New Zealand Indigenous Grasses - a Study of Their Nuclear Dna Variation, Chromosome Numbers and Polyploidy Just Published
A major study of nuclear DNA (DNA C-values), chromosome numbers and polyploidy within the New Zealand indigenous grasses (Poaceae) has just been published in volume 96 of the University of Oxford managed Annals of Botany. The study by New Zealand botanists Murray et al. (2005) reports C-values from 171 taxa and seven unnamed entities, and provides 55 new chromosome counts. The grass sampling covers all the New Zealand grass genera except Lepturus R.Br. Variation in C-value and percentage polyploidy showed no clear relationship with respect to plant distribution. The study provides a substantial contribution to worldwide knowledge of C-values in the Poaceae. Several potentially new entities were either confirmed or discovered during the study….Variation in the amount of nuclear DNA of the entire chromosome complement (the holoploid genome size) is often called the C-value. Together with chromosome number and structure it is a useful guide toward speciation in flowering plants. From a C-value perspective, prior to the publication of Murray et al. (2005) Australasia was considered very under sampled. Murray et al. (2005) undertook a four year study of the chromosome numbers and C-values variation within the New Zealand Poaceae. Their decision was largely based on the recent publication of Flora 5 (Edgar & Connor 2000), an issue dealing solely with the New Zealand grass flora. Due to the helpful contributions from such New Zealand botanists as Dean Baigent-Mercer, Amanda Baird, John Barkla, Steve Benham, Jonathon Boow, John Braggins, Andrea Brandon, Jim Clarkson, Shannel Courtney, Geoff Davidson, Lisa Forester, Rhys Gardner, Bridget Gibb, Terry Hatch, Graham Jane, Peter Johnson, Phil Knightbridge, Kelvin Lloyd, Jeff McCauley, Brian Molloy, David Norton, Colin Ogle, Brian and Chris Rance, Matt Renner, Nick Singers, Mike Thorsen and Matt von Konrat, c.90% of the New Zealand Poaceae were obtained for study at the University of Auckland. In addition to the current publication many of the grass specimens received were sequenced for the nrDNA Internal transcribed Spacer Region, with the sequences uploaded to GenBank.
The study reported a wide range of C-values for the New Zealand endemic and indigenous grasses. The variation was explained in terms of the phylogenetic position of the genera, i.e. those in the BOP (Bambusoideae, Oryzoideae, Pooideae) clade having, in general, higher C-values than those in the PACC (Panicoideae, Arundinoideae, Chloridoideae + Centothecoideae) clade. Within genera, polyploids usually had smaller genome sizes than diploids, and commonly there was a progressive decrease with increasing ploidy. The high frequency of polyploidy in the New Zealand grasses was confirmed by their additional counts – only 10% of the grass flora is considered diploid. Contrary to other studies, no clear relationship between C-value, polyploidy and rarity was evident. The data obtained hints at or confirms the existence of new entities within Deyeuxia avenoides (Hook.f.) Buchanan, Lachnagrostis lyallii (Hook.f.) Zotov, Poa cita Edgar, Rytidosperma buchananii (Hook.f.) Connor et Edgar, R. thomsonii (Buchanan) Connor et Edgar, and Trisetum spicatum (L.) K.Richt. Cytoraces were recorded in Deyeuxia aucklandica (Hook.f.) Zotov, Rytidosperma buchananii, R. thomsonii and Trisetum tenellum (Petrie) A.W.Hill. Lachnagrostis littoralis subsp. salaria Edgar seems to be quite distinct from subsp. littoralis, and probably merits elevation to species rank.
Reference
Murray, B.G.; de Lange, P.J.; Ferguson, A.R. 2005: Nuclear DNA variation, Chromosome Numbers and Polyploidy in the Endemic and Indigenous Grass Flora of New Zealand. Annals of Botany 96: 1293-1305.
Posted: 22/12/2005