The effect of interplant distance on the effectiveness of honeycomb selection. II. Results of the second selection cycle

Summary For a second consecutive generation, the efficiency of the honeycomb selection procedure was observed at low and at high density, i.e. interplant distance being 100 cm and 15 cm respectively. Progress due to selection was determined for each of the two plant densities applied by comparing the performance of offspring from selected plants with that of offspring from plants taken at random. The relation between selection intensity and selection response was observed to study the relation between competing and yielding ability in presence and in absence of interplant competition.Compared to results obtained in a previous generation, it is now dared to be more positive about the perspectives of selection in absence of interplant competition. It is tentatively concluded that single plant selection for yield at wide spacing gives a higher progress and allows a better identification of outstanding genotypes. However, the superiority of selection at low density is not confirmed neither by any estimator of a quantitative genetic parameter nor by the correlation between single plant yield and plot yield of their offspring. The disturbing factors found already in the former generation, namely variation in seed quality and a biased sample of random plants, exerted a less important role in the estimation of the progress. Nevertheless, it is believed that only when they can be reduced more reliable results can be achieved.     

Indirect selection for grain protein and grain yield in winter wheat

Summary The efficiency of the honeycomb selection procedure in selecting outstanding genotypes was observed at two interplant distances (d), i.e. d=100 cm, low density, representing noncompetitive conditions and d=15 cm, high density, representing presence of interplant competition. Progress due to selection among the plants grown with and without competition was established by comparison of the plot performance of offspring from selected plants with that of offspring from plants taken at random. The relation between selection intensity and response to selection was observed to detect a possible negative correlation between competing and yielding ability.So far, the results obtained do not yet allow to make a choice between selection of individual plants in presence or in absence of interplant competition. No significant correlation between single plant yield and plot yield was found at any of the two densities. However, response to selection for yield was higher when selecting at low density supporting Fasoulas' preference for selecting single plants in absence of competition. These results must be taken with caution since seed quality and a biassed sample of random plants exerted an important effect on the obtained response to selection.     

Effectiveness of honeycomb selection for yield superiority at three interplant distances: a field simulation study using chickpea (Cicer arietinum L.) inbred lines

The effect of interplant distance on differentiation and selection a) of the superior lines from a mixture of inbred lines, and b) of individual plants originating from the top lines, was studied in chickpeas (Cicer arietinum L.). For this, 28 chickpea inbred lines were evaluated on a single plant basis in a honeycomb design and in the same field at three interplant distances, for four growing seasons, at Larissa, Greece. The interplant distances were 15 cm (520000plants/ha, strong allo-competition), 30 cm(128630 plants/ha, medium allo-competition) and 100 cm (11500plants/ha, without competition). In addition, the inbred lines were evaluated in replicated plot trials under an agronomically accepted plant stand (520000plants/ha, crop environment) and the ranking of the 28 lines based on the average yield per plot over growing seasons was determined. Selection was applied in each season for each interplant distance and the three and six top lines with the highest average yield per plant were identified. These top lines from each interplant distance were compared with the three and six top lines(say: proven superior lines) identified after their evaluation under crop environment over seasons. In addition, selection was applied at the individual plant level with six selection pressures in each season and each interplant distance. Then we determined for each experiment and selection pressure the number of the selected plants which belonged to the six proven top lines. It was observed that the ranking obtained under crop environment was best correlated with the ranking at the intermediate interplant distance (30 cm), followed by the ranking at the high interplant distance (100 cm). In contrast this correlation was very weak for the ranking at low interplant distance (15 cm).In addition, the interplant distance identifying the highest number of the proven high yielding lines after their evaluation in one season was the intermediate interplant distance followed by the high interplant distance and certainly not the low interplant distance. The relative effectiveness was further increased when selection was based on average performance of the lines across seasons. This, together with the relatively small number of seeds produced per plant, renders selection at low interplant distance less favorable than selection at the intermediate or high interplant distance.The individual plant selection was effective at all three interplant distances. Selection effectiveness generally increased as the selection pressure increased. Again the best results were obtained when selection was applied at intermediate or at high interplant distance. It was concluded that line selection as well as individual plant selection was more effective at intermediate interplant distance and certainly not at low interplant distance. This revised version was published online in July 2006 with corrections to the Cover Date.     

Effects of competition and selection pressure on yield response in winter rye (Secale cereale L.)

Summary Three intensities of mass honeycomb selection (14.3,5.3 and 1.6%) applied to an unselected rye population gave respectively an annual yield response of 0.28, -3.69 and -5.20% at 15 cm spacing, and of 4.07, 5.39 and 8.99% at 90 cm spacing. The negative response with competition was explained by strong negative correlation between competing and yielding ability which causes positive skewness because of transposition of low yielders and strong competitors from the left to the right tail of the distribution. The positive response in the absence of competition was mainly due to the increased genotypic differentiation which allowed effective discrimination between high and low yielding genotypes. The efficiency of the selection in the absence of competition was further improved by using the honeycomb designs which adjust soil heterogeneity and application of very high family and individual selection pressures.Two cycles of mass honeycomb selection increased the population yield by 29.4%, one cycle of mass plus one cycle of pedigree honeycomb selection did so by 34.5%. The results are discussed in relation to the selection response and to the efficiency of various breeding schemes.Part of senior author's doctoral thesis     

A comparison of several procedures for mass selection in winter rye I. The relative quality of the procedures

Summary The HS-family offspring from each of 463 plants occurring in a population of winter rye were grown in a randomized complete block design. According to 4 sets of requirements, 4 groups of HS-families were created. The HS-families belonging to a certain group were considered to be superior with regard to the specified requirements.Independently from this, selection among the 463 parental plants was simulated. The selection was according to 3 methods (truncation selection, grid selection and honeycomb selection) applied with regard to a single plant trait or with regard to two plant traits. Altogether 9 different single-trait and two-trait criteria were studied for each selection method.The quality of some selection procedure or the other, i.e. a combination of a selection method and a selection criterion, was measured on the basis of the frequency of plants giving rise to a superior HS-family among all plants selected by the procedure.It is concluded that grid selection and honeycomb selection are more effective than truncation selection. Further it is tentatively concluded that honeycomb selection is more reliable than grid selection.     

A comparison of several procedures for mass selection in winter rye. II. What are the merits of adjusting phenotypic values?

Summary To get an improved impression of the genotypic value of individual plants the literature suggests to adjust their phenotypic values according to a moving mean correction or by means of an analysis of covariance, where the mean phenotypic value calculated across neighbours is used as the concomitant variable. In the present paper it is shown that the theoretical merits of these adjustments are promising: they eliminate the contribution due to the trend in soil fertility from the phenotypic value. In an experimental verification actual merits did, however, not show up.It is concluded that interplant competition is the main cause for the failure of the studied adjustments. These may be effective in virtual absence of intergenotypic competition. Thus, in case of single plant selection an extremely low plant density would be required, whereas selection among lines or families would require evaluation by means of multi-row plots.     

Influence of selected wheat and rye genotypes on the direct synthesis of hexaploid triticale

Summary In the synthesis of primary hexaploid triticale, a cross-incompatibility barrier exists when tetraploid wheat (4X) is crossed with diploid (2X) rye. Fertilization may occur, however, abnormal endosperm development usually leads to premature embryo death. Four selected tetraploid wheat lines were crossed as females with seven open-pollinated rye lines and the resulting embryos were rescued in vitro 13–16 days after pollination. The wheat genotypes showed a major influence on crossability (seed set), embryo development and plant recovery. The highest efficiency of amphihaploid plant recovery (18.3 plants per 100 pollinated florets) was obtained from one 4X wheat line originally selected from the cross T. carthlicum × T. dicoccoides. Some of the 3X amphihaploid plants (ABR) derived from two wheat lines showed relatively high level of partial fertility presumably as a result of meiotic restitution. Correlation analysis showed that crossability (seed set), normal hybrid embryo development in vivo and embryo culturability were independent of each other.     

Effect of various plant factors on the expression of creeping-rootedness in lucerne (Medicago sativa L. complex)

Although agronomically interesting, selection of creeping-rootedness inlucerne, that is, the ability to form adventitious shoots on horizontal,spreading roots, remains difficult because of the complex and still unclear geneticcontrol of this character, coupled with the possible occurrence of external factorsthat affect unpredictably its expression. Two experiments were undertaken onprogenies of creeping-rooted plants, to verify previous findings and inferences,and test novel hypotheses, concerning the effect of various plant factors on theexpression of creeping-rootedness. The ultimate aim was to provide information onthe most appropriate germplasm, procedures, or indirect selection criteria, that wouldimprove the efficiency of breeding for this character. The factors here examinedincluded genotype, age, kind of progeny, vigour, spreading ability, and undergroundmorphology. Some genotypes appeared to be good donors of the character, whereasothers did not. The proportion of creeping-rooted plants increased in allcases with the plant age. Selfing consistently depressed the expression ofthe character compared with clonal propagation or crossing. It is suggestedthat the effect of age and selfing on the penetrance of creeping-rootedness ismediated through their effect on plant vigour. Both aerial and root vigour showedindeed an effect per se on the presence of the character. Beside thevigour, possible indirect selection criteria were identified in the frequenciesof swollen zones and latent stem primordia on horizontal roots. Proportion ofcreeping-rooted plants in progenies after one year of growth appeared as a simple anduseful criterion to predict future trends. Consistent with previous conclusions, theresults provided evidence that a combination of family and individualselection may enhance the character expression.