Evolution over 16 years in a bulk-hybrid population of subterranean clover (Trifolium subterraneum L.) at two contrasting sites in south-western Australia

Abstract

Evolution was measured over 16 years in a self-regenerating, bulk-hybrid subterranean clover population, consisting of F 2 seed from 253 crosses, sown at Nabawa and Mt Barker, short and long growing season sites, respectively, in south-western Australia. Seed bank samples harvested annually were grown in a common garden. Experiment 1 measured flowering time in plants from each year, while Experiment 2 measured 26 variables in the populations 3 and 16 years after sowing, in comparison with the ancestral population. Changes in population means were observed in 20 characters and variability declined in 11 characters at one or both sites, with much of this occurring within the first three years. Natural selection at Nabawa favoured early flowering of long duration, thick peduncles, high harvest index and high hardseededness. At Mt Barker it favoured late flowering of short duration, large leaves and long, thick petioles at flowering, thick stems with long internodes, long, thin peduncles with a high burial angle, large plants at maturity, low hardseededness and high biochanin A and total isoflavone contents. High seed production capacity, with high seed weight and seeds per burr, was important at both sites. The use of bulk-hybrid populations is demonstrated as a low-input means of breeding and selecting well-adapted subterranean clovers.

Hotspots and gaps in the world collection of subterranean clover (Trifolium subterraneumL.)

“…Contents of the phyto-oestrogenic isoflavones formononetin, genistein and biochanin A are also highly heritable, with each subterranean clover type having a distinctive pattern (Francis & Millington 1965; Gladstones 1966; Nichols et al . 1996, 2009, 2013).…”

Evolutionary Plant Breeding in Cereals—Into a New Era

“…On the other hand, when environmental variance is small, selection forces will drive the evolving population relatively quickly to a targeted composition of genotypes that are well adapted to the (new) environmental mean. Populations in markedly different environments will diverge in their composition of genotypes [32], thus exhibiting the capacity aspect of diversity. In effect, we do not need to know the size of the environmental variance (or even the direction of where the mean is going) to decide whether to grow a more diverse 'mixture' or a targeted genotype, because this will be decided by the evolutionary forces acting on the population.…”

Morphological diversity within a core collection of subterranean clover (Trifolium subterraneum L.): Lessons in pasture adaptation from the wild

“…Diversity within subterranean clover is high for a range of phenological and growth traits [4,7,15,16]. Flowering time is highly responsive to environment, with several studies demonstrating that early flowering is important for adaptation to short-season environments, with later flowering favoured in longer growing-season areas [15,16,17,18,19,20]. Diversity has also been found for plant diameter, petiole length and thickness, leaf size, internode length, stem thickness, peduncle length and thickness and mean seed size [16,18,19,21,20].…”