The genetic variability of the yield components in the Kenyan pyrethrum population

Summary Pyrethrum is grown for the insecticidal pyrethrins, extracted from the dried and ground flowers. It is a cross-fertilizing, self-incompatible perennial plant, which can be propagated vegetatively.The genetic variation of several, commercially important, characteristics was studied. The range of observed variation is very wide for fresh flower yield, flower size, number of flowers per stem, pyrethrins content, lodging resistance and the Pyrethrins I/Pyrethrins II ratio, and quite narrow for the dry matter content of the flowers. Populations to select from are obtained by crossing two (single crosses) or more clones (polycrosses). The genotypic variation of two single and one polycross (42 clones) was studied. The single crosses showed, for the three characteristics measured, pyrethrins content, flower size and Py. I/Py. II ratio, a considerable transgression. The progeny means were very similar to the mid-parent values. This indicates a polygenic inheritance for these traits. The variation of the polycross for these three traits was not greater than those of the two single crosses, suggesting a very high level of heterozygosity in the parental clones. It is in fact possible to reconstitute a large part of the genotypic variation observed in Kenya from only a very few single crosses. In view of the selection relationships between traits were investigated. Flower size appeared negatively related to dry matter content of the flowers and to flower yield. A suspected negative relation between flower yield and pyrethrins content could not be confirmed. The results indicate, that large genetic improvements are possible in a fairly short time.