J. Battjes et al., MERISTEM GEOMETRY AND HERITABLE VARIATION IN NUMBERS OF FLORETS AND INVOLUCRAL BRACTS IN MICROSERIS-PYGMAEA (ASTERACEAE, LACTUCEAE), Acta botanica neerlandica, 42(3), 1993, pp. 255-268
Strains A92 and C96 of the Chilean annual, Microseris pygmaea, represe
nt the genetically most divergent biotypes within the species. They di
ffer, among other characters, in the numbers of florets and inner and
outer phyllaries (involucral bracts) per head. Higher numbers in A92 a
re mainly the consequence of smaller primordia while the capitulum bud
s in both strains are about equal in size. Disruptive selection from a
large F2 of the hybrid between A92 and C96 has produced lines with tr
ansgressive numbers of parts with non-parental correlations among numb
ers of parts. The early development of the capitula was studied in F4
families derived from two F2 plants selected for extreme organ number
phenotypes. Differences in organ numbers among these families are prim
arily due to differences in capitulum size which did not differ signif
icantly between the parental strains. Values for other parameters such
as floret primordium size, height of the zone in which inner phyllari
es arise, and difference in size between peripheral and central floret
s, did not significantly contribute to the observed differences in org
an numbers. The multiple gene differences suggested by the transgressi
ve segregation in the F2 can be partly traced back to various primary
effects on meristem differentiation.