Genetic and non-genetic variations in the number of pappus parts in Microseris douglasii strain D37 (Asteraceae, Lactuceae)
1991
Vlot, E.C. | Bachmann, K.
The pappus of the annual species of Microseris usually consists of a constant number of five paleaceous, awn-tipped scales. In some populations of Microseris douglasii, plants with variable numbers of pappus parts, always five or fewer, are frequent. Here we study inbred lines derived from a plant with an average of slightly less than five pappus parts (strain D40), from a plant with an average near three pappus parts (strain B14), and from F2 plants of a hybrid (D37) between these two strains. The average deviation from five pappus parts is subject to various sources of non-genetic variation. The peripheral achenes in each head have more pappus parts than the central ones, and the overall average number decreases in later-formed capitula of a plant. Both effects are strongly affected by environmental factors. Against this background, we show (polygenic) genetic variation for the average deviation from five, and additional heritable differences in the strength of the gradient in pappus part numbers from the periphery to the centre of the capitulum, while the decrease of pappus part numbers in later-formed capitula is essentially identical in both parental strains, even in its response to environmental factors. Visible phenotypic variation due to all sources decreases as the average nears a constant number of five pappus parts.
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