Cycles Of Phenotypic Selection Research Articles

Recurrent selection for Fusarium head blight resistance in a durum wheat population

AbstractFusarium head blight (FHB) is a devastating fungal disease of wheat. Since early 1990s, frequent FHB epidemics in major wheat‐growing regions have caused massive economic losses. Developing FHB‐resistant varieties is key to minimize the loss caused by the disease. In durum wheat (Triticum turgidum L. ssp. durum), however, it is challenged by lack of resistant sources. Introgression of resistance genes from wild relatives and bread wheat has resulted in some durum wheat lines with moderate resistance. Due to its complex genetic nature, integrating more resistance genes with moderate and even minor effects promises to provide high and durable FHB resistance. In this study, a base population was developed using diverse resistant lines and elite durum wheat breeding lines as founders and went through three cycles of phenotypic selection from 2019 to 2022, with FHB severity decreased by 34%. Six S0:1 lines in Cycle 2 and Cycle 3 populations exhibited significantly lower FHB severity than the moderately susceptible check variety ND Riveland. The results suggested that recurrent phenotypic selection could effectively improve FHB resistance. Analysis of the founders and Cycle 2 and Cycle 3 populations with 2706 single nucleotide polymorphism markers indicated that there was little decrease in genetic variation due to selection. Genome‐wide association analysis found no markers significantly associated with FHB severity. Genomic prediction accuracies based on cross‐validation for FHB severity, plant height, and days‐to‐flowering were 0.51, 0.69, and 0.61, respectively. Recurrent genomic selection can shorten the select cycle to 4 months and therefore is promising to accelerate genetic improvement of FHB severity.

Genomic Prediction of Biomass Yield in Two Selection Cycles of a Tetraploid Alfalfa Breeding Population.

Alfalfa (Medicago sativa L.) is a widely planted perennial forage legume grown throughout temperate and dry subtropical regions in the world. Long breeding cycles limit genetic improvement of alfalfa, particularly for complex traits such as biomass yield. Genomic selection (GS), based on predicted breeding values obtained using genome-wide molecular markers, could enhance breeding efficiency in terms of gain per unit time and cost. In this study, we genotyped tetraploid alfalfa plants that had previously been evaluated for yield during two cycles of phenotypic selection using genotyping-by-sequencing (GBS). We then developed prediction equations using yield data from three locations. Approximately 10,000 single nucleotide polymorphism (SNP) markers were used for GS modeling. The genomic prediction accuracy of total biomass yield ranged from 0.34 to 0.51 for the Cycle 0 population and from 0.21 to 0.66 for the Cycle 1 population, depending on the location. The GS model developed using Cycle 0 as the training population in predicting total biomass yield in Cycle 1 resulted in accuracies up to 0.40. Both genotype × environment interaction and the number of harvests and years used to generate yield phenotypes had effects on prediction accuracy across generations and locations, Based on our results, the selection efficiency per unit time for GS is higher than phenotypic selection, although accuracies will likely decline across multiple selection cycles. This study provided evidence that GS can accelerate genetic gain in alfalfa for biomass yield.

Selection for Drought Tolerance in Wheat Population (<i>Triticum aestivum</i> L.) by Independent Culling Levels

Field experiments were carried out at Faculty of Agriculture, Sohag University, Egypt to estimate observed and expected response to selection and genetic parameters after two cycles of phenotypic selection in F2 population. Highly significant differences among F3 and F4 families under normal and drought stress conditions for no. of spikes/plant (NS), 100-Seed weight (SW), plant height (PH), days to heading (DH) and grain yield/plant (GY) were observed. Direct response to selection for NS, SW and PH were positive and highly significant with values of 15.16, 26.34 and 6.18 %, respectively compared with check cultivar ( 1) in F4 generation under normal conditions. Meanwhile, under drought conditions, they were 14.39, 20.35 and 6.35%, respectively. Correlated response to selection was significant and positive for GY compared with check cultivar under two conditions. While, it was very significant and negative for HD under normal and drought stress. Expected response to selection for NS, SW and PH were (1.45 and 1.62 spikes/plant), (0.37 and 0.23 gm) and (6.21 and 5.90 cm), respectively in F4 under normal and water stress conditions, respectively. High broad sense heritability values for NS, SW and PH was obtained under normal and drought stress in F3 and F4 generations. Narrow sense heritability in F4 were (48.24 and 55.31%), (53.34 and 43.43%) and (52.12 and 48.73%) for NS, SW and PH, respectively, under normal and drought stress, respectively. Positive and significant correlation between three characters (no. of spikes/pant, 100 kernel weight and plant height) and grain yield/plant under normal and drought stress conditions. Thus, direct selection of these characters should be of major concern for increased grain yield under two conditions. Drought susceptibility index (DSI) showed that four families were superior for drought tolerance and had high grain yield under drought stress in F4 generations. These genotypes could be used as source of drought tolerance/or factors contributing to general adaptation.

EVALUATION OF SOME BREEDING METHODS IN DURUM WHEAT

Four breeding methods representing different cycles of phenotypic selection were evaluated using durum wheat (Triticum durum L.) crosses. This included ; 1) pedigree method (PM) with three cycles of selection in F3, F, and F5, 2 ) modified bulk' (MB5) two cycles of selection in F., and F5, 3) modified bulk2 (M32) where only one cycle of selection in F3 was exercised, 4 ) bulk method (EM) where only natural breeding or selection was involved. This study was conducted at the farm of Et-Giza Agric. Res. Station, ARC, Egypt, during four successive seasons from 2005/2006 through 2008/2009 to evaluate the efficiency of four different breeding methods in improving grain yield potentiality and some other agronomic traits in six durum wheat crosses. The lines derived from various selection cycles were evaluated in terms of number of spikes/plant, number of kernels/spike, 100-kernel weight and grain yield/plant Results of analysis of variance for every cross showed significant differences among breeding methods in all crosses. Moreover, the genotypes showed significant differences in number of spikes/plant except crosses No. 1, 2 and 5, number of kemels/spike, except cross No. 1, 100-kernel weight except cross No. 2 and grain yield/plant for all crosses. The interaction between genotypes and methods of breeding was significant in all characteristics studied for all crosses except number of spikes/plant in cross No. 5, number of kernels/spike in cross No. 4, 100-kernel weight in crosses No. 1 and 6 and grain yield/plant for all crosses. Combined analysis for all methods of breeding crosses and genotypes showed significant differences for crosses (C), methods of breeding (M), genotypes (G), (C x M), (M x G) and (C x M x G). The best methods of breeding for all studied traits were pedigree method (PM) followed by modified bulk 2 (MP2) .Results revealed that the six durum wheat crosses differed in all studied characteristics. Cross No. 5 had the highest number of spikes/plant, cross No. 2 had the highest number of kemds/spike, cross No. 3 had the highest 100-kernel weght and cross No. 5 the highest grain yield/plant.

Comparative analysis of marker-assisted and phenotypic selection for yield components in cucumber

Theoretical studies suggest that marker-assisted selection (MAS) has case-specific advantages over phenotypic selection (PHE) for selection of quantitative traits. However, few studies have been conducted that empirically compare these selection methods in the context of a plant breeding program. For direct comparison of the effectiveness of MAS and PHE, four cucumber (Cucumis sativus L.; 2n = 2x = 14) inbred lines were intermated and then maternal bulks were used to create four base populations for recurrent mass selection. Each of these populations then underwent three cycles of PHE (open-field evaluations), MAS (genotyping at 18 marker loci), and random mating without selection. Both MAS and PHE were practiced for yield indirectly by selecting for four yield-component traits that are quantitatively inherited with 2-6 quantitative trait loci per trait. These traits were multiple lateral branching, gynoecious sex expression (gynoecy), earliness, and fruit length to diameter ratio. Both MAS and PHE were useful for multi-trait improvement, but their effectiveness depended upon the traits and populations under selection. Both MAS and PHE provided improvements in all traits under selection in at least one population, except for earliness, which did not respond to MAS. The populations with maternal parents that were inferior for a trait responded favorably to both MAS and PHE, while those with maternal parents of superior trait values either did not change or decreased during selection. Generally, PHE was most effective for gynoecy, earliness, and fruit length to diameter ratio, while MAS was most effective for multiple lateral branching and provided the only increase in yield (fruit per plant).

A Genome May Reduce Your Carbon Footprint

A Genome May Reduce Your Carbon Footprint

Genomewide selection in oil palm: increasing selection gain per unit time and cost with small populations

Oil palm (Elaeis guineensis Jacq.) requires 19 years per cycle of phenotypic selection. The use of molecular markers may reduce the generation interval and the cost of oil-palm breeding. Our objectives were to compare, by simulation, the response to phenotypic selection, marker-assisted recurrent selection (MARS), and genomewide selection with small population sizes in oil palm, and assess the efficiency of each method in terms of years and cost per unit gain. Markers significantly associated with the trait were used to calculate the marker scores in MARS, whereas all markers were used (without significance tests) to calculate the marker scores in genomewide selection. Responses to phenotypic selection and genomewide selection were consistently greater than the response to MARS. With population sizes of N = 50 or 70, responses to genomewide selection were 4-25% larger than the corresponding responses to phenotypic selection, depending on the heritability and number of quantitative trait loci. Cost per unit gain was 26-57% lower with genomewide selection than with phenotypic selection when markers cost US $1.50 per data point, and 35-65% lower when markers cost $0.15 per data point. With population sizes of N = 50 or 70, time per unit gain was 11-23 years with genomewide selection and 14-25 years with phenotypic selection. We conclude that for a realistic yet relatively small population size of N = 50 in oil palm, genomewide selection is superior to MARS and phenotypic selection in terms of gain per unit cost and time. Our results should be generally applicable to other tree species that are characterized by long generation intervals, high costs of maintaining breeding plantations, and small population sizes in selection programs.

Divergent Selection for Nodule Aspartate Aminotransferase and Asparagine Synthetase Activities in Alfalfa

Root nodule aspartate aminotransferase (AAT) and asparagine synthetase (AS) catalyze synthesis of the two primary nitrogenous compounds translocated from alfalfa (Medicago sativa L.) nodules. The objectives of this research were to (i) determine the heritability nodule AAT and AS activities, (ii) evaluate the effect of selection for AAT and AS activities on characteristics associated with N2 fixation, and (iii) assess relationships among nodule characteristics, N concentration, and plant dry weight. One nondormant and two moderately dormant alfalfa populations were divergently selected for nodule AAT and AS activities. Plants were grown in a greenhouse under N2‐dependent conditions and the first regrowth at early bloom was measured for nodule fresh weight, nodule soluble protein concentration, plant dry weight, N concentration, acetylene reduction activity (ARA), and nodule activities of AAT, AS, glutamate synthase (GOGAT), and phosphoenolpyruvate carboxylase (PEPC). Realized heritabilities for AAT and AS were 0.64 and 0.15, respectively, after one cycle of phenotypic selection. Nodule fresh weight responded negatively to divergent selection for AAT and AS activities in populations that had previously been selected for high nodule enzyme activity. Simple correlations among the activities of AAT, AS, GOGAT, and PEPC and nodule soluble protein concentration ranged between r = 0.60 and r = 0.87 (P = 0.01). Specific activities of nodule AAT and AS did not appear to be desirable selection criteria for improving N2 fixation because correlated responses of ARA, plant dry weight, and N concentration were variable or nonsignificant.

Genetic Variation in Tall Fescue Digestibility Estimated Using a Prepared Cellulase Solution

Breeding tail fescue (Festuca arundinacea Schreb.) for improved digestibility in the fall is an important goal for improving animal performance. Objectives of this study were to determine the extent and nature of genetic variability for in vitro digestibility and to predict genetic gain from selection. Fifteen parents were randomly chosen from a broad‐based population, and their half‐sib (HS) families were generated using a polycross mating design. Herbage samples were incubated in a neutral detergent solution (NDS) before being subjected to degradation in a prepared ceilulase solution (PCS) obtain estimates of in vitro digestibility (NDSPCS). Neutral detergent fiber (NDF), acid detergent fiber (ADF), hemicellulose (HEM), and NDSPCS estimates were obtained for parents and their HS families for the summer and fall seasons of 2 yr. Significant (P < 0.01) variation was observed for NDSPCS estimates for HS families and parents in summer and fall, respectively. Genetic variance components for NDSPCS estimates were high among HS families and parents in the summer and fall, respectively. Narrow‐sense heritability estimates for NDSPCS were 0.65 in the summer and 0.30 for the fall. Narrow‐sense heritability estimates for crude fiber ranged from medium to high, while broad‐sense heritability estimates ranged from low to medium. Estimates of broad‐ and narrow‐sense heritabilities were similar for NDSPCS for the summer and fall harvests, because additive genetic variance appeared to be the most important component of the toal genetic variance. The narrow‐sense heritability estimated by parent‐offspring regression (h2op) for NDSPCS was higher for the fall harvest, which suggests that initiation of a breeding program to improve in vitro digestibility in the fall is possible. Predicted genetic gains per cycle of phenotypic selection were 53, 21, and 48% of the population means for the fall harvest for NDSPCS, NDF, and ADF, respectively. Phenotypic selection for improved digestibility in the fall for this population should be possible using the NDSPCS procedure.

Selection strategies for developing smooth bromegrass cell wall ideotypes

A random sample of 80 families of the B8HD smooth bromegrass (Bromus inermis Leyss.) population were tested in three environments for forage yield and cell wall constituents. Expected progress from one cycle of family selection was computed for single-trait selection and multiple-trait restricted selection. Expected gains were compared to desired goals and actual results from one cycle of phenotypic selection. Desired goals were: Model I = reduced lignin and cellulose, with increased hemicellulose, resulting in no change in cell wall content; Model II = reduced lignin and cellulose with no change in hemicellulose; or Model III = reduced lignin, cellulose, and hemicellulose. Single-trait selection for high hemicellulose in first harvest or low cellulose in second harvest had the best expected responses, of any single trait, for Model I. Possible undesirable effects of selection for low cellulose would be a reduction in forage yield potential. Multiple-trait restricted selection was judged to be more effective, with responses all in the desired direction, by specifying increased hemicellulose in index development. Selection in second harvest was expected to have similar responses as first harvest, except for a greater increase in forage yield. Development of Models II or III is expected to be difficult due to a negative correlation estimate between first and second harvest cell wall concentration.

Selection Among Early Generation Peanut Progeny for Enhanced Nitrogen Fixation1

Abstract Recurrent selection provides an established methodology for host improvement which should be applicable to increasing N2 fixation. This study was conducted to evaluate response to three cycles of phenotypic selection for fresh plant weight, nodule number and dry weight, and acetylene reduction when individual peanut (Arachis hypogaea L.) plants were evaluated in the greenhouse using a mixture of four Bradyrhizobium strains as inoculum. The F2 generation derived from a single cross, Florigiant x CES 101, constituted the base population. In each of three cycles the 20 superior individuals were selected and randomly intermated to generate the subsequent cycle for selection. The 20 selections from each cycle were bulked and evaluated with the original parents in two greenhouse trials to evaluate response to selection. No variability for fresh plant weight, nodule number or dry weight, or acetylene reduction was detected among cycles. Realized heritability estimates were 0.01 ± 0.02, 0.05 ± 0.03, −0.06 ± 0.06, and 0.31 ± 0.32 for fresh plant weight, nodule number, nodule dry weight, and acetylene reduction, respectively. Agronomic traits of the same entries were evaluated in one field study. No variability for these traits was detected among cycles. Insufficient control of environmental variation was suggested as a possible cause of lack of response to selection.

Breeding for Rust Resistance in Orchardgrass by Phenotypic and Phenotypic‐Genotypic Selection1

Effectiveness of alternative selection methods is an important consideration in any plant breeding program. The purpose of this research was to evaluate recurrent phenotypic selection and selection based on both phenotypic performance and a polycross progeny test (phenotypic‐genotypic method) for resistance to rust (Puccinia graminis Pers.) in ‘Sterling’ orchardgrass (Dactylis glomerata L.). Rust resistance was improved by each of three cycles of phenotypic selection. One cycle of phenotypic‐genotypic selection (Cl‐PG) achieved the same level of rust resistance and required the same length of time as did two cycles of phenotypic selection (C2‐P). The mean rust rating of C1‐PG and C2‐P did not change with advancement from the first to the second generation; however, plant to plant phenotypic variation increased. Smaller phenotypic variances in both generations of C1‐PG and C2‐P than in Sterling suggested a decrease in genetic variance with selection; however, significant genetic variation was found in all derived populations. High parent clone‐topcross progeny correlations indicated that progeny testing for rust resistance is unnecessary. The recurrent phenotypic selection method would favor maintenance of greater genetic diversity for resistance than the phenotypic‐genotypic method because more plants could be selected in each cycle.