الفهرس 
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Abstract
Basil is considered one of the most important crops in Egypt and the world. Basil plantations in Egypt are subjected to many foliar diseases caused by fungi which lead to severe losses in yield and quality of basil crop. One of these diseases is downy mildew that was taken into consideration in this study.
However, the obtained data could be summarized as follows:
• Pathological studies
-Basil downy mildew was occurred in all districts investigated, and Maghagha exhibited the lowest infection but Nasser gave the highest infection
-Disease symptoms and morphological characterize were observed from 20 days old crop to 90 day Morphology of sporangia of Peronospora belbahrii from survey accorded different areas from Minia and Beni-suef governorates. Conidiophore lengths were varied with counties served.
-Peronospora belbahrii proved to be pathogenic to basil plants, causing symptoms of downy mildew, compared with the control. Growing basil plants cv. Balady from seeds give downy mildew incidence and severity higher than which grown transplants. Incubation period was shorter (6 days) in case seed plants than transplanting (8 days).
- Both basil cultivars were liable to downy mildew infection with various degrees. Basil plants of cv. Balady were more susptable to P.belbahrii infection than cv. Grand-Vert science Balady plants give shorter incubation period (8 days)and greater severity and incidence as compared to basil cv Grend-Vert that expressed (12 days) incubation period disease incidence and disease severity .
- Basil downy mildew P. belbahrii was recovered more often from all inoculated basil plants but not recovered from any other plant species tested.
-Sowing dates resulted significant differences in mean percent disease incidence of downy mildew in sweet basil plants with different sowing dates. Generally, the incidence of downy mildew was significantly higher in the April planting compared with the March and February plantings in both years. % in the second cut and 98.4% in the third cut during the growing season 2016 and recorded 0.8, 75.5 and 98.2% for the three plants cuts, respectively in the second growing season (2017).
• Physiological studies:
- The sporangia did not germinate when they were incubated at temperature of 5 ºC and 30 ºC, while germination started at 15 ºC and recorded, the maximum germination was obtained 18 ºC, followed by15 and 20ºC resulted in reduction of germination.
- A gradual increase in germination of P. belbahrii sporangia percentage with increasing relative humidity and reached the maximum percent germination (25%) at 100 per cent relative humidity followed by 95 per cent relative humidity.
- Leaf extracts of both basil cultivars, Balady and Grand-Vert, reduced of sporangia germination of basil downy mildew causal agent P. belbahrii. Leaf extract Grand-Vert of basil cultivar were more inhibited sporangial germination than Balady cultivar. However, significant reduction in P. belbahrii sporangial germination between leaves extract of balady and water treatment.
- Inhibition of sporangia germination percent was significantly noticed with all bio-agents tested alone and the highest inhibition was exhibited in case of Fungicide and S. platensis treatments with significant differences between them which caused reduction in spore germination followed by B. subtilis treatments with averages, respectively.
- All essential oils tested caused a significant decrease in P. belbahrii sporangial germination. Increasing oil concentrations led to decreasing sporangial germination .Thyme oil give least germination, followed by neem oil and camphor oil.
- All organic compounds tested exhibited a significant sporangia germination reduction for P belbahrii. Increasing concentration resulted in reducing sporangial germination. Salicylic acid provided the lowest germination followed by H2O2, ascorbic acid and humic acid, as compared with control.
-An obvious significant P. belbahrii sporangia germination reduction was expressed by CaCl2, KHCO3 and KCl. Increasing salts concentration diminished sporangial germination of P.belbahrii. The lest germination was given by KCl followed by KHCO3 and CaCl2.
- Combining bio agents (biocides) with varies chemical compounds showed significant P. belbharii sporangia germination. The highest reduction was pronouns by mixing S. platensis with KCl,
• Control studies:
- Individual application of bio agent tested was significantly reduced basil downy mildew along two growing season, using S . platensis showed the most effective to reduced downy mildew incidence and severity, followed by P . florescens.
- Individual application of essential oils tested significantly reduced basil downy mildew along two growing seasons. Using thyme oil concentration 7 cm/L showed the most effective to reduce downy mildew incidence and severity, followed by neem oil concentration 7 cm/. More ever, essential oil caused significant fresh and dry weights enhancement and thyme oil 7cm/L gave the highest fresh and dry weight, followed by neem oil 7cm/L.
- All organic compounds of tested exhibited a significant reduction of basil downy mildew along two growing. Using salicylic acid concentration 75pmm was the most effective to reduce downy mildew incidence and severity, followed by hydrogen peroxide concentration 15cm/L.
- Mineral Salts: Obviously mineral salts tested significant reduced basil downy mildew along two growing season. Using KCl concentration 750mg/L showed the most effective to reduce downy mildew incidence and severity, followed by KHCO3 concentration 750mg/L.
- All combinations tested exhibited a significant along two growing season, using mix S. platensis with potassium chloride reduced basil downy mildew incidence and severity with significant differences between them which caused followed by mix S.platensis with Potassium bicarbonate reduced basil downy mildew incidence and severity.