Combining Ability Mean Squares Research Articles

Genetic Responses of Single Crosses of Maize to Striga hermonthica (Del.) Benth. and Striga asiatica (L.) Kuntze

Striga hermonthica (Del.) Benth. and Striga asiatica (L.) Kuntze infest millions of hectares of land under cereals in sub Saharan Africa, threatening food security. One of the major crops threatened is maize (Zea mays L.), a staple food for many Kenyans. A diallel cross involving 16 inbred lines was used to study the genetics of resistance to S. hermonthica and S. asiatica. Three inbred lines each from TZL comp 1, Zea diploperennis Iltis, Doebley & Guzman x Zea mays (Diplo pool), and a low emergence stimulant pool (LE Pool) classified as resistant were crossed to adapted but susceptible inbred lines CML-204, CML-373, and CML-395 from CIMMYT and MUG-1, MUG-2, MUG-3, and MUG-4 from Kenya. The hybrids were evaluated for two seasons at Matuga for S. asiatica and at Kibos and Alupe for S. hermonthica. General combining ability mean squares were higher than specific combining ability mean squares for all traits for the two species, indicating additive genetic effects were more important. Inbreds producing crosses with better resistance than the local checks were identified for both Striga species. Diplo pool and LE Pool were better sources of resistance to S. hermonthica and LE Pool and TZL pools were better sources of resistance or tolerance to S. asiatica.

Responses and genetics of maize germplasm resistant to the maize weevil Sitophilus zeamais Motschulsky in West Africa

The maize weevil, Sitophilus zeamais Motschulsky causes considerable damage to maize grain during storage in the tropics. The objectives of this study were to determine through two experiments the genetic basis of resistance to S. zeamais in African maize germplasm of open-pollinated cultivars, lines and hybrids. The first experiment tested for resistance of 20 maize cultivars (10 white and 10 yellow-grained) developed for lowland Africa grown in three relatively weevil-free savanna locations. The second experiment tested two sets of diallel crosses without reciprocals of 66 F 1 progeny from 12 inbred lines and 78 F 1 crosses from 13 inbred lines of subtropical and temperate origins. Variables studied for the first experiment included husk cover, grain texture, number of egg plugs, number of weevils produced, and number of grains damaged by the weevil. Results showed highly significant differences among the 20 maize cultivars tested. Significant cultivar×location interactions for egg plug and weevil production indicate the importance of environmental effects and complexity in weevil resistance. Of the 20 cultivars tested, Ikenne 83-TZSR-W-1 (open pollinated) and 8329-15 (hybrid) were the most promising for restricted weevil production and minimal grain damage. The results of genetic studies in the second experiment with 144 crosses indicated the presence of genetic differences in maize lines to weevil attack. General combining ability (GCA) and specific combining ability mean squares were highly significant, suggesting that the maize weevil resistance was controlled by both additive and non-additive gene actions and the inheritance was quantitative and polygenic. Among the lines used in the crosses, the two most weevil resistant lines with high GCA effects were TZi 30 (International Institute of Tropical Agriculture) and FLA2BT 106 (Florida).

A Comparison of Pseudomonas solanacearum- resistant Tomato Cultivars as Hybrid Parents

Seven tomato Lycopersicon esculentum lines, `Venus', `Saturn', `Rodade', `Rotam 4', `Hawaii 7998', `UC-82B', and `Stevens', and their 21 crosses were evaluated for their ability to resist infection by seven virulent strains of Pseudomonas solanacearum E.F. Sm. representing race 1 biovars 1 and 3. The Gardner and Eberhart model III analysis was used to evaluate the response of lines in crosses to P. solunaceurum infection. General combining ability mean squares were significant for all strains and in 5 of 7 instances specific combining ability mean squares were significant. In four instances the parent vs. cross contrast was significant. `Hawaii 7998' was resistant to all seven strains of P. solanacearum, whereas `Rotam 4' and `Rodade' were resistant to biovar 3 and two races of biovar 1. `Venus' and `Saturn' were resistant to two other biovar 1 strains. `Hawaii 7998' transmitted greater resistance than the other resistant parents, but its small fruit size and indeterminate growth habit make it a poor choice for a hybrid parent.

Influence of plant age, disease incubation time, and host plant resistance on Verticillium wilt symptom expression in lucerne (Medicago sativa)

The most economical means to control Verticillium wilt in lucerne, caused by Verticillium albo-atrum, is through resistant cultivars. Most Verticillium wilt resistance evaluations use some form of root-cut-soak inoculation procedure. In Trial 1, three lucerne cultivars were inoculated at eight plant ages and plant symptoms were scored at ten successive weekly intervals. Trial 2 consisted of two cultivars inoculated at ten plant ages and symptoms were evaluated at eight weekly intervals. In an experiment to study the genetics of resistance to this pathogen, four plants showing no visual symptoms were selected from each of four germplasms. The selected populations were crossed in diallel fashion. The population crosses plus the parents were evaluated for resistance to V. albo-atrum. Results from Trial 1 and Trial 2 showed disease severity increased with increasing inoculation age and with increasing scoring age. Cultivar symptom expression interacted with inoculation age, but not with scoring age. The diallel analysis supported resistance to Verticillium wilt being conferred by additive gene action, as heterosis was not detected and general combining ability mean square was 3.75 times larger than the specific combining ability mean square.

Combining Ability Analyses of Fruit Yield and Quality in Near-homozygous Lines Derived from Cucumber

Abstract Combining ability estimates for characters relating to yield and fruit quality were undertaken to determine if lines derived from Cucumis sativus var. hardwickii (R.) Alef. (hardwickii) could be used in the development of higher-yielding commercial cucumbers. General and specific combining ability estimates were obtained in a North Carolina Design II experiment for nine near-homozygous processing cucumber (Cucumis sativus L.) lines, five of which were derived from hardwickii germplasm. Lines were evaluated under two planting densities (29,000 and 58,000 plants/ha) for three harvests, and environments sampled were two planting times (2 weeks apart within the same year). Traits evaluated included fruit number per plant, primary lateral branch number, percentage of pistillate flowers, days to anthesis, fruit length, and fruit length : diameter (L:D) ratio. General combining ability (GCA) mean squares were significant at both planting densities for all traits when combined over planting times, except for fruit L:D ratio at the higher density. Specific combining ability mean squares were significant for days to anthesis. Of the lines evaluated, WI 2963 and 4H261 produced the greatest GCA female and male effects, respectively, for three harvest yield and primary lateral branch number, but the lowest effects for fruit size. Our results suggest that further selection within these high-performance hardwickii derivatives for fruit shape will produce lines that perform well at a high planting density when crossed with sativus lines having good general combining ability.

Combining Ability of Tannin Content and Protein Characteristics of Raw and Cooked Dry Beans

Tannin in dry bean (Phaseolus vulgaris L.) seeds has been associated with low protein availability and digestibility. Protein losses may occur during soaking and cooking and lessen the potential nutritional benefit from eating beans. The aim of the present study was to evaluate general combining ability (GCA) and specific combining ability (SCA) effects on tannin content and protein characteristics of dry and cooked beans. A fixed‐effect model permitted the evaluation of parents for use in breeding programs to improve bean nutritional quality. Eight parents were crossed in diallel to produce the F2 and F3 generations on which combining ability mean squares and genetic effects were calculated. Tannin was determined by the vanillin‐HCl method and protein of dry and cooked beans was measured using an infrared reflectance instrument. Protein loss during soaking and cooking was determined by subtracting the protein in cooked beans from that in dry beans. Significant differences were detected among parents and progeny for all traits, indicating the presence of genetic variability. Mean squares for both GCA and SCA were significant, indicating the presence of additive and dominance effects in the populations. Ratios of GCA:SCA mean square components were greater than unity for all traits, indicating that GCA predominated. Maternal effects influenced tannin content. The distribution of points representing the parental arrays along the regression line of the Wr, Vr graph revealed that genes with partial dominance controlled tannin content. Genes for protein content of raw and cooked beans showed partial dominance in some cases and complete dominance in other cases. Genes controlling the protein loss trait had the property of complete dominance. Seed protein contents of raw and cooked beans were correlated but raw bean protein and tannin were not. Study results suggested that it is not feasible to simultaneously breed for multiple traits, except for seed protein of raw and cooked beans. Screening for raw bean protein and tannin content should be done independently.

Genetic analysis of anther culture response in maize

Response frequencies in maize (Zea mays L.) anthers cultured in vitro were examined in a diallel set of crosses among four commercial inbred lines. Significant differences among the genotypes were observed, with the crosses H99xFR16 and Pa91xFR16 displaying the highest responses. General (GCA) and specific (SCA) combining ability mean squares were calculated and determined to be highly significant. GCA effects among the parental lines were highest for FR16 and lowest for LH38. Nongenotypic, plant-toplant differences were also found to make a significant contribution to the overall variation observed. The results from this study indicate that parents which give rise to highly responsive hybrids can be identified and that genetic improvement is possible through selection.

Inheritance of Ripening Uniformity and Relationship to Crop Load in Blueberry Progenies

Abstract The intervals, in days, between 10%, 50%, and 90% ripened fruit, as well as crop load, were estimated over 2 years in progenies from a partial diallel cross among 17 blueberry (Vaccinium corymbosum L., V. angustifolium Ait., and V. corymbosum × V. angustifolium hybrids) parents. General combining ability (GCA) mean squares were highly significant for all ripening intervals and for crop load, while specific combining ability mean squares were nonsignificant, indicating a large proportion of additive genetic variance. Narrow-sense heritability estimates were about 0.50 for the three ripening intervals (10–50%, 50–90%, and 10–90%). Several parents had large positive GCA effects, indicating their contribution to a long ripening interval. Most progenies with large crop loads required >15 days between 10% and 90% ripened fruit. Despite the consistently positive relationship between ripening interval length and crop load, variation among families and the potential for within-family segregation suggest the possibility of obtaining genotypes with high yield potential and improved uniform ripening.

Southwestern Corn Borer Larval Growth on Corn Callus and its Relationship with Leaf Feeding Resistance1

Leaf feeding damage by the southwestern corn borer [Diatraea grandiosella (Dyar)] can significantly reduce corn (Zea mays L.) yields. Inbred lines with reistance to such damage have been developed; however, little information is available on the inheritance or basis of this resistance. Earlier investigations indicated a relationship between level of leaf feeding resistance of corn genotypes and growth of larvae on plants or on callus initiated from these genotypes. To gain additional information on the relationship between level of leaf feeding resistance and larval growth rate on corn callus, the F1 hybrid progeny of a six‐parent (three leaf feeding resistant and three susceptible inbred lines) diallel cross were evaluated for leaf feeding damage in field tests in 1982 and 1983 as well as larval growth on corn callus initiated from each of the 15 hybrids. Leaf feeding damage sustained by a hybrid and larval growth on callus of the hybrid were highly correlated (r = 0.81). Mean squares for general combining ability were highly significant for leaf feeding damage and larval growth rate on callus. The specific combining ability mean square was significant for larval growth rate on callus but not for leaf feeding damage. Larvae reared for 7 days on hybrids of two susceptible inbreds had a mean weight of 17.8 mg compared to 10.8 mg for larvae reared on hybrids of two resistant inbreds. The differences among hybrids in larval weights on callus and their high correlation with leaf feeding ratings indicate that weights might be used as an additional technique in selecting corn genotypes with resistance and investigating the basis of resistance.

Estimates of combining ability, reciprocal effects and heterosis for yield and yield components in a common bean diallel cross

SUMMARYA diallel crossing system involving two Pinto and two Kidney common bean (Phaseolus vulgarisL.) cultivars was evaluated in the field. Pin toes were significantly different from the Kidneys in seed yield and numbers of pods and seeds per plant and 100·seed weight. All the traits showed statistical significance among crosses and in comparisons involving parentalv.cross means. Heterosis values were large and significant for yield, numbers of pods and seeds per plant, number of seeds per pod and number of days from planting to flowering. The ratio of general to specific combining ability mean squares was low for yield, numbers of pods and seeds per plant and high for 100·seed weight and number of days to flowering. Significant reciprocal effects were found for seed yield and number of seeds per plant, but this effect was completely absent for 100·seed weight.

Evaluation of F1 Hybrid Tomato Cultivars for Earliness, Fruit Size, and Yield Using Diallel Analysis1

Abstract Twelve cultivars and one breeding line of tomatoes, (Lycopersicon esculentum Mill.) which varied in maturity from early to late cultivars, were crossed in a diallel to estimate general and specific combining ability for earliness, fruit size, and yield using Griffing's method II, model II. General combining ability mean squares for earliness at 3 stages expressed as growing degree days (GDD) (10–32°C); and for number of days were larger than specific combining ability mean squares except for the index of first flowering stage to first fruit set. Days from seeding to first flowering and of first fruit set to first ripe fruit were positively correlated with each other and with total earliness. However, days from first flowering to first fruit set was not correlated either with the period from first fruit set to first ripe fruit or with total earliness. Fruit sizes, measured at the 3 different times were positively correlated with each other and with overall average size. A positive correlation resulted between the September 1st and October 1st yields and total yield. There was no significant correlation between fruit size and yield. General and specific combining ability mean squares were estimated on August 1st, September 1st, and October 1st for fruit size and yield. Broad sense heritability estimates were high and narrow sense heritability estimates were low, for both fruit size and yield.

Combining ability estimates of sulfate uptake efficiency in maize

Plant root nutrient uptake efficiency may be expressed by the kinetic parameters, Vmax and Km, as well as by normal enzymatic reactions. These parameters are apparently useful indices of the level of adaptation of genotypes to the nutrient conditions in the soil. Moreover, sulfate uptake capacity has been considered a valuable index for selecting superior hybrid characterized by both high grain yield and efficiency in nutrient uptake. Therefore, the purpose of this research was to determine combining ability for sulfate uptake, in a diallel series of maize hybrids among five inbreds. Wide differences among the 20 single crosses were obtained for Vmax and Km. The general and specific combining ability mean squares were significant and important for each trait, indicating the presence of considerable amount of both additive and nonadditive gene effects in the control of sulfate uptake. In addition, maternal and nonmaternal components of F1 reciprocal variation showed sizeable effects on all the traits considered. A relatively high correlation was also detected between Vmax and Km. However, both traits displayed enough variation to suggest that simultaneous improvement of both Vmax and Km should be feasible. A further noteworthy finding in this study was the identification of one inbred line, which was the best overall parent for improving both affinity and velocity strategies of sulfate uptake.

Genetic variability of mineral concentrations in Festuca arundinacea Schreb.

Nine randomly chosen clones of tall fescue (Festuca arundinacea Schreb.) were mated in all possible combinations to determine the nature of genetic variation for Mg, Ca, K, and P concentrations in a broad genetic base population. General combining ability mean squares were significant for most variables, whereas specific combining ability mean squares were not significant in most instances indicating that additive genetic variance was more important. Genotype x year interactions were significant for most variables, suggesting that selection should be evaluated over many environments. Broad-sense heritability estimates based on parental and progeny variance components were generally high for P, K, Ca, and Mg but low for the ratio K/(Ca + Mg). Narrow-sense heritabilities for these minerals were close to the broad sense values since the additive genetic variance was the largest component of the total genetic variation. Correlations between mineral concentrations and herbage dry matter yield were low. It was concluded that adequate genetic variation exists to improve mineral concentration without altering herbage dry matter yields.

Inheritance of Husk Numbers and Ear Insect Damage in Maize1

Studies were made to determine the extent and genetic control of husk number variations in maize (Zea mays L.), and to test their association with ear insect resistance and response to environmental influences. Husk numbers were highly uniform within inbreds and single‐cross hybrids, ranging from 6 to 19. Twelve inbreds were chosen to represent this range for diallel and generation‐mean analyses. Analyses were made in Cali, Colombia, and in Waimanalo, Hawaii, of husk numbers from 10‐ and nine‐parent diallels. General combining ability (g.c.a.) mean squares were highly significant at both locations. Specific combining ability mean squares were also significant, but were exceeded by the g.c.a, values by ratios of 5.3 to 1 (Colombia) and 19.9 to 1 (Hawaii). Hybrids showed a significant positive heterotic effect of 11%, and array means correlated well with parental values (r = 0.93). Means and array means for the hybrids grown at both locations were also highly correlated (r = 0.94 and r = 0.86, respectively). F2 and backcross progenies of 10 crosses involving high ✕ low husk numbers were analyzed. Backcross progenies commonly reverted sharply toward parental means, and F2 and F1 means were quite similar. Environmental variability was high and narrow‐sense heritability estimates were low (average 24%). The Cuban Flint‐derived inbred CM111 (India) provided the best genetic source for increasing husk numbers, which is proposed as a practical and efficient alternative to selection for low insect injury for improved ear pest resistance.Damage by the larvae of ear insects was evaluated for earwrm (Heliothis zea Boddie) and fall armyworm [Spodoptera frugiperda (J. E. Smith)] in relation husk numbers in Hawaii and Colombia. Resistance was notably higher in tropical lowland types of maize with high husk numbers. Ear damage in Hawaii (largely earworm) correlated significantly (r = −0.40) with husk numbers that ranged from 6 to 14 in a broad‐based composite. Ear insect damage in Colombia (largely fall armyworm) also correlated significantly (r = −0.68) with husk numbers that ranged from 8.0 to 14.9 in a 45‐entry diallel. Husk numbers were highest for lowland tropical races of maize and lowest for temperate and montane races, correlating significantly (r = −0.71) with elevation at which the race was indigenous. It was concluded that ear pests provided strong selection pressure for higher husk numbers during evolution of maize. Environmental effects on husk numbers appeared solely to relate to temperature during growth, and a reduction of one husk was observed for a corresponding increase of 4 C in growing temperature during early growth.

Issues in Diallel Analysis

Critical issues in the use of diallel analysis are reviewed. From a statistical point of view the critical issue concerns the choice of a model with fixed or random genotypic effects. From a genetical point of view, two assumptions are critical in attempts to interpret the resuits of diallel analyses. The assumption concerning the independent distribution of genees in the parents is most critical to proper interpretation and seems to be least acceptable in actual practice. The second assumption, that there is no epistasis, may frequently be incorrect. Epistasis affects estimates of general and specific combining ability mean squares, variances, and effects in an unpredictable manner. As an alternative to genetic interpretation, the statistical description provided by dialiel analysis can be used to help answer questions concerning the importance of specific combining ability and the predictability of hybrid performance using general combining ability or parental performance.

Diallel Analysis of Ear Height and Associated Characters in Corn1

Early and late low ear corn (Zea mays L.) synthetics were developed by sib‐mating for lower ear height over 12 cycles of selection. Cycles 1, 3, 5, 7, 8, 9, and 10 were crossed in a diallel set for a study on inheritance of ear height and associated characters.Ear height was reduced an average of 3.20 cm per cycle in the early synthetic and 2.98 cm in the late synthetic. Plant height remained fairly constant in both synthetics. The plant‐to‐ear height ratio increased from 3.03 to 4.84 in the early synthetic and from 2.96 to 4.56 in the late synthetic.Lower ear placement was associated with a change from a fewer number of nodes below the ear to a greater number of nodes above the ear in both synthetics. Over 12 cycles of selection, ears were lowered more than one node in each synthetic. Therefore, the lower ear heights were due to placement on the stalk as well as shorter internodes.Large general combining ability mean squares indicated that the characters were controlled by additive gene action. Significant changes of the estimate of the general combining ability effects were less with each succeeding cycle of selection, indicating less progress in lowering ear height with each succeeding cycle.

Parental Inbreeding and Performance of Alfalfa Single‐crosses1

AbstractS2 and S4 progenies were obtained from 10 S0 parents each from ‘MSA‐W4’ and ‘MSB‐W4’ alfalfa (Medicago sativa L.). Two five‐parent diallel sets were attempted within S0, S2, and S4 parental generations in each cultivar. All but one of the sets with S2 and S4 parents gave incomplete diallels. First harvest dry matter yields were measured in small row plots during each of two growing seasons.Average yields of the S2−crosses were less than those of the S0−crosses in all sets. Individual exceptions to the average trend occurred in both populations, but more frequently in MSA‐W4 than in MSB‐W4. The number of S4−crosses was small, and the results with them were variable. Yields of all S4crosses in one set, which had one parent common to all crosses, were greater than yields of the corresponding S0 or S2−crosses. Other S4 crosses generally yielded less than the corresponding S0 or S2−crosses.Mean squares for both general (GCA) and specific combinnig ability (SCA) pooled over sets in MSA‐W4 increased from the S0 to the S2 parental generation. This increase was greater for SCA than for GCA. GCA was significant in the S2−crosses from MSB‐W4, but no combining ability mean square was significant in the S2 or S4−crosses from MSB‐W4.

Performance of Crosses Within and Between Two Diverse Sources of Birdsfoot Trefoil, Lotus corniculatus L.1

Nine clones derived from the cultivar ‘Empire’ and nine clones derived from two Russian introductions of birdsfoot trefoil (Lotus eorniculatus L.) were crossed in a partial diallel fashion, both within and between sources, to evaluate the influence of genetic diversity on expression of heterosis, to study combining ability of the parent clones, and to study interrelationships among characters that affect forage yield, seed size, and seed production. Sibmating was practiced in 16 F1 progenies to study breeding behavior in the second generation.In a space‐planted test, intersource F1 progenies yielded 14% more forage than intrasource progenies; however, they did not outyield crosses within the Russian source. General combining ability mean squares usually were considerably larger than specific combining ability mean squares. Full‐sib progenies derived from intersource crosses were superior to those from intrasource crosses in forage yield, winterhardiness, spring vigor, and pod production.High forage yield was closely associated with spring vigor and winterhardiness in F1 and full‐sib progenies and tended to be associated with a more prostrate growth habit and good pod production. Large seed size showed a low but significant association with low forage yield. Seed size was independent of pod production.

Combining Ability in Durum Wheat: I. Agronomic Characteristics1

The parents and 45 F1 and F2 populations from a diallel cross among 10 genetically diverse varieties or lines of durum wheat (Triticum durum Desf.) were evaluated at two locations in North Dakota in 1965. Parental, Fu and F2 populations of 17 of the 45 crosses were evaluated again in 1966 at one location. The traits studied were grain yield, number of tillers per unit area, kernels per spike, kernel weight, test weight, seedling vigor, maturity, height, and lodging.Heterosis percentages for grain yield in 1965, based on means of the higher parent of each cross, ranged from —19 to 84% for the F1's and from —23 to 26% for the F2's. Seventeen hybrids displayed significant heterosis for yield, but none was significantly higher than the check variety, ‘Wells.’ The best hybrid yielded 16 and 9% more than Wells when Wells was sown at 33 and 67 kg/ha, respectively. Heterosis also occurred for the other character studied. Twenty‐seven F2 populations yielded significantly less than their respective F1's.An estimate of genotype ✕ environment interaction was calculated for grain yield on the means of the 17 F1's, F2's, and parents for the crosses grown in 1965 and 1966. The analyses were based on mean values from three environments, Fargo 1965, Langdon 1965, and Fargo 1966. Genotype ✕ environment mean squares were significant for the F1 hybrids and parents, but nonsignificant for the F2 populations.General and specific combining ability mean squares were obtained from F1 and F2 populations grown in 1965. General combining ability mean squares were highly significant among F1's and among F2's for all nine characteristics.Specific combining ability mean squares among F1's were significant for kernel weight, test weight, and seedling vigor, and were significant among F2's for kernel weight, test weight, and lodging score. Maximum yields of durum wheat may be attainable only with a system that can exploit both additive and nonadditive genetic effects.

Inheritance of Resistance to Isolates of Fusarium oxysporum var. batatas in Burley Tobacco1,3

Two genetic experiments designed for diallel analysis and generation means analysis were utilized to study the nature of gene action conditioning resistance to four isolates of Fusarium oxysporum var. batatas in burley tobacco (Nicotiana tabacum L.). Plants were evaluated for their reaction as seedlings in the greenhouse. The diallel experiment, consisting of all possible crosses among five burley tobacco parents, was analyzed according to the procedures of Griffing and Jinks‐Hayman. The generation means experiment included the P1, P2, F1, F2, P1F1, and P2, F1 generations of the cross between ‘Kentucky 12’ and ‘Judy's Pride.’General combining ability mean squares and Hayman's D (additive component) were highly significant for each isolate. There was close association between the ranking of the parental entries for general combining ability effects and parental performance per se, indicating that predictions of Fl hybrid performance can be made from parental performance. The generation means analyses showed additive gene effects to be most important and dominance and epistatic effects to be relatively unimportant in the inheritance of resistance to each of the isolates and their mixture. Narrow‐sense heritability estimates indicated that rapid genetic advances through selection could be made for resistance to Fusarium wilt.