A comparison of androgenetic doubled-haploid,and single seed descent lines in Triticale

Summary Sixty single seed descent (SSD) lines and about 25 anther-derived doubled-haploid (DH) lines were obtained from two triticale crosses. The frequency distributions of 10 quantitative agronomic traits were compared using parametric and non-parametric tests. A multivariate discriminant analysis was subsequently carried out. Gliadin patterns obtained from each line by polyacrylamide gel electrophoresis were used to calculate intra- and inter-population diversities from relative dissimilarity indices. It was found that DH and SSD lines show significant differences in frequency distributions of 1000 grain weight in both crosses, of heading date for one cross, and of lodging susceptibility for the other cross. The results of intra- and inter-population gliadin diversity indicate that although the SSD method theoretically provides more opportunity for recombination to occur than the DH method, it did not produce a greater range of recombinants. Since there is no significant difference between SSD- and DH-line distributions for grain yield, anther culture appears to be an efficient method for producing high yielding homozygous lines from F₁ hybrids of triticale in a relatively short time.     

Comparative efficiency of four selection methods for deriving high-yielding lines in mungbean [Vigna radiata (L.) Wilczek]

The comparative efficiency of four selection methods, viz., honeycomb (HC), pedigree selection (PS), single-seed descent (SSD) and the bulk method (BM), was assessed in three crosses of mungbean. The lines derived by each method, along with check varieties, were yield-tested in a compact family block design in F₅ and F₆ generations during summer and kharif of 1990. On the basis of the mean of the lines, the range, the number of superior lines over the best check, and the proportion of the top 10% lines in all the crosses and generations, the honeycomb method exhibited superiority over PS, SSD and BM for yield per plant and its component traits. PS, SSD and BM did not differ from each other. The honeycomb and SSD methods were found suitable for deriving superior lines for seed yield and pods per plant in mungbean.     

Comparison of frequency distributions of doubled haploid and single seed descent lines in barley

Summary Both doubled haploid (DH) and single seed descent (SSD) methods were used to derive homozygous lines from two crosses of barley. The frequency distributions of grain yield, heading date, and plant height of the DH and SSD lines were compared by the Mann-Whitney U test, Kolmogorov-Smirnov twosample test and Wald-Wolfowitz runs test. It was found that the DH lines distributed in the same manner as the SSD lines with respect to the three characters. The results indicated that although the SSD method had more opportunity for recombination than the DH method, it did not produce a sample of recombinants which differed significantly from the DH sample; thus both methods were equally efficient for use in deriving homozygous lines from F₁ hybrids in a relatively short time.Contribution no. 455 Charlottetown Research Station, Agriculture Canada, P.E.I. (Canada)     

A comparison of inbred lines derived by doubled haploidy and single seed descent in spring barley (Hordeum vulgare)

Samples of F_x inbred lines, derived by doubled haploidy (DH) and single seed descent (SSD) from five spring barley crosses were compared for agronomic characters. It was shown that, over this range of diverse crosses, inbreds derived by either technique could surpass the better parent or even the heterotic F₁. The means of the DH and SSD were, however, different for a number of characters, as well as differing from the mid-parent value. It was concluded that these differences stemmed from the presence of interacting genes showing linkage disequilibrium, although there was no unambiguous test to distinguish this from differential survival during the production of inbreds. This view was further supported by the finding that the DH sample, which tends to preserve existing linkages, produced a higher proportion of lines exceeding the better scoring parent when compared with the SSD population.     

Comparison of methods for calculating the heritability of adult field resistance to yellow rust and grain yield in spring wheat

Several methods are available for estimating heritability in disomic species, including parent-offspring regression, realized heritability, intraclass correlations of recombinant inbred lines, and diallel-cross analysis. Estimates were obtained by these various methods for a set of eight bread wheat (Triticum aestivum) lines adapted to the East African highlands, which had been intercrossed and selfed in a half-diallel arrangement to give F₁, F₂ and F₃ generations, and F₆ recombinant inbred lines. Significant genetic variation existed among parents and crosses for both grain yield and yellow rust resistance in all generations. Based on the heritability calculated from the analysis of F₆ recombinant inbred lines, analysis of the F₂ diallel crosses was recommended for determining the heritability of both characters in early segregating generations. The results also suggest that a form of tandem selection may be effective in developing locally adapted germplasm which combines high grain yield with yellow rust resistance. Received: 15 February 1999 / Accepted: 11 March 1999     

Genetic variability and advance under four selection procedures in wheat pedigree breeding programme

Summary Four methods of generation advance (SPS, SSD, BP and MMS) were compared in F₃ and F₄ generations. In the F₃ generation, the SPS and SSD methods of generation advance proved superior to the BP and MMS methods for grain yield per plant and for at least one of the yield component traits. The F₃ SSD population did not differ significantly from the F₃ SPS for any of the traits. However, the F₃ SSD population retained more range and cv for different traits than with other methods of generation advance. F₄ progenies derived from F₃ SSD population were significantly superior for grain yield than lines derived from the other three F₃ populations. The MMS method of generation advance proved useful for increasing the 1,000-grain weight for which initial selection was made.Part of Ph.D. Thesis submitted by senior author to Haryana Agricultural University, Hisar     

Inheritance of grain filling duration in spring wheat (<Emphasis Type="Italic">Triticum aestivum</Emphasis> L. em thell)

To understand the genetic control of grain filling duration (GFD), i.e., the number of days from anthesis to physiological maturity, we studied the F₁, F₂, BC1 and BC₂ generations of six spring wheat crosses from nine varieties/genotypes. Generation mean analysis for gene effects indicated that one or more types of epistasis were significant in all crosses. In each pairing, the F₁ and F₂ means were either intermediate or closer to the mean of the parent having the longer GFD. Our narrow-sense heritability estimate was reasonably high, at 47.67 (based on diallel analysis). This demonstrated that progress could be made from the selection in these crosses for either long or short GFD. The two early varieties that had identical maturity durations differed in their GFD values, indicating that maturity dates are not good criteria when choosing parents for modifying GFD. To utilize favorable additive × additive effects during this selection, we suggest that a single seed descent (SSD) or bulk popula-tion approach be adopted. In comparison, dominance effects would prove quite useful in hybrid wheat breeding programs.     

Breeding Enrichment of Genetic Variation of Grain Yield and Its Attributes in Bread Wheat under Drought Stress and Well Irrigation

Drought stress (DS) is one of the most critical environmental abiotic stresses for wheat production in the arid environments. Selection of high-yielding genotypes tolerant to DS can play a significant role in mitigation the negative impacts associated with DS. In the present study, generation means analysis (GMA) was used to study the performance of two crosses under well irrigation (WI) and deficit irrigation [cross I (Line 44 × Shandweel-1) and cross II (Line 20 × Sakha 93)]. Significant differences were observed for days to heading (DH), days to maturity (DM), plant height (PH), spike length (SL), number of spikes per plant (NS/P), number of grains per spike (NG/S), thousand-grain weight (TGW), grain yield per plant (GY/P), and proline content (PC) in the six populations of the two crosses within each irrigation level. Cross II had early maturity and the highest PC, NS/P, TGW, and GY/P regardless of the irrigation level. Cross I showed positive significant relative heterosis and heterobeltiosis for GY/P under the two irrigation levels. The inheritance of characters of cross I revealed additive, dominant, and epistatic effects, which varied with trait and stress. Additive genetic effects predominated in DH, SL, and PC, while non- additive were found in DM, NS/P, NG/S, and GY/P. Narrow-sense heritability estimates (h²_n) were high for DH and PC, moderate to high for PH and SL, moderate for DM, NG/S, NS/P, and TGW, and low for GY/P. Based on different drought indices the populations BC₁, BC₂, F₁, and P₁ of cross II and BC1 of cross I were more tolerant to drought stress. Therefore, PC, TGW and DH can be used as selection indicators to improve wheat for drought tolerance in early generations and other yield components traits in late generations. The second cross (Line 20 × Sakha 93) shows promise and is of interest to a drought tolerance breeding program, where wheat breeders can use recombinant breeding strategies to construct desirable drought stress genes. Correlation and path coefficient revealed that TGW and PC were the main contributor in grain yield in both environments.     

The feasibility of producing inbred rather than F1 hybrid cultivars in Brussels sprouts: predictions from early generations

Predicting the performance of recombinant inbred lines derived by single seed descent (SSD) following crosses between inbred lines is most reliable for traits in which epistasis and genotype environment interaction are absent. The analysis of two field trials of Brussels sprouts indicated the presence of such effects in seven quantitative characters. These effects could be minimised by transforming the scale on which each character was measured. Predictions were made of the likely performance of the recombinant inbred lines currently being produced by SSD at the Institute of Horticultural Research, Wellesbourne, compared with that of current F₁ hybrid varieties. The predictions from the first trial of F₂ material were encouraging for harvest date, stem length and waste weight, but low for sprout number, quality, marketable yield and total yield. Predictions from F₃ material in the second trial were good for sprout number and total yield (in addition to harvest date, stem length and waste weight as before), but still low for marketable yield and quality, with less than 0 01% of lines expected to perform better than the F₁. Model fitting to variances suggested the presence of linkage disequilibrium in dispersion for waste weight, but no information could be obtained about linkage disequilibrium for the two most important characters, marketable yield and quality. The broad heritability of each character except stem length was lower than 0 5 (0 3 or lower for total yield, waste weight and quality), suggesting that advanced generation selection, as used in SSD, might be more successful than selection in the early generations.     

Early generation selection for high yielding cowpea genotypes in additive series intercropping systems with sorghum

Defining appropriate selection strategies for developing cowpea varieties adapted to additive series intercropping systems is an important requirement for cowpea breeders and producers in sub‐Saharan Africa. One hundred and forty‐three F_2:3 cowpea families and their subsequent 99 F_3:4 families derived from a cross between a sole bred cultivar, Apagbaala, and a traditional variety, SARC‐L02, were evaluated under additive series intercropping with sorghum. Intercropping imposed a strong selection pressure for days to flowering such that 31% of F_2:3 families that flowered after 50 days produced too few grains to permit their subsequent evaluation in the F_3:4 generation. Narrow‐sense heritabilities estimated by parent–offspring regression were high for 100 seed weight and days to flowering, moderate for biomass, low for grain yield and insignificant for branches/plant and pods/plant. Retrospective selection at 40% intensity based on F₃ grain yield recovered 5 of the 10 top yielding families in the F₄. No significant difference was observed between mean grain yield of selected and rejected families (at the 40% selection intensity) as estimated by a t‐test. Sole and intercrop yields produced by six advanced breeding lines included as controls showed poor correlation, and suggests selecting cultivars under the target cropping system will produce better selection response.     

Hybrid maize breeding with doubled haploids: V. Selection strategies for testcross performance with variable sizes of crosses and S1 families

In hybrid maize (Zea mays L.) breeding, doubled haploids (DH) are increasingly replacing inbreds developed by recurrent selfing. Doubled haploids may be developed directly from S₀ plants in the parental cross or via S₁ families. In both these breeding schemes, we examined 2 two-stage selecting strategies, i.e., considering or ignoring cross and family structure while selection among and within parental crosses and S₁ families. We examined the optimum allocation of resources to maximize the selection gain ΔG and the probability P(q) of identifying the q% best genotypes. Our specific objectives were to (1) determine the optimum number and size of crosses and S₁ families, as well as the optimum number of test environments and (2) identify the superior selection strategy. Selection was based on the evaluation of testcross progenies of (1) DH lines in both stages (DHTC) and (2) S₁ families in the first stage and of DH lines within S₁ families in the second stage (S₁TC-DHTC) with uniform and variable sizes of crosses and S₁ families. We developed and employed simulation programs for selection with variable sizes of crosses and S₁ families within crosses. The breeding schemes and selection strategies showed similar relative efficiency for both optimization criteria ΔG and P (0.1%). As compared with DHTC, S₁TC-DHTC had larger ΔG and P (0.1%), but a higher standard deviation of ΔG. The superiority of S₁TC-DHTC was increased when the selection was done among all DH lines ignoring their cross and family structure and using variable sizes of crosses and S₁ families. In DHTC, the best selection strategy was to ignore cross structures and use uniform size of crosses.     

Frequency — dependent advantage in wheat

Summary The effect of frequency-dependent advantage in wheat was investigated by growing F₁. hybrid seeds of the crosses (Warimek X Halberd) and (Wariquam x Halberd) in a stand of Halberd at 5 frequencies: 4 %, 6.25 %, 11.11 %, 25 % and 50 %. A reduction of 35 % to 40 % in grain yield of individual plants was observed with both hybrids as their frequencies changed from 4% to 50 %. A similar trend with frequency was noted for several other plant characteristics, including total grain number, particularly with those measured towards the end of the growing season. Halberd plants did not show a corresponding increase as their frequency declined from 96 % to 50%. — The following season, 76 F₄ lines from the cross (Warimek X Halberd) and 70 F₄ lines from (Wariquam x Gabo) were grown at frequencies of 6.25% and 18.75% in machine sown stands of Wariquam and Halberd, respectively. Again grain yield decreased as genotypic frequency increased. Furthermore, there was a positive correlation between frequency-dependent advantage and relative grain yield, suggesting that high yielding genotypes show a greater advantage at low frequencies than lower yielding ones.     

The TaDREB3 transgene transferred by conventional crossings to different genetic backgrounds of bread wheat improves drought tolerance

Drought tolerance of the wheat cultivar Bobwhite was previously enhanced by transformation with a construct containing the wheat DREB3 gene driven by the stress‐inducible maize Rab17 promoter. Progeny of a single T₂ transgenic line were used as pollinators in crosses with four elite bread wheat cultivars from Western Australia: Bonnie Rock, IGW‐2971, Magenta and Wyalkatchem, with the aim of evaluating transgene performance in different genetic backgrounds. The selected pollinator line, BW8‐9‐10‐3, contained multiple transgene copies, had significantly improved drought tolerance compared with wild‐type plants and showed no growth and development penalties or abnormalities. A single hybrid plant was selected from each cross‐combination for three rounds of backcrossing with the corresponding maternal wheat cultivar. The transgene was detected in all four F₁BC₃ combinations, but stress‐inducible transgene expression was found in only three of the four combinations. Under well‐watered conditions, the phenotypes and grain yield components of the F₂BC₃ transgene‐expressing lines were similar to those of corresponding recurrent parents and null‐segregants. Under severe drought conditions, the backcross lines demonstrated 12–18% higher survival rates than the corresponding control plants. Two from four F₃BC₃ transgenic lines showed significantly higher yield (18.9% and 21.5%) than control plants under limited water conditions. There was no induction of transgene expression under cold stress, and therefore, no improvement of frost tolerance observed in the progenies of drought‐tolerant F₃BC₃ lines.     

Genetics of transgressive segregation for yield and yield components in wheat

Three crosses of spring wheat (Triticum aestivum L. em Thell) involving six cultivars (WC29, WH291, SGP 14, RAJ. 1972, WH377 and HD 2329) were selected on the basis of combining ability analysis to study genetics of transgressive segregation for tillers/plant, grains/spike, 1000 grain weight and grain yield/plant using various mating designs. Diallel analysis indicated that both additive and non- additive components were significant for all the characters. On the basis of general combining ability and specific combining ability effects, the parents WH 291 and WH 377 were found to be good general combiners for tillers/ plant, 1000 grain weight and grain yield/plant. For grains/spike SGP 14 was found to be a good general combiner. The cross WH 377 × HD 2329 for tillers/plant, SGP 14 × Raj. 1972 for grains/spike and grain yield/plant and WC 29 × WH 291 for 1000 grain weight were found to be good cross combinations. Generation mean analysis indicated that the additive-dominance model was inadequate for all the characters in all the crosses except for 1000 grain weight in WC29 × WH291. Additive component was more pronounced than non-additive components for all the characters in all the crosses except for tillers/ plant in WH 377 × HD 2329. Predictions for transgressive segregants from F₃ was more accurate than that from generation mean analysis. However, prediction from both the sources were equally efficient if additive-dominance model was adequate. In general, observed frequencies of transgressive segregants were more in F₂ and BIPi than F₄ but the majority of them were discarded on progeny testing. Biparental mating had an impact in increasing the frequencies of transgressive segregants for different characters in all the crosses. The crosses, WH 377 × HD 2329 for grain yield/ plant, SGP 14 × Raj. 1972 for tillers/plant and WC 29 × WH 291 for grains/spike and 1000 grain weight were found to be potential crosses for transgressive segregants. A comparison of combining ability of parents and crosses, and observed and predicted frequencies of transgressive segregants indicated that the potential crosses for transgressive segregants were those that had high sea effects and involved high and low general combiners. The crosses involving low general combiners irrespective of their sea effects showed poor performance with respect to transgressive segregation.     

Should maize doubled haploids be induced among F<Subscript>1</Subscript> or F<Subscript>2</Subscript> plants?

Maize (Zea mays L.) doubled haploid lines are typically produced from F₁ plants. Studies have suggested that the low frequency of recombinants in doubled haploids may reduce the response to selection. My objective was to determine if, for sustaining long-term response, doubled haploids should be induced in F₁ or F₂ plants during maize inbred development. In simulation experiments, I examined the response to multiple cycles of testcross selection among doubled haploid lines derived from F₁ plants (denoted by DH), doubled haploid lines derived from F₂ plants (DH_F2), and recombinant inbred (RI) lines derived by single-seed descent. For a trait controlled by 100 or more quantitative trait loci (QTL), the cumulative responses to selection were up to 4–6% larger among DH_F2 lines than among DH lines. The cumulative responses were up to 5–8% larger among RI lines than among DH lines. The QTL become unlinked as the number of QTL in a finite genome decreases, and the responses among RI, DH, and DH_F2 lines were equal or nearly equal when only 20 QTL controlled the trait. Metabolic-flux epistasis reduced the differences in the response among RI, DH, and DH_F2 lines. Overall, the results indicated that doubled haploids should be induced from F₂ plants rather than from F₁ plants. If year-round nurseries are used and new F₁ crosses for inbred development are initially created on a speculative basis, the development of doubled haploids from F₂ rather than F₁ plants should not cause a delay in inbred development.     

Impact of biparental mating on correlation coefficients in bread wheat

Summary Phenotypic and genotypic correlation coefficients and path-coefficients were studied in the biparental (BIPs) and F₃ self progenies of the two wheat crosses. A comparison of correlation coefficients in the BIPs and the F₃'s revealed that as many as twelve new significant correlations were noticed in case of the BIPs in cross I although some of them occurred in the undesirable direction. On the other hand, only three new correlations were observed in the BIPs of cross II, although as many as fifteen correlations were not significant. Results suggested that intermating in the F₂ was effective in breaking the linkages. Path-coefficient analysis further revealed that the direct effect of tillers/ plant on grain yield was important and remained unchanged in both populations of cross I. In cross II, the direct effect of tillers/plants on grain yield was also high and it increased in the BIPs. Intermating seemed to have influenced considerably both the direct and indirect effects.     

Effects of selection criteria on yield stability in chickpea (Cicer arietinum L.)

Summary Selection in the F₃ generation for seed yield, fruiting branches/plant, effective pods/plant, and seed index (100-seed weight) was carried out in two chickpea crosses. Sixty F₅ lines (15 lines/selection criterion) along with check variety were evaluated for seed yield in three distinct environments. The effects of selection criteria on yield stability was examined using linear regression approach and genotype-grouping technique. There were no differences between selection criteria for linear yield responses of F₅ lines to different environments. Within all four selection criteria the lines showed similar linear responses. The non-linear component was relatively higher for lines selected for effective pods and seed index than lines selected for yield and fruiting branches. On the basis of mean yield and coefficient of variation across environments, the seed index was the least effective selection criterion for developing high yielding and stable lines. When the results of stability parameters and genotype-grouping technique were considered together, selection for yield and fruiting branches was highly effective for isolating stable and high yielding lines.     

Predicting the frequencies of transgressive segregants for yield and yield components in wheat

Summary Genetical analysis of the F₂ triple test cross design combined with conventional early generations was used to elucidate the genetical control of yield and yield components in two crosses of winter wheat. From estimates of the additive, {d}, and additive X additive, {i}, components of means, together with the additive genetical variance, D, predicted frequencies of recombinant inbred lines that would transgress the parental range were calculated for each cross. The accuracy of predictions was evaluated by comparing expected frequencies with observed numbers in populations of F₆ lines previously developed by single seed descent.For both crosses and all characters where an adequate genetical model was found to explain the observed variation between the early generations, good agreement between predicted and observed frequencies of transgressive segregants was obtained. Furthermore, for characters exhibiting significant epistasis, allowance for additive X additive {i} epistasis in the prediction equations was sufficient to allow for skewness of the recombinant inbred population.These results demonstrate that cross performance in wheat can be predicted from genetical analysis of early generations, and the value of this approach in breeding new varieties is discussed.     

A modified pedigree method of selection

Summary A dismal 81% failure of newly bulked lines against checks was observed in Indian wheat material evolved by the pedigree method. This is considered to be the consequence of selection in space planting in early generations followed by yield tests in a competitive environment which did not allow any scope of selection for competitive ability. Thus, most of the homozygous lines, which were until now raised and carried forward under space planting, failed to compete with the checks for yield in close planting. It is, therefore, necessary to modify the method to combine both the competitive ability and identity of selected plants. The proposed modified procedure involves raising the population under spaced planting as well as under drilling from F₂ onwards. Evaluation for tiller index marks an important step. On the basis of tiller index, single plants are isolated from spaced populations. Steps of the modified procedure are outlined in detail. The modified method, which economises on breeders' workload and other physical inputs, besides having other advantages, can also be used for certain other grain crops. Preliminary results based on the modified method during the past two seasons have indicated its utility.     

Advanced backcross QTL analysis in progenies derived from a cross between a German elite winter wheat variety and a synthetic wheat (<Emphasis Type="Italic">Triticum aestivum</Emphasis>L.)

We report here the second advanced backcross quantitative trait locus (AB-QTL) analysis carried out in winter wheat. Seven agronomic traits were studied in a BC₂F₁population derived from a cross between the German winter wheat variety Flair and the synthetic wheat line XX86 developed in Japan. We selected 111 BC₂F₁ lines and genotyped these with 197 microsatellite markers. Field data for seven agronomic traits were collected from corresponding BC₂F₃ families that were grown at up to six locations in Germany. QTL analyses for yield and yield components were performed using single-marker regression and interval mapping. A total of 57 putative QTLs derived from XX86 were detected, of which 24 (42.1%) were found to have a positive effect from the synthetic wheat XX86. These favourable QTLs were mainly associated with thousand-grain weight and grain weight per ear. Many QTLs for correlated traits were mapped in similar chromosomal regions. The AB-QTL data obtained in the present study are discussed and compared with results from previous QTL analyses.