under greenhouse conditions, studying the effect of T. harzianum and compost individually and or in combination on Rhizoctonia root rot disease showed that:
a) Generally, the treatments combination between bio-control agents (T.hrzianum) and compost materials significantly reduced the root rot severity compared to infected control. Treatments with (Th1+PC) and (Th1 +AC) reduced disease severity percentage and root rot rating from 97.5% and 3.90 in control to 63.33, and 73.33 %, 2.53 and 2.93 respectively.
b) Treatments containing T. harzianum only or combination between T. harzianum and different types of compost gave the highest increment percentage of growth parameters (root length, root fresh weight, root dry weight, shoot length, shoot fresh weight and shoot dry weight) compared with the control or treatments containing compost only.
8- Studying the effect of T. harzianum and compost individually and their combination on Rhizoctonia root rot disease Under field conditions showed that:
a) In both tested 2011 and 2012 seasons, Th10 or combination Th1+AC gave the highest reduction of Rhizoctonia root rot disease and reduced disease severity percentage.
b) Addition of T. harzianum (Th1) and (Th10), separately to infested soil with pathogen isolate caused the highest increase in yield than fungicide treatment, followed by treatments containing combination between T. harzianum and different types of compost (Th1 + PC) and (Th1 + AC).