الفهرس 
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Abstract
This study aimed to :
1. Survey for potential biocontrol agents was conducted in three of the most important governorates in the cultivation of rice crop, namely Dakahleia, Kafr El-Sheik, and El-Gharbeia. during three consecutive growing seasons (2012 - 2014). Eighty seven fungal isolates were obtained including the following genera : Trichoderma, Ulocladium, Cladosporium, Alternaria, Nigrospora, Curvularia, Bipolaris, and Stemphylium.
2. The retrieved fungal isolates were screened for their biocontrol activities against barnyard grass weed plants in the greenhouse. Three isolates of the genus Curvularia (CP01, CP02, and CP03) proved to be pathogenic to the weed. They were isolated from Dakahleia and Gharbia. Identified as Curvularia prasadii.
3. Host range studies were conducted to determine the host specificity and safety of these three isolates of C. prasadii on 23 non-target plant species and cultivars of economic importance grown in Egypt. No disease symptoms appeared on any of them, while it produced disease symptoms only on barnyard grass weed plants. Thus, these isolates are host-specific to barnyard grass and safe to other plants.
4. Nutrition and physical factors were tested for their effect on the mycelial growth and spore production of the three promising C. prasadii isolates to determine the optimum conditions for production of the inoculum of biocontrol agents. Results of this study can be summarized as follows :
a) The best medium for maximum linear growth of the three isolates was malt extract agar (MEA), while the best medium for highest yield of spores of the three isolates was potato dextrose agar (PDA).
b) Contentious darkness was the best light regime for the mycelial growth and sporulation of CP01 and CP02 isolates, while contentious or diurnal light were best for CP03 growth. However, all light regimes were proper with no significant differences for the spore production of the isolate CP03.
c) The pH levels of 6, 7, and 8 induced the highest mycelial growth of the three isolates. However, the latter two pH levels (7 & 8) were best for the sporulation of all three isolates.
d) The maximum mycelial growth was obtained at incubation temperature of 30°C (for CP01 and CP03) and 35°C (for CP02). For spore production, the optimum level of temperature for isolates CP01 and CP02 was 35°C, while it was 30°C for CP03.
e) Aeration level (as adversely correlated with the number of Parafilm® layers around the culture plate edge) was also tested. There was no effect of the number of Parafilm® layers (aeration level) on the CP02 mycelial growth. However, two layers of sealing culture plates with Parafilm® provided optimum level of aeration for best mycelial growth for isolates CP02 and CP03 and highest spore production for all three isolates.
5. The culture filtrate of only CP03 isolate had significantly reduced the total chlorophyll of barnyard grass seedlings in comparison with the untreated control.
6. The vegetable oil emulsion formulation containing 5% or more of oil (for the three isolates of the biocontrol agent) has incited high levels of disease incidence on barnyard grass weed plants with no need for dew, whereas were not significantly different from the disease incidence caused by fungal suspension in water but exposed to the dew for 48 hr.