Natural triploidy in phyto-oestrogen producing Curcuma species and cultivars from Thailand

Abstract

Triploidy is relatively common in Curcuma, especially among vegetatively propagated species in cultivation. The aim of this study was to investigate the extent of triploidy and the level of genome size variation among commercially cultivated phyto-oestrogen producing Curcuma and related species in Thailand. Meiosis was also examined in order to validate the triploid status and to infer genomic relationship in the triploids. A total of 47 accessions belonging to C. comosa, C. latifolia, C. sp.‘elata-latifolia’, C. caesia, C. cf. zedoaroides, C. cf. zedoaria and Curcuma sp. 1 were differentiated by ploidy based on chromosome numbers and by genome size based on flow cytometry data. The results revealed three distinct groups: (1) diploid C. comosa cultivars with small rhizomes, having 2n = 42 and mean 2C DNA content of 1.690 pg; (2) triploid cultivars from all but one Curcuma species investigated, with 2n = 63 and mean 2C DNA content of 2.549 pg; and (3) tetraploid cultivars of C. latifolia and C. cf. zedoaria, with 2n = 84 and mean 2C DNA content of 3.439 pg. The mean triploid genome size is right between the diploid and tetraploid values. Only Curcuma caesia showed statistically significant difference in genome size from all other triploid taxa. The study of male meiosis revealed different meiotic figures. The triploid C. comosa is clearly an autotriploid as it showed 21 trivalents, whereas the diploid C. comosa showed 21 bivalents. This confirms the base number x = 21. Triploid cultivars of C. latifolia and C. sp. ‘elata-latifolia’ showed irregularities in their meiotic figures, thus indicating allotriploidy.