الفهرس 
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Abstract
Rice is one of the main field crops raised in Egypt. It is rated
the second exported crop after cotton. More than one million feddans
(0.42 million hectar) are under rice cultivation annually. Egypt for the
time being is the first country in the world in rice production from land
unit, among various rice producing countries. Thus, the national
average yield was 3.44 tons/feddan in last season 1995 which is
equivalent to 8.2 tons/ha, (Harnissa et al., 1996). However, rice plants
are subject to various diseases that affect plants at different stages of
growth. Rice blast caused by Pyricularia oryzae Cavara, followed by
brown spot disease caused by Helminthosporium oryzae , Breda de
Haan, are the most destructive diseases in Egypt as well as in various
rice growing countiies which cau:;e ;;cn-.rrt:al significant yield losses,
(Goto, 1965; Ou, 1972; Atkins, 1974; Abdel-Hak et al., 1975;
El-Refaei, 1977; Singh, 1988 (a&b) and Fomba and Singh, 1990).
Therefore, these diseases have attracted the attention of many workers
in Egypt as well as in most rice producing countries (El-Kazzaz et al.,
1985 (a&b); Osman, 1985; Ou, 1985; Sehly et al., 1988; Kim et al.,
1988; Salem, 1990; Chakrabarti and Chaudhuri, 1992 and Teng, 1995).