Effect of tetraploidization on morphological and fertility characteristics in Iris × norrisii Lenz

Abstract

Tetraploids have been widely regarded as important contributors to the development of prime cultivars in many horticultural groups of Iris. These tetraploid plants tend to display intense flower color, increased flower size, and larger growth vitality compared to their diploid progenitors. However, no polyploid has ever been found or induced in the interspecific hybrid Iris × norrisii. In order to obtain new, innovative polyploid germplasm in I. × norrisii, 64 pre-germinated seeds were soaked with 0.05% colchicine, of which 14 survived and 6 flowered in the first growing season. Eight tetraploids were identified from the self-fertilized progeny of one of the six adult plants. The synthetic tetraploid I. × norrisii showed greater viability and developed wider leaves with larger stomata and pollen grains than their diploid counterparts. With tetraploidization, flowers were larger (by 26%), fruits became longer (by 54%), and selfing seeds were a little wider (by 10%) and significantly longer (by 33%) in size. The synthetic tetraploids exhibited a 9.10% selfing fruit-setting rate with 100% plump seeds. Conversely, most seeds collected from the interploidy cross between tetraploids and diploids were empty, with only 4.11% being plump. As a rare Iris species capable of flowering in the first growing season, the induced tetraploid I. × norrisii offers great potential to produce more genetically diverse progenies in a relatively short time, and thus provides a foundation for further research into polyploidization in Iris.