The genetic variability of the yield components in the Kenyan pyrethrum population
SummaryPyrethrum 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.
Clonal selection for yield in pyrethrum, Chrysanthemum cinerariaefoliumVis.
SummaryPyrethrum is grown for the insecticides found in the flowers. Due to its perennial habit each selection stage should last three years. Most traits can be adequately observed or measured within one-year cycles. However, it has not previously been investigated whether flower yield, one of the most important traits, could be adequately assessed in one year.Seven replicated yield trials, comprising 110 clones in a similar stage of selection, were observed over a period of three years. The clone effect on flower yield, pyrethrins yield and pyrethrins content were very significant in all trials. The correlation coefficients between the first year's results and the total results averaged +0.91 for flower yield and +0.93 for pyrethrins content. Selection of the highest yielding clones comprising one third of the total number resulted in an increase in pyrethrins yield of 34.3% when selected after the first year and in an increase of 37.5% when selected after three years. This increase was predominantly due to an increase in flower yield, which is caused by the much greater variation for flower yield than for pyrethrins content together with an inverse relation between these two traits.It is therefore possible to select in one-year stages with only a final testing over a 2 to 3 year period.
Genotypic diversity in field isolates of Babesia bovis from cattle with babesiosis after vaccination.
OBJECTIVE
To determine whether particular genotypes of Babesia bovis were common to field isolates obtained from cattle properties in Queensland where the B bovis vaccine had apparently failed.


DESIGN
A comparative study of polymerase chain reaction genotypes in different populations of B bovis.


PROCEDURE
Two polymerase chain reaction assays were applied to analyse DNA extracts of B bovis vaccine (K, T and Dixie strains) and 27 field isolates from 24 properties where disease outbreaks had occurred despite the use of the vaccine. To evaluate the stability of the genotypes identified, 11 of the field isolates were inoculated into experimental cattle that had either been previously vaccinated with T strain or not vaccinated.


RESULTS
No particular genotype of B bovis was responsible for the problems observed in previously vaccinated herds. None of the isolates had genotypes identical to the vaccine strains used. No geographic trends among the genotypes were observed. Isolates that originated from the same property also had different genotypes. Blood passage of the 11 field isolates in either previously vaccinated or nonvaccinated cattle did not alter the original genotype.


CONCLUSION
No particular genotypes identified by the Bv80 and BvVA1 polymerase chain reaction assays could be associated with vaccine failures.