3 Egypt. J. Phytopathol., Vol. 34, No. 2, pp. 29-41 (2006) Mating Populations and Effective Population Number in Gibberella fujikuroi species Complex of Rotted Maize Ears under Egyptian Conditions K.K. Sabet*, A.M.A. Ashour*, E.M. El-Assiuty** and E.M. El-Shabrawy** * Pl. Pathol. Dept., Fac. Agic., Cairo Univ., Egypt. ** Pl. Pathol. Res. Inst., Agric. Res. Centre, Giza, Egypt. aize growing fields surveyed for the infection with ear rots throughout 8 locations in Egypt indicated the prevalence of ear rots caused by Fusarium spp. The toxigenic isolates from the whole number recovered from this group of fungi were subjected to identification biologically. Two mating populations were only identified as MAT-A (F. verticillioides) and MAT-D (F. proliferatum). MAT-A prevailed in all locations, but only 5 isolates were identified as MAT-D. Isolates belong to MAT-A produced considerable amounts of fumonisin compared to those belong to MAT-D. Female fertile strains could produce higher amounts of the toxin than female sterile. Through measuring the parameters of the effective population number in biological species recovered from maize ears, it was found that the female sterility was lesser than 50%. This caused an increase in the inbreeding effective population number and decrease in the variance effective population number overall locations. Key words: Ear rot, fumonisin, Fusarium spp., F. proliferatum, F. verticillioides, maize and mating populations. Kernel and ear rot is one of the most prevalent diseases of maize that threaten productivity in Egypt. Surveying harvested maize grains done by many investigators (Munkvold and Desjardins, 1997; Desjardins et al., 2000; and El-Shabrawy, 2001), who reported that Fusarium spp. is the major fungal population recovered from the rotted maize ears. F. verticillioides (Sacc.) Nirenberg (syn. F. moniliforme Sheldon) is the most dominant species and earlier colonist of the pre-harvest maize ears before other moulds such as Penicillium spp. and Aspergillus spp. (El-Shabrawy, 2001). F. verticillioides and F. proliferatum, to some extent, are responsible for the production of fumonisin which have become the most contaminants of maize grain and maize commodities (Chelkowski and Lew, 1992; Musser and Plattner, 1997). This group of mycotoxins are of concern due to their toxicological implications to man and animal (Franceschi et al., 1990 and Abbas et al., 1999). Gibberella fujikuroi (Sawada) is the teleomorph for many of the species of conidial anamorphs in Fusarium section Liseola including F. verticillioides and F. proliferatum. M