Al-Azhar Bull. Sci. (ISCAZ 2010). (March, 2010): pp. 231-250. ECO-PHYSIOLOGICAL FACTORS AFFECTING SEED GERMINATION AND SEEDLINGS GROWTH OF SOLANUM DIPHYLLUM L., A PROMISING MEDICINAL PLANT MOHAMED G. SHEDED, FATMA A. HAMADA, ARAFA I. HAMED AND ABDEL SAMAI M. SHAHEEN South Valley University, Faculty of science, Botany department, Aswan 81528, Egypt. Abstract Seed germination is affected by many factors, the effects of temperature, light, soil type, seed planting depth and the exposure to salt and drought stresses on seed germination performance and seedlings growth of Solanum diphyllum L. were investigated. The results obtained revealed that the optimum temperature for seeds germination was 20 °C with germination percentage reached 96.7%. The present study showed that exposing S. diphyllum L. seeds to light (8 hrs) lead to non significant increase in the germination percentage associated with slower rate, if compared with germination in complete darkness. There was a significant difference in germination in response to the soil texture type and the depth at which seeds were sown. The result showed that S. diphyllum L. can sustain low water potential resulting from drought stress using PEG 6000, but is sensitive to high salinity induced by NaCl. The analysis of certain metabolites content that stored in S. diphyllum L. seeds reflects to some extent the successful potentiality of S. diphyllum L. seeds germination under hostile habitats. Key words: Solanum diphyllum L., seed germination, seed planting depth, drought stress, compatible solutes. Introduction Within family Solanaceae, Solanum is the largest genus, Solanum diphyllum L. is a small shrub around 2 meters long, a native of Mexico and Central America, widespread in dry habitats (Knapp, 2002). It has been widely cultivated as a foliage shrub for its pretty flowers and brightly colored fruits in tropic and subtropic regions; the plant has escaped in many of these areas (D'Arcy, 1974). Solanum diphyllum L. was recorded by Shaheen et al. (2004) as a new record to the Egyptian flora. The root, shoot and fruit methanolic extract of Solanum diphyllum L. exhibited a highly cytotoxic activity against HCT116 (colon carcinoma) and MFC7 (breast carcinoma) (Hamada et al., 2010). Also a steroidal alkaloid compound, 3-O-(β-D- Glucopyranosyl) Etioline was separated from the methanolic extract of Solanum diphyllum L. root, exhibited a cytotoxic effects against the cervical cancer cell line; Hela cells (El-Sayed et al., 2009). Despite the promising applicability of this species, little is known about the ecological factors pre-requisite for its seeds germination. A detailed knowledge about factors affecting S. diphyllum L. seed germination could play a crucial role in evaluating and explaining its distribution and abundance patterns under different environmental conditions.