Screening Potential New Tropical Ornamentals for Alkalinity, Salinity, and Irradiance Tolerances

Abstract

Abstract With the rapid introduction of new herbaceous or woody perennial tropical and subtropical taxa to the U.S. nursery trade for use as summer annuals, methods for quickly assessing their tolerances to various environmental stresses will be needed. Three screening methods, one each for substrate alkalinity, soil salinity, and varied irradiance levels, were tested on four tropical taxa, Rotheca myricoides (Hochst.) Steane & Mabb. (blue butterfly bush), Graptophyllum pictum (L.) Griff, (caricature plant), Jatropha integerrima Jacq. (firecracker jatropha), and Chrysothemis pulchella (Don. ex J. Sims) Desc. (dozakie), with potential for use as summer annuals. Specialized portable structures for testing irradiance levels were developed which minimized confounding of restricted air movement often associated with imposing shade treatments. Irradiance and salinity screening procedures were deemed successful, while further refinement is needed with the alkalinity screening method tested. Decreased irradiance levels suppressed flowering of R. myricoides, while full sun exposure decreased foliar appearance and growth of C. pulchella. Only J. integerrima showed adverse responses to elevated substrate alkalinity. Jatropha integerrima and G. pictum exhibited adaptation to a wide range of light exposures and salinity levels while maintaining attractive foliage. Although flowering of J. integerrima was reduced with heavy shade (66%), some flowering continued.