Chromosome numbers, karyotypes, and nuclear DNA variation in Pratia Gaudin (Lobeliaceae)

Abstract

Chromosome numbers and karyotypes were studied in five New Zealand endemic species and one Australian species of Pratia. The species range from diploids with 2n = 2x = 14 to 20 ploids with 2n = 20x = 140. With the exception of P. angulata, within each species there appears to be a single chromosome number. P. angulata has a 10x and 20x race but also comprises plants that look like interspecific hybrids with P. perpusilla and have chromosome numbers of 2n = 11x = 77 and 2n = 13x = 91. There is some variation between species in chromosome size with P. macrodon, 2n = 2x = 14, having the largest chromosomes, but with a few exceptions it is difficult to identify specific chromosomes within species due to their small size and uniform appearance. Measurements of nuclear DNA amounts by flow cytometry show that there are large differences between species and also in genome size per haploid set. The diploid and tetraploid species have more DNA per haploid set than the higher polyploids. Flow cytometry is shown to be a useful method for identifying the chromosome races and ploidy levels of Pratia.

Keywords:

• Pratia
• chromosome number
• karyotype
• nuclear DNA amount
• flow cytometry
• interspecific hybrids