1 Egypt. J. Phytopathol., Vol. 35, No. 1, pp. 1-11 (2007) Interaction between Certain Root-Rot Fungi and the Root-Knot Nematode, Meloidogyne incognita on Sunflower Plants Asmaa A. Mokbel; I.K.A. Ibrahim; M.R.A. Shehata and M.A.M. El-Saedy Plant Pathol. Dept., Fac. of Agric., Alexandria Univ., Alexandria, Egypt. ffects of the root-rot fungi: Rhizoctonia solani, Macrophomina phaseolina and Fusarium solani on sunflower plants cv. Myak infected by Meloidogyne incognita were studied. The results indicated that combined infection with M. incognita plus any of the tested fungi resulted in significant reduction in number of root galls and nematode egg masses. Plant growth reduction and disease severity were greatly evident when M. incognita was inoculated simultaneously with R. solani. Inoculation with M. incognita alone or in combination with three different inoculum levels of R. solani, M. phaseolina or F. solani on sunflower cv. Myak was studied in three greenhouse experiments. Treatments with M. incognita in combination with different inoculum levels of the tested fungi caused significant reduction in number of root galls and nematode egg-masses and the dry weight of sunflower plants. Effect of inoculation time of M. incognita applied alone or in combination with R. solani, M. phaseolina and F. solani on sunflower cv. Myak was also studied. Treatments with any of the tested fungi either at the same time or one week before M. incognita inoculation resulted in significant reduction in number of root galls and nematode egg-masses. Treatments with M. incognita alone or in combination with any of the examined fungi caused significant reduction in the dry weight of sunflower plants. Keywords: Fusarium solani, Macrophomina phaseolina, Meloidogyne incognita, Rhizoctonia solani, root- rot and sunflower plants. Oil field crops represent a great economic importance in the Egyptian agriculture and industry. Sunflower crop plays a major role in the diet of many people in Egypt and other countries. Previous investigations showed that sunflower plants have been attacked by many phytoparasitic nematodes and pathogenic fungi (Shohla, 1980; Sharma, 1990 and Ahmed et al., 1994). Several root pathogenic fungi attack sunflower plants during the growing season inducing diseases such as damping-off, root rot, charcoal rot and wilt. Previous studies showed that the root-rot fungi: Fusarium moniliforme, F. oxysporum, F. semitectum, Macrophomina phaseolina, Phytophthora nicotianae var parasitica, Pythium irregulare, Sclerotinia sclerotiorum and S. rolfsii were pathogenic to germinating seeds and seedlings of sunflower (Sadashivaiah et al., 1986; Zazzerini and Tosi, 1987; Ahmed et al., 1994 and EL-Komy, 2001). Importance of the plant parasitic nematodes in root disease complex has received much attention. Many reports have shown that infection with the root-knot nematodes (Meloidogyne spp.) and some root pathogenic fungi may result in greater damage on the host plant than either pathogen acting alone (France and Abawi, 1994; Mahgoub, 1996; Mohamed et al., 1990; Shahda and EL-Saedy 1990; Srivastava and Singh, 1991 and Khan and Hossini- Nejad, 1991). E