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Responses of seed germination to temperature, water potential, time after harvest, and light were investigated for Stenocereus queretaroensis, a columnar cactus native to west central Mexico. Germination was optimal between 20degreesC and 30degreesC, and the germination percentage decreased as the water potential was lowered from 0(.)00 to -1(.)0 MPa. Maximal germination of 85% occurred for seeds that were 11 - 28 months old. Germination required light but became light saturated at a photosynthetic photon flux over 10 days of only 0(.)15 mumol m(-2) s(-1) (equivalent to a fluence of 67 Mmol m(-2)). Germination was apparently phytochrome mediated, as evidenced by its relative spectral sensitivity (greatest at 660 nm). The environmental requirements for breaking seed dormancy for S. queretaroensis are finely tuned to those typical of the rainy season in its native habitat. (C) 2002 Elsevier Science Ltd.