Showing papers on "Diallel cross published in 2005"

DIALLEL‐SAS05: A Comprehensive Program for Griffing's and Gardner–Eberhart Analyses

Abstract: Diallel mating designs provide to breeders useful genetic information, such as general combining ability (GCA) and specific combining ability (SCA), to help them devise appropriate breeding and selection strategies. Here we report a much-improved version of DIALLEL-SAS that was originally released in 1997. The new program, DIALLEL-SAS05 has a clear and user-friendly interface that was designed to meet users' needs for various diallel-cross design experiments. DIALLEL-SAS05 has major advantages over DIALLEL-SAS in that: (i) it analyzes not only all four Grifflng's diallel methods (both fixed and random models), but it also computes Gardner-Eberhart's Analyses II and III; (ii) it provides desired results from diallel experiments with parent number from 4 to 12, (iii) it can analyze diallel data from any number of environments, and (iv) for a random-effects model, it provides estimates of GCA (σ 2 g ) and SCA (or,2) variances, which can be used to estimate additive (σ 2 A ) and dominance (σ 2 D ) variances, and ultimately narrow-sense heritability (h 2 ). DIALLEL-SAS05 also provides information on GCA x ENV, SCA x ENV, reciprocal x ENV, maternal x ENV, and nonmaternal x ENV interactions, when applicable. DIALLEL-SAS05 should greatly improve researchers' efficiency in analyzing and interpreting diallel-cross data. The program code is available on a CD from the corresponding author.

Genetic Analysis of Maize Root Characteristics in Response to Low Nitrogen Stress

Abstract: Under low-input cropping systems, nitrogen (N) can be a limiting factor in plant growth and yield. Identifying genotypes that are more efficient at capturing limited N resources and the traits and mechanisms responsible for this ability is important. Root trait has a substantial influence on N acquisition from soils. Nevertheless, inconsistencies still exist as to the effect of low N on root length and its architecture in terms of lateral and axial roots. For maize, a crop utilizing heterosis, little is known about the relationship between parents and their crosses in the response of root architecture to N availability. Here 7 inbred maize lines and 21 of their crosses created by diallel mating were used to study the effect of N stress on root morphology as well as the relationship between the inbreds and their crosses. With large genotypic differences, low N generally suppresses shoot growth and increases the root to shoot ratio with or without increasing root biomass in maize. Maize plants responded to N deficiency by increasing total root length and altering root architecture by increasing the elongation of individual axial roots and enhancing lateral root growth, but with a reduction in the number of axial roots. Here, the inbreds showed weaker responses in root biomass and other root parameters than their crosses. Heterosis of root traits was significant at both N levels and was attributed to both the general combining ability (GCA) and special combining ability (SCA). Low N had substantial affects on the pattern of heterosis, GCA and SCA affects on root traits for each of the crosses suggesting that selection under N stress is necessary in generating low N-tolerant maize genotypes.

Maternal and paternal effects determine size, growth and performance in larvae of a tropical reef fish

Abstract: Larval mortality in marine fishes is strongly linked to individual life history traits such as size and growth, but the processes that influence variability in these traits are poorly understood. We explore the relative importance of maternal and paternal influences and water temperature on the larval growth and performance characteristics of the tropical clownfish Amphiprion melanopus (Pomacentridae). Larvae were reared from an incomplete 4 male × 4 female diallel breeding cross at 2 temperatures (25 and 28°C). Paternity interacted with maternity and affected traits immediately prior to and after hatching. Size of larvae at metamorphosis was primarily affected by maternal and paternal influences, but not by rearing temperature. Paternity explained 52% of the variance in growth rates to metamorphosis, while the combination of paternity, maternity and temperature explained 30%. This strong paternal influence may be due to the extensive role males play in nest-tending coupled with the relatively long embryonic duration of the species. A negative relationship between larval growth rate and mortality within a tank emphasised the importance of these parental effects to larval survival and also provides support for the ‘bigger is better’ hypothesis.

Alternative Maize Heterotic Patterns for the Northern Corn Belt

Abstract: Development of maize (Zea mays L.) inbred lines is based on the identification and utilization of heterotic groups and patterns. The objective of this research was to identify alternative heterotic patterns for the northern Corn Belt. Ten maize populations [BS5, BS21 (R)C7, BS22(R)C7, CGL(S 1 -S 2 )C5, CGSS(S 1 -S 2 )C5, LEAMING(S)C4, NDSAB(MER)C12, NDSCD(M)C10, NDSG(M)C15, and NDSM(M) C7] were crossed in a diallel mating design. The 45 F 1 crosses along with nine checks were evaluated in experiments with two replicates at each of four North Dakota and three Iowa locations in 2002. Data were collected for grain yield, harvest grain moisture, and root and stalk lodging. Analyses of variance were performed following the Gardner and Eberhart Analysis III model. Differences among genotypes existed for all of the traits, and the general combining ability (GCA) sums of squares were larger than the specific combining ability (SCA) sums of squares, indicating the predominance of additive genetic effects. Alternative heterotic patterns to 'Iowa Stiff Stalk Synthetic' (BSSS) x 'Lancaster Sure Crop' (LSC) were found for grain yield among early-maturing populations. The most promising crosses were those in which BS21(R)C7 was combined with CGL(S 1 -S 2 )C5, BS22(R)C7, NDSG(M)C15, LEAMING(S)C4, CGSS(S 1 -S 2 )C5, and NDSAB(MER)C12, and the heterotic pattern formed by BS22(R)C7 and LEAMING(S)C4. A strong association was found between the grain yield of populations per se and their GCA for harvest grain moisture. The population CGSS(S 1 -S 2 )C5 was the earliest among the 10 populations studied and had the best GCA value for grain moisture.

Heterosis and Combining Ability in a Diallel Cross of Ethiopian Mustard Inbred Lines

Abstract: Heterosis is commercially exploited in rapeseed (Brassica napus L.) and its potential use has been demonstrated in turnip rape (B. rapa L.) and Indian mustard (B. juncea L.). In Ethiopian mustard (B. carinata A. Braun), however, information regarding heterosis has not been previously reported. This study, therefore, was conducted to generate information on heterosis and combining ability in B. carinata. Nine inbred parents and their 36 F 1 s, obtained by half-diallel cross, were evaluated for 12 traits at three locations in Ethiopia. Analysis of variance showed the presence of significant heterosis for all the traits. Seed yield showed the highest relative mid-parent heterosis that varied from 25 to 145% with a mean of 67%. Relative high-parent heterosis for seed yield varied from 16 to 124% with a mean of 53%. General combining ability (GCA) effects were predominant in all traits except secondary branches and pods per plant. Specific combining ability (SCA) was significant for days to flowering, secondary branches, pods per plant, pod length, seeds per pod, 1000-seed weight and oil content. Interaction effects of GCA x location were significant for all traits except days to flowering, days to maturity, and oil content. All traits had significant SCA × location interaction effects. GCA effect for seed yield was positively correlated with F 1 performance (r = 0.77) and absolute mid-parent heterosis (r = 0.67). The presence of high levels of mid- and high-parent heterosis indicates a considerable potential to embark on breeding of hybrid or synthetic cultivars in Ethiopian mustard.

Diallel Analysis in Cassava Adapted to the Midaltitude Valleys Environment

Abstract: Cassava (Manihot esculenta Crantz) is an important commodity for industrial processes in tropical countries as one of the few alternatives to compete with imported maize (Zea mays L.). To maintain this competitiveness, cassava breeding needs to be as efficient as possible. This study provides one of the first attempts to produce quantitative genetic data to aid breeding efficiency, through the analysis of a diallel set among nine parental clones adapted to the midaltitude valleys environment. Thirty clones represented each F 1 cross (with three exceptions). Evaluations were conducted in two contrasting environments with three replications in each location. The specific combining ability (SCA) effects were relatively more important than general combining ability (GCA) effects for root yield. In the case of harvest index, dry matter content (DMC) and plant type architecture GCA effects were about twice as large as those from SCA effects. Reaction to mites (Mononychellus tanajoa Bondar) and white flies (Aleurofrachelus socialis Bondar) (based on single-location data) showed the strongest influence of GCA effects on the expression of a given trait Yield data demonstrates the excellent potential of this crop for the tropical production of starch and source of energy in animal feed that could compete with the international markets.

The use of SSRs for predicting the hybrid yield and yield heterosis in 15 key inbred lines of Chinese maize.

Abstract: A challenge to maize breeders is to predict and identify inbred lines that can produce highly heterotic hybrids precisely In the present study we surveyed the genetic diversity among 15 elite inbred lines of maize in China with SSR markers and assessed the relationship between SSR marker and hybrid yield/yield heterosis in a diallel set of 105 crosses Forty-three SSR primers selected from all sixty-three primers gave stable profiles amplified in the sample of 15 inbred lines, which could clearly resolve on 4% metaphor agarose gel The average number of alleles per SSR locus was 444 with a range from 2 to 9 The polymorphism information content (PIC) for the SSR loci varied from 028 to 081 with a mean of 06281 Genetic similarity (GS) among 15 lines was estimated with 191 alleles identified as raw data, the Nei's coefficient of GS ranged from 0492 for 478 vs HZ4 up to 0745 for E28 to ZH64 with a mean of 0619 The cluster diagram based upon the SSR data grouped the 15 lines into families consistent with the yield heterotic response of these Genetic distance (GD) based on SSR data was significantly correlated with hybrid yield/yield heterosis, the correlation coefficient (r) being 05432 and 04271 in 1999 and 04305 and 03614 in 1998 field test, respectively, whereas the determination coefficient (r2) was lower The correlation between GD based on SSR data and hybrid yield/yield heterosis changed alone with the difference of number and pedigree relationship among parents that were used in this study SSR makers showed high polymorphism and could be used to assess the relationship between inbred lines of maize, but it was difficult to predict the yield heterosis of maize

Heterosis and combining ability for maize adaptation to tropical acid soils: Implications for future breeding strategies

Abstract: Soil acidity reduces maize (Zea mays L.) yields by up to 70% on 8 million hectares in developing countries. Several breeding programs have produced populations better adapted to these conditions. The objectives of this study were to evaluate these populations for both per se cultivation and the development of new breeding germplasm. To do so, we generated a diallel cross design, which included six acid soil-tolerant and five susceptible populations with high yield potential or tolerance to other stresses. Populations and crosses were evaluated in five environments, on acidic Al-toxic soils and in comparable limed soils in Guadeloupe, Cameroon, and Colombia. Soil acidity decreased grain yield by 46 to 73%, depending on the location and year. Significant genotype × soil condition interactions were observed for grain yield. Mid-parent heterosis for yield was significantly higher in acid soils (32%) than in nonacid soils (20%). This suggests that the development of variety crosses between acid soil-tolerant populations could be used to increase maize yields in add-soil cropping systems. The observed high general combining ability (GCA) for yield variation of the crosses in add soil and its close relationship to per se performance suggest that parental populations of variety crosses could be efficiently screened on the basis of per se performance in acid soil.

Combining Ability for Resistance to Maize Weevil among 14 Southern African Maize Inbred Lines

Abstract: Maize weevil, Sitophilus zeamais Motschulsky, is an important pest of stored maize (Zea mays L.) in the tropics. We used 14 southern African maize inbred lines to assess (i) combining ability for resistance to maize weevil in F 2 and F 2 -Syn 1 grain, (ii) the importance of maternal effects for resistance of F 2 and F 2 -Syn 1 grain to maize weevil, and (iii) combining ability for grain yield of F 1 hybrids. Maize weevil resistance of F 2 grain was evaluated in 2000 for a 14-parent diallel, and in 2002 for F 2 and F 2 -Syn 1 grain of a 10-parent subset diallel. Fifty-gram grain samples of each hybrid were infested with 32 weevils for a 10-d oviposition period, after which the samples were incubated in a laboratory. Grain yield was evaluated for the 14-parent diallel during the summer of 1999-2000 at four locations in Zimbabwe. General combining ability (GCA), specific combining ability (SCA), and reciprocal effects were highly significant (P < 0.01) for number of F 1 weevils emerged from F 2 grain samples for the combined 2000 and 2002 analysis for the 10-parent subset diallel. For weevil resistance of F 2 -Syn 1 grain, GCA and SCA effects were significant (P < 0.01), while reciprocal effects were not important. The GCA was more important than SCA for grain yield, indicating that yield was controlled mainly by additive gene action among these lines. There was no significant relationship between grain yield and weevil resistance. Although inheritance of weevil resistance was complex, our results suggest using inbred lines with good GCA for weevil resistance as female parents for hybrids or as components of synthetic (open-pollinated) cultivars for regions where farmers often store maize grain without chemical protection against weevils.

Diallel analyses of agronomic traits using Chinese and U.S. maize germplasm

Abstract: Added genetic diversity among commercial maize (Zea mays L.) hybrids may further increase yields and safeguard against vulnerability. Introducing exotic germplasm into breeding programs would increase the genetic base from which elite commercial inbreds are derived. Ten populations of maize, created from Chinese and/or U.S. inbreds or strains, were evaluated by Griffing's diallel analysis for combining ability of grain yield, stalk lodging, ear height, flowering time, and European corn borer (ECB; Ostrinia nubilalis Hubner) resistance to estimate their potential as sources of exotic germplasm for U.S. breeding programs. Grain yield general combining ability was largest for the population Mol7 Syn.(H14)C5, a synthetic improved by half-sib selection using US13 as a tester. Grain yield specific combining ability was largest in the cross Chinese Mix 2 × Mol7 Syn.(H14)C5. Chinese Mix 2 X Mo17 Syn.(H14)C5 had more stalk lodging than the B73 x Mo17 and Pioneer Brand 3394 checks. Because of the high yield potential and other moderate-to-good agronomic traits of the cross combination, Chinese Mix 2 was selected as the best population for selection. Its large specific combining ability effect with Lancaster type material, which is commonly known in breeding programs, shows potential for further improvement. No native ECB resistance in Chinese germplasm was detected (two environments in 1 yr) compared with the resistant check Pioneer Brand 3184.

Análise dialélica de genótipos de milho doce e comum para caracteres agronômicos e proteína total

Abstract: The combining ability as well as reciprocal effect in diallel of sweet and regular corn genotypes was investigated for six agronomic and industrial characters: plant height, stand, percentage of ears attacked by insects, grain protein content, and average (mean) dehusked ear length and weight. General Combining Ability () and Specific Combining Ability (Sij) mean square values were statistically significant when evaluating the following characters: plant height, average (mean) dehusked ear length and weight, and grain protein content, indicating that additive and non-additive genetic effects control these characters. There was no statistical difference regarding mean square effects of average (mean) dehusked ear length and weight characters suggesting the utilization of intra and interpopulational breeding methods. 'Doce 13' and 'Sol da Manha' are among the most indicated genotypes for breeding programs due to observed trend of values. Based on specific combining ability estimates, the best hybrid originated from 'Doce 13' and 'Sol da Manha' crossing.

Genetic combining ability of glucoraphanin level and other horticultural traits of broccoli

Abstract: Broccoli (Brassica oleracea L., Italica Group) is a source of glucosinolates and their respective isothiocyanate metabolites that are believed to have chemoprotective properties in humans. Glucoraphanin (4-methylsulfinyl-butyl glucosinolate) is a predominant glucosinolate of broccoli. Its cognate isothiocyanate, sulforaphane, has proven a potent inducer of phase II detoxification enzymes that protect cells against carcinogens and toxic electrophiles. Little is known about the genetic combining ability for glucosinolate levels or the types of genetic variation (i.e., additive vs. dominance) that influence those levels in broccoli. In this study, a diallel mating design was employed in two field experiments to estimate combining abilities for glucoraphanin content. The diallel population was developed by crossing nine doubled-haploid (inbred) parents in all possible combinations (36), excluding the reciprocals. Horticultural traits of all entries were assessed on a plot basis. In fall 2001, glucoraphanin concentration of broccoli heads ranged from 0.83 to 6.00 μmol/gdw, and in spring 2002, ranged from 0.26 to 7.82 μmol/gdw. In both years, significant general combining ability was observed for glucoraphanin concentration and total head content, days from transplant to harvest, head weight, and stem diameter. Conversely, no significant specific combining ability was observed for any trait in either year. Results indicate that a given inbred will combine with others to make hybrids with relatively predictable levels of head glucoraphanin as well as, other important horticultural traits. This should allow identification of inbreds that typically contribute high glucoraphanin levels when hybridized with others.

Diallel inheritance of relevant traits in cassava (Manihot esculenta Crantz) adapted to acid-soil savannas

Abstract: There is a limited knowledge on the inheritance of traits with agronomic relevance in cassava. A diallel study among 10 parental clones was conducted in the acid-soils environment in the eastern savannas of Colombia. Thirty clones were obtained for each F1 cross. Each clone was represented by six plants, which were distributed in three replications at two locations. Therefore, the same 30 genotypes of each F1 cross were planted in the three replications at the two locations. Analysis of variance suggested significant effects for five of the six variables analyzed (harvest index, dry matter content, height of first branching, reaction to super elongation disease, and plant type scores). Fresh root yield showed strong genotype × environment interaction and differences between crosses reached statistical significance in only one of the two environments analyzed. General and specific combining ability effects and their interaction with the environment were significant for most of the variables as well. Results suggested that dominance plays an important role particularly in the cases of fresh root yield and harvest index.

Combining ability under drought stress relative to SSR diversity in common wheat

Abstract: Eight-parental diallel cross and SSR molecular markers were used to determine the combining ability of common wheat lines grown under well-watered (WW) and water-stress (WS) conditions. Analysis of variance of yield indicated highly significant differences among the progenies. General combining ability (GCA) determined most of the differences among the crosses. Specific combing ability (SCA) was also significant but less important. The estimates of GCA effects indicated that one line was the best general combiner for grain yield under drought. Nei’s genetic distance, measured using SSR markers, differed from 0.20 to 0.48 among the eight genotypes. The correlation of Nei’s genetic distance with SCA for grain yield and heterosis ranged from 0.4 to 0.5. These results indicate that the level of SCA and heterosis depends on the level of genetic diversity between the wheat genotypes examined. Microsatellite markers were effective in predicting the mean and the variance of SCA in various cultivars combinations. However, selection of crosses solely on microsatellite data would miss superior combinations.

Selection aiming at upright growth habit common bean with carioca type grains

Abstract: Aiming at common bean lines with a high grain yield, upright growth habit and carioca type grains, ten common bean lines were crossed in a diallel scheme. The resulting populations were evaluated as to their capacity of generating superior lines. Eleven of the 42 evaluated populations were chosen to form the base population (S0) of the first cycle (C-0). The resultant families were evaluated up to the S0:5 generation for yield, plant architecture and grain type. In this generation, a total of 14 families was evaluated with two controls to estimate the genetic gain considering the three traits of interest together. The obtained genetic gain was 3.1% after one selection cycle, confirming the efficiency of the realized selection. The estimates of genetic and phenotypic parameters in the different generations associated to the mean family performance allow a prediction of the success of recurrent selection in future cycles.

Within-family genetic variation and epistasis in cassava (Manihot esculenta Crantz) adapted to the acid-soils environment

Abstract: Little is known about the inheritance of agronomic traits in cassava, or on the relative importance of epistasis for most crops. A group of 10 clones, adapted to the acid-soils environment was used as parents in a diallel study. Thirty genotypes were obtained from each F1 cross and cloned. Each clone was represented by six plants, which were distributed in three replications at two contrasting locations. Genetic variability concentrated in the within-family component, which was statistically significant for all the variables analyzed (fresh root yield (FRY), fresh foliage yield (FFY), harvest index, root dry matter content, and plant type score (PTS)) except for the reaction to super elongation disease (SED). Estimates of dominance variance were considerably larger than those of additive variance for fresh root and foliage yields. The reverse was observed for harvest index, dry matter content, PTS and SED score. Epistasis played an important role only for fresh root and foliage productions. These results agree with those from similar studies targeting different environments. The common assumption of absence of significant epistatic effects frequent in many quantitative genetic designs is, therefore, challenged from the results for these two variables. Alternative breeding approaches are suggested according to the results obtained from this study.

Genetic variance and breeding values for resistance to a wind-borne disease [ Sphaerotheca macularis (Wallr. ex Fr.)] in strawberry ( Fragaria × ananassa Duch.) estimated by exploring mixed and spatial models and pedigree information

Abstract: A mixed model approach was used to estimate variance components and heritabilities for resistance to powdery mildew, a wind-borne disease in strawberry. In order to improve precision in the statistical computations, spatial error control effects were included to account for systematic environmental variations in the large field trials. Pedigree information was included where feasible. Seedling families obtained from an incomplete 63-by-63 diallel cross were grown at six locations and scored subjectively for mildew attack three times during the growing season. The 63 parents included both European and American cultivars as well as advanced selections from various breeding programmes. A total of 298 full-sib families were realized, including 26 reciprocal families. No reciprocal differences were found. On a plot-mean basis, the broad-sense heritability was found to be intermediate, H2=0.44−0.50, depending on whether the pedigree information was included in the model or not. The increase was mainly due to a substantial increase in the additive variance component. Likewise, the narrow-sense heritability increased from h2=0.39 to h2=0.45 when the pedigree information was included, while the ratio of the specific combining ability variance to the general combining ability variance fell from 13% to 10%. The predicted breeding values of the 63 parents demonstrate that important cultivars such as Elsanta and Korona are unlikely to produce progenies with a high degree of resistance. On the other hand, the Norwegian cultivar Solprins, the Canadian cultivar Kent and the Italian cultivar Patty appeared to give highly resistant progeny. At the full-sib level, the estimated disease scores ranged from 1.15 (Kent × Induka) to 4.19 (Cavendish × Avanta), revealing a huge range of variation for powdery mildew resistance available for selection.

Epistasis in the Expression of Relevant Traits in Cassava (Manihot esculenta Crantz) for Subhumid Conditions

Abstract: There is limited knowledge on the inheritance of agronomic traits in cassava and the importance of epistasis for most crops. A nine-parent diallel study was conducted in subhumid environments. Thirty clones were obtained from each F1 cross. Each clone was represented by six plants, which were distributed in three replications at two locations. Therefore the same 30 genotypes of each F1 cross were planted in the three replications at the two locations. Analysis of variance suggested significant genetic effects for all variables analyzed (reaction to thrips, fresh root and foliage yields, harvest index, dry matter content, and root dry matter yield). Significant epistatic effects were observed for all variables, except harvest index. Dominance variance was always significant, except for dry matter content and dry matter yield. Additive variance was significant only for reaction to thrips. Results suggested that dominance plays an important role in complex traits such as root yield. The significance of epistasis can help us understand the difficulties of quantitative genetics models and QTLs in satisfactorily explaining phenotypic variation in traits with complex inheritance. Significant epistasis would justify the production of inbred parental lines to fix favorable allele combinations in the production of hybrid cassava cultivars.

Genetic Effects on Grain Characteristics of indica Black Rice and their Useson Indirect Selections for some Mineral Element Contents in Grains

Abstract: Complete diallel crosses with Oryza sativa L., six varieties of black rice and one variety of aromatic white rice were conducted to study the seed, maternal and cytoplasmic genetic effects on grain characteristics such as 100-grain weight, length, width and shape and their genetic correlations with Fe, Zn, Mn and P mineral contents in kernels by using the genetic model on quantitative traits of seed in parents and their F1s and F2s. The seed genetic effects were found more important than the maternal genetic effects for grain characteristics, and seed additive effects constituted a major part of their genetic effects. The heritabilities of seed effects were high for 100-grain weight, width and shape and moderate for grain length. Single seed selection based on the 100-grain weight, width and shape was advocated in early generations, whereas single plant and seed selection based on grain length were advocated in late generations. Significant genetic correlations including seed additive, dominance, cytoplasmic, maternal additive and dominance between 100-grain weight, length, width and shape and Fe, Zn, Mn and P mineral contents were observed. Indirect selection of grain characteristics may be one of the breeding methods to select for higher contents of Fe, Zn, Mn and P in black pericarp indica rice.

Combining ability studies in brinjal

Abstract: A 10 × 10 diallel set of crosses was attempted to study the extent of heterosis in brinjal for maturity, yield and its component characters. Estimates of gca effects and per se performance indicated that parents P10 followed by P8 and P4 were good general combiner as they showed desirable gca effects for many characters including fruit yield. In general, the parents, which have the best per se performance, were also the best general combiners, indicating a positive association between the two parameters. The cross combination P1 × P4 have recorded significantly high sea effects for days to first flowering, days to 75 per cent flowering and for days to first fruit harvest, P4 × P7 for leaf area, P7 × P8 for plant height, plant spread, fruit clusters per plant and average fruit yield per plant, P3 × P6 for fruit length, P1 × P8 for fruit width, P2 × P7 for number of fruits per plant and P6 × P9 for average fruit weight indicating the importance of both additive and non-additive effects for these characters. This suggests that the crosses having high sea effects and also involved at least one good general combiner parent may be considered useful because such crosses provide transgressive type of segregants in the advanced generation more frequently than crosses with the poor combiner parents.

Combining ability for grain yield, agronomic traits and Striga lutea tolerance of maize hybrids under artificial striga infestation

Abstract: A study was carried out using diallel crosses in maize to determine the general and specific combining abilities in the mode of inheritance of tolerance to Striga lutea. Ten inbred parents of varying tolerance to S. lutea were crossed in half diallel to generate 45 F1 hybrids. The hybrids were evaluated in three striga endemic locations of Southwestern Nigeria under artificial infestation in 1998 growing seasons. The results showed that general combining ability effects were significant for almost all traits under infested and uninfested conditions. Progeny performance showed that hybrids were 86 and 40% better than their parent inbreds for striga tolerance rating and maize grain yield under artificial infestation. General combining ability (gca) effects for striga syndrome ratings were generally low with negative gca effects of -080. -0.40, -0.21,-0.15 and -0.26 in parents Tzi 97, Tzli100, Tzpi43-22, Tzmi105 and Tzpi260, respectively. Parents inbreds Tzpi97, Tzmi104, Tzpi57 and Tzli10 are good sources of gene for higher grain yield. Specific combining ability (sca) effects were also generally low for striga syndrome rating with values of -0.94, -0.77, -1.14 and 0.83 showing good tolerance. These tolerant inbreds may be adopted for commercial hybrid maize production for S. lutea endemic areas of south western Nigeria.

Study of gene effects for boll number, boll weight, and seed index in cotton

Abstract: Sixty four cross combinations were produced by a complete diallel-mating system with eight varieties (Laokra5.5, DPL-7340-424, Fregobract, Glandless 4195-220, SA100, Stoneville-857, S-14 and B-557). The results showed that non-additive over dominance type of gene action governed the inheritance of number of bolls per plant (Wr + Vr) 30.31 ns and boll weight (Wr + Vr) 0.063 ns in F 1 generation. Additive with partial dominance was operative in the inheritance of seed index (Wr + Vr) 1.30** in F 1 generation. Estimates of narrow sense heritability for boll number (0.373 F 1 and 0.751 F 2 ), boll weight (0.238 F 1 , 0.230 F 2 ) & seed index (0.695 F 1 , 1.042 F 2 ) along with expected genetic gain because of selection, a potentially useful advance in these characters seems possible to achieve by selecting individual plants showing better qualities. Biparental mating in early generation among the selected lines, or diallel selective mating can be adopted in breeding programs for the improvement of the characters studied.

Diallel analysis of yield components of snap beans exposed to two temperature stress environments

Abstract: Ten snap beans (‘Barrier’, ‘Brio’, ‘Carson’, ‘Cornell 502’, ‘CT 70’, ‘HB 1880’, ‘Hystyle’, ‘Labrador’, ‘Opus’ and ‘Venture’) were selected for differential temperature tolerance and used as parents in a complete diallel mating design. The 45 F1 hybrid lines (with reciprocals) and parents were screened at 32 ∘C day/28 ∘C night, and in a separate experiment, 16 ∘C day/10 ∘C night, during reproductive development in replicated controlled environments. Variation for yield under temperature treatments was observed among parents and hybrids, with certain hybrids exceeding parental performance. Significant (P≤ 0.0001) general combining ability (GCA), and significant (P≤ 0.05) specific combining ability (SCA) were observed for yield components including pod number, seed number, and seeds per pod. There was evidence that pod number and seeds per pod under temperature stress are under separate genetic control. Reciprocal effects and heterosis were not significant. GCA could not be predicted from parental performance. The breeding line ‘Cornell 502’ had the highest GCA under high temperature, and the cultivar ‘Brio’ had the highest GCA under low temperature. The cross ‘Brio’ × ‘Venture’ was high yielding in both temperature treatments. Heat tolerance and chilling tolerance were associated in certain parents and hybrids. However, performance under high and low temperature treatments was not generally correlated in the parents and hybrids, indicating that these traits should be selected separately.

Epistasis in cassava adapted to midaltitude valley environments

Abstract: Little is known about the inheritance of agronomic traits in cassava (Manihot esculenta Crantz). The vegetative multiplication of cassava allows cloning of individual genotypes, and separates environmental from genetic variation in the within-family variation. Knowing the magnitude of between- and within-family variation is important for defining breeding strategies and for measuring different components of genetic variances, particularly the seldom-estimated epistasis. A group of nine genotypes, adapted to midaltitude environments, was used for a diallel study. Thirty clones were obtained from every F 1 cross (each clone was represented by six plants), and planted in three replications at two locations. Statistical differences among crosses were found for fresh-root yield, harvest index, root dry-matter content, and reaction to mites (Mononychellus tanajoa Bondar) and to whiteflies (Aleurotrachelus socialis Bondar). General combining ability (GCA) was significant for all traits except fresh-root yield and dry-matter content, and specific combining ability (SCA) was significant for all traits except whitefly damage score. Fresh-root yield was the only trait with significant epistatic effects, which, combined with a large dominance variance, suggested a prevalence of nonadditive effects. The introduction of inbreeding would be one approach for the efficient exploitation of these nonadditive effects found for fresh-root yield. For the remaining traits, epistasis was negligible and current schemes exploiting additive effects may suffice.

Comparison of QTLs for Early Elongation Ability between Two Floating Rice Cultivars with a Different Phylogenetic Origin

Abstract: The ability to initiate stem elongation at the early growth stages of a plant is the major survival mechanism of floating rice in the presence of flooding. We previously identified two quantitative trait loci (QTLs) for this “early elongation ability” on chromosomes 3 and 12 using a Patnai23 (a non-floating cultivar) × Goai (a floating cultivar) F2 population. The objectives of the present study were: (1) to identify QTLs for early elongation ability in the cross Habiganj Aman VIII (a floating cultivar) × Patnai23, and (2) to confirm the results obtained in our previous diallel analysis indicating that Habiganj Aman VIII might harbour additional gene(s) for early elongation ability compared with Goai. The genotype of a total of 192 F2 plants was investigated using 85 (9 RFLP and 76 SSR) markers and the plants were assessed for early elongation ability. We scaled early elongation ability based on the position of the lowermost internode that exhibited elongation (“lowest elongated internode”, LEI), since the LEI position parallels the time of the onset of stem elongation. As a result, a large QTL detected on chromosome 12 seemed to be common to the two crosses. A small QTL detected on chromosome 1 was unique to the Habiganj Aman VIII × Patnai23 cross, which was consistent with the results obtained in our previous diallel analysis. No QTLs were found on chromosome 3 in this cross. These results suggested that (1) the QTL on chromosome 12 might be the most important one for the expression of early elongation ability in terms of the to percentage of phenotypic variation and consistency in different backgrounds, and (2) diallel analysis might be an effective method for examining differences in genetic control among diverse parents.

Potential of soybean genotypes as insect resistance sources

Abstract: Partial diallel crosses between insect-attack susceptible and resistant soybean genotypes were realized in order to check the possibility of joining favorable alleles of insect resistance and high grain yield in the same genotype. F2 progeny was evaluated in three distinct locations, each one with a different priority: grain yield and responses to sucking and chewing insects. The experimental design was of randomized blocks with six replicates to evaluate F2 generation from 16 crosses and eight parent lines, amounting to 24 treatments. The experimental plot was represented by 12 individual plants with a row/plant spacing of 0.5 x 0.6 m. The best general combining ability was detected in parent IAC-100 for insect resistance and grain yield. Cross Davis x IAC-100 showed a higher potential for specific combining ability to grain yield and resistance to sucking and chewing insects.

Genetic analysis of embryo, cytoplasmic, and maternal effects and their environment interactions for protein content in Brassica napus L.

Abstract: A genetic model for quantitative traits of seeds in diploid plants was applied to estimate the genetic main effects and genotype × environment (GE) interaction effects for protein content (PC) of rapeseed (Brassica napus L.) by using 2 years of experimental data with a diallel mating design of 8 parents. Results showed that PC of rapeseed was simultaneously controlled by genetic effects of embryo, cytoplasm, and maternal plant, of which the maternal genetic effects were most important, followed by embryo and cytoplasmic genetic effects. Therefore, improvement of PC of rapeseed would be more efficient when selection is based on maternal plants than that on single seeds. Since the GE interaction effects accounted for about 60.10% of total genetic effect, they were more important than the genetic main effects, and selection for PC might be influenced by environmental conditions. The total narrow-sense heritability for PC was 64.17%, of which the interaction heritability was larger than the general heritability. Selection for improving PC can therefore be conducted in early generations. Maternal heritability (41.59%) was most important for PC, followed by cytoplasmic heritability (17.62%) and then by embryo heritability (5.25%). Based on prediction of genetic effects, parent Youcai 601 was better than others for increasing PC in rapeseed breeding.