Reproductive ecophysiology of cacti, with emphasis on fruit development and seed germination

The reproductive ecophysiology of cactus fruit crops was studied. Responses of germination to temperature, water potential, time after harvest and light were investigated for the columnar cactus Stenocereus queretaroensis , which closely matched the typical climate of the rainy season in the native habitat of this columnar cactus from west-central Mexico. The water and carbon relations for young fruits of six platyopuntias were also investigated; the phloem, and not the xylem, is the sole supplier of water to young fruits. The phloem supplies about 90% of the daily increase in mass, the rest results from fruit photosynthesis. The nocturnal patterns of gas exchange reveal that fruits utilize Crassulacean acid metabolism. Finally, the carbon and water balances for fruits of Opuntia ficus-indica were studied throughout their development, including effects of drought and gibberellic acid. Fruit development occurred over 110 days. Fruits undergoing drought did not ripen at 80 d after anthesis, fruits treated with gibberellic acid did ripen, but were smaller and had aborted seeds at 80 d after anthesis. An additional chapter compares the acclimation responses to extreme temperatures of fruits versus young stems and old stems of Opuntia ficus-indica , revealing that the tolerance of reproductive organs is lower than for stems and it even decreases with fruit age. Supplementary chapters characterize the growth and photosynthetic responses to high temperatures, short-term drought, and available soil nitrogen by the hemiepiphytic cactus Hylocereus undatus; the responses to temperature for this species and for Opuntia ficus-indica are then incorporated in a geographic information system to create maps identifying areas suitable for cultivation of these crop cacti in California.