Genetic and Nongenetic Factors Influencing Deviations from Five Pappus Parts in a Hybrid between Microseris douglasii and M. bigelovii (Asteraceae, Lactuceae)

The genetic basis responsible for deviations from a basic number of five pappus parts was analyzed in a cross between M. douglasii inbred strain B14 (0-5 pappus parts, modal number 3) and M. bigelovii strain C94 (4-7 pappus parts, modal number 5). The F1 pappus part number is near 5, and most F2 plants have averages near 5. Offspring of F2 plants with relatively low pappus part numbers also had low pappus part numbers. The strong correlation between the segregation of average pappus part numbers in the F2 and the genotypes of a restriction fragment length polymorphism (RFLP) in the nuclear DNA suggests that most of the F2 segregation can be explained by the segregation of a single major gene, linked to the RFLP, with dominance for the higher number of pappus parts and minor modifiers that keep the F2 phenotypes from reaching the parental high and low values. Various components of the variation in pappus part numbers within one plant are illustrated. Independent genetic effects determining changes in average pappus part number with plant age and with the position of the achene on the capitulum seem to segregate in the F2.