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.
Selection for combining ability in Pyrethrum,Chrysanthemum cinerariaefoliumVis.
SummaryPyrethrum is grown for the insecticidal “pyrethrins”, present mainly in the flowers. It is a cross-fertilizing perennial which can be propagated vegetatively. The main selection criteria are fresh flower yield and pyrethrins content; important secondary criteria are flower size and resistance to lodging; dry matter content varies very little.For these traits, the breeding values (general combining ability) of 22 clones were determined by means of a polycross. The heritabilities were estimated from the regressions of the polycross progeny data on those of the female parent clones; these were: flower yield 0.31; pyrethrins content 0.70; flower size 0.80 and resistance to lodging 0.87. For dry matter content no correlation between parents and progenies could be measured. Independent heritability estimates, obtained from 33 single crosses between clones not represented in the polycross, were: flower yield 0.56; pyrethrins content 0.64. Of 18 single crosses, made between clones also represented in the polycross, the actual flower yields and pyrethrins contents were highly correlated with the estimated yields and contents which were calculated from the breeding values of the parent clones (r = +0.87 and +0.86, respectively).These data show that the performance of single crosses is caused predominantly by the general combining ability of the parent clones. Therefore, single crosses offer no fundamental advantages over synthetic varieties, so that, for practical reasons, the latter are preferred. At the same time it is recommended to practise reciprocal recurrent selection as this will exploit the general combining ability in the initial stages of selection and the specific component increasingly in later selection cycles.
On the fractionation of β-lactoglobulin and α-lactalbumin
Abstract Existing methods for the preparation of α-lactalbumin and β-lactoglobulin are examined critically. It is proposed that the most satisfactory method for the preparation of the whey protein fraction from bovine milk is (NH 4 ) 2 SO 4 fractionation. A number of new gentle procedures for the fractionation of the whey proteins are compared with some existing methods. The distribution of total protein at various stages is determined by total Kjeldahl nitrogen and the kind of protein by starch-gel electrophoresis. The effect of variables, such as pH, salt concentration and temperature on the separation of α-lactalbumin and serum albumin from β-lactoglobulin is studied. Differences in the behavior ( e.g. solubility) of genetic variants of β-lactoglobulin are noted. The solubility of each of the major whey proteins, under similar conditions to those used in the fractionation, is compared with its solubility in the whey protein mixture. The understanding gained of factors important in the fractionation is used in recommending new procedures for α-lactalbumin and β-lactoglobulin isolation.