Creating Non-Fruiting Forms of Prolific Seed Producing Landscape Species

The prolific production of messy and sometimes hazardous fruits and seeds make the typical diploid (2n) forms of many tropical tree species high maintenance and potentially invasive. Triploid (3n) plants are usually sterile, since three sets of chromosomes cannot evenly divide during meiosis, resulting in non-functional gametes or total meiotic failure. Triploid plants result from crossing tetraploid (4n) to diploid plants. Tetraploid forms of autograph tree (Clusia roseae), octopus tree (Schefflera actinophylla), kamani (Callophyllum inophyllum) and Malibar chestnut (Pachira aquatica) were obtained by treating meristems of 2n seedlings with 0.5% oryzalin solution for 24 or 48 h. At maturity the 4n plants will be crossed to 2n plants of the same species. The resulting progeny will be 3n.

Fifty 3n progeny seedlings from each of five crosses using a previously converted 4n pink and white shower tree Cassia javanica for the maternal parent are growing in a greenhouse on the University of Hawaii, Manoa campus. The 2n paternal parents are C. javanica, C. bakeriana, C. fistula, and the rainbow shower tree hybrids C. 'Lunalilo Gold' and C. Queen's White'. These will be field-grown and assessed for seedlessness and horticultural characteristics. Superior individuals will be propagated by air layering and grafting and provided to the Hawaii landscape nursery industry. The non-fruiting triploid forms of these popular landscape plants will be less expensive to maintain, will be non-threatening to native ecosystems, and may have slightly larger flowers and bloom over a longer flowering season.