110 JOURNAL OF OIL PALM RESEARCH 17 (DECEMBER 2005) POLYPLOIDY INDUCTION OF OIL PALM THROUGH COLCHICINE AND ORYZALIN TREATMENTS MADON, M*; CLYDE, M M**; HASHIM, H**; MOHD YUSUF, Y**; MAT, H** and SARATHA, S** * Malaysian Palm Oil Board, P. O. Box 10620, 50720 Kuala Lumpur, Malaysia. E-mail: maria@mpob.gov.my ** Faculty of Science and Technology, Universiti Kebangsaan Malaysia, 43650 UKM Bangi, Selangor, Malaysia. Keywords: tetraploids, triploids, mixoploids, flow cytometry, stomata counts. Date received: 14 December 2004; Sent for revision: 23 December 2004; Received in final form: 2 June 2005; Accepted: 24 November 2005. ABSTRACT Germinated oil palm seeds were treated with two antimitotic chemicals, colchicine and oryzalin, to induce polyploidy. The colchicine concentrations used varied from 2.5 to 10.0 mM, and the oryzalin concentrations from 15 ∝M to 120 ∝M. The incubation period vary inversely with the chemical concentration from 48 to 6 hr. Colchicine treatments produced nine tetraploids, two triploids and a number of mixoploids. The oryzalin treatments produced four triploids and many mixoploids of 2n+3n and 3n+4n. However, one-way ANOVA showed that none of the treatments were able to induce polyploidy efficiently. Flow cytometry was found to be the most efficient method for detecting induced changes in the genome size or polyploidy level compared to stomata and chromosome counts. One-way ANOVA showed no significant difference in the stomata density between polyploids and controls (2n) while for plant morphology, polyploids seemed to be significantly shorter than their respective controls. INTRODUCTION The commercial oil palm Elaeis guineensis Jacq. (2n=32) planted in Malaysia is the tenera (DxP) fruit type with thick mesocarp and thin-shell. It is a hybrid obtained by crossing the thick-shelled dura (D) with the shell-less female sterile pisifera (P). This perennial monocot grows to a height of 12 m. It starts to bear fruit as early as three years after field planting and continues to do so for up to 25 years. The oil palm yields 4-6 t ha -1 yr -1 when at full yield. Currently, major DxP seed programmes are based on very restricted breeding populations derived from a few specific breeding materials, i.e. Deli dura and AVROS pisifera (Kushairi and Rajanaidu, 2000). Realizing this, MPOB (Malaysian Palm Oil Board) initiated and established a sizeable oil palm gene bank with materials collected from Africa and South America since 1975 for conservation as well as to broaden the genetic base of the breeding populations (Rajanaidu, 1994). All these palms are presumably diploid (2n). Rival et al. (1997), using flow cytometry, estimated the DNA content for E. guineensis as 2C = 3.786 ± 0.125 pg. Ploidy manipulation has been found to be a valuable tool in the genetic improvement of many plants such as Solanum (Chauvin et al., 2003); citrus (Wu and Mooney, 2002); Scutellaria baicalensis (Gao et al. , 2002); pomegranate (Shao et al. , 2003); Miscanthus sinensis (Petersen et al., 2003); Artemisia annua (De Jesus-Gonzalez and Weathers, 2003); Allium cepa (Jakse et al., 2003); Alocasia (Thao et al., 2003) and azaleas (De Schepper et al., 2004). Ploidy induction has been carried out for a variety of reasons. In citrus, tetraploid (4n) parents were produced to create seedless triploids by crossing 4n and 2n parents (Wu and Mooney, 2002). In the medicinal plants, Scutellaria (Gao et al., 2002) and Artemisia (De Jesus-Gonzalez and Weathers, 2003), tetraploidy increases the amounts of the secondary metabolites, baicalin and artemisinin. In azalea (De Schepper et al., 2004) and pomegranate (Shao et al., Journal of Oil Palm Research Vol. 17 December 2005, p. 110-123