Inheritance of emergence time and seedling growth at low temperatures in four lines of maize

Summary The improvement of rate of seedling emergence and early seedling growth of maize (Zea mays L.) under cool conditions has been an objective of breeding programs in cool regions for many years. To study inheritance of emergence time, and to determine if differences in emergence time were due to differences in seedling growth, F₁, F₂ and backcross generations of a diallel cross of two rapidly emerging lines from CIMMYT Pool 5, 5-113 and 5-154, and two elite Corn Belt Dent lines, A619 and A632, were grown in controlled environment rooms at low temperatures.The lines from Pool 5 emerged significantly faster than A619 and A632 over a range of low temperature conditions. This difference occurred both when the lines themselves were tested and when the lines were tested as male and female parents in crosses. The Pool 5 lines converted a higher proportion of their original seed to new root and shoot tissue than did A619 and A632, indicating that they had a faster seedling growth rate. Primarily this was due to a faster loss of seed reserve, rather than a more efficient conversion process.A significant difference occurred between A619 and A632 for emergence time, but this was not due to a difference in seedling growth rate.Reciprocal differences occurred only in the F₁ generation in crosses involving A619, and then marked effects could be attributed to the male parent. Reciprocal differences tended to disappear in the F₂. This suggested that the genotype of the embryo and endosperm was of much greater importance than the genotype of the maternal parent in determining differences of time to emergence and seedling growth.Mid-parent heterosis occurred for time to emergence and seed loss, a measure of mean rate of utilization of seed reserve, in all crosses. High parent heterosis occurred in several crosses for these traits. High parent heterosis occurred in all crosses for efficiency of utilization of seed reserve.A generation means analysis indicated that both additive and dominance effects were present for rate of seedling growth in crosses between A632 and the Pool 5 lines.     

Genetics of tassel branch number in maize and its implications for a selection program for small tassel size

Summary Tassel branch numbers of six crosses of maize (Zea mays L.) were analyzed to determine inheritance of this trait. Generation mean analyses were used to estimate genetic effects, and additive and nonadditive components of variance were calculated and evaluated for bias due to linkage. Both narrow-sense and broad-sense heritabilities were estimated. Additive genetic variance estimates were significant in five of the six crosses, whereas estimates of variance due to nonadditive components were significant in only three crosses. Additionally, estimates of additive variance components usually were larger than corresponding nonadditive components. There was no evidence for linkage bias in these estimates. Estimates of additive genetic effects were significant in four of six crosses, but significant dominance, additive × additive and additive × dominance effects also were detected. Additive, dominance, and epistatic gene action, therefore, all influenced the inheritance of tassel branch number, but additive gene action was most important. Both narrow-sense and broadsense heritability estimates were larger than those reported for other physiological traits of maize and corroborated conclusions concerning the importance of additive gene action inferred from analyses of genetic effects and variances. We concluded that selection for smalltasseled inbreds could be accomplished most easily through a mass-selection and/or pedigree-selection system. Production of a small-tasseled hybrid would require crossing of two small-tasseled inbreds. We proposed two genetic models to explain unexpected results obtained for two crosses. One model involved five interacting loci and the other employed two loci displaying only additive and additive × additive gene action.Journal Paper No. J-9231 of the Iowa Agriculture and Home Economics Experiment Station, Ames, Iowa 50011. Project No. 2152     

Evaluation of inheritance to leaf rust in wheat using area under disease progress curve

Six varieties, Kundan (K), Galvez-87 (G), Trap (T), Chris (C), Mango (M) and PBW-348 (P) along with fast ruster, Agra Local (AL), were screened for seedling reaction and adult pant response to leaf rust. Seedlings of all six varieties were susceptible while adult plants showed lower susceptability response than Agra Local. The F1s among the varieties, and also with Agra Local, showed the values lesser than the respective mid parental values for AUDPC suggesting a polygenic mode of inheritance. ANOVA for combining ability effects indicated variation due to the GCA and SCA effects, which indicated that both additive as well as non-additive type of genetic variances, govern AUDPC. The higher values for the GCA variance over the SCA variance indicated the predominance of an additive component over the dominance component for AUDPC. Significant values for GCA effects indicated that Kundan, Galvez-87 and Trap can be used as good general combiners for AUDPC. The crosses, KxAL, GxAL and TxAL showed significant sca effects for AUDPC, which indicated the predominance of non-additive gene effects in these crosses. Additive x additive and dominance x dominance components of the 5- parameter model were highly significant and contributed maximum extent compared to the additive and dominance components in the cross KxG, while dominance and dominance x dominance components contributed maximum in the remaining crosses. Under such a situation, improvement in the character may be expected through standard selection procedure, which may first exploit the additive gene effects and simultaneously care should be taken to see that the dominance effects are not dissipated, but rather they should be concentrated.     

Inheritance of partial resistance to powdery mildew in spring wheat

Summary Four spring wheat (Triticum aestivum L.) cultivars exhibiting partial resistance to powdery mildew induced by Erysiphe graminis f.sp. tritici were crossed to a common susceptible cultivar to study the inheritance of resistance. The genetic parameters contributing to resistance were estimated by generation means analyses. Additive gene action was the most important genetic component of variation among generation means in all four crosses. Additive by additive effects were significant in one cross and both additive by additive and additive by dominance effects were significant in another. Dominance effects were not significant. The F2/F3 correlations in three crosses ranged from 0.27 to 0.43. Three additional crosses among resistant cultivars were employed to study the effectiveness of selection in improving resistance. By selecting the most resistant plants from the F2 and evaluating the progenies in the F4, increases in resistance ranging from 21% to 31% were obtained. In all crosses, there was transgressive segregation in both directions indicating that the genes conferring resistance to these cultivars differ and exhibit additive effects.     

Gene action for cold tolerance in chickpea

Summary Six crosses were investigated using combining ability and generation mean analyses for reaction to cold tolerance in chickpea (Cicer arietinum L.). The combining ability variances revealed the significance of both additive and nonadditive gene effects, with preponderance of additive gene effects. The generation mean analysis revealed the presence of genie interactions in addition to additive and dominance gene effects. Among the interactions, additive×additive and dominance×dominance with duplicate epistasis were present. Cold tolerance was dominant over susceptibility to cold. Selection for cold tolerance would be more effective if dominance and epistatic effects were reduced after a few generations of selfing.Joint contribution from ICARDA and ICRISAT (International Crops Research Institute for the Semi-Arid Tropics), Patancheru P.O., A.P. 502 324, India. ICRISAT JA No. 1239.     

Prediction of progeny variation in oat from parental genetic relationships

Summary The ability to predict agronomic performance of progeny from a cross would be a great benefit to plant breeders in selecting parents. The predictive value of parental genetic relationships estimating F₁ progeny means and F₄ family variances of nine argronomic traits was tested in 76 oat crosses, using genetic distance measures based on coefficients-of-parentage, quantitatively inherited morphological characters, and discretely inherited biochemical and morphological characters. Coefficients-of-parentage were better predictors of F₁ performance than similarity measures derived from plant morphology or discretely inherited characters. Combined distance measures were better estimators of F₁ specific combining ability (SCA) effects than any single measure. Among cultivars of similar adaptation and quantitative morphology, crosses between parents with high coefficients-of-parentage gave higher SCA effect values than crosses of distantly related parents for grain yield and total biomass. The opposite was found for crosses among cultivars of different adaptation or quantitative morphology. The best predictor of trait variances among F₄ families was coefficients-of-parentage. Crosses between more distantly related parents produced larger variances among families than crosses between closely related parents for plant biomass. For grain yield, test weight, heading date, grain filling period, and maturity date, crosses between more closely related parents produced larger among-family variances than crosses of distantly related parents. Crosses between more distantly related parents involved at least one parent unadapted to central New York, and resulted in most of the progeny being generally unadapted. This, in part, may account for the low genetic variances for heading date, test weight, and grain yield in crosses of distantly related parents.     

Combining ability analysis over F1-F5 generations in diallel crosses of bread wheat

Summary Combining ability studies for grain yield and its primary component traits in diallel crosses involving seven diverse wheat cultivars of bread wheat (Triticum aestivum L.) over generations F₁-F₅ are reported. The general and specific combining ability variances were significant in all generations for all the traits except specific combining ability variance for number of spikes per plant in the F₅. The ratio of general to specific combining ability variances was significant for all the traits except grain yield in all the generations. This indicated an equal role of additive and non-additive gene effects in the inheritance of grain yield, and the predominance of the former for its component traits. The presence of significant specific combining ability variances in even the advanced generations may be the result of an additive x additive type of epistasis or evolutionary divergence among progenies in the same parental array. The relative breeding values of the parental varieties, as indicated by their general combining ability effects, did not vary much over the generations. The cheap and reliable procedure observed for making the choice of parents, selecting hybrids and predicting advanced generation (F₅) bulk hybrid performance was the determination of breeding values of the parents on the relative performance of their F₂ progeny bulks.     

Segregation for somatic embryogenesis on stem-internode explants from potato seedlings

Differences in productivity for somatic embryos (SEs) in vitro among 18 potato cultivars and three wild Solanum species in an earlier study led to the hypothesis that regeneration of SEs may be under genetic control. To examine this possibility, three test crosses were initiated; Coastal Russet×AF 186-2; Costal Russet×Lenape; AF 186-2×Lenape. True potato seedlings from these crosses were germinated in vitro. Five stem internode explants from each seedling were excised and cultured on two successive media to promote the formation of SEs. Seedling explants Costal Russet×AF 186-2 cross produced more SE than the other two crosses, and explants from the AF 186-2×Lenape cross generally only produced <10 SEs per explant. SEs were produced on the stem-internode explants from the three crosses at different rates. Data for the number of explants producing SEs and numbers of SEs per explant were highly significant. Regeneration of SEs is probably under nuclear control and the inheritance for regeneration may be quite straightforward. This revised version was published online in June 2006 with corrections to the Cover Date.     

Generation means analysis for productivity in two diverse peanut crosses

Summary Utilization of exotic germplasm resources for population improvement in peanut (Arachis hypogaea L.) has increased as the need to increase genetic diversity among peanut cultivars was recognized. Progeny of crosses of two unadapted germplasm lines (GP-NC 343 and FESR-11-P11-32) with an adapted cultivar (NCV11) of peanut were evaluated for the genetic factors influencing the inheritance of yield and fruit characters in crosses among diverse lines. Objectives were to (1) estimate the relative importance of additive and nonadditive genetic effects in the inheritance of yield and fruit characters in two diverse peanut crosses; (2) determine the proportion of exotic germplasm that gave the optimum combination of mean productivity and genetic variability for each of the crosses; (3) relate the results to theories regarding the transfer of desirable alleles from exotic germplasm into adapted breeding populations. Crosses and backcrosses were made to generate germplasm lines (ten generations) ranging from 0 to 100% exotic germplasm for each cross. The populations were evaluated in replicated field trials. Yield and six fruit characters were measured, and a weighted analysis of variance was conducted to determine if significant differences existed among generations. Generation means analyses were performed for each trait measured in each of the crosses using both three- and six-parameter models, which were tested for goodness-of-fit with a joint-scaling test. Significant differences were detected among generations for most traits measured in both crosses. Estimates of additive genetic effects were significant for pod weight and seed weight in cross 1 (NC-V11 x GP-NC 343) and for all traits in cross 2 (NC-V11 x FESR-11-P11-32) except seedpod ratio. Significant estimates of dominance effects were found for pod length, pod width, and pod weight in cross 1 and for pod length in cross 2. No significant estimates of digenic effects were observed in cross 1, whereas in cross 2 estimates of additive x dominance epistatic effects were significant for yield and pod length, while estimates of additive x additive effects were significant for seed number. Regression of trait means on generations showed a curvilinear response for all traits in cross 1 except seed weight, which gave a linear response. For all traits in cross 2, the relationship between productivity and proportion of unadapted germplasm was effectively linear. Based on generation means and variances, progeny from the first or second backcross generation to the recurrent parent should be expected to give an optimum combination of mean productivity and relative variability in the population.The research reported in this publication was funded in part by the North Carolina Agricultural Research Service     

Combined genetic analysis of partial blast resistance in an upland rice population and recurrent selection for line and hybrid values

The CNA-IRAT 5 upland rice population has been improved for 4 years by recurrent selection for blast resistance in Brazil. In order to predict the efficiency of recurrent selection in different test systems and to compare the relative advantage of hybrids versus pure line breeding, a combined genetic analysis of partial blast resistance in the CNA-IRAT 5 population was undertaken. A three-level hierarchical design in inbreeding and a factorial design were derived from the base population. Partial blast resistance of lines and hybrids was evaluated in the greenhouse and in the field by inoculation with one virulent blast isolate. The means and genetic variances of the hybrids and lines were estimated. Genetic advance by recurrent selection was predicted from estimates of variance components. The inheritance of partial blast resistance was mainly additive but non-additive effects were detected at both levels of means and variances. Mean heterosis ranged from 4%–8% for lesion size and lesion density to 10–12% for leaf and panicle resistance. High dominance or homozygous dominance variances relative to additive variance and negative covariance between additive and homozygous dominance effects were estimated. A low frequency of favourable alleles for partial resistance would explain the observed organisation of genetic variability in the base population. Recurrent selection will efficiently improve partial blast resistance of the CNA-IRAT 5 population. Genetic advance for line or hybrid values was expected to be higher testing doubled haploid lines than S1 lines, or than general combining ability. Two components of partial resistance assessed in the greenhouse, lesion size and lesion density, could be used as indirect selection criteria to improve field resistance. On the whole, hybrid breeding for partial blast resistance appeared to be slightly more advantageous than pure line breeding.     

Chloroplast DNA inheritance in theStellaria longipes complex (Caryophyllaceae)

Inheritance of chloroplast DNA (cpDNA) was examined in F₁ progenies derived from three crosses and three corresponding reciprocal crosses betweenStellaria porsildii andS. longifolia. Chloroplast DNA restriction fragments were analyzed using methods of nonradioactive digoxigenin-11-dUTP labeling and chemiluminescent detection with Lumi-Phos 530. Distinct interspecific restriction fragment polymorphisms were identified and used to demonstrate the mode of cpDNA inheritance. Mode of cpDNA inheritance differed among crosses. Two crosses in whichS. porsildii, SP2920-21, was the maternal parent exhibited three different types of plastids, maternal, paternal and biparental, among the F₁ hybrids, suggesting a biparental cpDNA inheritance and plastid sorting-out inStellaria.     

Segregating random amplified polymorphic DNAs (RAPDs) in Betula alleghaniensis

Summary Molecular markers are currently being developed for Betula alleghaniensis Britton using random amplified polymorphic DNA (RAPD). Arbitrarily designed 11-mer primers were tested on three intraspecific controlled crosses for which more than 15 full-sibs were available. Using two of these primers, we were able to genetically characterize a total of nine polymorphic RAPD markers. Segregation of these markers was consistent with a biparental diploid mode of inheritance, and all appeared dominant. RAPDs were valuable in detecting contaminants and, therefore, in assessing the validity of controlled crosses. Limitations of the technique are discussed in relation to the determination of parental genotypes and construction of linkage maps for hardwood species.     

Analysis of recombination rate in female and male gametogenesis in pearl millet (Pennisetum glaucum) using RFLP markers

Sex as a factor affecting recovered recombination in plant gametes was investigated in pearl millet, Pennisetum glaucum, by using reciprocal three-way crosses [(AxB)xCvCx(A x B)]. The two populations were mapped at 42 loci pre-selected to cover the majority of the genome. No differences in recombination distances were observed at the whole-genome level and only a few individual linkage intervals were found to differ, all in favour of increased recombination through the male. Distorted segregations found in the three-way crosses provide evidence of post-gametic selection for particular gene(s) or chromosome regions. The significance of these results for the design of pearl millet breeding programmes and inheritance experiments, as well as for other experimental strategies, is discussed.     

Genetic basis of resistance to zonate leaf spot disease in forage sorghum

Summary Generation mean analysis was carried out for ten crosses between two resistant and two susceptible parents to find the genetic basic of resistance to zonate leaf spot disease in forage sorghum. In all crosses except one, at least one type of non-allelic interaction was present. Both additive and dominance gene effects were significant for most crosses. Duplicate type epistasis was present for the inheritance of this disease. Resistance to this disease revealed overdominance. Appropriate breeding plans were suggested to exploit the disease resistance.     

Paternal inheritance of chloroplast DNA in Larix

Restriction enzyme analysis was used to determine the inheritance of chloroplast DNA in conifers. The plant material studied included five individual trees of European larch (Larix decidua Mill.) and Japanese larch (Larix leptolepis Sieb. & Zucc.) and six hybrids from controlled crosses between these species. The chloroplast DNA fragment patterns generated by Bam-HI and Bcl-I were species-specific. Paternal inheritance of chloroplast DNA patterns was found in most Larix crosses. One hybrid showed maternal chloroplast DNA patterns. In addition, two other hybrids had mixed Bam-HI patterns suggesting recombination between maternal and paternal chloroplast DNA. The mechanisms favoring paternal inheritance in conifers are not known. Paternal inheritance of chloroplast DNA is suggested it to be a general phenomenon in conifers.     

Spatial patterns of tree seedling establishment and their relationship to environmental variables in a cold-temperate deciduous forest of eastern North America

Patterns of seedling recruitment may have persistent effects on population and community processes. Assuming seed availability is not limiting, the environmental sieve (i.e., the suite of factors influencing seed germination and seedling emergence and survival) determines how many seedlings establish and, most importantly, where they do so. In this study, we identify the spatial structure of some resources and abiotic conditions known to be significant for tree seedling emergence and survival and determine how these environmental factors influence the establishment of Fagus grandifolia, Acer saccharum, Fraxinus americana, and Ostrya virginiana in a deciduous forest of southern Québec (Canada). We expect an increase from Fagus, through Acer and Fraxinus, to Ostrya in the control of environmental variables on seedling emergence and survival, because of differences in the seed size of these species. Density of newly-emerged seedlings of all four species showed positive spatial autocorrelation at distances of up to ca. 10 m. Environmental variables were also structured at the same spatial scale, except for soil moisture. Acer seedling emergence pattern was positively correlated to photosynthetic photon flux density (PPFD), and the pattern of Fraxinus to soil N and moisture. Seedling survival was not spatially autocorrelated for any of the four species, although it was positively density-dependent in Acer and Fagus. In only Ostrya was seedling survival correlated (positively) to one of the environmental variables studied, i.e., PPFD. Overall, environmental variables were spatially less heterogeneous than seedling emergence and survival. Either seed availability was not saturating or factors not considered here, such as competition and predation (the intensity of which often varies with resources and/or abiotic conditions), modified the influence that the physical environment had on patterns of seedling establishment. Our prediction of a greater environmental control on seedling emergence and survival in small-seed species was not totally confirmed.     

Patterns of inheritance of mating signals in interspecific hybrids between sailfin and shortfin mollies (Poeciliidae: Poecilia: Mollienesia)

Differences in male morphology and mating behaviors are thought to confer species sexual isolation between sailfin and shortfin species of mollies. This study used interspecific crosses between the sailfin molly, P. latipinna, and the shortfin molly, P. mexicana, to investigate patterns of inheritance of morphological traits and behavioral rates of three mating behaviors in F1 hybrid males. The two parental species showed clear species differences with respect to the length of the dorsal fin and dorsal fin ray number. First generation hybrid males were intermediate between the two parental species for dorsal fin length and fin ray number, suggesting autosomal control of this trait with little effect of dominance by genes from either parental species. Parental species showed clear species differences in their rates of courtship displays. Unlike the pattern for dorsal fin morphology, F1 hybrid males showed a clear distinction in display rates with respect to the direction of the interspecific cross. Male hybrids whose sires were P. latipinna had courtship display rates that were up to three times higher than the rates of displays performed by hybrid males whose fathers were P. mexicana. The distribution of phenotypes between the parental species and that of hybrid males sired by that parental species was nearly identical. Such a pattern suggests the influence of Y-linked genes on the inheritance of courtship display rates in mollies.     

甘蔗生物量育种的ADGE遗传分析

对甘蔗11个亲本品种及不完全双列杂交(NCdesignⅡ)遗传设计的30个组合的F1代实生苗生物量进行加性-显型-随机环境效应模型(ADGE)分析。结果表明:甘蔗的生物量性状遗传主要是由基因的加性、显性及加性×环境互作效应共同决定的,但基因的加性效应作用较大;甘蔗杂交亲本对其后代表型的遗传作用主要为母本的遗传效应影响;甘蔗生物量性状都具有较高的广义遗传率(h2B)和狭义遗传率(h2N),且h2B>h2N,说明了对甘蔗生物量性状在选育种早期阶段的选择效果好;通过对亲本的加性基因随机效应分析的综合,较优良的甘蔗亲本有粤糖72/426、粤糖79/177、粤糖85/177、ROC24和ROC25;根据杂交组合显性随机效应分析,认为粤糖72/426×ROC16、粤糖79/177×ROC24、粤糖79/177×ROC23及粤糖80/101×ROC22是较优良的高生物量甘蔗杂交组合,可以应用于甘蔗的高生物量育种。     

Generation mean analyses for flowering and maturity in Indian mustard (Brassica junces (L.) Czern & Coss)

Summary Components of generation means were partitioned for days to flower initiation and maturity in three crosses of Indian mustard (Brassica juncea (L.) Czern and Coss) cultivars. A linked digenics model was adequate for flowering in cross II and maturity in Cross I. All three types of digenic interactions among the linked pairs of genes, additive X additive (i), additive X dominance (j) and dominance X dominance (1), contributed significantly in the inheritance of flowering in cross II and maturity in cross I. A complete association among the genes of greater effects in higher mean parent was detected for flowering in cross II and maturity in Cross I. Duplicate epistasis was evident for flowering in Crosses I and II and maturity in Crosses I and III.Inadequacy of all the fitted models for days to flowering in Cross III and maturity in Cross II indicated the presence of higher order interactions.Part of PhD (plant breeding) Thesis, submitted by senior author to GBPUAT, Pantnagar (Nainital) U.P., India (unpublished). Research paper No. 4262     

Genetic analysis of larval survival and larval growth of two populations of Leptinotarsa decemlineata on tomato

The genetics of adaptation to tomato in Leptinotarsa decemlineata (Say) were investigated in reciprocal F₁, F₂, and backcross populations generated from crosses between beetles from a tomato adapted population and from a population that was poorly adapted to tomato. Larvae from the parent and test populations were reared on tomato for four days, after which survivorship and larval weights were recorded. Most results indicate that differences in larval growth and survival on tomato between the parent populations are largely determined by autosomal, polygenic mechanisms, the inheritance of which involves a significant dominance component. However, results from F₂ crosses are not consistent with this conclusion. A significant difference in larval weights, but not in survival, between reciprocal F₁ populations in an analysis of combined data from four separate experiments suggests that maternal cytoplasmic effects may contribute to differences in larval performance on tomato between the adapted and unadapted populations. The unusual results obtained from F₂ crosses in this study are not atypical of results from previous studies of the genetics of adaptation to host plants by the Colorado potato beetle. Host plant adaptation by Colorado potato beetles may therefore involve unusual genetic mechanisms that are not easily assessed by classical Mendelian analysis.