1. Symposium on the timing of field production of vegetables,Tampa, Florida U.S.A (1985)

2. 82nd Annual meeting of the American Society for Horticultural science, Blacksburg, Virginia, U.S.A (1985)

3. 22nd International Horticultural Congress, Davis, California, U.S.A (1986)

      4. Symposium on the production and multiplication of seed in the Sudan (1995)