الفهرس 
IntroductionOnly 14 pages are availabe for public view
 |  | from | 122 |  |  |
| | | from | 122 | | |
Abstract
This thesis is considered the 1st study concerning sweet potato fusarium wilt disease in Eggypt, particularly in the Middle Egypt regiones viz., Beni Sweif and Minia governorates.
The obtained results of this study could be summerizied as follow:
Pathological studies :
• Sweet potato wilt prevalence (SWP), incidence (SWDI) and severity (SWDS) were surveyed. All pathometeric criteria were significantly varied with observed regions. The highest SWP, SWDI and SWDS values were recorded in Mallawi county, Minia governorate followed by Beba county, Beni Sweif governorate. The least values were reported at Nasser county, Beni Sweif governorate.
• Fungi belonging to five genera, e.g. Alternaria, Ceratocystis, Fusarium, Macrophomina and Rhizoctonia were found to be associated with wilted sweet potato plants. Fusarium spp recorded the highest frequency (80.5%) and Fusarium oxysporum showed 51.5%. frequency.
• Sweet potato genotypes were varied in their response to infection by Fusarium oxysporum isolate F1. Genotypes Menoufia 6 and Menoufia 2 reacted as resistant, while Local A and Line 26 were highly susceptible.
• Fusarium oxysporum f.sp. batatas isolate F1 was infective to convolvulaceous plants such as Cairo morning glory and field bindweed but was not pathogenic to non convolvulaceous plants such as alfalfa, carrot, cotton, potato, sugarbeet, sugarcane, turnip and wheat.
• Sweet potato fusarium wilt was significantly affected by soil types. Sandy soil (100% sand) reacted as suppensive soil against SWDI and SWDS. In contrast, clay soil (10% sand) was the most favorable for sweet potato wilt development.
Laboratory studies :
• Growth of F. oxysporum f. sp. batatas was significantly affected by various degrees of temperature. Optimum linear growth of F. oxysporum f. sp. batatas was occurred at 25oC while temperature degrees at either low or above 25oC were caused linear growth reduction.
• Growth medium amendment with AA+H2O2 (PAA) combination cause significant inhibitory linear growth of F. oxysporum f. sp. batatas. Inhibitory effect for PAA against F. oxysporum f. sp. batatas linear growth was positive with increase it concentration.
• All bioagents tested individually appeared significant antagonistic effects. The bioagent Trichoderma harazianum revealed the strongest antagonistic effects followed by Pseudomonas fluorescens. The weakest antagonistic effect was proved by Bacillus subtils.
• Chlorophyll degradation was rilated to sweet potato genotypes reaction towards Fusarium oxysporum f.sp. batatas infection. The least degradation values were found in resistant genotypes and vice versa exhibited by susceptible genotypes.
• Phenols were enhanced when Fusarium oxysporum f.sp. batatas infected the resistant genotypes and decreased in the susceptible genotypes compared with uninfected .
Possible management of sweet potato fusarium wilt :
In accordance to sustenable plant disease control for healthy plant using fungicide atternatives 3 pot experiments were conducted.
• The 1st experiment was concered to study the role of PAA on the development of sweet potato fusarium wilt. Both SWDI and SWDS were significantly reduced upon PAA treatment. A positive correlation between the PAA concentration tested and protection values. The highest protection value was obtained by the highest AA+H2O2 concentration tested.
• The 2nd experiment was to study the role of bioagents for controlling sweet potato fusarium wilt. The bioagent T. harazianum gave the highest protection against SWD through CS or SI. Using P. fluorescens bioagent was only preceded by T. harazianum. However, B. subtils was also significantly protected sweet potato plant against F. oxysporum f. sp. batatas infection but it considered the weakest bioagent as compared to T. harazianum and P. fluorescens.
• The 3rd experiment was to study the interaction effects for PAA and bioagents against F. oxysporum f. sp. batatas infection. Singly application of each bioagent was more effective than it combined with PAA. However, PAA insignificantly lowered the efficaciously of bioagent to control sweet potato wilt disease.