Combining ability and correlations for yield components in early generations of potato breeding

A partial diallel set of crosses was made between 14 potato cultivars chosen for their fertility, from those included in a potato breeding programme at the NEIKER – Basque Institute for Agricultural Research. The progeny were grown in completely randomized trials from 1997 to 1999. Performance for yield, tuber number and average tuber weight was analysed in seedling and two clonal generations. Variance estimates due to both general combining ability (GCA) and specific combining ability (SCA) were significant in all generations for all traits under study. However, SCA was more important than GCA in almost all cases. Correlation coefficients among characters, generations, GCA and SCA effects were examined. For tuber yield no relation was obtained between generations; however, average tuber weight and yield were positively associated in all generations. The results indicate that appropriate selection criteria depend strongly on the particular cross. The implication for a breeding strategy are discussed.     

Analysis of an incomplete diallel cross among three ssp. tuberosum varieties and seven long-day adapted ssp. andigena clones of the potato (Solanum tuberosum L.)

Summary The main aim of the experiment was to study the behaviour of seven long-day adapted clones of Solanum tuberosum ssp. andigena (A) and three varieties of S. tuberosum ssp. tuberosum (T) in an incomplete diallel cross. The four groups of crosses, TxT, TxA, AxT and AxA, held 2, 12, 20 and 21 populations, respectively. Eleven of the intersubspecific crosses were exact reciprocals. Thirty random clones per population were grown as second clonal generation in an incomplete block design with four replications in plots of two plants per clone in 1980, the parents included in many plots. Data were recorded on ten characters.The results showed that group TxA gave the highest tuber yield and AxT the second highest. The F-values indicated highly significant genotypic effects for all characters in all populations. The mean genotypic coefficients of variation (GCV), were the highest for group AxA for all characters. The ANOVA, based on population means showed significant mean squares for general combining abilities (GCA) and for differences of reciprocalls for all characters; the specific combining ability (SCA) mean squares were significant only for date of emergence, plant height and haulm type. Almost all GCA effects of the parents were significant positive or negative. Several populations showed also significant SCA effects. The correlations between the GCA effects and the parental values were of about the same magnitude as the heritabilities; those between the population means and the midparental values were slightly lower.Compared to the midparental values, most populations showed significant positive heterosis for date of emergence, haulm type, number of tubers and under water weight; all populations had significant negative heterosis for mean tuber weight and nearly all for plant height and general impression. All populations from groups TxT and AxA had significant negative heterosis for tuber yield and so had 13 out of the 20 populations from group AxT, while seven of the 12 from group TxA showed significant positive and four significant negative heterosis. The average heterosis for tuber yield of group TxT was –11%, of TxA 3.4%, of AxT–9% and of AxA–18%. The highest mean tuber yields were obtained from crosses with a very high yielding A-parent as female, while the heterosis was negative. Though significant differences between the 11 reciprocals occurred for all characters, consistent differences occurred only for tuber yield. Averaged over the 11 crosses the TxA populations outyielded their exact reciprocals by 10.7%. For the highest tuber yields in A-T crosses, therefore, the tuberosum cytoplasm seems to be preferable. By contrast for a high male fertility the andigena cytoplasm is preferable.     

Inheritance of resistance to late blight (Phytophthora infestans) in potato

Under epiphytotic conditions for late blight in spring seasons, data were recorded on its intensity four times at 4 days intervals from the start of the disease in the field, in 114 (19 females × 6 males) progenies and their parents planted in randomized complete block design in the years 2005 and 2006. Regression and stepwise regression analysis showed that observations during the rapidly increasing phase of disease between initial and last phase of disease are more important than the observations at initial and last phase of the disease. Combining ability analysis on a sub-set of 68 progenies showed that the additive component of genetic variance was more important than the non-additive component of variance in inheritance of quantitative resistance to late blight. The per se performance of the parents does give an idea about their general combining ability (GCA). However, selection of parents based on their GCA will be very useful for breeding for quantitative resistance to late blight. Parents JX 90, JF 4841, CP 3356, CP 1358, CP 3290, JN 1197 and CP 3125 were found to have good GCA for quantitative resistance for late blight and the best six crosses for late bilght resistance based on mean performance involved parents with good combining ability only.     

Heterosis and combining ability for biomass and harvest index in chickpea under a drought-prone, short-duration environment

Heterosis and combining ability studies were conducted on selected chickpea genotypes in order to (1) acquire an understanding of the predominant type of gene action governing biomass (BY) and harvest index (HI), (2) estimate the magnitude of heterosis, (3) estimate combining ability effects and (4) assess correlations between per se performance and general combining ability (GCA) of the parents under a drought-prone, rainfed short-duration environment (SDE) where BY is considered to be an important trait for enhancing chickpea productivity. The experimental material comprised 30 F₁s obtained by crossing ten adapted genotypes as females to three testers as males in a line × tester design. The GCA variances were significant and of a high magnitude, while specific combining ability (SCA) variances were non-significant, indicating the predominant role of additive gene action on BY and the HI. A large number of crosses showed positive mid-parent heterosis (MPH) and better-parent heterosis (BPH). The average MPH and BPH for BY was 22.36 and 12.65, respectively, and the average MPH and BPH for the HI was 2.22 and −0.92, respectively. The higher magnitude of the MPH and BPH recorded for BY indicated that the scope for increasing the HI in chickpea in a drought-prone, SDE is limited and that further increases in productivity have to come mainly through enhanced BY. The majority of the heterotic crosses involved poor × good combiners. This study demonstrates that in order to achieve greater progress in improving BY and the HI in chickpea, the selection of parents should be based on per se performance as well as combining ability and heterosis.     

Effect of tester on combining ability estimates of maize germplasm complexes

Eight maize complexes and varieties representing high and low yield levels were tested for their suitability as top cross testers by comparing the performance of the crosses in relation to the combining ability of the parents estimated by diallel analysis. The discriminating ability of the testers was compared by Schumann and Bradley test. In both cases the results clearly showed that the low performing testers were better and more reliable than the high performing complexes. The utility of per se performance as an indication of general combining ability of the complexes has been discussed.     

Heterotic effects for yield and tuber solids and type of gene action for five traits in 4x potato families derived from interploid (4x-2x) crosses

The degree of heterosis for total tuber yield (TTY) and total solids (TS) in 4x‐2x crosses was estimated by comparing the performance of 12 families with their respective parents in two locations in Wisconsin (USA). The parental 2x clones were Phureja‐haploid Tuberosum hybrids with 2n‐pollen production by first‐division restitution. The general combining ability (GCA) and specific combining ability (SCA) were estimated for TTY, TS, vine maturity (VM), length of tuber sprout dormancy (LD), and tuber eye depth (ED). Family performance for TTY ranged from 74 to 146% at Hancock (E#1) and from 77 to 287 at Rhinelander (E#2) when compared with that of the 4x parent group. For VM, the families were late maturing, but a few precocious ones were identified. For TS, the families had heterosis of 5.1% over the 4x parent group. The families had slightly higher ED values than the 4x parents, but families with values within the commercial range were identified. The family average for LD (54 days) was closer to the 2x group (51 days) than to the 4x group (88 days). The direction and magnitude of the parent‐family relationships were variable. The 4x parent TTY was correlated with progeny in E#1 but not E#2. The 2x parent VM had correlation with the offspring at E#2 but not at E#1. The type of gene action had a trait‐specific expression. Significant SCA and GCA variances were observed, suggesting that additive as well as non‐additive genetic effects were operating. The 4x‐2x crosses were able to generate heterotic families for TTY and TS in combination with other useful traits. However, no promising results were found for LD because of the apparent dominance of the short‐dormancy phenotype. This result indicates the need of additional selection and breeding efforts for some specific traits when using S. phureja‐derived germplasm.     

Combining ability of non‐adapted sources for male‐fertility restoration in Pampa CMS of hybrid rye*

Hybrid rye breeding and seed production relies on the cytoplasmic male sterility‐inducing Pampa (P)‐Cytoplasm. High levels of restoration were recently found in non‐adapted rye accessions from Argentina (Pico Gentario, Pastoreo Massaux) and Iran (IRAN IX). To analyse their relative superiority, five seed‐parent lines in P cytoplasm were crossed with five inbred lines of these sources and four adapted restorer lines. The 45 F1 hybrids were tested for male‐fertility restoration in three locations. Significant (P = 0.01) general and specific combining ability (GCA and SCA respectively) for male‐fertility restoration were found. The non‐adapted restorer lines were able to restore all seed‐parent lines similarly, resulting in hybrids with 55‐90% pollen shedding (mean 78%) compared with 2‐74% pollen shedding (mean 44%) when adapted restorer lines were used. Significant (P = 0.05) SCA effects were detected in 11 of 45 combinations, nine of them were crosses with adapted pollinator lines. Non‐adapted restorer lines showed a high phenotypic stability of male‐fertility restoration across locations. Introgression of these exotic sources into the adapted restorer gene pool by repeated backcrossing should result in environmentally stable male fertility in Pampa‐based rye hybrids.     

Inheritance of resistance to head bugs and its interaction with grain molds in Sorghum bicolor

Sorghum head bug, Calocoris angustatus Lethiery is one of the most important pests of grain sorghum in India. Head bug damage increases the severity of grain molds, which renders the grain unfit for human consumption. Therefore, we studied the gene action for resistance to head bugs and grain molds in a diverse array of male-sterile lines and testers in a line × tester mating design under natural infestation. Mean squares for parents, parents vs crosses, lines, testers, and lines × testers were significant for head bug damage and grain mold severity. General combining ability (GCA) effects were significant and negative for ICSA 88019 for head bug damage, and ICSA 88019 and ICSA 88020 for grain molds (except for ICSA 88020 in 1993). General combining ability effects were positive for ICSA 42 and 296 A. GCA effects of lines and testers for head bug damage and grain mold severity were in the same direction (+ve or −ve). Head bug damage in the grain was significantly correlated with grain mold severity. Testers IS 8891, IS 15107, and TAM 2566 (with colored grain and less susceptibility to molds) produced mold-resistant hybrids in combination with all the male-sterile lines, while the reverse was true in the case of Swarna and ICSV 112. Resistance to head bugs showed dominance to partial dominance type of gene action, while in the case of grain molds, it showed dominance to over dominance. Resistance to these pests is governed by both additive and nonadditive types of gene action. The implications of these results are discussed in relation to need for crop improvement in sorghum. This revised version was published online in July 2006 with corrections to the Cover Date.     

Combining ability and testcross performance of drought‐tolerant maize inbred lines under stress and non‐stress environments in Kenya

Drought and poor soil fertility are among the major abiotic stresses affecting maize productivity in sub‐Saharan Africa. Maize breeding efforts at the International Maize and Wheat Improvement Center (CIMMYT) have focused on incorporating drought stress tolerance and nitrogen‐use efficiency (NUE) into tropical maize germplasm. The objectives of this study were to estimate the general combining ability (GCA) and specific combining ability (SCA) of selected maize inbred lines under drought stress (DS), low‐nitrogen (LN) and optimum moisture and nitrogen (optimum) conditions, and to assess the yield potential and stability of experimental hybrids under these management conditions. Forty‐nine experimental three‐way cross hybrids, generated from a 7 × 7 line by tester crosses, and six commercial checks were evaluated across 11 optimum, DS and LN sites in Kenya in 2014 using an alpha lattice design with two replicates per entry at each site. DS reduced both grain yield (GY) and plant height (PH), while anthesis–silking interval (ASI) increased under both DS and LN. Hybrids ‘L4/T2’ and ‘L4/T1’ were found to be superior and stable, while inbreds ‘L4’ and ‘L6’ were good combiners for GY and other secondary traits across sites. Additive variance played a greater role for most traits under the three management conditions, suggesting that further progress in the improvement of these traits should be possible. GY under optimum conditions was positively correlated with GY under both DS and LN conditions, but GY under DS and LN was not correlated. Our results suggest the feasibility for simultaneous improvement in grain yield performance of genotypes under optimum, DS and LN conditions.     

Identifying quantitative trait loci for the general combining ability of yield-relevant traits in maize

Maize is the most important staple crop worldwide. Many of its agronomic traits present with a high level of heterosis. Combining ability was proposed to exploit the rule of heterosis, and general combining ability (GCA) is a crucial measure of parental performance. In this study, a recombinant inbred line population was used to construct testcross populations by crossing with four testers based on North Carolina design II. Six yield-relevant traits were investigated as phenotypic data. GCA effects were estimated for three scenarios based on the heterotic group and the number of tester lines. These estimates were then used to identify quantitative trait loci (QTL) and dissect genetic basis of GCA. A higher heritability of GCA was obtained for each trait. Thus, testing in early generation of breeding may effectively select candidate lines with relatively superior GCA performance. The GCA QTL detected in each scenario was slightly different according to the linkage mapping. Most of the GCA-relevant loci were simultaneously detected in all three datasets. Therefore, the genetic basis of GCA was nearly constant although discrepant inbred lines were appointed as testers. In addition, favorable alleles corresponding to GCA could be pyramided via marker-assisted selection and made available for maize hybrid breeding.     

Genetic divergence for cross prediction in potato

To study the effectiveness of genetic divergence for cross prediction in potato, progeny means, heterosis and specific combining ability effects were correlated with parents’ genetic distances (D values) estimated under six in vitro and four in vivo conditions, for tuber yield in 72 crosses (18 × 4) of 22 parents under autumn crop conditions for three successive generations. Genetic distances under in vitro conditions had no relationship with the progeny means for tuber yield. Whereas, those under in vivo conditions in the autumn seasons were positively associated with the progeny means. Similarly, heterosis for tuber yield had a stronger relationship with genetic distances based on an in vivo crop than those based on an in vitro crop. All correlation coefficients between genetic distances and specific combining ability effects were non-significant. The magnitudes of the significant correlation coefficients showed that genetic divergence can be used as an indirect parameter of moderate effectiveness in selecting parents to produce heterotic high yielding progenies. Such cross predictions, however, would be effective only if parents are evaluated under the conditions similar to those under which crosses are likely to be evaluated. This revised version was published online in July 2006 with corrections to the Cover Date.     

Genomic prediction of the general combining ability of maize lines (Zea mays L.) and the performance of their single crosses

The objective of this study was to assess the effectiveness of genomic selection (GS) on predicting the general combining ability (GCA) of maize lines and the performance of their single crosses. Eight maize lines developed from the different self‐pollination generations of Chalqueño race, along with their 24 single crosses, were evaluated in the field during the years of 2011, 2012 and 2013. Genomic prediction results using genotyping‐by‐sequencing‐based single nucleotide polymorphisms showed that the GCA classification of the parental lines estimated from the SNP information was consistent with the phenotypic classification of the lines evaluated from the field trial data. The prediction accuracy values estimated from the cross‐validation method ranged from 0.49 to 0.61 in the different prediction models. Yield performance of the unevaluated single crosses was predicted based on their SNP information. The total genetic variance of the yield of the single crosses was most explained by the GCA effects. Compared with phenotyping method, GS is a more effective and efficient approach to predict the GCA of maize lines and their hybrid performance.     

Combining ability analysis and correlation between breeding values in true potato seed

True potato seed (TPS) requires the selection of appropriate parents for developing hybrid offspring. Parents for routine crossing schemes need to be selected according to their combining ability. Hierarchical and factorial mating designs provide a mean values to assess the general combining ability (GCA) of clones included in crossing schemes. Furthermore, specific combining ability (SCA) may be investigated using the factorial mating design. The aim of this research was to determine the combining ability of clones included in early and intermediate TPS breeding populations developed by the Centro Internacional de la Papa (CIP). Likewise, correlations between breeding values (or additive genetic correlation, p_A) were calculated. Two hierarchical mating designs (in both the early and intermediate populations) and one factorial mating design (in the intermediate population) were evaluated in two contrasting Peruvian locations (La Molina ‐ coastal desert, and San Ramon, warm humid tropics). Plant and tuber characteristics were recorded in these experiments. Significant GCA was observed for tuber yield in all experiments. The male's p_A between plant vigour after transplanting and tuber yield was significant, thereby suggesting that offspring with early vigorous growth are high yielding. Plant vigour was also correlated with tuber set, but only among the breeding value of female parents, which suggests that high tuber yield could be achieved because offspring with early, vigorous growth have many tubers. High tuber yielding hybrids can be obtained by choosing parents with significant GCA, whose tuber yield can also be further enhanced if the crosses have a significant SCA.     

Combining ability and gene action controlling yield and yield components in bread wheat (Triticum aestivum L.) under drought‐stressed and nonstressed conditions

This study determined the combining ability and gene action controlling yield and yield‐related traits in wheat under drought‐stressed and nonstressed conditions. Twelve parents possessing Rht‐B1b and Rht‐D1a genes and their 66 half‐diallel crosses were evaluated under field and glasshouse conditions. Plant height (PH), productive tiller number (TN), kernels per spike (KPS), thousand seed weight (TSW) and grain yield (GY) were recorded. Analysis of variance, heritability, correlation and combining ability analyses were performed. Heritability estimates ranged from 53.00% (TN) to 63.07% (KPS). Yield showed positive correlations with all other traits under all test conditions. Significant GCA effects were observed for all traits recorded across test conditions, except for yield in the glasshouse. All Baker's ratios were less than a unit, indicating predominance of nonadditive gene action. Consistently high positive GCA effects were observed on LM02 for GY; LM02 and LM23 for KPS; and LM04 and LM09 for TSW, while LM17 and LM21 had negative effects for PH. Good general and specific combiners will be used for further breeding and selection.     

Combining ability analysis of resistance to head blight caused by <Emphasis Type="Italic">Fusarium graminearum</Emphasis> in spring wheat

Fusarium head blight (FHB) caused by Fusarium spp. is one of the most important fungal diseases of wheat (Triticum aestivum L.) in regions with wet climatic conditions. Improvement of the FHB resistance by developing new varieties requires sound knowledge on the inheritance of resistance. An 8 × 8 diallel analysis was performed to estimate general (GCA) and specific (SCA) combining ability of resistance to FHB. The F₁s and parental lines were evaluated under artificial inoculation at the experimental field of IFA-Tulln, Austria during 2001 and 2002. Disease severity was evaluated by repeated scoring of the percentage of infected spikelets and calculating an area under the disease progress curve (AUDPC). The analysis of combining ability across two years showed highly significant GCA and non-significant SCA effects indicating the importance of additive genetic components in controlling FHB resistance. The significant GCA-by-year interaction presented the role of environmental factors in influencing the FHB reaction of wheat lines. The comparison of the crosses with low FHB infection and GCA effects of their parents showed that such crosses involved at least one parent with high or average negative GCA effect. The results revealed that it is feasible to use highly or moderately resistant genotypes and conventional breeding methods to achieve genetic improvement of FHB resistance in spring wheat.     

Genetic analysis of yield and fruit traits in cantaloupe cultivars

The purpose of this research was to evaluate the combining ability of six local Iranian and one imported cantaloupe cultivar. Heritability of traits was estimated using a half‐diallel mating design. Seven parents and their crosses were evaluated in 2013 and 2014. The greatest general combining ability (GCA) for yield and fruit number was for “Rish‐baba” (0.53 kg/plant and 0.3, respectively). The cultivar “Ananasi” had the highest GCA for fruit weight and soluble solids content (SSC) (0.088 kg and 1.4, respectively). “Ananasi” presented the highest GCA values for fruit firmness, chlorophyll a and b and carotenoid content, as well as the highest total chlorophyll content. The cross Garmak × Rish‐baba showed the highest specific combining ability (SCA) for yield with heterosis value of 99%. High heritability estimates for SSC (0.52), flesh thickness (0.61) and concentration of chlorophyll a (0.7) were obtained. Although there were significant SCAs for yield, the parents are suggested to be improved prior to hybrid development. The parent “Ananasi” appears to be a suitable donor in breeding programmes.     

Analysis of diallel crosses between wheat genotypes with genetically different resistance to Pseudocercosporella herpotrichoides (Fron) Deighton

Two diallels were analysed for general combining ability (GCA) and specific combining ability (SCA) to study the resistance of crosses‐between wheat genotypes, advanced to the F₅ generation, to Pseudocer‐cosporella herpotrichoides. The parents either carried the resistance‐gene Pch‐1 or had different levels of quantitative resistance, one genotype was susceptible. At medium milk‐ripening, significant effects were‐found for GCA and SCA. GCA effects were the more important. Diallel crosses between genotypes, all carrying Pch‐1, revealed interactions‐of the gene with the genotypic background. Some combinations had a‐higher level of resistance than the best parent. In these populations'CH‐75417’ was involved as a parent. Both ‘CH‐75417’ and ‘F–210.13.4.42’ had significant GCA effects. Crosses between quantitatively resistant parents yielded populations that transgressed both parents. The increased resistance level was associated with ‘Cappelle‐Desprez’, distinguished by its high GCA. In some crosses SCA contributed significantly to an increase in resistance level. Selection for resistance within the best advanced populations is recommended since it‐takes advantage of additive gene action and the high heritability estimates based on ELISA values in plant progenies.     

Assessing the suitability of stress tolerant early-maturing maize (Zea mays) inbred lines for hybrid development using combining ability effects and DArTseq markers

Identification of hybrids for commercialization is crucial for sustainable maize production in sub-Saharan Africa (SSA). One hundred and ninety test crosses, 10 tester × tester crosses + 10 hybrid checks were evaluated across 11 environments, 2017 to 2019. Inheritance of grain yield under Striga infestation, optimal and across environments was influenced by additive genetic action, but there was greater influence of nonadditive gene action under drought stress conditions. Nine, seven and two inbreds had significant and positive general combining ability (GCA) effects for grain yield under Striga-infested, optimal and drought stress environments, respectively, and would contribute high grain yield to their progenies. Heterotic grouping methods based on specific and GCA, GCA effects of multiple traits and DArTseq markers classified the inbreds into five, three and two heterotic groups, respectively, across research conditions. The DArTseq markers method that classified the inbred lines into two major heterotic groups and was one of the most efficient methods should be adopted for practical purposes in maize breeding programmes in SSA. Hybrids TZEI 7 × TZdEI 352, TZEI 1238 × TZEI 7 and TZEI 1252 × TZEI 7 had outstanding grain yield under contrasting environments and should be tested on-farm for commercialization in SSA.     

甘薯配合力分析的若干问题

首次将不完全双列杂交(NCⅡ)模式,结合甘薯遗传特点应用于甘薯育种。根据4年试验结果,提出了可行的试验方法、群体规模和评定指标;并就高淀粉、高产育种亲本选配中的若干问题提出了看法。     

Combining ability estimates for yield and fibre quality traits in 4 × 13 line × tester crosses of Gossypium hirsutum

The aim of this study was to estimate the general combining ability of the parents and specific combining ability of hybrids considered for the development of high yielding and better quality cultivars. Seventeen genotypes and 52 F₁ hybrids obtained by crossing 4 lines and 13 testers in line × tester mating system during 2003 were sown in randomized complete block design in 2004. Line × Tester analysis revealed significant GCA and SCA effects for all the traits except fibre elongation. Preponderance of non-additive gene action was obtained for seed cotton yield per␣plant and majority of its component traits including fibre traits. Among the parents: PIL-8 for days to 50% flowering, CCH-526612 for boll weight, CITH-77 for number of open bolls per plant and CNH-36 for seed cotton yield per plant were detected with higher general combining ability. Parent, CCH-526612 for 2.5% span length, fibre strength and fibre elongation and AKH-9618 for micronaire value, fibre strength and fibre elongation were good combiners for fibre quality traits. The F₁s achieved high seed cotton yield by producing more number of open bolls. The high yielding hybrids with acceptable fibre quality traits were: CISV-24 × LH-1995, H-1242 × PIL-8 and RS-2283 × SGNR-2 deducted with significant SCA effects for seed cotton yield and fibre characteristics; 2.5% span length and fibre strength. These cross combinations involved at least one parent with high or average GCA effect for a particular trait.