Comparison of two methods of reciprocal recurrent selection in maize (Zea mays L.)

Reciprocal recurrent selection (RRS) was proposed for simultaneously improving two populations and their cross. A modification of the classical full-sib RRS (FS-RRS) was proposed in which the performance of full-sibs and S₂ families is combined in a selection index (FS-S₂-RRS). The Mediterranean corn borer (MCB) is the main corn borer species in the Mediterranean and adjacent areas and produces important yield losses. We started two RRS programs (FS-RRS and FS-S₂-RRS) from the same maize population in which the selection criterion was grain yield under artificial infestation with MCB eggs. Original populations, two cycles of selection derived from them by both RRS methods, and population crosses were evaluated under MCB attack and under insecticide treatment in three different environments. The objective was to compare the efficiency of the FS-RRS and the FS-S₂-RRS methods for improving grain yield. We found that the FS-S₂-RRS method was successful for improving the yield of the population cross under optimum conditions (the regression coefficient over cycles was b = 0.87** Mg ha⁻¹ cycle⁻¹) without losing yield under high pressure of MCB attack (b = 0.07). On the contrary, FS-RRS failed to improve the yield of the population cross under optimum conditions (b = 0.65) and tended to decrease the yield under high levels of MCB attack (b = −0.26). We conclude that for developing high yielding and stable varieties, FS-S₂-RRS is more efficient than the classical FS-RRS method.     

Predictive potential of DNA markers in heterosis breeding of maize

PCR-analysis of maize inbred lines has been carried out. Genetic distances between the lines have been calculated, allelic composition and heterosis level of F-hybrids have been determined. Heterosis level of hybrid seed yield rised according to increasing of genetic distances between initial lines. Correlation of allelic composition of inbred line microsatellite loci and heterosis level of the respective hybrids has been revealed.     

Choice of environments in reciprocal recurrent selection programs

Summary An alternative method of reciprocal recurrent selection (RRS) in which populations A and B are each evaluated in a different environment is proposed. This method is called dual-environment reciprocal recurrent selection (DERRS). Two genetic models are considered in the theoretical study. A comparison of selection methods shows that genetic gain is larger in DERRS than in RRS for the two models. The difference grows greater as the dominance effects operating in the two environments are more divergent and as the number of selection cycles increases. A greater gain is obtained when the genetic covariances between crosses in the two chosen environments are lower.     

Comparison of full and half-sib reciprocal recurrent selection

Summary Full and half-sib reciprocal recurrent selection (RRS) were compared algebraically and with computer simulation. The relative performance of the two schemes depended on the selection intensity and the environmental variance. Full-sib RRS was favoured at less intense selection and when the environmental variance was large relative to the total genetic variation. As selection intensity increased its advantage declined. Full-sib RRS enables a breeder to combine the efficient development of new hybrids with population improvement and should be a valuable technique in plant breeding.Published with the approval of the Director as paper No. 2466 Journal series, Nebraska Agr. Exp. Sta., Lincoln, Nebr. and as Atomic Energy Commission Technical Information Document No. COO-1512-17.     

Combined S2 and crossbred family selection in full-sib reciprocal recurrent selection

Summary A method (CRRS) that combines S₂ and crossbred family selection in full-sib reciprocal recurrent selection (FSRRS) is proposed. The method requires four generations per cycle in single-eared maize populations. Selection is based on performance of S₂ and full-sib families by applying selection index theory. Equations to estimate the coefficients included in the index are given. These estimates are functions of the genetic and phenotypic variances and covariances among and between the two kinds of families. Comparisons of FSRRS and CRRS under equivalent amount of effort show that CRRS has some advantage over FSRRS for low heritability of the trait being selected (e.g., maize yield) and when only one or two locations with two replications are involved in the selection experiment.Joint contribution: Institute Nacional de Investigaciones Agrarias, La Coruna, Spain; and Agricultural Research, Science and Education Administration, U.S. Department of Agriculture, and Journal Paper No. J-10118 of the Iowa Agriculture and Home Economics Experiment Station, Ames, IA 50011. Project 2194     

Relative efficiency of the genotypic value and combining ability effects on reciprocal recurrent selection

Reciprocal recurrent selection (RRS) has been successfully applied to maize breeding for more than 60 years. Our objective was to assess the relative efficiency of the genotypic value and the effects of general and specific combining abilities (GCA and SCA) on selection. The GCA effect reflects the number of favorable genes in the parent. The SCA effect primarily reflects the differences in the gene frequencies between the parents. We simulated three traits, three classes of populations, and 10 cycles of half- and full-sib RRS. The RRS is a highly efficient process for intra- and interpopulation breeding, regardless of the trait or the level of divergence among the populations. The RRS increases the heterosis of the interpopulation cross when there is dominance, and it decreases the inbreeding depression in the populations and the genetic variability in the populations and in the hybrid. When there is not dominance and the populations are not divergent, the RRS also determines population differentiation. The half-sib RRS, which is equivalent to selection based on the GCA effect, is more efficient than the full-sib RRS based on the genotypic value, regardless of the trait or the level of improvement of the populations. The full-sib RRS based on the SCA effect is not efficient for intra- and interpopulation breeding.     

Molecular markers in genetic and selection studies of maize

The review represents the literature data and the data of personal research demonstrating the modern achievements in molecular-genetic analysis of maize (Zea mays L.). The importance of the use of DNA-technologies in genetics, breeding and seed-production of maize is shown. The examples of application of molecular-genetic markers in breeding process to increase its efficacy are demonstrated.     

Full-sib and reciprocal recurrent selection in relation to pearl millet improvement

Summary During the years 1973 to 1976 two populations of Pearl millet with wide genetic base, namely, Delhi composite (DC) and Vijay composite (VC) were used to compare the response to selection by the full-sib family method from biparental material and reciprocal recurrent selection (RRS). The results indicated that it was possible to advance grain yield with one cycle of RRS by about 23 percent in the case of population DC and 21 percent in population VC, while for the full-sib selection method, the improvement in grain yield was not so rapid. The studies on the nature of gene action indicated that both additive and dominance gene actions were important for grain yield, ear length and ear girth. The coefficient of variation as a result of RRS was reduced in population DC, while it was comparable to base population in the other population. The correlation studies indicated that the magnitude of favourable correlation of different characters with grain yield were higher in case of RRS compared to the full-sib system. The presence of negative correlation of plant height with grain yield in both the improved populations indicated the possibility of breakage of unfavourable gene combinations through RRS and full-sibs developed from biparental mating.     

Prediction of heterosis in rice based on divergence of morphological and molecular markers

Identifying the best performing hybrid without a field test was essential to save resources and time. In this study, the genetic divergence was estimated using morphological and expressed sequence tag (EST)-derived simple sequence repeats (SSR) markers. Cluster analysis showed that APMS6A and RPHR 1005 belong to groups I and II, respectively, and the hybrid combination recorded the highest mean grain yield of 32.25 g among generated 40 \(\hbox {F}_{1}\hbox {s}\) with standard heterosis of 8.4% over hybrid check, KRH2. The coefficient of marker polymorphism (CMP) value was calculated based on EST-SSR markers; it ranged from 0.40 to 0.80, and a higher CMP value of 0.80 was obtained for the parental combination APMS6A \(\times \) RPHR1005. We predicted heterosis for 40 \(\hbox {F}_{1}\hbox {s}\) based on correlation between CMP and standard heterosis in different traits with standard varietal and hybrid checks indicating positive correlation and significant value for grain yield per plant (\(r=0.58\)**), productivity per day (\(r=0.54\)**), productive tillers (\(r=0.34\)*) and panicle weight (\(r=0.42\)**). This study revealed that the relationship of molecular marker heterozygosity, along with the combining ability, high mean value of different traits, grouping of parental lines based on morphological and molecular characterization is helpful to identify heterotic patterns in rice.     

Genetic basis of heterosis explored by simple sequence repeat markers in a random-mated maize population

We investigated the isozyme profiles of antioxidant enzymes in cultivars and lines with different seed productivity in cool climate conditions as a step towards understanding the physiological and genetical mechanisms underlying chilling tolerance in soybean. While no difference in superoxide dismutase, or catalase isozyme profiles was observed among the cultivars and lines tested, we found polymorphism in the ascorbate peroxidase isozyme profile; there were two types, with or without a cytosolic isoform (APX1). The cultivars and lines lacking APX1 proved more tolerant to chilling temperatures, as evaluated by yielding ability. The genotype-dependent deficiency of APX1 was consistent in plants and tissues under various oxidative stress conditions including the exposure to low-temperatures. In addition, the genetic analysis of progeny derived from crossing between cultivars differing in the isozyme profile indicated that the APX1 deficiency is controlled by a single recessive gene (apx1), and is inherited independently of the genes that have previously been identified for their association with chilling tolerance. Molecular and linkage analyses suggested that the variant gene of the APX1-absent genotype coding for a cytosolic APX, which contained a single nucleotide substitution and a single nucleotide deletion in the coding region, is responsible for the genotype-dependent deficiency of APX1. The association of APX1 deficiency with chilling tolerance is discussed in detail.     

Genetic drift and selection effects of modified recurrent full-sib selection programs in two F2 populations of European flint maize

Selection response of a modified recurrent full-sib (FS) selection scheme conducted in two European flint F₂ maize (Zea mays L.) populations was re-evaluated. Our objectives were to (1) determine the selection response for per se and testcross performance in both populations and (2) separate genetic effects due to selection from those due to random genetic drift. Modified recurrent FS selection was conducted at three locations using an effective population size N _e = 32 and a selection rate of 25% for a selection index, based on grain yield and grain moisture. Recombination was performed according to a pseudo-factorial mating scheme. Selection response was assessed using a population diallel including the source population and advanced selection cycles, as well as testcrosses with unrelatesd inbred line testers and the parental F₁ generation. Selection response per cycle was significant for grain yield and grain moisture in both populations. Effects of random genetic drift caused only a small reduction in the selection response. No significant selection response was observed for testcrosses, suggesting that for heterotic traits, such as grain yield, a high frequency of favorable alleles in the elite tester masked the effects of genes segregating in the populations. We conclude that our modified recurrent FS selection is an alternative to other commonly applied intrapopulation recurrent selection schemes, and some of its features may also be useful for increasing the efficiency of interpopulation recurrent selection programs.     

Estimation of coefficient of coancestry using molecular markers in maize

Summary The coefficient of coancestry (f_AB) between individuals A and B is the classical measure of genetic relationship. f_AB is determined from pedigree records and is the probability that random alleles at the same locus in A and B are copies of the same ancestral allele or identical by descent (ibd). Recently, the proportion of molecular marker variants shared between A and B (S_AB) has been used to measure genetic relationship. But S_AB is an upwardly-biased estimator of f_AB, especially between distantly-related lines. f_AB, S_AB, and adjusted (to remove bias) estimates of molecular marker similarity (f _AB ^M ) were compared. RFLP banding patterns at 46 probe-restriction enzyme combinations were obtained for 23 maize inbred lines derived from the Iowa Stiff Stalk Synthetic (BSSS) maize (Zea mays L.) population, and for 4 non-BSSS lines. f _AB ^M was estimated as , where _A (or _B) was the average proportion of RFLP variants shared between inbred A (or inbred B) and the non-BSSS lines. The average f_AB among 253 pairwise combinations of BSSS lines was 0.212, whereas the average S_AB was 0.397. The average f _AB ^M was 0.162, indicating that the upward bias in S_AB was effectively removed. S_AB and f_AB were significantly different ( = 0.05) in 76.3% of the comparisons, whereas 24.9% of the f _AB ^M values differed significantly from f_AB. The latter result suggests that selection and/or drift were present during inbred line development and that f_AB may not be an accurate measure of the true proportion of ibd alleles between two lines. Cluster analyses based on S _AB ^M and f _AB ^M grouped lines according to pedigree, although several exceptions were noted. The presence of shared molecular marker variants between unrelated lines must be considered when setting S_AB-based minimum distances for varietal protection. Under simplified conditions, more than 250 molecular marker loci are necessary to obtain sufficiently precise estimates of coefficient of coancestry using molecular markers.A contribution from Limagrain Genetics, a Group Limagrain company     

Two-locus theory in recurrent selection for general combining ability in maize

Summary Two-locus theory for recurrent selection for general combining ability in maize was developed. The theory featured: (a) recombination of the selfed progeny of selected parents; and (b) linkage disequilibrium in the initial gametic array. The theory indicated: (a) that initial linkage disequilibrium exerts a permanent influence upon selection progress; (b) that interposition of one or more generations of random mating before each cycle reduces the permanent effect in ensuing cycles; and (c) that random mating done before initiation of selection is more efficient in removing the influence of linkage disequilibrium on selection progress than random mating done between subsequent cycles.     

Analysis of genetic recombination in maize populations using molecular markers

Summary Variation in recombination rate is important to plant breeders since a major objective is to obtain favorable recombinants of linked genes. The ability to increase recombination (R) in circumstances in which favorable and unvavorable genes are linked (Corn Belt x exotic populations) and to decrease recombination when many favorable genes are linked (narrow-based, elite populations) would be of immense value. However, the concept of variation in recombination frequencies between linked genes has received limited attention despite its implications in breeding and genetic linkage studies. Molecular techniques have allowed better estimations of this variation. In this study, attempts were made to characterize: (1) the R values in the Pgm1-Adh1 and Adh1-Phi1 adjacent regions of chromosome 1 and the Idh2-Mdh2 region of chromosome 6 in F₂ families of three maize (Zea mays L.) populations; (2) the environmental effect on R values of F₂s from two populations. One population, NSO, was a Corn Belt synthetic, and the other two populations, CBMEX3 and CBCAR5, were composites from crosses between Corn Belt and exotic germ-plams.Wide ranges of estimated recombination ( ) values were observed among families in each population for all three chromsomal regions. The distribution of values for the Pgm1-Adh1 region showed that the F₂ families of each population fell into two broad categories: 0.30–0.50 and 0.02–0.20. No intermediates (0.21–0.29) were found. The distributions were almost normal for the Adh1-Phi1 and the Idh2-Mdh2 regions. It would appear that the major dispersion in the Pgm1-Adh1 region was controlled by the effects of a single gene, while the Adh1-Phi1 and Idh2-Mdh2 regions were only affected by polygenes. No correlation was found between recombination values of the two adjacent regions, indicating that the genes affecting recombination for the Pgm1-Adh1 region may be specific for that region.For the Pgm1-Adh1 region, no differences in values were found among the three populations. For the Adh1-Phi1 region, frequencies of CBMEX3 and NSO were not significantly different, but both had significantly greater values than CBCAR5. For the Idh2-Mdh2 region, CBMEX3 was significantly different from NSO. There were significant differences between some paired F₂ families within each population for each chromosome region.No significant differences in response to the two environments were detected in CBMEX3 and NSO for either region in chromosome 1.Published as Journal Paper No. 9498 of the Nebraska Agric Res Div, University of Nebraska, Lincoln, Neb. Research supported in part by USDA Competitive Grant 87-CRCR-2359     

Genetic gains from reciprocal recurrent and within-line selection for egg production in the fowl

Summary Selection for survivors percent egg production from first egg to 40 weeks of age was conducted for six generations. Within-line selection (WLS) on the basis of an index of individual records plus sire family and dam family means was compared with reciprocal recurrent selection (RRS) based on sire family selection among cross progeny. Genetically heterogeneous synthetic populations, the Cornell Control and the Purdue Pool strains were used.The responses to WLS (3.84 °) and RRS (2.57 °) were both significantly greater than zero, but were not significantly different from each other. Nevertheless, the responses were proportional to their predicted values (.363 vs. 340). The advantage of WLS was due to the mechanics of selection resulting in slightly greater selection intensity and an increased correlation between the criterion of selection and the trait being improved. On the contrary, the RRS method had a slightly larger realized heritability as would be expected in the presence of non-additive genetic variance. Four of five pure-lines selected under both methods had statistically significant declines in performance due to inbreeding depression effects. All of the results observed are comparable with known genetic theory.Some problems in comparing genetic gains from different selection methods or selection criteria are discussed.Journal Paper No. 4986 of the Purdue University Agricultural Experiment Station. Conducted in cooperation with the Regional Poultry Breeding Laboratory, Project N. C. 89. Supported in part by N. I. H. Grant No. ES00310.     

Combining ability and heterosis in diallel crosses of maize

Summary The present investigation involved crosses among 20 elite yellow maize populations. These were evaluated in four environments in a randomized block design with four replications in each environment. Variety Cuba was observed to be the best general combiner for grain yield, followed by St Croix and Prolific. No clear association could be discerned between general combining ability (GCA) effects for grain yield and its components, and mean grain yield performance and GCA effects. Heterosis was observed in general and all the crosses involving Cuba yielded better than the midparent. The five hybrids, Kisan × Cuba, Antigua 3D × St Croix, Prolific × St Croix, Vijay × Antigua Gr. I and A 23 × Cuba, yielded more than the standard check. Significant yield superiority of these varietal hybrids over the best commercial composite (Jawahar) suggested the possibility of their commercial exploitation.Part of the thesis submitted by the senior author in the partial fulfilment of the requirements for the Ph.D. degree