Reciprocal recurrent selection applied to Coffea canephora Pierre

Summary Genetic parameters were estimated in trials planted in connection with a reciprocal recurrent selection programme applied to Coffea canephora in Côte d'Ivoire. Narrow sense heritability values, estimated from a breakdown of the analysis of variance, were high for architectural characters (0.22 to 0.78) and medium for tree vigour (0.13 to 0.40) and for bean weight (0.15 to 0.28). Calculated heritability values for the first two harvests were high (h²>0.7), but much lower for the following harvests (less than 0.2). Heritability estimates by parent-offspring regressions gave variable results, though they were often similar to those obtained by variance analysis, especially for bean weight. Phenotypic and genetic correlations between tree vigour traits and productivity were high. Bean weight was not correlated with vigour or production. Canopy diameter of 4 year-old trees was closely correlated with cumulated productivity from 2 to 5 years in the absence of development competition between trees, but the correlation was low if trees were in competition with each other. The consequences of the results for the choice of characters to be selected among intergroup hybrids or the parents of both populations are discussed.     

Responses to selection and changes in combining ability after three cycles of a modified reciprocal recurrent selection in maize

This research reports responses to selection and changes in general (GCA) and specific (SCA) combining abilities after three cycles of a modified reciprocal recurrent selection procedure (MRRS) in EPB-4 and EPB-5 maize populations. In the MRRS procedure a cycle can be completed in 1 or 2 years depending on the availability of winter breeding nurseries. The original and the three selection cycles of the two populations per se (eight entries) and the partial diallel developed from the crosses between them (16 entries) were evaluated in six environments. Realized response to selection on the population cross was 7.25% cycle⁻¹ for grain yield, −13.63% cycle⁻¹ for plant lodging, and 11.93% cyle⁻¹ for prolificacy, whereas plant and ear heights remained unchanged. GCA estimates increased with selection cycles for both populations for grain yield and prolificacy, and decreased for plant lodging, indicating that the frequency of favorable alleles with additive effects for these traits increased with the MRRS cycles in both populations. SCA estimates increased for grain yield and prolificacy indicating that the frequency of favorable complementary alleles at loci with non-additive effects in the reciprocal populations increased with the MRRS cycles. For grain yield, SCA effects increased more than GCA effects with selection cycles, indicating that MRRS exploited more the non-additive effects than the additive effects for the improvement of this trait. The overall results showed that the MRRS procedure was highly effective in improving the population cross, exploiting both GCA and SCA effects.     

Reciprocal recurrent selection applied to Coffea canephora Pierre. I. Characterization and evaluation of breeding populations and value of intergroup hybrids

Summary Two breeding populations have been identified with Coffea canephora, based on geographical and genetic differences: the Guinean group from West Africa and the Congolese group from central Africa. A reciprocal recurrent selection programme based on these groups was initiated in Côte d'Ivoire in 1984. Genotypes of both groups available in field collections are either of cultivated or wild origin.Genotypic and phenotypic variability was evaluated within and between the groups for the following characteristics: isozyme patterns, architecture, drought tolerance and vigour, technological and organoleptic traits, pest and disease resistance. Variation between and within groups was found to be large. Based on isozyme analysis and phenotypic observations, two subgroups were identified within the Congolese group. Phenotypic values of parents and testers used in the first cycle of reciprocal recurrent selection are presented.Results of two intergroup hybrid trials indicate high yield and vigour for these hybrids compared to intragroup hybrids, justifying the reciprocal selection approach. Furthermore, the variation observed indicates that recurrent selection would allow progress for selection traits for both populations and intergroup hybrids.     

Partial resistance to black spot disease in diploid and tetraploid roses: general combining ability and implications for breeding and selection

Black spot disease, incited by the fungus Diplocarpon rosae Wolf, is the most important disease of roses (Rosa hybrida L.) in the outdoor landscape. Though partial resistance exists in cultivated germplasm, the genetic basis of this trait has not yet been elucidated. Six diploid and six tetraploid rose cultivars were crossed in two factorial combining ability arrays. Whole plant and detached leaf inoculation methods were used to assess partial resistance under two different disease pressures using a characterized single-spore isolate. Parents from both arrays had significant general combining ability effects across multiple inoculation methods and environments. Specific combining ability was not significant for either array. Parent per se performance was highly correlated with progeny performance on a family mean basis. High positive correlations among whole plant and detached leaf inoculation methods indicate that detached leaf assays can substitute for whole plant assays. Based on these results, a breeding strategy including parental selection and early, among-family selection is proposed. To our knowledge, this is the first investigation of combining ability for disease resistance in rose.     

Changes in morphological and physiological traits associated with recurrent selection for grain yield in maize

Summary Experiments were conducted during the growing seasons of 1975 and 1976 to determine changes in morphological and physiological traits associated with recurrent selection for grain yield in maize (Zea mays L.). Four variety hybrids, BSSS(R)CO x BSCB1(R)CO, BSSS(R)C7 x BSCB1(R)C7 [from a reciprocal recurrent selection program involving Iowa Stiff Stalk Synthetic (BSSS) and Iowa Corn Borer Synthetic #1 (BSCB1)], BS12CO x B14A, and BS12C6 x B14A [from a half-sib selection program involving the open-pollinated variety Alph (BS12) and the inbred tester B14A] were grown at 59 300 and 98 800 plants/ha near Ames, Iowa We obtained data on CO₂-exchange rate (an estimate of photosynthetic rate), grain yield, grain-yield components, flowering dates, maturity traits, light interception and use, shelling percentage, harvest index, and various other plant traits.CO₂-exchange rate did not change appreciably with recurrent selection for yield. Grain yield per hectare and per plant were larger for the improved than unimproved hybrids. Grain-yield components did not change significantly with recurrent selection. Kernel weight of BSSS(R)C7 x BSCB1 (R)C7, however, was larger than that of BSSS(R)C0 x BSCB1(R)C0. Pollen-shed-to-silking interval was shorter for the improved than the unimproved hybrids, and grain-filling duration was longer in C7 x C7 than in C₀ x C₀ of the reciprocal recurrent selection program. Furthermore, improved hybrids were characterized by smaller tassels and more upright canopies. Usually, plant traits and leaf-area-related traits were similar for all hybiids.Although dry-matter productivity was similar for all hybrids, those that were improved by recurrent selection produced more grain per unit leaf area and per unit light interception. Also, BS12C6 x B14A was characterized by a higher harvest index than BS12CO x B14A.We concluded that the source (i.e., photosynthetic capacity) was not limiting grain yield in BSSS(R) x BSCB1(R) and BS12. Increased grain yields that resulted from recurrent selection were consequences of longer grain-filling duration for BSSS(R) x BSCB1(R) and increased translocation of photosynthate from source to sink for both BSSS(R) x BSCB1(R) and BS12.Journal Paper J-8953 of the Iowa Agriculture and Home Economics Exp. Stn., Ames, Iowa. Project No. 2152.     

Reciprocal recurrent selection for multitrait indices in maize

Summary Reciprocal recurrent selection was carried out with two populations of maize (Zea mays L.) having good combining ability. We selected for higher grain yield, early maturity, shorter plant height and lodging resistance. Two cycles were completed in two years (four seasons), by resorting to late planting of S1 lines for recombination in the main season in which top-cross families were assessed. Top-crosses and selfings were made in the off-season. The original and improved versions of the populations and their crosses were evaluated in multilocation trials. The superiority of the population hybrid was 10.3% for grain yield, 5.5% for plant height and 1.8 days to silk. The improved hybrid had delayed leaf senescence and better resistance to lodging and post-flowering stalk rots. Among the yield components, only ear girth showed improvement. Syn 2 of the improved population cross showed a yield reduction of 6.2% in comparison to Syn 1. Intrapopulation gains were not significant except for lodging resistance in one population.     

Use of index selection in recurrent selection programs in maize

Summary Phenotypic and genotypic correlations were examined for four traits in seven populations of maize (Zea mays L.) undergoing recurrent selection. Correlations among grain yield and percentage of grain moisture, root lodging, and stalk lodging were low (|r|<0.3) except for the correlation between grain yield and stalk lodging, which was high and negative. The phenotypic and genotypic correlations agreed well from cycle to cycle within populations. Variation of correlations among populations was not significantly larger than variation among cycles. Heritabilities of these traits generally were high (h²>0.5). Two indices, one that used heritabilities as index weights and one that used relative economic weights (base index) as index weights, were compared with the Smith-Hazel index (optimim index). Relative efficiencies of the two indices, in terms of predicted gains for the individual traits and the composite trait, compared with the Smith-Hazel index, were high. The use of an index in which heritabilities were used as index weights was recommended because:1) the heritabilities were the same as the optimum weights when the traits were uncorrelated, and for the data examined the correlations were low; and 2) heritabilities were computed in routine data analyses and were available at no additional cost.Joint contribution: USDA-SEA-AR and Journal Paper No. 10152 of the Iowa Agriculture and Home Economics Exp. Stn., Ames, Iowa. Project 2194.     

Effects of recurrent selection for grain yield on plant and ear traits of five maize populations

Summary Maize (Zea mays L.) breeders are interested in the effects of recurrent selection for grain yield on other traits. Changes in plant traits could alter agronomic acceptability of the populations under selection, and observed improvements in grain yield could be explained by changes in ear traits. We evaluated changes in combining ability for plant and ear traits of BS10(FR), BS11(FR), BSSS(R), BSCB1(R), and Lancaster Surecrop associated with recurrent selection for grain yield.Recurrent selection procedures generally did not change plant and ear heights or date of silking of testcrosses of populations or of the population crosses, BS10(FR)×BSS11(FR) and BSSS(R)×BSCB1(R). Grain yield improvements, however, were associated with increases in ear-sink size.Journal Paper No. J 9517 of the Iowa Agriculture and Home Economics Exp. Stn., Ames, Iowa. Project 2152.     

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.     

Breeding and combining ability of heterostylous genotypes for hybrid seed production in Lycopersicon esculentum Mill

Summary A subjective rating scale was used to select tomato inbreds with inserted stigmas (inserted) for crossing with inbreds possessing exserted stigmas (exserted) in a combining a bility study. Six inserted parents were inbred to F₅ or F₆, but were not stable for stigma position in most cases. The exserted x inserted hybrids were all slightly exserted and it appeared stigma exsertion was incompletely dominant to stigma insertion. No reciprocal cross differences were detected for stigma position indicating the absence of cytoplasmic inheritance. There was no clear relationship between hybrid stigma positions and the level of insertion of the inserted parents. Stigma insertion was more consistently detrimental to fruit set than was stigma exsertion. Hybrids were either heterotic or dominant for yield.The inability to attain hybrids with standard stigma positions by crossing exserted x inserted genotypes could limit fruit-set under some environmental conditions. Furthermore, difficulty in breeding stable inserted lines and the incomplete dominance of exserted over inserted genotypes limits the feasibility of using heterostyly alone for producing reliable hybrids.Ohio Agricultural Research and Development Center Article No. 166-78.     

Correlated response to recurrent selection for groat-oil content in oats

Summary One hundred random oat (Avena sativa L.) lines from a base (C₀) and each of three populations (C₁, C₂, and C₃) improved for groat (caryopsis) oil content by phenotypic recurrent selection were evaluated for correlated changes in several unselected agronomic traits. In addition, the parents of the base population and four check varieties were evaluated for the same traits. Phenotypic recurrent selection for high groat-oil content resulted in no significant correlated response in mean expression of any trait. Mean grain yield, biomass, groat yield, and harvest index of the improved populations were equal or superior to the mean of the parents and, with the exception of harvest index, equivalent to the mean of the check varieties. Mean test weight and seed weight of all populations were lower than for parents or check varieties. Selection for high groat-oil content caused a decline in genotypic variance for test weight and groat fraction, but reductions in genotypic variance for heading date and plant height may have resulted from culling for good agronomic type. Broad-sense heritability remained moderate to high for all traits except groat fraction. Phenotypic and genotypic correlation coefficients revealed negative, though mostly nonsignificant, relationships between groat-oil content and several traits, which may reflect a purported bioenergetic limitation to increasing groat-oil content in oats. Oil yield, however, was positively correlated with grain and groat yield, groat fraction, biomass, and harvest index. Results suggest that development of high-oil oat cultivars with current levels of production traits via phenotypic recurrent selection is possible.Journal Paper no. J-13038 of the Iowa Agric. and Home Econ. Exp. Stn., Ames, IA 50011. Project 2447.     

Phenotypic recurrent selection for oil content in East Indian lemongrass

Summary Phenotypic recurrent selection was carried out for oil content in East Indian lemongrass, Cymbopogon flexuosus (Steud) Wats. In each cycle, the top 5% of plants for oil content were selected. Their ramets were used for the establishment of replicated polycross blocks in isolation. Realized gains from selection were determined by evaluating the populations and the best clones from each population in separate two-year replicated trials. Three cycles of recurrent selection increased oil content by 32% per cycle at the population level. Realized gains from selection were slightly smaller or similar to predicted gains. Mean realized heritability for oil content was 0.56. At the clonal level, the best C₁ and the best C₂ clones had, respectively, a 22% and 73% higher oil content than the best clone from the base population (C₀). Selection for oil content did not adversely affect leaf yield, dry matter content or citral content in oil. Probable reasons for the high response to selection are mentioned.     

Changes in fatty acid composition associated with recurrent selection for groat-oil content in oat

Summary Groat oil of oat (Avena sativa L.) is a well-balanced oil with respect to saturated, monounsaturated, and polyunsaturated fatty acids. In this study, we measured the effect of six cycles of recurrent selection for high groat-oil content on the fatty acid composition of the groat oil. From each cycle of selection, 50 oat lines were grown in a replicated field experiment at two sites and were evaluated for groat-oil content and fatty acid composition.Concentrations of palmitate and linolenate decreased moderately over cycles of selection, whereas stearate content increased. A major increase occurred in the content of oleate and a major decrease in linoleate. Most of the modification of fatty acid composition took place within the saturated and unsaturated classes. The ratio of unsaturated to saturated fatty acids increased over cycles of selection. Significant genetic variation was present for each fatty acid, indicating that selection for different desired fatty acid compositions in groat oil of oat should be possible in this population.Abbreviations GO groat-oil content - 16:1 palmitate - 18:0 stearate - 18:1 oleate - 18:2 linoleate - 18:3 linolenate     

Application of the concepts of test value and varietal value to the study of genetic advance in recurrent selection: A synthesis

Summary The concepts of varietal ability and value in test of a genotype or group of genotypes are specified according to the type of variety (clones, hybrids, lines, synthetics) and the testing system (phenotype, S₁, General combining ability (GCA), line value, General synthesizing ability (GSA)). Varietal ability and value in test are to be considered as any quantitative characters for which it is possible to define additive effects, dominance effects and epistasis. For diploids in recurrent selection, only additive effects and additive× additive epistasis for varietal value contribute to genetic advance. Genetic advance depends on the covariance between the testing value of the parents and the test value of the progeny by intercrossing. Such a parent-offspring covariance is, in the absence of epistasis and inbreeding, one half of the covariance between additive effects in test of the parents and additive effects in test of their progenies. This allows one to express directly the genetic advance in varietal value according to the type of variety and to the testing system used in recurrent selection. The case of biallelic populations is considered; it allows some discussions on the relative values of components of variance of varietal and test values.     

Effects of recurrent selection for resistance to scab (Gibberella zeae) in wheat

Summary Scab caused by Gibberella zeae Petch., in common wheat, is one of the most severe diseases in China. A source population C0, bred for scab resistance, was developed through three cycles of multiple-parent crossing and intercrossing by means of the dominant male-sterile gene Ta1 (Ms2), according to Wu's scheme. Phenotypic recurrent selection methods for increasing the resistance to scab-infection of spikelets and seeds with the male-sterile plants were carried out simultaneously in Nanjing and Shanghai and at Jianyang, Fujian Province, for three cycles. The generations from C0 to C3 and two check cultivars were evaluated, using a randomized block design, under conditions of an artificially induced epidemic of scab during 1988–1990. The results indicate that there were significant differences in the resistance to scab between these generations. On average, the percentages of diseased spikelets and seeds of the male-fertile plants were reduced by 9% and 10%, respectively. The frequency of resistant plants was distinctly enhanced by recurrent selection. Analysis of variance showed that no significant differences existed between cycles of recurrent selection in agronomic characters such as plant height, spikes per plant, spike length, numbers of spikelets and seeds per spike, weight of seeds per spike and 100-kernel weight, days to heading and to maturity. Except for plant height, most of these traits tended to be slightly improved with improvement of resistance in the gene pool. The variance for resistance in the generations was decreased under selection. Recurrent selection for scab resistance using the dominant male-sterile gene Ta1 (Ms2) was both an effective and feasible breeding method for producing this character in wheat.     

Breeding transgressive lines of pepper for resistance to Phytophthora capsici in a recurrent selection system

Summary In order to increase the resistance level of pepper (Capsicum annuum) to Phytophthora capsici the main sources of genetic resistance were intercrossed. The parents included 7 varieties from different origins of partial resistance to P. capsici and to other soilborne pathogens. Two cycles of recurrent selection were performed by 7 plant breeders who screened the plants at two developmental stages with various isolates and at two temperatures. Analysis of data revealed a strong influence of the testing conditions on the evaluation of the plants. The level of resistance of the progenies further depended on the pathogen isolate used to screen the plants. Improvement of the whole population was more significant during the first cycle and lines with enhanced level of resistance as compared to the parents i.e. transgressive lines were fixed from the two cycles. These lines were resistant to much higher inoculum concentrations than the original parents and the expression of resistance was stable at high temperature (32°C). These new sources of polygenic resistance were included into a new breeding program to improve the agronomic characters.     

Genetic progress after four cycles of recurrent selection for yield and grain traits in common bean

The objective of this study was to evaluate the genetic progress after four cycles of recurrent selection in common bean. The base segregating population was obtained from 10 parents, and derived the S_0:1 and S_0:2 families that were evaluated. The S_0:3 families with higher grain yield and grain color, like the standard carioca were selected, and were intercrossed to generate the population of the following cycle. This process was repeated for four cycles. The best families were evaluated in each cycle by many generations and locations, and the five best lines of each cycle were identified. The 20 lines thus obtained were evaluated in two growing seasons, sown in July and November 2002. The grain yield (kg/ha) and grain type (scale of scores) were evaluated. Genetic progress was confirmed for both traits. The mean annual gain with selection for the grain type was 10.5% and 5.7% for grain yield, with no evidence of variability reduction in the population. These results show that recurrent selection is a good alternative for improving common bean quantitative traits.     

Recurrent selection for resistance to Verticillium dahliae in pepper

Summary Two cycles of recurrent selection were performed in a population including 7 small fruited varieties of pepper (Capsicum annuum) with low resistance level to Verticillium and resistance to other soilborne pathogens. The collaboration of 7 plant breeders in this work and the use of 2 artificial methods of inoculation allowed screening of numerous plants for resistance to V. dahliae under different conditions. The population was simultaneously improved for resistance to V. dahliae and for resistance to Phytophthora capsici, and at each cycle, intercrosses were performed between all these plants. The general level of resistance to V. dahliae increased continuously during the 2 cycles of seles of selection. Selfed progenies of plants from the 2 cycles displayed a higher resistance than the original parents, whatever the method of inoculation used. This gave evidence of transgressions for resistance. Crosses involving parents that did not seem resistant by themselves also produced transgressive lines, indicating that resistance genes were present but not active in these varieties. The transgressive lines with polygenic resistance to V. dahliae were included into a further breeding program to introduce genes of agronomic value.     

Divergent full-sib recurrent selection for germination at low temperature in a maize population

Summary Four cycles of divergent full-sib recurrent selection for the ability to germinate at low temperature were conducted in a maize (Zea mays L.) F₂ population. The selection criterion was the high (H) or the low (L) value in algebraic terms of the difference (DG) between germination percentage at 9.5°C (G9.5) detected 19 days after sowing and germination percentage at 25°C (G 25) seven days after sowing; both traits were evaluated in a controlled environment (germinator). Direct and correlated responses estimated during the course of selection were in accordance with those evaluated at the end. Selection for H led to populations with higher DG values, while the reverse was noted for L; differences between H and L populations increased in successive selection cycles, though divergence tended to level off. Selection for H also resulted in higher G 9.5 (day 19), shorter germination time and more flinty kernels, while selection for L led to responses in the opposite direction as well as to a lower G 9.5 detected 37 days after sowing (i.e. at the end of germination). In contrast, responses were negligible for G 25 and varied erratically from one cycle to another for kernel weight.Abbreviations DG (G 9.5–G 25) - FS full sib - GI germination index - G 9.5 germination percentage at 9.5°C - G 25 germination percentage at 25°C - H high DG value in algebraic terms - KT kernel type - KW kernel weight - L low DG value in algebraic terms     

Phenotypic recurrent selection in common bean (Phaseolus vulgaris L.) based on performance of S2 progenies

Summary The effect of a recurrent selection procedure for improving seed yield per plant was evaluated in common bean. Progress was registered after three cycles of recurrent selection with S2 progeny evaluation performed on the grain yield/plant. Gain from selection was estimated by field testing 45 random S2 lines from each of the C0, C1 and C2 populations. Response to selection for seed yield/plant was 6 g from C0 to C1 and 4.4 g from C1 to C2. The seed yield improvement was due principally to an increase in pods/plant; little contribution was provided by the 1000-seed weight and seeds/pod traits. Broad-sense heritability and genotypic variance for grain yield remained high in all cycles which suggests further gain from additional selection cycles. Grain yield/plant is significantly correlated to pods/plant and seeds/pod traits in all cycles, indicating that plants with favourable combinations of these traits could be identified. The proposed recurrent selection procedure appears to be effective in improving the population and extracting superior genotypes for varietal development.