Population improvement in pyrethrum (Chrysanthemum cinerariaefolium Vis.)

Summary A population improvement programme in pyrethrum had progressively increased the mean pyrethrins content from 1.33 percent in the unselected base population to 1.97 percent in the population developed after one cycle of each of mass and recurrent selections. The selection had also increased the range of variation and the relative frequency of desirable plants.     

Pollen of pyrethrum (Chrysanthemum cinerariaefolium Vis.). Fine structure and recognition reaction

Summary Both transmission and scanning electron microscopy were utilised to follow fine structural changes in the pollen of pyrethrum in the last stages of sporogenesis and during pollination. The ripe pollen appears to be covered with a proteinaceous skin. The role of the skin is protective. The skin also is the first site of recognition in the pollen-stigma interaction.     

Selection for combining ability in Pyrethrum,Chrysanthemum cinerariaefolium Vis.

Summary Pyrethrum 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.Published with the approval of the Director of Agriculture, Kenya.     

Incompatibility relationship in pyrethrum (Chrysanthemum cinerariaefolium vis.)

Summary Evidence that a one-locus sporophytic incompatibility system operates in pyrethrum is presented after analysing the F₁ of a clonal cross. Secondary factors, as the site of inhibition of the pollen tube on the stigma and three-nucleate pollen further support this evidence.     

Clonal selection in 'Uzunmusa' hazelnut

Clonal selection was practised in ‘Uzunmusa’ hazelnut over the past 3 years (1999‐2001) to select the highest quality types. Based on an initial assessment of a total of 102 types, 45 were selected for further study. The best types were selection numbers (SN) 397 and 570. The two selected clones have very good characteristics and seem to be superior to the standard clone. The clones had a higher kernel percentage (62.72%), a higher number of nuts per cluster (5.5), thinner shells (0.75 mm) and heavier nuts (2.34 g). On the other hand, the clones seem to be very suitable for the nut industry because of their oil content and size. These types have very thin shells which are suitable for in‐shell market.     

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.     

Plant selection for yield improvement

This paper is concerned with the consequences of variations in the quantities that specify a programme of selection based upon yields, and in particular with the overall intensity of selection, the manner in which this is compounded of fractions selected in successive seasons, the total area or other measure of resources expended upon field trials, the allocation of this total between successive seasons, and the total number of sesons or stages over which selection is spread.

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A.R.C. Unit of Statistics and University of Aberdeen     

Single plant selection for yield in lentil

Summary Individual plant selection for yield in lentil is problematic at a commercial crop density primarily because of inter-plant entanglement by tendrils. Visual plant selection for yield was compared with random selection in the F₅ at three plant densities (66, 133 and 200 seeds/m²) by an evaluation of F₇ progeny yields over two seasons in two populations of lentil. Random plant sampling was as effective as visual plant selection in isolating high-yielding F₇ lines. The plant density of the selection environment did not affect the response to selection. The correlations between the seed number of selected F₅ plants and the mean yield of their F₇ progenies were r=+–0.26 and –0.06 in two populations, indicating the lack of positive response to plant selection for seed number. The results show that 1) random sampling is the most economic of the methods tested of plant selection for yield and 2) the plant density of the environment for plant selection can be low enough to avoid inter-plant entanglement by tendrils, allowing a focus in plant selection on characters, other than yield, of importance to the breeding program and with a higher heritability than yield.     

Recurrent phenotypic selection for forage yield in rye

Summary Cultivars of Cucurbita pepo and other Cucurbita species were characterized by RFLP analysis using different fragments of the ribosomal intergenic spacer (IGS) of Cucurbita pepo as hybridization probes. Several cultivars could be distinguished by a specific rDNA restriction pattern, whereas some cultivars showed an identical RFLP pattern suggesting a closer relationship. Other species of the genus Cucurbita exhibited strong cross-reaction with the C. pepo spacer probes, in contrast to DNA of Cucumis species which did not cross-hybridize.Abbreviations IGS intergenic spacer - ITS internal transcribed spacer - kbp kilo base pairs - rDNA ribosomal DNA - RFLP restriction fragment length polymorphism - rRNA ribosomal RNA     

Direct and indirect selection for yield in chickpea

Summary The efficiency of indirect selection for seed yield was compared with direct selection for yield per se in chickpea. A total of 2500 single F₂ plants, derived from 50 crosses with 50 plants from each cross, were divided into five sub-populations (SP1 to SP5) of 500 plants each by including 10 plants from each of the 50 crosses. The five sub-populations were advanced upto F₆ by exercising 10% selection intensity for four successive generations for number of pods per plant in SP1, number of seeds per pod in SP2, seed weight in SP3, seed yield in SP4 and random selection in SP5. The efficiency of direct and indirect selection for yield was evaluated by comparing groups of 50 F₆ lines from each sub-population. SP1 and SP3 F₆ lines showed higher mean grain yield than the other three methods. SP1 and SP3 were found to be almost equally efficient in developing F₆ lines which were significantly superior to the check. This suggests that indirect selection for yield via pod number and seed weight is more efficient than direct selection for yield.     

Half-sib family selection for forage yield in orchardgrass

Genetic variation for forage yield of orchardgrass is abundant, but there are few reports of progress from selection for increased forage yield. The objective of this study was to estimate direct effects of selection from one cycle of half‐sib family selection for forage yield in orchardgrass. Eleven selected populations were compared with their parent populations within three maturity groups. Populations were evaluated under hay management at three locations and management‐intensive rotational grazing at two locations. Nine of the 11 selected populations differed, by an average of 7.4%, from their parent population in forage yield. Nine of the selected populations also showed changes in Drechslera leafspot reaction, all indicating a negative genetic correlation with forage yield. Selection for high forage yield tended to result in greater ground cover and later relative maturity. However, changes in net herbage accumulation (NHA) under rotational grazing were generally not significant and were uncorrelated with changes in forage yield, indicating that forage yield of hay plots is not correlated with the NHA of grazed plots. Although genetic gains in forage yield measured under hay management were very favourable relative to other reports from the literature, the lack of correlated progress under grazing management indicates that directed selection for NHA of orchardgrass should be conducted under grazing management.     

Rhodes grass breeding in Kenya II. Clonal evaluation for seed yield within maturity classes of two varieties

Summary A study was made over three seasons of seed yield characters in replicated genotypes of two maturity classes selected from within both Mbarara and Masaba Rhodes.Within maturity classes significant 2–4 fold ranges were observed in PGS (pure germinating seed) yield. The component most responsible for this increase was seed setting. Significant differences were also observed in seed retention, 1000-seed weight, head number and the number and length of racemes.Even though heading date, within a maturity class of a variety did not vary more than 10 days, differences were significant and the early-heading plants were the most productive in seed yield characters.Heritability estimates, based on individual plants, ranged from less than 0.10 for % PGS to over 0.30 for 1000-seed weight and raceme characters.     

Selection for sugar yield in sugar beet, Beta vulgaris, using different selection indices

In sugar beet breeding, sugar yield is mainly influenced by root yield and sugar content. In this short communication several indices to select for both traits simultaneously are compared in order to find the best one. The indices are correlated with the base index of Williams (1962) from independent experiments. The indices differ in the amount of information necessary for the calculation of their weights. Three different series of each eight sites gave similar results. The optimum index using all information from phenotypic and genotypic variances and covariances, did not perform best. Sugar content with its higher herit ability must have a larger weight than root yield. Heritabilities as index weights performed best, but two other indices using heritabilities and phenotypic but no genetic covariances also performed well.     

An evaluation of a new rhombic grid selection,gridded mass selection and simple mass selection methods for yield improvement in wheat

Summary An experiment was conducted in Winnipeg, Manitoba, Canada to: (1) ascertain the efficiency of gridded mass selection; (2) to determine if additional selection efficiency can be achieved through refinement of the gridded mass selection procedure; and (3) to determine if the degree of homozygosity has an effect on response to single-plant selection. Three selection methods [simple mass selection (SMS); gridded mass selection (GMS); and a new rhombic grid selection (RGS)] were applied to four populations [a conventional F₂ (CON-F₂); an intermated F₂ (INT-F₂); and 2 partial backcrossed populations] developed from a biparental cross involving the Canadian spring wheat cultivars, Glenlea and Sinton. Averaged over the 4 populations, a single cycle of RGS (10% selection intensity) increased yield by about 9.5%, whereas GMS and SMS increased yield by approximately 4.5% and 3.1%, respectively. The degree of homozygosity of individual plants that make up the population appeared to have an effect on the efficiency of selection. In general, selection was more efficient in the two partial backcrossed populations, and least efficient in the CON-F₂ and INT-F₂ populations. The largest response to selection (15.9%) was attained when RGS was applied in the backcross to Glenlea population, and the lowest response (1.2%) when SMS was enforced in the CON-F₂ population. This paper represents the first report on the efficiency of rhombic grid selection for yield improvement in cereal crops.Contribution No. 550 of Agriculture Canada, Lacombe Research Station, Bag Service 5000, Lacombe, Alberta, Canada TOC ISO     

Optimizing selection for rough rice yield, head rice, and total milled rice

High rough rice yields are important for the profitable production of rice (Oryza sativa L.). The value of rough rice is determined primarily by head rice (whole milled grains) and broken rice, together referred to as total milled rice. The objective of this study was to optimize selection for rough rice yield, head rice, and total milled rice using path-coefficient analysis and selection indices. Thirty-seven long grain pure lines were grown in an experiment at three Arkansas locations during 1993 and 1994. In another test, twenty-eight F₁ hybrids obtained from an eight-parent half diallel of long-grain rices were grown at two locations in Arkansas during 1991. For the pure lines, path analysis revealed that rough rice yield was approximately twice as important in determining total milled rice/ha than head rice. Path analysis for the hybrids revealed that rough rice yield was an even greater component in determining total milled rice/ha. Based on yield components for hybrid rice, panicle density had the largest direct effect determining total milled rice/ha. Filled grain/panicle, grain weight, and head rice, in that order, were secondary, but positive, factors determining total milled rice/ha. A selection index for pure lines based only on selection for head rice was 19.2 percent as effective as selection for total milled rice/ha directly. When selection for total milled rice/ha was based solely on rough rice yield, selection was 82.7 percent as effective as selecting for total milled rice/ha directly. Selection to improve total milled rice/ha should concentrate on increasing both rough rice yield and head rice. Rough rice yield should receive greater priority than head rice in selection strategies. This revised version was published online in July 2006 with corrections to the Cover Date.     

Recurrent selection for yield in Glycine max using genetic male-sterility

Summary Recurrent selection, using genetic male sterility to facilitate intermating in Glycine max, was evaluated when selecting among individual space-planted S₀ soybean plants for three yield-related traits: 1) seed yield per se (YLD), 2) apparent harvest index (AHI), and 3) a selection index in which seed yield was regressed on maturity (REG). The original intermating population was a combination of the cultivar Century and two F₂ populations segregating for male sterility. The selection intensity through three cycles of selection was 20%. The YLD population increased in mean yield by 2.8±2.2 g plant^-1 cycle^-1 buf shifted significantly toward late maturity by 3.9±0.6 days cycle^-1. The AHI population decreased in yield by 4.4±2.6 g cycle^-1 while maturity shifted slightly earlier; there was very little change in AHI. The REG population increased in yield by 5.7±2.4 g plant^-1 cycle^-1 while shifting toward later maturity by only 0.8±0.5 day cycle^-1. We concluded that selection among S₀ plants in these populations, using the selection index of yield regressed on maturity, was affective in increasing single plant yields without causing a significant shift in maturity. Selecting for yield per se caused an unacceptable shift toward late maturity and selection for AHI was ineffective for increasing yield or AHI.     

Indonesian mungbean landraces I. Pure-line selection for yield when intercropped with maize

Summary When mungbean landraces from East Java were intercropped with maize, genetic variation for grain yield was observed. Three cycles of selection resulted in a yield increase of 24% as compared to the original landraces. The yield of the maize component in the mixture was not affected by the increase of the mungbean yield.     

A recurrent selection programme for grain yield in winter barley

Summary The effect of a recurrent selection procedure was evaluated in a winter barley (Hordeum vulgare L.) population. Cycle zero (C₀) was initiated by crossing six high yielding winter barley cultivars with the short straw cv Onice. The F₁'s were crossed according to a diallel scheme without reciprocals. A total of 750 S₀ plants were derived and evaluated; 329 S₀ plants were selected and their progenies (S₁ lines) tested. Fifteen S₁ lines were chosen and used as parents of cycle 1 (C₁), by producing 105 F₁ hybrids which simulated a random mating offspring. One hundred and three randomly chosen S₁ lines belonging to C₀, and 103 S₁ lines belonging to C₁, were evaluated at two locations.For grain yield a significant difference between cycles was observed. From C₀ to C₁ the grain yield increased with 307 g/m². This increase was due to a higher number of seeds per m². For plant height, heading date and 100-kernel weight no differences between cycles were observed.The positive results obtained in this study indicate the potential usefulness of recurrent selection for developing parents or lines superior for grain yield, with little change in other important agronomic traits.