Prediction of testcross means and variances among F3 progenies of F1 crosses from testcross means and genetic distances of their parents in maize

 Prediction of the means and genetic variances in segregating generations could help to assess the breeding potential of base populations. In this study, we investigated whether the testcross (TC) means and variances of F₃ progenies from F₁ crosses in European maize can be predicted from the TC means of their parents and F₁ crosses and four measures of parental genetic divergence: genetic distance (GD) determined by 194 RFLP or 691 AFLP^{TM 1} markers, mid-parent heterosis (MPH), and absolute difference between the TC means of parents (∣P₁−P₂∣). The experimental materials comprised six sets of crosses; each set consisted of four elite inbreds from the flint or dent germplasm and the six possible F₁ crosses between them, which were evaluated for mid-parent heterosis. Testcross progenies of these materials and 20 random F₃ plants per F₁ cross were produced with a single-cross tester from the opposite heterotic group and evaluated in two environments. The characters studied were plant height, dry matter content and grain yield. The genetic distance between parent lines ranged between 0.17 and 0.70 for RFLPs and between 0.14 and 0.57 for AFLPs in the six sets. Testcross-means of parents, F₁ crosses, and F₃ populations averaged across the six crosses in a particular set generally agreed well for all three traits. Bartlett’s test revealed heterogeneous TC variances among the six crosses in all sets for plant height, in four sets for grain yield and in five sets for dry matter content. Correlations among the TC means of the parents, F₁ crosses, and F₃ populations were highly significant and positive for all traits. Estimates of the TC variance among F₃ progenies for the 36 crosses showed only low correlations with the four measures of parental genetic divergence for all traits. The results demonstrated that for our material, the TC means of the parents or the parental F₁ cross can be used as predictors for the TC means of F₃ populations. However, the prediction of the TC variance remains an unsolved problem. Received: 4 August 1997 / Accepted: 17 November 1997     

A method to establish an “immortalized F2” sporophyte population in the economic brown alga Undaria pinnatifida (Laminariales: Alariaceae)

Studies of quantitative trait loci based on genetic linkage maps require the establishment of a mapping population. Permanent mapping populations are more ideal than temporary ones because they can be used repeatedly. However, there has been no reported permanent sporophyte population of economically important kelp species. Based on the characteristics of the kelp life cycle, we proposed a method to establish, and then constructed experimentally, an “immortalized F₂” (IF₂) population of Undaria pinnatifida. Doubled-haploid “female” and “male” sporophytes were obtained through the parthenogenesis of a female gametophyte clone and the selfing of a “monoicous” gametophyte clone (originally male), respectively, and they were used as the parents. The F₁ hybrid line was generated by crossing the female and male gametophytes derived from the respective female and male parents. Full-sibling F₂ gametophyte clones, consisting of 260 females and 260 males, were established from an F₁ hybrid sporophyte. Thirty-five females and 35 males were randomly selected and paired to give rise to an IF₂ population containing 35 crossing lines. A parentage analysis using 10 microsatellite markers confirmed the accuracy of the IF₂ population and indicated the feasibility of this method. This proposed method may be adapted for use in other kelp species, and thus, it will be useful for genetic studies of kelp.     

A comparative analysis of biparental mating and selfing in pearl millet (Pennisetum typhoïdes) S & H

Summary A study was made of the nature of variation and changes in association for characters related to yield, development and disease resistance in two sets of progenies one set derived through biparental mating (A-series) and the other by traditional inbreeding (selfing) from the F₂ onwards (T-series), in a 22 × 22 diallel of dwarf derivatives of Pennisetum typhoides S & H. Comparison of means and variances within and between the two groups of progenies (A and T-series) and with those of released hybrids (HB-1, HB-2, HB-3, HB-4) for seventeen characters (six related to development, six to productivity, three to vegetative growth and one each to earliness and disease incidence) showed significant variation among the lines of the two series for synchrony of tillering, earliness, disease incidence, chlorophyll depth, grain hairiness, tiller number, plant height, length of earhead, grain yield and grain weight. The A-series selections were significantly superior to the T-series for most of the characters, indicating the effectiveness of selection in biparental matings compared with selection in selfed progenies for these traits. Many of the A-series (220 out of 800) selections were also superior to the existing released hybrids.Changes in the magnitude and nature of association among twelve important characters in the two populations were more favourable in the biparental matings: of 66 possible correlation coefficients examined, 25 cases were found with changes in favour of selections from biparental matings (A-series). These changes were probably due to the breakage of unfavourable linkages and changes in phase of linkage, and indicate the usefulness of biparental matings in the simultaneous improvement of the population for several attributes.     

Mapping QTLs with digenic epistasis under multiple environments and predicting heterosis based on QTL effects

Mixed linear model approach was proposed for mapping QTLs with the digenic epistasis and QTL by environment (QE) interaction as well as additive and dominant effects. Monte Carlo simulations indicated that the proposed method could provide unbiased estimations for both positions and genetic main effects of QTLs, as well as unbiased predictions for QE interaction effects. A method was suggested for predicting heterosis based on individual QTL effects. The immortalized F₂ (IF₂) population constructed by random mating among RI or DH lines is appropriate for mapping QTLs with epistasis and their QE interaction. Based on the models and methodology proposed, we developed a QTL mapping software, QTLMapper 2.0 on the basis of QTLmapper 1.0, which is suitable for analyzing populations of DH, RIL, F₂ and IF₂. Data of thousand grain weight of IF₂ population with 240 lines derived from elite hybrid rice Shanyou 63 were analyzed as a worked example.     

Analysis of a combined F1/F2 diallel cross in wheat

Analysis of a conventional diallel cross offers only perfect-fit estimates of the genetic components of variation, but no test for the goodness of fit of the model based on these estimates. When F₂ progenies are available, however, combining F₁ and F₂ diallels in a single experiment overcomes these problems. Least-squares estimates of these components can be calculated, errors attached to them and the goodness of fit of the resultant model tested. This analysis was applied to data on the severity of yellow rust infection in an F₁/F₂ half-diallel cross among eight bread wheat lines adapted to the East African highlands. After removing two interacting arrays, genetic analysis indicated that an additive/dominance model of gene action satisfactorily explained the variation observed among the remaining six parents and their progenies, in both the individual F₁ and F₂ diallels and the combined F₁/F₂ diallel. Resistance to yellow rust was dominant to susceptibility and genes for increased resistance were more frequent. Received: 25 May 2000 / Accepted: 31 July 2000     

Characterization of two cDNA clones encoding isozymes of the F1F0-ATPase inhibitor protein of rice mitochondria

Two cDNA clones encoding F₁F₀-ATPase inhibitor proteins, which are loosely associated with the F₁ part of the mitochondrial F₁F₀-ATPase, were characterized from rice (Oryza sativa L. cv. Nipponbare). A Northern hybridization showed that the two genes (designated as IF ₁ -1 and IF ₁ -2) are transcribed in all the organs examined. However, the steady-state mRNA levels varied among organs. A comparison of the deduced amino acid sequences of the two IF ₁ genes and the amino acid sequence of the mature IF₁ protein from potato revealed that IF₁-1 and IF₁-2 have N-terminal extensions with features that are characteristic of a mitochondrial targeting signal. To determine the subcellular localization of the gene products, the IF₁-1 or IF₁-2 proteins were fused in frame to the green fluorescent protein (GFP) or the fused GFP-β-glucuronidase, and expressed transiently in onion or dayflower epidermal cells. Localized fluorescence was detected in mitochondria, confirming that the two IF₁ proteins are targeted to mitochondria. Received: 9 July 1999 / Accepted: 17 August 1999     

Genetic analysis of vertical root pulling resistance (VRPR) in maize using two genetic populations

Root traits are important in improving nutrient and water use efficiency. Vertical root pulling resistance (VRPR) has been shown to be closely related to root system characteristics in maize (Zea mays L.). In the present study, two genetic populations derived from the same parents, one containing 218 recombinant inbred lines (RILs) and the other containing 187 advanced backcross BC₄F₃ lines, were genotyped using 184 SSR markers and evaluated for VRPR, grain yield (GY), stover yield (SY), and nitrogen uptake (N_up) under field conditions over 2 years. Our aims were (1) to locate QTLs associated with VRPR, SY, GY, and N_up, (2) to determine whether QTL detection is consistent between the BC₄F₃ and RIL populations, and (3) to identify backcross lines harboring favorable VRPR QTLs for use in future breeding programs. Using composite interval mapping (CIM), 12 and 17 QTLs were detected in BC₄F₃ and RIL populations, respectively. An important QTL region in bin 6.02 within the interval umc1006-umc1257 was found to control VRPR, SY, and N_up in both populations. These favorable alleles were contributed by the large-rooted parent Ye478. A significant positive correlation was detected between VRPR, SY, and N_up, but not between VRPR and GY. Backcross lines harboring VRPR QTLs could be useful germplasm for developing near isogenic lines (NILs) and for map-based cloning of genes controlling root growth.     

Estimation of in situ mating systems in wild sorghum (Sorghum bicolor (L.) Moench) in Ethiopia using SSR-based progeny array data: implications for the spread of crop genes into the wild

Because transgenic sorghum (Sorghum bicolor L.) is being developed for Africa, we investigated the potential for transgenes to spread to conspecific wild/weedy sorghum populations in Ethiopia, which is considered the centre of origin of cultivated sorghum. In the current study, the extent of outcrossing, and uniparental and biparental inbreeding were investigated in seven wild/weedy sorghum populations collected at elevations ranging from 631 to 1709 m. Based on allele frequency data of 1120 progenies and 140 maternal plants from five polymorphic microsatellite markers, outcrossing rates were estimated using standard procedures. The average multilocus outcrossing rate was 0.51, with a range of 0.31–0.65 among populations, and the family outcrossing rate was in the extreme range of 0 to 100%. The highest outcrossing (t _m?=?0.65) was recorded in a weedy population that was intermixed with an improved crop variety in Abuare (Wello region). It was also observed that the inbreeding coefficient of the progenies (F _p) tend to be more than the inbreeding coefficient of both their maternal parents (F _m) and the level of inbreeding expected at equilibrium (F _eq), which is a characteristic of predominantly outbreeding species. Biparental inbreeding was evident in all populations and averaged 0.24 (range = 0.10–0.33). The high outcrossing rates of wild/weedy sorghum populations in Ethiopia indicate a high potential for crop genes (including transgenes) to spread within the wild pool. Therefore, effective risk management strategies may be needed if the introgression of transgenes or other crop genes from improved cultivars into wild or weedy populations is deemed to be undesirable.     

Impact of biparental mating on correlation coefficients in bread wheat

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

Regulation of mitochondrial structure and function by the F1Fo-ATPase inhibitor protein, IF1

When mitochondrial respiration is compromised, the F₁F_o-ATP synthase reverses and consumes ATP, serving to maintain the mitochondrial membrane potential (Δψ_m). This process is mitigated by IF₁. As little is known of the cell biology of IF₁, we have investigated the functional consequences of varying IF₁ expression. We report that, (1) during inhibition of respiration, IF₁ conserves ATP at the expense of Δψ_m; (2) overexpression of IF₁ is protective against ischemic injury; (3) relative IF₁ expression level varies between tissues and cell types and dictates the response to inhibition of mitochondrial respiration; (4) the density of mitochondrial cristae is increased by IF₁ overexpression and decreased by IF₁ suppression; and (5) IF₁ overexpression increases the formation of dimeric ATP synthase complexes and increases F₁F_o-ATP synthase activity. Thus, IF₁ regulates mitochondrial function and structure under both physiological and pathological conditions.     

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.     

IF<Subscript>1</Subscript> distribution in HepG2 cells in relation to ecto–F<Subscript>0</Subscript>F<Subscript>1</Subscript>ATPsynthase and calmodulin

F₀F₁ATPsynthase is now known to be expressed as a plasma membrane receptor for several extracellular ligands. On hepatocytes, ecto–F₀F₁ATPsynthase binds apoA–I and triggers HDL endocytosis concomitant with ATP hydrolysis. Considering that inhibitor protein IF₁ was shown to regulate the hydrolytic activity of ecto–F₀F₁ATPsynthase and to interact with calmodulin (CaM) in vitro, we investigated the subcellular distributions of IF₁, calmodulin (CaM), OSCP and β subunits of F₀F₁ATPsynthase in HepG2 cells. Using immunofluorescence and Western blotting, we found that around 50% of total cellular IF₁ is localized outside mitochondria, a relevant amount of which is associated to the plasma membrane where we also found Ca²⁺–CaM, OSCP and β. Confocal microscopy showed that IF₁ colocalized with Ca²⁺–CaM on plasma membrane but not in mitochondria, suggesting that Ca²⁺–CaM may modulate the cell surface availability of IF₁ and thus its ability to inhibit ATP hydrolysis by ecto–F₀F₁ATPsynthase. These observations support a hypothesis that the IF₁–Ca²⁺–CaM complex, forming on plasma membrane, functions in the cellular regulation of HDL endocytosis by hepatocytes.     

Spontaneous aggregation of the mitochondrial natural ATPase inhibitor in salt solutions as demonstrated by gel filtration and neutron scattering. Application to the concomitant purification of the ATPase inhibitor and F1-ATPase

(1) The natural ATPase inhibitor (IF₁) from beef heart mitochondria has a tendency to form aggregates in aqueous solutions. The extent of aggregation and the structure of the aggregates were assessed by gel filtration and small-angle neutron scattering. IF₁ polymerization was found to depend on the salt concentrations, pH of the medium and concentration of IF₁. The higher the salt concentration, the lower the aggregation state. Aggregation of IF₁ was decreased at slightly acidic pH. It increased with the concentration of IF₁ as expected from the law of mass action. (2) Neutron scattering showed the aggregation of IF₁ in 2 M ammonium sulfate solutions. The predominant species is the dimer which has a somewhat elongated shape. (3) The Sephadex G-50 chromatography that is supposed to deprive beef heart submitochondrial particles of loosely bound IF₁ (Racker, E. and Horstman, L.L. (1967) J. Biol. Chem. 242, 2547–2551) was shown to have a limited effectiveness as a trap for IF₁. The reason was that IF₁ released from the particles formed high molecular weight aggregates that were not separated from the membrane vesicles by Sephadex G-50 chromatography. (4) The above observations provide the basis for a simple method of purification of beef heart IF₁ which combines the recovery of the supernatant from submitochondrial particles with the last three steps of the IF₁ preparation described by Horstman and Racker (J. Biol. Chem. (1970) 265, 1336–1344). The particles recovered in the sediment were deprived of IF₁ and could therefore be used for preparation of F₁-ATPase. The advantage of this method is that both IF₁ and F₁-ATPase can be prepared from the same batch of mitochondria.     

IF1 limits the apoptotic-signalling cascade by preventing mitochondrial remodelling

Mitochondrial structure has a central role both in energy conversion and in the regulation of cell death. We have previously shown that IF₁ protects cells from necrotic cell death and supports cristae structure by promoting the oligomerisation of the F₁F_o-ATPsynthase. As IF₁ is upregulated in a large proportion of human cancers, we have here explored its contribution to the progression of apoptosis and report that an increased expression of IF₁, relative to the F₁F_o-ATPsynthase, protects cells from apoptotic death. We show that IF₁ expression serves as a checkpoint for the release of Cytochrome c (Cyt c) and hence the completion of the apoptotic program. We show that the progression of apoptosis engages an amplification pathway mediated by: (i) Cyt c-dependent release of ER Ca²⁺, (ii) Ca²⁺-dependent recruitment of the GTPase Dynamin-related protein 1 (Drp1), (iii) Bax insertion into the outer mitochondrial membrane and (iv) further release of Cyt c. This pathway is accelerated by suppression of IF₁ and delayed by its overexpression. IF₁ overexpression is associated with the preservation of mitochondrial morphology and ultrastructure, consistent with a central role for IF₁ as a determinant of the inner membrane architecture and with the role of mitochondrial ultrastructure in the regulation of Cyt c release. These data suggest that IF₁ is an antiapoptotic and potentially tumorigenic factor and may be a valuable predictor of responsiveness to chemotherapy.     

Mixed linear model approach for mapping quantitative trait loci underlying crop seed traits

The crop seed is a complex organ that may be composed of the diploid embryo, the triploid endosperm and the diploid maternal tissues. According to the genetic features of seed characters, two genetic models for mapping quantitative trait loci (QTLs) of crop seed traits are proposed, with inclusion of maternal effects, embryo or endosperm effects of QTL, environmental effects and QTL-by-environment (QE) interactions. The mapping population can be generated either from double back-cross of immortalized F₂ (IF₂) to the two parents, from random-cross of IF₂ or from selfing of IF₂ population. Candidate marker intervals potentially harboring QTLs are first selected through one-dimensional scanning across the whole genome. The selected candidate marker intervals are then included in the model as cofactors to control background genetic effects on the putative QTL(s). Finally, a QTL full model is constructed and model selection is conducted to eliminate false positive QTLs. The genetic main effects of QTLs, QE interaction effects and the corresponding P-values are computed by Markov chain Monte Carlo algorithm for Gaussian mixed linear model via Gibbs sampling. Monte Carlo simulations were performed to investigate the reliability and efficiency of the proposed method. The simulation results showed that the proposed method had higher power to accurately detect simulated QTLs and properly estimated effect of these QTLs. To demonstrate the usefulness, the proposed method was used to identify the QTLs underlying fiber percentage in an upland cotton IF₂ population. A computer software, QTLNetwork-Seed, was developed for QTL analysis of seed traits.     

Correlation studies on yield and fibre traits in upland cotton (Gossypium hirsutum L.)

Summary Two diverse parents of upland cotton namely J.34 and I.C. 1926 were crossed. A comparison between biparental intermated progenies and F₃ families indicated alteration of correlation coefficient between yield and halo length. The significant negative correlation in F₃ population between these two attributes changed to a positive but non significant one in biparental intermated progenies. A change in correlation coefficients was expected due to breakage of linkage upon intermating. An increase in the correlation coefficients could also be expected when linkages are predominantly in the repulsion phase. It is suggested that intermating in early generations coupled with selection of desirable segregants may prove a useful method for improving yield and quality simultaneously. The diallel selective mating system may also supplement intermating to improve yield and quality in cotton.Part of Ph.D. Thesis submitted to the Haryana Agricultural University. Hissar-125004, India     

Identifying wheat genomic regions for improving grain protein concentration independently of grain yield using multiple inter-related populations

Grain yield (GY) and grain protein concentration (GPC) are two major traits contributing to the economic value of the wheat crop. These are, consequently, major targets in wheat breeding programs, but their simultaneous improvement is hampered by the negative correlation between GPC and GY. Identifying the genetic determinants of GPC and GY through quantitative trait loci (QTL) analysis would be one way to identify chromosomal regions, allowing improvement of GPC without reducing GY using marker-assisted selection. Therefore, QTL detection was carried out for GY and GPC using three inter-connected doubled haploid populations grown in a large multi-environment trial network. Chromosomes 2A, 2D, 3B, 7B and 7D showed co-location of QTL for GPC and GY with antagonistic effects, thus contributing to the negative GPC–GY relationship. Nonetheless, genomic regions determining GPC independently of GY across experiments were found on chromosomes 3A and 5D and could help breeders to move the GPC–GY relationship in a desirable direction.     

Identification of a Conserved Calmodulin-Binding Motif &;#x220A; the Sequence of F<Subscript>0</Subscript>F<Subscript>1</Subscript>ATPsynthase Inhibitor Protein

The natural inhibitor proteins IF₁ regulate mitochondrial F₀F₁ATPsynthase in a wide range of species. We characterized the interaction of CaM with purified bovine IF₁, two bovine IF₁ synthetic peptides, as well as two homologous proteins from yeast, namely IF₁ and STF₁. Fluorometric analyses showed that bovine and yeast inhibitors bind CaM with a 1:1 stoichiometry in the pH range between 5 and 8 and that CaM-IF₁ interaction is Ca²⁺-dependent. Bovine and yeast IF₁ have intermediate binding affinity for CaM, while the K_d (dissociation constant) of the STF₁-CaM interaction is slightly higher. Binding studies of CaM with bovine IF₁ synthetic peptides allowed us to identify bovine IF₁ sequence 33–42 as the putative CaM-binding region. Sequence alignment revealed that this region contains a hydrophobic motif for CaM binding, highly conserved in both yeast IF₁ and STF₁ sequences. In addition, the same region in bovine IF₁ has an IQ motif for CaM binding, conserved as an IQ-like motif in yeast IF₁ but not in STF₁. Based on the pH and Ca²⁺ dependence of IF₁ interaction with CaM, we suggest that the complex can be formed outside mitochondria, where CaM could regulate IF₁ trafficking or additional IF₁ roles not yet clarified.     

Cross-linking of the endogenous inhibitor protein (IF1) with rotor (gamma,epsilon) and stator (alpha) subunits of the mitochondrial ATP synthase

The location of the endogenous inhibitor protein ( IF₁) in the rotor/stator architecture of the bovine mitochondrial ATP synthase was studied by reversible cross-linking with dithiobis(succinimidylpropionate) in soluble F₁I and intact F₁F₀I complexes of submitochondrial particles. Reducing two-dimensional electrophoresis, Western blotting, and fluorescent cysteine labeling showed formation of –IF₁, IF₁–IF₁, –IF₁, and –IF₁ cross-linkages in soluble F₁I and in native F₁F₀I complexes. Cross-linking blocked the release of IF₁ from its inhibitory site and therefore the activation of F₁I and F₁F₀I complexes in a dithiothreitol-sensitive process. These results show that the endogenous IF₁ is at a distance 12 Å,to and subunits of the central rotor of the native mitochondrial ATP synthase. This finding strongly suggests that, without excluding the classical assumption that IF₁ inhibits conformational changes of the catalytic subunits, the inhibitory mechanism of IF₁ may involve the interference with rotation of the central stalk.     

Genetic variability and structure of natural and domesticated populations of Caribbean pine (Pinus caribaea Morelet)

 Isozyme analysis of seed samples derived from natural and managed populations of the tropical pine Pinus caribaea vars ‘bahamensis’ and ‘caribaea’ was used to assess population genetic structure in its native range and to detect changes occurring during early domestication of the species. Baseline data from natural populations of the two varieties showed that populations sampled as seed are characterized by high gene diversity (mean H_e=0.26) and a low level of inbreeding ( mean F_is=0.15). A UPGMA tree of genetic relatedness among populations indicates that the two varieties represent distinct evolutionary units. Within each variety there is significant differentiation among populations, and this is greater for the more fragmented populations of var ‘bahamensis’ (F_st=0.08) than for var ‘caribaea’ (F_st=0.02). Seed from a seed orchard population of var ‘caribaea’ established within its natural range showed no change in genetic diversity but did show a reduced inbreeding coefficient (F_is=0.09) compared with its progenitor populations, suggesting a decrease in selfing and/or biparental inbreeding. A bulked seed sample from an exotic plantation of var ‘bahamensis’ in Australia displayed a large increase in the inbreeding coefficient (F_is=0.324) compared with that found in natural populations, possibly due to elevated self-fertilization. Finally, a bulked seed sample from an exotic plantation population of var ‘caribaea’ from China showed enhanced genetic diversity, an increase in the inbreeding coefficient and more linkage disequilibrium than its presumed progenitor populations. It was also genetically divergent from them. RFLP analysis of chloroplast DNA variation in the Chinese sample suggested that seeds of the related taxa P. elliottii and P. taeda, or seeds derived from hybridization with these taxa growing in the seed production area, had been included in the seed crop during harvesting. We conclude that monitoring of appropriate genetic markers may be an effective means of identifying potentially deleterious genetic changes occurring during forest tree domestication. Received: 10 August 1998 / Accepted: 8 September 1998