Response to selection for grain yield and harvest index in F2, F3 and F4 derived lines of two wheat crosses

Summary Aspects of selection for yield and harvest index were investigated by simulating selection using data from random pedigreed F₂, F₃, F₄ and F₅ derived lines from two crosses grown in plots at two sites over two years.Improvement in yield through selection was obtained when the response was measured at the same site and in the same year as the selection. Selecting the best 10 per cent of F₂ to F₄ derived lines gave F₅ derived lines that outyielded random selections by 19 to 53 per cent for one cross and 5 to 23 per cent for the second cross. These lines were 41 to 50 per cent better than the mid-parent in one cross, but were less than the mid-parent in the other cross.However, the response to selection when measured in a different year was little better than random selection. The effect of different sites also reduced the effectiveness of selection.Selection of harvest index in early generations for improvement of yield was ineffective when response was measured at the same site in the same year, or in different years.Contrary to some theoretical proposals, the same improvement in yield was obtained by selecting in early or late generations. While high yielding genotypes may be lost by delaying selection, this is counteracted by the better predictive value of late generations due to their greater homozygosity and homogeneity.     

Honeycomb selection for yield in early generations of spring wheat

Summary The effectiveness of the honeycomb selection method for yield in spring wheat (Triticum aestivum L.) was evaluated using progenies from two wheat crosses, Glenlea x NB131 and Glenlea x Era. Honeycomb selection was carried out in the F₂ and F₃ generations, grown at the University of Manitoba in the summers of 1980 and 1981, respectively. In both generations, divergent selection was made for both high and low yield. Plants selected in the F₃ generation were entered in an F₄ yield test in the summer of 1982. Results of the experiment showed that honeycomb selection for yield in the F₂ and F₃ generations was effective in identifying parents of high- and low-yielding lines. F₃ plants from highyielding F₂ selections gave higher yields than those from low-yielding F₂ selections by 11.5% and 13.0% for Glenlea x NB131 and Glenlea x Era crosses, respectively. The F₄ yield test showed that high yielding selections from both crosses significantly outyielded by 8.9% low yielding selections and by 14.4% the unselected composite lines. It is concluded that the honeycomb selection method can be used for early generation selection in spring wheat.     

Comparison of two crossing and four selection schemes for yield, yield traits, and slow rusting resistance to leaf rust in wheat

The most important breeding objectives in crop improvement are improving grain yield, grain quality, and resistances to various biotic and abiotic stresses. The objectives of our study were to compare two crossing and four selection schemes for grain yield, yield traits, and slow rusting resistance to leaf rust (Puccinia recondita) based on additive genes in wheat (Triticum aestivum), and to identify the most efficient crossing and selection methodologies in terms of genetic gains and cost efficiency. Segregating populations were derived from 18 simple crosses and the same number of top (three-way) crosses. Half of the crosses were derived from Yecora 70 and the other half from Veery #10 as the common leaf rust susceptible parents. The four selection schemes were: pedigree, modified bulk (F₂ and F₁-top as pedigree, selected lines in F₃, F₄, F₂-top, F₃-top as bulk; and pedigree in F₅ and F₄-top populations), selected bulk (selected plants in F₂, F₃, F₄, F₁-top, F₂-top and F₃-top as bulk; and pedigree in F₅ and F₄-top populations), and nonselected bulk (bulk in F₂, F₃, F₄, F₁-top, F₂-top and F₃-top; and pedigree in F₅ and F₄-top populations). A total of 320 progeny lines, parents and checks were tested for grain yield, other agronomic traits and leaf rust resistance during the 1992/93 and 1993/94 seasons in Ciudad Obregon (Sonora State, Mexico) which represents a typical high yielding irrigated site. The influence of the type of cross and the selection scheme on the mean grain yield and other traits of the progenies was minimal. The selection of parents was the most important feature in imparting yield potential and other favourable agronomic traits. Moreover, the highest yielding lines were distributed equally. Progeny lines derived from Veery #10 crosses had significantly higher mean grain yield compared to those derived from the Yecora 70 crosses. Furthermore, a large proportion of the highest yielding lines also originated from Veery #10 crosses. Mean leaf rust severity of the top cross progenies was lower than that of the simple cross progenies possibly because two parents contributed resistance to top cross progenies. Mean leaf rust severity of the nonselected bulk derivatives was twice that of lines derived from the other three schemes. Selected bulk appears to be the most attractive selection scheme in terms of genetic gains and cost efficiency. This revised version was published online in August 2006 with corrections to the Cover Date.     

Development of an appropriate breeding scheme for tolerance to Empoasca kraemeri in common bean

Summary Significant advances in increasing tolerance to the leafhopper Empoasca kraemeri Ross & Moore in common bean have been obtained using a new breeding scheme where yield under leafhopper attack is the principal selection criterion in the evaluation of progenies. However, to further refine this breeding scheme, a study was conducted to determine whether selection for nonprotected yield would be more effective in early versus late generations. Two selection strategies were compared. In Strategy I, early generation selections in the F₂ and F₃ were compared to Strategy II where late generation selections were made in the F₄ and F₅, with the F₂ and F₃ generations advanced using single pod descent and bulk practices, respectively. Yield trials of the F₆ lines from both selection strategies were conducted under nonprotected and insecticide protected treatments. No significant differences were detected between the two selection strategies. However, Strategy II did produce advanced lines with greater nonprotected yields than did Strategy I, with the best F₆ line, in three out of four crosses, coming out of Strategy II. Late generation selection is recommended over early generation selection. Results of the new leafhopper breeding scheme, based on yield, are compared to the old breeding scheme where selections were made using visual selection practices in early generations.     

Divergent Selection for Heading Date in Barley

Divergent selection for heading time was performed in two F₂ barley population. Five populations were obtained for each cross: F₅ SSD (unselected control), 3E and 3L (from three cycles of selection for earliness or lateness), 2E1L and ZL1E (from two cycles of direct and one of reverse selection). These populations, together with corresponding parents and F₂ generations, were evaluated over two years. The response to selection was 5.6 and 6.5 days inane direction (earlier heading) and 7.7 and 6.7 clays in the other direction (later heading) in the two crosses, respectively. 3E and 3L populations were highly transgressive as compared to their parents. A sizeable amount of genetic variability was still present after two cycles of selection. Heading was probably controlled by a polygenic system with prevailing additive effects and alleles for earliness and earliness somewhat equally distributed in the parents. Selection fur heading time led to significant changes in plant height, yield and kernel weight. Early progenies were higher yielding than lace ones.     

Breeding for yield and quality in durum wheat

Three populations of an intervarietal durum wheat cross IWP5308/PDW208, F₅, F₅BIP₁ (population derived after intermating in F₂) and F₅BIP₂ (population derived after intermating in BIPF₁), were evaluated under three different agronomic environments for mean performance and stability of genotypes for grain yield, yield components and protein content. Though the biparental progenies indicated a higher mean performance, they did not differ significantly from progenies of the pedigree method for almost all characters. The biparental progenies, however, produced a higher number of stable genotypes for grain yield per plant, grains per ear and protein content. The F₅ population had a higher number of stable genotypes for 1000 grain weight and number of tillers per plant. The BIP progenies also had a higher number of genotypes with above average mean performance, and many were significantly higher than the checks WH896 and WH542, compared with F₅ progenies. Hence, in spite of high G x E interactions, the use of cycles of biparental mating and selection of top yielding lines on the basis of yield components can enable selection of stable genotypes with high protein content. Number of tillers per plant and 1000 grain weight were the yield component characters which made maximum contribution to phenotypic stability of the genotypes. This revised version was published online in August 2006 with corrections to the Cover Date.     

The effectiveness of early generation (F3) yield testing and the single seed descent procedures in two cowpea (Vigna unguiculata (L.) Walp.) crosses

Summary Two breeding procedures were compared in two cowpea crosses. Both procedures were started from the same selected F₂ plants in each cross. For the early generation yield testing, the F₃ lines were yield tested and a pedigree and bulk methods followed in F₄ and F₅. Each F₅ line was bulked to provide seed for a yield test in F₆. In the Single Seed Descent (SSD) procedure, a single seed was taken from each F₂ plant to produce the F₃ generation. The procedure was repeated for the F₄ and F₅. The F₆ SSD lines and the F₆ yield testing lines were compared in yield tests.The results showed that differences in yielding ability of F₃ lines persisted over generations indicating that selection was effective. This was confirmed by the high significant correlations between F₃ yields and those of later generations which ranged from r=0.51^* to 0.85^**.The grain yields of lines derived by the single seed descent procedure were as good as those derived from early generation yield testing.Significant linear correlation between visual rating of F₃ and F₆ yields with actual yields revealed that it is possible to identify promising lines of cowpea visually.     

Potential of wild germplasm for increasing yield of grain sorghum

Summary Sorghum [Sorghum bicolor (L.) Moench] backcross populations containing 3 to 50% wild germplasm were evaluated in south central India for grain yield and nine related traits. No individual BC₀F₂- to BC₂F₂-derived lines were high transgressive segregates for grain yield. Only 1.5% of all BC₃F₂- or BC₄F₂-derived lines were transgressive segragates, with 26% higher mean grain yield than their respective recurrent parents. The ten highest-yielding BC₂F₂- to BC₄F₂-derived lines per mating having parent CK60B yielded an average of 14% more than CK60B, which was, at the 5% level, a statistically significant difference. However, the increased yield was associated with increased plant height. The highest-yilding lines from RS/R/A2725 x virgatum and RS/R/A2725 x verticilliflorum were an average of 13.5% higher-yielding than RS/R/A2725 (a significant difference) and were equal in plant height. Selection increased BC₂ mean grain yields by 6 to 27%. Population mean yield, mean yield of selected lines, and frequency of high-yielding lines were highest in the BC₄.Journal paper no. 380, ICRISAT, Patancheru, India; Journal paper no. J-11114, Iowa Agriculture and Home Economics Experiment Station, Ames, Iowa, USA.     

Early generation selection for yield and breadmaking quality of hard red spring wheat (Triticum aestivum L. em thell.)

Summary Evaluation of the effect of selection in 3 different F₃ populations of hard red spring wheat was achieved for yield and breadmaking quality parameters by examining the subsequent performance of F₃ selections as populations of F₅ lines. For baking absorption the mean performance of the F₅ populations was positively related to the performance of the F₃ selections in each of the 3 population-years. A significant relationship between the performance in F₃ and in F₅ was not obtained in any of the 3 years for bushel weight, flour ash, remix loaf volume, farinograph mixing tolerance index or for flour color grade. A high positive relationship between performance in F₃ and F₅ was found in two out of three years for protein content, flour protein content and 1,000-kernel weight. Predictive ability for sedimentation value, flour yield, farinograph development time and blend loaf volume was inconsistent for different population-years.A positive relationship between the yield of F₃ plots and the mean yield of F₅ populations was found in only 1 year. In the other 2 years the relationship between F₃ and F₅ yields ranged from nonsignificant to low, negative and significant. The latter results were possibly related to the relatively narrow high yielding range of the total F₃ variability for yield which was sampled in each of those years. In all 3 population-years the highest yielding F₅ populations were derived from F₃ lines which were high yielding on a plot basis and also very high yielding relative to the yield of their adjacent control in the F₃ nursery.Broad sense heritabilities calculated for the F₅ generation support the thesis that selection between F₃-derived populations would be a worthwhile plant breeding procedure for many of the breadmaking quality parameters.Contribution number 267 of the Department of Plant Science, University of Manitoba.     

Selection for Increased Seed Nitrogen Accumulation in Common Bean: Implications for Improving Dinitrogen Fixation and Seed Yield

Estimates of N₂ fixation in segregating populations of bean plants based on ¹⁵N-isotope methods are technically demanding and expensive; therefore, indirect measures based on related traits including total seed N were used to select for improved N₂ fixation and yield. In 1985, six populations of F₂-derived F₃ families resulting from six parental lines crossed to a common tester were grown in field trials on a low-N soil. In 1986, 25 selected half-sib families and two populations of full-sib F₄ families were grown under similar conditions. Parents and a non-nodulating soybean line were included both years. Narrow sense (H_NS) heritability estimates based on parent-offspring regressions ranged from 0.57 for total seed N to 0.39 for shoot biomass in one population, but were near zero for all measured traits in a second population. Among the criteria used to identify parental lines with superior potential for producing progenies with high total seed N, testcross population means combined with estimates of realized heritability were the most reliable. Selection of the best F₃ families for total seed N resulted in F₄ families with increased total seed N and higher seed yields, while seed protein percentage was unchanged. When plants are grown on low-N soils, selection for total seed N offers a useful alternative to selection for increased N₂ fixation based on ¹⁵N-isotopic or total-N-difference method.     

Selection for seed yield in Andean intra-gene pool and Andean × Middle American inter-gene pool populations of common bean

Yields of large-seeded Andean (A) common bean (Phaseolus vulgaris L.) cultivars of Chile and Nueva Granada races are 40 to 60% lower compared to their Middle American (M) counterparts of small-seeded Mesoamerica and medium-seeded Durango races. Our objective was to use the concept of congruity backcrossing between Andean x Middle American inter-gene pool [AM 11833 = A 483 (A)///// A 686 (M) //// PVA 800A(A)/// ‘Carioca’ (M)// Carioca (M)/ G 19833 (A)] and between races within Andean gene pool [i.e., intra-gene pool Andean, AA 11834 = A483 (A)//// ‘Cardinal’(A) /// ‘Blanco Español’(A) // BlancoEspañol (A) / ‘Taylor’ (A)] to compare selection for seed yield improvement of large-seeded Andean beans. Seven hundred sixty seven F₂-derived F₃ (F_2:3) families were produced for each population. Visual appraisal for total plant performance, combined with seed yield from non-replicated plots was used for selection of 551 families in F_2:3, 182 families in F_2:4, and 91 families in F_2:5 in each population. Eight hundred twenty three F_5:6 lines were developed from the 91 F_2:5 families in each population. Visual selection, combined with seed yield in non-replicated plots was again used to select 294 lines in F_5:6 in each population. Similarly, 44 highest yielding F_5:7 lines were selected in AM 11833 and 39 F_5:7 lines in AA 11834. Thus, single plant selections were made in the F₂ and F₅, and plants within each plot were harvested in bulk in F₃, F₄, F₆, and F₇. Thirty nine F_5:8 lines from AA 11834 and 44 lines from AM 11833, parents, and checks were evaluated at Popayán and Quilichao, Colombia in 1998 and 1999. Selected lines in both populations, on average, out-yielded the mean of their large-seeded Andean parents. Mean yield of the lines selected from AM 11833 was 50% higher than AA 11834 lines. Twelve F_5:8 lines out-yielded the highest yielding Andean parents G 19833 and A 483 in AM 11833, whereas only one line yielded significantly higher (p < 0.05) than the highest yielding parent A 483 in AA 11834. However, none of selected lines out-yielded small-seeded Middle American parents used in AM 11833 (A 686 and ‘Carioca’). The mean 100 seed-weight of AA 11834 was 36 g compared to 28 G for AM 11833 F_5:8 lines. Selected lines had similar days to maturity as parents in AM 11833, and matured 3 d later in AA11834. Correlation coefficients between yield and 100 seed-weight were negative in both populations. Yield and days to maturity were positively correlated in AA 11834.     

Selection for biomass yield in wheat

Summary Biomass (above ground plant parts) yield may be a useful selection trait for yield improvement in wheat (Triticum aestivum L.). This study was conducted to estimate realized heritability of biomass yield and to determine the response to selection for high and low biomass yield in 8 genetically diverse populations of spring wheat under two production systems. Selections were made among the F₃ lines. Progenies of the selected lines were evaluated in replicated field tests in the F₄ generation under high fertility and low fertility production systems at Rampur, Nepal, in 1991. Fertility level had a significant effect on biomass yield, grain yield, effective tiller number, number of kernels per spike, thousand kernel weight, and harvest index. Selection in the F₃ for high and low biomass yield was effective in identifying F₄ lines with high and low biomass yield, respectively. Biomass yield differences between high and low selection groups in the F₄ generation, expressed as percent of the mean of the low selection group and averaged over the eight populations, were 53.9 and 36.5% higher than the mean of the low selection group under the high and the low fertility production systems, respectively. The corresponding figures for grain yield were 48.8 and 34.9% under the high and the low production systems, respectively. Also, selection for high biomass yield resulted in higher effective tiller number, and number of kernels per spike, but lower harvest index. Realized heritability estimates for biomass yield were greater at high fertility (range 0.49 to 0.85) than at low fertility (range 0.22 to 0.44). Biomass yield showed positive genotypic correlations with grain yield, effective tiller number, and number of kernels per spike but a negative correlation with harvest index. The results indicated that selection for high biomass yield should bring about positive improvements in biomass yield, grain yield, effective tiller number, and number of kernels per spike. The correlation between F₃ and F₄ generations suggested that biomass yield in the F₃ generation was a good predictor of biomass yield and grain yield in the F₄ generation. Selection for biomass yield in wheat should be made under the standard production system to obtain a realistic response.     

Improvement of large-seeded common bean cultivars under sustainable cropping systems in Spain

Approaches are needed to broaden the genetic base and improve earliness and yield potential of large-seeded beans under sustainable cropping systems. The objective of this research was to develop adapted dwarf bean populations having a commercial seed quality and yield suitable for the production in the South of Europe. The original base populations were produced from crosses between genotypes within each Mesoamerica, Nueva Granada and Peru races, and between Peru and Nueva Granada, and Mesoamerica and Nueva Granada races. Visual mass selection for plant performance was practised in the F₂ and F₃ generations. In the F₄ and F₅, single plants were harvested under two cropping systems (sole cropping and intercropping with maize). From F₄, selection was based on precocity, combined with seed yield and seed commercial type. The F_4:7 selected lines from each original population were compared with their parents and five checks at four environments and two cropping systems. Differences among environments, populations, parents and checks were observed for all traits. Under intercropping with maize, there was a 50% reduction in seed yield. Yield of parents and checks belonging to Andean South American races, intraracial (Nueva Granada × Nueva Granada) and interracial (Nueva Granada × Peru) populations, was higher than that of those of Middle American origin. Intraracial crosses within large-seeded Andean South American (Peru race) and Middle American gene pools (Mesoamerica race) did not produce lines yielding more than the highest yielding parent. Only two large-seeded lines selected from crosses between small- and large-seeded gene pools out-yielded the best parent and check cultivar.     

Studies on the breeding of self-pollinating cereals

Summary The limitations of the pedigree and mass methods of selection in the improvement of self pollinating cereal crops are discussed and the value of quantitative data in the early generations of selection is emphasised. Two systems of selection which provide such data have been introduced at the Cambridge Plant Breeding Institute.In one, known as the F₂ progeny method of selection, the progenies of selected F₂ plants are grown in yield trials without further selection during F₄, F₅ and F₆ after which single plant selections are made within the more promising progenies.In the other system, known as the pedigree trial method of selection, normal pedigree selection is carried out in F₂ and F₃. In the F₄ generation single plants are selected from the better families for continued pedigree selection and within each of these families the remaining plants are bulked to give grain for a yield trial in the following year. This process is repeated in F₅ and F₆, the grain for trial being in each case obtained from the progeny rows and not from the preceding trial.The use of these methods is illustrated by reference to wheat hybrids grown at Cambridge, and the data obtained is shown to be useful in comparing the value of different parental combinations as well as in assessing the relative merits of the selections within each cross.     

Selecting superior spring wheat crosses in early generations

Summary Three methods were evaluated as potential aids in identifying superior crosses early in the breeding program: (1) F₁ yield, (2) F₂ yield, and (3) midparental yield. Two sets of spring wheat (Triticum aestivum L. em. Thell.) crosses and parents were evaluated in replicated single row plots in F₁ and in replicated multi-row plots in F₂ over a period of five years. On the basis of F₁ yields, two of the highest yielding and two of the lowest yielding crosses in each set were chosen for a more detailed selection study in subsequent generations.In Set 1, random F₂ head selections for each of the selected four crosses were evaluated in 3-row yield plots in F₄. In Set 2, F₂ plant selections were made on the basis of head weight and the highest yielding 10% evaluated for yield in F₄.Lines of crosses identified as high yielding in F₁ had significantly greater mean yields in F₄ than those of crosses that were low yielding in F₁. The high yielding crosses had three to four times as many lines yielding in the top 10% in F₄ than did the low yielding crosses.Correlations for yield were obtained between F₁ and F₂ in different years, F₂ and midparents in the same year, lower or no correlations between F₁ and midparents in the same year, and no correlations between F₁ and midparent and F₂ and midparent in different years. It is suggested that larger plot sizes rather than single rows be used to evaluate parents.Midparental yield, F₁ yield and F₂ yield tests are recommended as a progressive set of screening tests for a given set of crosses to effectively maintain the superior crosses in the breeding program.     

Selection in Early Generations of Dried Peas, Pisurm sativum L.

Seed production in peas is limited by early and severe lodging and by a low multiplication rate and pea breeders have tried to overcome such disadvantages by growing plants in early generations widely-spaced against wire netting. Progenies of four pea crosses were each tested over a period of tour years to investigate whether single plant selection for quantitative characters, in particular grain yield, is efficient in such circumstances in the Is generation. Efficiency of selection was also studied for yield and yield related characters in the F₃ based on f₂ derived single plant progenies grown in unreplicated microplots. Early yield selection in the F₂ as well as in the F₃ proved to be of poor efficiency. Heritability values of all recorded traits were only slightly higher in the F₃ than in the F₂. Efficiency of yield selection could not be increased significantly in these early generations by indirect selection, either for single traits or for index traits. Possible reasons are discussed for the low efficiency of direct and indirect selection for grain yield in early generations and proposals are made for its improvement and for alternative selection strategies.     

Mass selection for seed width in oat populations

Heterogeneous and segregating oat populations subjected to no selection and to mass selection for seed width for five consecutive generations were evaluated for 100-seed weight, heading date and plant height.The mass-selection technique, which consisted of passing the seeds over a screen with 12.7×2.4 mm slots and propagating the seeds too wide to go through the slots, was repeated for five consecutive generations (F₃ through F₇). Comparable unselected populations were grown each year. Remnant seeds from each check and mass-selected population were stored for future studies.In 1963, 500 random seeds from each of the six unselected populations (F₂ through F₇), from each of the five mass-selected populations (F₃ through F₇) and from a pure line were space-planted in the field. In 1964, the progenies from 75 random strains (a strain was the progeny of one spaced plant) from each of the 12 populations were sown in a randomized-block experiment with three replicates. In 1966, the strains from the last (F₇) generation of the unselected and mass-selected lines of descent (75 strains from each) were tested for yield in a 7-replicate randomized block experiment.The mass-selection technique increased the mean 100-seed weight, whereas in the unselected line of descent, the mean 100-seed weight did not change. The mean heading dates became later and the mean plant heights taller with the mass-selection procedure. The mean yield of the final mass-selection population was nine percent higher than that of the comparable unselected population.In spite of the associated changes between 100-seed weight and plant height and heading date in successive generations; the genotypic correlations among strains within populations indicated that these three traits were inherited independently. In advanced generations (F₆ and F₇), the genotypic variances for heading date and 100-seed weight were reduced in both the unselected and mass-selected lines of descent, whereas, for plant height no significant change occurred in either.Journal No. J-5586 of the Iowa Agricultural and Home Economics Experiment Station, Ames, Iowa, Project 1176. In cooperation with the Crops Research Division, Agricultural Research Service. U.S. Department of Agriculture.Professor of Plant Breeding.     

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.     

Means and variances for Fusarium head blight resistance of F2-derived bulks from winter triticale and winter wheat crosses

Fusarium head blight (FHB), caused by Fusarium graminearum and Fusarium culmorum, is a devastating disease in cereals. This study was undertaken to estimate progeny means and variances in each of five winter triticale and winter wheat crosses using unselected F₂−derived lines in F₄ or F₅ generation bulked at harvest of the previous generation. Fifty (triticale) and 95 (wheat) progeny per cross were inoculated in two (triticale) or three (wheat) field environments. FHB rating was assessed on a whole-plot basis. Mean disease severities of the parents ranged from 2.3 to 6.4 in triticale and from 3.1 to 6.5 in wheat on a 1-to-9 scale (1 = symptomless, 9 = 100% infected). The midparent values generally resembled the means of their derived progeny. Significant (P < 0.01) genotypic variance was detected within each cross, but genotype × environment interaction and error variances were also high for both crops. Medium to high entry-mean heritabilities (0.6–0.8) underline the feasibility of selecting F₂-derived bulks on a plot basis in several environments. Phenotypic correlation of FHB resistance between generation F_2:4 and F_2:5 was r = 0.87 (P < 0.01) tested across 150 wheat bulks at two locations. Our estimates of selection gain are encouraging for breeders to improve FHB resistance in triticale and wheat by recurrent selection within adapted materials.     

Genetic response to index selection for grain yield, kernel weight and per cent protein in four wheat crosses

Quantitative genetic theory was used to investigate selection differentials, expected and observed direct and correlated responses to simultaneous improvement of grain yield, kernel weight, and grain protein content in F₃ and F₄ populations of four spring wheat (Triticum aestivum L.) crosses. Selection in the F₃ generation based on the Smith-Hazel index (SH) and yield was found to be superior to the other methods studied in identifying high-yielding lines, but resulted in substantial decrease in grain protein level. Consequently, a 1.0% increase in protein from selection for protein depressed grain yield as much as 536 kg/ha below the population mean, reducing the expected yield gains per generation selection cycle by 250%. The weight-free indices (EW), particularly the index involving only yield and kernel weight (EW3) and its linear approximation (EW4), and the desired gains indices were effective in improving protein content but were less efficient in selecting top-yielding lines. Selection in the opposite direction using truncation of the lowest 10% of the population based on weight-free-index involving yield, kernel weight and protein (EW2) reduced all traits significantly compared with the mean of the unselected population indicating the effectiveness of the unweighted selection index. The observed genetic gains (Ra) from selection based on yield, the SH, EW3 and EW4 indices were slightly lower than the expected advances per cycle (R) in populations from crosses ‘Sinton’בGlenlea’ (C1), ‘Glenlea’בNB505’ (C2), and ‘A2P5’בNB320’ (C6) (Ra/R = 70 to 85%) but were higher in cross ‘NB505’בA2P5’ (C5) (Ra/R = 126 to 143%). It was concluded that weight-free and the desired gains indices can be used to improve wheat grain yield and grain protein simultaneously in F₃ generation selection, as revealed by response to selection measured in the F₄ generation.