Mechanisms of resistance to Helicoverpa armigera and introgression of resistance genes into F1 hybrids in chickpea

The noctuid pod borer, Helicoverpa armigera is a major pest of chickpea, and host plant resistance is an important component for managing this pest. We evaluated a set of diverse chickpea genotypes with different levels of resistance to H. armigera, and their F₁ hybrids for oviposition non-preference, antibiosis, and tolerance components of resistance under uniform insect infestation under greenhouse/laboratory conditions. The genotypes ICC 12476, ICC 12477, ICC 12478, ICC 12479, and ICC 506EB were non-preferred for oviposition under no-choice, dual-choice, and multi-choice conditions, and also suffered lower leaf damage in no-choice tests as compared to the susceptible check, ICCC 37. Antibiosis expressed in terms of low larval weights was observed in insects reared on ICC 12476, ICC 12478, and ICC 506EB. Weight gain by the third-instars was also low on ICC 12476, ICC 12477, ICC 12478, ICC 12479, and ICC 506EB at the podding stage. Non-preference for oviposition and antibiosis (poor larval growth) were also expressed in hybrids based on ICC 12477, ICC 12476, ICC 12478, ICC 12479, and ICC 506EB as compared to the hybrids based on the susceptible check, ICCC 37, indicating that oviposition non-preference and antibiosis in the F₁ hybrids is influenced by the parent genotype. Loss in grain yield was lower in ICC 12477, ICC 12478, ICC 12479, and ICC 506EB compared to that on ICCC 37. The genotypes ICC 12477, ICC 12478, ICC 12479, and ICC 506EB showing antixenosis, antibiosis, and tolerance mechanism of resistance to H. armigera can be used for developing chickpea cultivars for resistance to this pest.     

COMPARISON OF TETRAPLOID AND SINGLE GENE-INDUCED GIGAS VARIANTS IN CHICKPEA (CICER ARIETINUM). II. MORPHOLOGICAL AND ANATOMICAL LEAF CHARACTERS

Two genomic variants of a chickpea (Cicer arietinum L.) parental line have been developed which exhibit gigas characters. The two genotypes were the result of a single-gene mutation (gigas) and induced tetraploidy of a single parental line. The two genotypes plus parental strain were investigated to determine the similarity-of-effect of polyploidy and this single-gene mutation on leaf anatomy and morphology. Leaves consisted of two rows of alternatively arranged leaflets. Both the tetraploid and parental lines had the same mean number of leaflets per leaf while the gigas plants had fewer, but mean total leaf surface area was greater in the gigas plants. Quantitative comparison of mesophyll and vascular tissue and air space volume density (V_v) showed that leaves of the tetraploid plants had the greatest mesophyll cell density (V_vm) and least air space density. Mesophyll cell density was equal in the parental and single-gene mutant while parental leaves had the greatest vascular tissue density. The greater mesophyll cell density values of the polyploid were due to larger mean mesophyll cell size, not to greater cell numbers per unit area. Leaf models based on tissue density and leaflet size showed tetraploid plants had the greatest productivity potential per unit of leaflet surface area. However, if models were based on a whole leaf, gigas plants had the greatest productivity potential since they had larger total leaf area. The effectiveness of using structural models to predict physiological potential in plant tissues will be tested in future studies.     

Genetic analysis of agronomic characters in chickpea

Summary Twenty-eight diallel trials over 8 years and two locations were analysed to estimate genetic variances for agronomic characters of chickpea (Cicer arietinum L.). The data were analysed according to Method 4 and Model I of Griffing (1956). Days to flowering, plant height, and seed size were found to be predominantly under additive inheritance and were highly predictable. Both additive and non-additive genetic components were important for seed yield, number of branches, pods per plant, and seeds per pod. Although both general combining ability (gca) and specific combining ability (sca) varied significantly with generation, components of gca mean squares were invariably much larger than gca x generation interaction components, indicating that either the F₁ or the F₂ generation can be used to estimate the gca components effectively. Combined diallel analysis of F₂s over locations revealed the importance of combining ability x location interactions and emphasized the need for testing over more than one location for the precise estimation of combining ability. The implications of these findings and those reported earlier in the literature on the breeding strategies/methods for the genetic improvement of agronomic characters in chickpea are discussed.ICRISAT journal article no. 1199     

Genetic analysis of agronomic characters in chickpea. II. Estimates of genetic variances from line × tester mating designs

Summary Thirty line x tester experiments involving diverse chickpea (Cicer arietinum L.) germplasm were conducted over 8 years and three locations to determine the nature of the genetic variance for grain yield and related characters, and the effects of generation and environment on these genetic parameters. Days-to-flowering, 100-seed mass, and seeds per pod were predominantly under the control of additive genetic variance, while both additive and non-additive genetic components of variance were important for days-to-maturity, plant height, primary and secondary branches, pods per plant, and seed yield. The F₁ and F₂ generations were found equally useful in estimating the genetic variances for different characters because the generation did not significantly interact with genetic parameters in the majority of cases. Sites or seasons, on the other hand, showed significant interaction with genetic components of variances; additive variance showed a larger interaction with environments than non-additive variance. This indicated the importance of more than one site and/ or season for unbiased estimation of the genetic components of variance. The results were compared with previous findings from diallel analyses.ICRISAT Journal Article No. 1200     

Fine genetic mapping of the genomic region controlling leaflet shape and number of seeds per pod in the soybean

Narrow leaflet cultivars tend to have more seeds per pod than broad leaflet cultivars in soybean [Glycine max (L.) Merr.], which suggests that the leaflet-shape trait locus is tightly linked to or cosegregates with the trait locus controlling the number of seeds per pod (NSPP). Here, we attempted to further elucidate the relationship between leaflet shape and NSPP. A BC₃F₂ population from a cross between the ‘Sowon’ (narrow leaflets and high NSPP) and ‘V94-5152’ (broad leaflets and low NSPP) variants was used. The results of the molecular genetic analyses indicated that, although the NSPP characteristic, in particular, the occurrence of 4-seeded pods, is governed by additional modifying genes that are likely present in Sowon, the two traits cosegregate in the BC₃F₂ population. The mapping results generated using public markers demonstrated that the narrow leaflet-determining gene in Sowon is an allele of the previously highly studied ln gene on chromosome 20. A high-resolution map delimited the genomic region controlling both the leaflet shape and NSPP traits to a sequence length of 66 kb, corresponding to 0.7 cM. Among the three genes annotated in this 66 kb region, Glyma20g25000.1 appeared to be a good candidate for the Ln-encoding gene, owing to its 47.8% homology with the protein encoding for the JAGGED gene that regulates lateral organ development in Arabidopsis. Taken together, our results suggested that phenotypic variations for narrow leaflet and NSPP are predominantly from the pleiotropic effects of the ln gene. Thus, our results should provide a molecular framework for soybean breeding programs with the objective of improving soybean yield.     

Breeding for increased nitrogen fixing ability among wild and cultivated species of chickpea

Two chickpea species, one wild (Cicer reticulatum JM2106) and one cultivated (C. arietinum ICC8923) were selected as the parents for this study. C. reticulatum showed high nodule number, nodule dry weight and nitrogen content/plant as compared to C. arietinum. In lines derived from the crosses H208 × (ICC8923 × JM2106) and BG274 × (ICC8923 × JM2106), increase in nodule dry weight, nitrogen content/plant, plant dry weight and grain yield was observed over the parent ICC8923. Similarly F₆ lines also showed improvement in these traits over the cultivated parent. It is concluded that the increase in grain yield and dry matter is the result of improvement in nitrogen utilisation together with an increase in the available fixed nitrogen.     

Use of RAPD and ISSR Markers in Detection of Genetic Variation and Population Structure among Fusarium oxysporum f. sp. ciceris Isolates on Chickpea in Turkey

Genetic variation among the isolates of Fusarium oxysporum f. sp. ciceris, the causal agent of chickpea wilt worldwide, was analysed using pathogenicity tests and molecular markers – random amplified polymorphic DNA (RAPD) and inter‐simple sequence repeat (ISSR) polymorphism. Hundred and eight isolates were obtained from diseased chickpea plants in 13 different provinces of Turkey, out of which 74 isolates were assessed using 30 arbitrary decamer primers and 20 ISSR primers. Unweighted pair‐grouped method by arithmetic average cluster analysis of RAPD, ISSR and RAPD + ISSR datasets provided a substantially similar discrimination among Turkish isolates and divided into three major groups. Group 1, 2 and 3 consisted of 41, 18 and 15 isolates, respectively. These methods revealed a considerable genetic variation among Turkish isolates, but no correlation with regard to the clustering of isolates from different geographic regions. Analysis of molecular variance confirmed that most genetic variability resulted from the differences among isolates within regions. Our results also indicated that the low‐genetic differentiation (F_ST) and high gene flow (Nm) among populations had a significant effect on the emergence and evolutionary development of F. oxysporum f. sp. ciceris. This is the first report on genetic diversity and population structure of F. oxysporum isolates on chickpea in Turkey.     

Genetics and characterization of an open flower mutant in chickpea

The chickpea (Cicer arietinum L.) is a self-pollinated grain legume with cleistogamous flowers. A spontaneous open-flower mutant, designated OFM-3, was identified in which reproductive organs were not enclosed by the keel petals and thus remained exposed. All 10 stamens in this mutant were free, whereas these are in diadelphous (9 fused + 1 free) condition in normal chickpea flowers. A large number of pods (73%) remained unfilled (empty) in OFM-3, though its pollen fertility was as high as the standard cultivars. The open-flower trait was found to be recessive and controlled by a single gene. OFM-3 was crossed with earlier reported open-flower mutants, ICC 16341 and ICC 16129, to establish trait relationships of genes controlling open flower traits in these mutants. It was found that each of these mutants has a unique gene for open flower trait. The genes controlling open flower trait in ICC 16341, ICC 16129, and OFM-3 were designated ofl-1, ofl-2, and ofl-3, respectively. Breeding lines with open flower trait and higher percentage of filled pods have been developed from the progenies of the crosses of OFM-3 with normal-flowered lines. The open flower trait offers opportunity for exploring hybrid technology in the chickpea.     

Use of fluorescein diacetate (FDA) to determine ploidy of in vitro watermelon shoots

Ploidy of watermelon [Citrullus lanatus (Thunb.) Matsum. and Nakai shoots and plantlets was estimated by painting the lower epidermis of intact in vitro-derived leaves with fluorescein diacetate (FDA) and observing fluorescence of guard cell chloroplasts with a microscope and UV light. Leaves from in vitro shoot-tip cultures of known diploid cultivars and tetraploid breeding lines were used to establish the mean number of chloroplasts per guard cell pair. Leaves from diploid and tetraploid shoot cultures had 9.7 and 17.8 chloroplasts per guard cell pair, respectively. This method then was used to estimate the ploidy of shoots regenerated from cotyledon explants of the diploid cultivar Minilee. Approximately 11% of the 188 regenerated shoots were classified as tetraploid during in vitro culture. Putative tetraploids were transplanted to the field and self-pollinated. About 45% of tetraploids identified in vitro produced fruit and viable seed. Chloroplast counts of R₁ progeny were used to confirm their ploidy. All of the putative diploids were confirmed diploid and all putative tetraploids proved to be non-chimeric true breeding tetraploids. This revised version was published online in June 2006 with corrections to the Cover Date.     

Potential of DNA markers in detecting divergence and in analysing heterosis in Indian elite chickpea cultivars

 Molecular markers such as RAPDs and microsatellites were used to study genetic diversity in 29 elite Indian chickpea genotypes. In general, microsatellites were more efficient than the RAPD markers in detecting polymorphism in these genotypes. Among the various microsatellites, (AAC)₅, (ACT)_5, (AAG)₅ and (GATA)₄ were able to differentiate all 29 chickpea cultivars. The mean value of probability of identical match by chance was 2.32×10^-25 using DraI-(ACT)₅, TaqI-(AAC)₅, TaqI-(AAG)₅ and TaqI-(GATA)₄ enzyme-probe combinations. The dendrogram, constructed on the basis of similarity index values, grouped the chickpea genotypes into five main clusters with 8 cultivars genetically distant and outgrouped from the main clusters. To investigate if DNA markers are useful in predicting F₁ performance and heterosis in chickpea, we crossed 8 genotypes having important agronomic characters in a diallel set. The F₁s and their parents in the diallel set were analysed for agronomic traits for better parent and midparent heterosis. Heterosis was found to be much higher for yield than for yield components that fit a multiplicative model. The analysis of genetic divergence using D² statistics clustered the 8 cultivars into two groups. Although molecular marker-based genetic distance did not linearly correlate to heterosis, two heterotic groups could be identified on the basis of the general marker heterozygosity. Received: 1 August 1998 / Accepted: 29 September 1998     

Photosynthetic characteristics of a new yellow-green mutant with high photosynthetic rate in rice (<Emphasis Type="Italic">Oryza sativa</Emphasis> L.)

Contents of chlorophylls and carotenoids in yellow-green mutant Biao 810S were approximately half those in control type 810S. Biao 810S had fewer grana lamellae and looser structure than 810S, lower volume of starch granules in chloroplasts, but under high temperature and high irradiance the net photosynthetic rate (P _N) of Biao 810S was higher than that of 810S. The chlorophyll fluorescence parameter F_v/F_m of Biao 810S was little higher and photochemical quenching q_P was obviously higher than those of 810S. No significant differences in P _N and biomass were observed in their hybrid combination. The yellow-green mutant phenotype may be a useful genetic marker of P(T)GMS rice used for hybrid seed production.     

Fertile progeny of a hybridization between soybean [Glycine max (L.) Merr.] and G. tomentella Hayata

Summary A colchicine-doubled F₁ hybrid (2n=118) of a cross between PI 360841 (Glycine max) (2n=40) x PI 378708 (G. tomentella) (2n=78), propagated by shoot cuttings since January 1984, produced approximately 100 F₂ seed during October 1988. One-fourth of the F₂ plants or their F₃ progeny have been analyzed for chromosome number, pollen viability, pubescence tip morphology, seed coat color, and isoenzyme variation. Without exception, all plants evaluated possessed the chromosome number of the G. max parent (2n=40). Most F₂ plants demonstrated a high level of fertility, although 2 of 24 plants had low pollen viability and had large numbers of fleshy pods. One F₂ plant possessed sharp pubescence tip morphology, whereas all others were blunt-tipped. All evaluated F₂ and F₃ plants expressed the malate dehydrogenase and diaphorase isoenzyme patterns of the G. max parent and the endopeptidase isoenzyme pattern of the G. tomentella parent. Mobility variants were observed among progeny for the isoenzymes phosphoglucomutase, aconitase, and phosphoglucoisomerase. This study suggests that the G. Tomentella chromosome complement has been eliminated after genetic exchange and/or modification has taken place between the genomes.Journal Paper No. J-13776 of the Iowa Agriculture and Home Economics Experiment Station, Ames, IA, USA, Project 2763     

Location of the recessive gene ym (yellow margin) on chromosome 12 of diploid Solatium tuberosum by means of trisomic analysis

Summary Ten out of twelve primary trisomics of dip-loid S. tuberosum were crossed as females with a recessive mutant for yellow margin (ym ym) obtained from S. phureja. All primary trisomics used proved to be homozygous dominant. Trisomic plants from all ten F₁'s were backcrossed with the mutant and trisomics from eight F₁'s were crossed also with a disomic heterozygous f₁ plant from triple 10 X mutant.In both BC₁ and half sib progeny of each trisomic type the mutant plants were easily identified because of their typical small roundish leaflets with yellow or reddish margins. The observed segregation ratios for normal to mutant were tested against the expected non-critical ratios and against various expected critical ratios.From the results of these tests it is concluded that the gene ym is located on chromosome 12 of the potato. A hypothesis of linkage between ym and a gene l _x for lethality is put forward. It is concluded that l _x is not identical with a previously detected recessive gene l ₂ which is responsible for yellow cotyledons and lethality.     

Is there hybridization between diploid and tetraploid Euphrasia in a secondary contact zone?

Premise

Strong postzygotic reproductive isolating barriers are usually expected to limit the extent of natural hybridization between species with contrasting ploidy. However, genomic sequencing has revealed previously overlooked examples of natural cross-ploidy hybridization in some flowering plant genera, suggesting that the phenomenon may be more common than once thought. We investigated potential cross-ploidy hybridization in British eyebrights (Euphrasia, Orobanchaceae), a group from which 13 putative cross-ploidy hybrid combinations have been reported based on morphology.

Methods

We analyzed a contact zone between diploid Euphrasia rostkoviana and tetraploid E. arctica in Wales. We sequenced part of the internal transcribed spacer (ITS) of nuclear ribosomal DNA and used genotyping by sequencing (GBS) to look for evidence of cross-ploidy hybridization and introgression.

Results

Common variant sites in the ITS region were fixed between diploids and tetraploids, indicating a strong barrier to hybridization. Clustering analyses of 356 single-nucleotide polymorphisms (SNPs) generated using GBS clearly separated samples by ploidy and revealed strong genetic structure (F_ST = 0.44). However, the F_ST distribution across all SNPs was bimodal, indicating potential differential selection on loci between diploids and tetraploids. Demographic inference suggested potential gene flow, limited to around one or fewer migrants per generation.

Conclusions

Our results suggest that recent cross-ploidy hybridization is rare or absent in a site of secondary contact in Euphrasia. While a strong ploidy barrier prevents hybridization over ecological timescales, such hybrids may form in stable populations over evolutionary timescales, potentially allowing cross-ploidy introgression to take place.     

Effects of selection criteria on yield stability in chickpea (Cicer arietinum L.)

Summary Selection in the F₃ generation for seed yield, fruiting branches/plant, effective pods/plant, and seed index (100-seed weight) was carried out in two chickpea crosses. Sixty F₅ lines (15 lines/selection criterion) along with check variety were evaluated for seed yield in three distinct environments. The effects of selection criteria on yield stability was examined using linear regression approach and genotype-grouping technique. There were no differences between selection criteria for linear yield responses of F₅ lines to different environments. Within all four selection criteria the lines showed similar linear responses. The non-linear component was relatively higher for lines selected for effective pods and seed index than lines selected for yield and fruiting branches. On the basis of mean yield and coefficient of variation across environments, the seed index was the least effective selection criterion for developing high yielding and stable lines. When the results of stability parameters and genotype-grouping technique were considered together, selection for yield and fruiting branches was highly effective for isolating stable and high yielding lines.     

Fast chlorophyll fluorescence transient and nitrogen fixing ability of chickpea nodulation variants

High nodulating (HN) selections of the cultivars ICC 4948 and ICC 5003 had the highest nodule number and nodule dry mass followed by low nodulating (LN) selections of the same cultivar. Both non-nodulating (NN) selections of cv. ICC 4993 and ICC 4918 did not show any nodule. Using N-difference method the HN selection of cv. 1CC 4948 was able to meet 73 % of its demand of N through biological fixation of N₂ [P(fix)], while 27 % of N demand was met by uptake from the soil, whereas its LN selection was able to meet only 54 % of its demand of N through biological fixation of N₂. Similarly in cv. ICC 5003 HN and LN selections the P(fix) was 76 and 64 %, respectively. Fast chlorophyll (Chl) fluorescence transient data analysis showed that performance index PI(abs) was 62.0 in cv. ICC 4948 HN selection and 44.5 in its respective LN selections. Corresponding values for cv. ICC 5003 were 32.4 and 28.4. In NN selections of ICC 4993 and ICC 4918 it was 12.6 and 30.7, respectively. Structure function index of the plants SFI(abs) and driving force for photosynthesis (DF) were highest in the HN selections followed by LN selections and lowest in the NN selections. The total uptake of N by chickpea plants was significantly and positively correlated with the density of reaction centres ABS/CS₀, TR₀/CS₀, and DI₀/CS_M, whereas total N uptake by chickpea seeds was significantly positively correlated with N and TR₀/CS₀. The percentage of P(fix) was highly significantly positively correlated with N, the so-called turnover number which indicates how many times Q_A has been reduced in the time span from 0 to t_Fmax and TR₀/CS₀. Fast Chl a fluorescence measurement can be used as a model system to assess the N fixation ability in chickpea.     

REPRODUCTIVE ISOLATION OF TRITICUM BOEOTICUM AND TRITICUM URARTU AND THE ORIGIN OF THE TETRAPLOID WHEATS

The diploid wheats Triticum boeoticum and T. urartu are sympatric with one another throughout the geographic range of the wild tetraploids. Reciprocal crosses between ecogeographic types within each diploid species gave viable seed, but interspecific crosses consistently gave viable seed only when T. boeoticum was the female parent. Apparently urartu cytoplasm in combination with the boeoticum genome resulted in nonviable seed. The endosperm failed to develop normally despite regular endosperm fertilization. The F₁ plants obtained were completely self sterile although they showed regular intergenomic pairing (7II) at meiosis. Presumably the accumulation of cryptic differences between the two closely related genomes under reproductive isolation accounts for this sterility. The same accumulated cryptic differences could largely account for the preferential diploid pairing in the tetrapolid wheats which presumably were derived from such hybrids by chromosome doubling. The behavior of reciprocal crosses between the diploids and tetraploids suggested that T. boeoticum contributed the cytoplasm to both of the wild tetraploid species.     

UPLC‐HRMS‐based untargeted metabolic profiling reveals changes in chickpea (Cicer arietinum) metabolome following long‐term drought stress

Genetic improvement for drought tolerance in chickpea requires a solid understanding of biochemical processes involved with different physiological mechanisms. The objective of this study is to demonstrate genetic variations in altered metabolic levels in chickpea varieties (tolerant and sensitive) grown under contrasting water regimes through ultrahigh‐performance liquid chromatography/high‐resolution mass spectrometry‐based untargeted metabolomic profiling. Chickpea plants were exposed to drought stress at the 3‐leaf stage for 25 days, and the leaves were harvested at 14 and 25 days after the imposition of drought stress. Stress produced significant reduction in chlorophyll content, F_v/F_m, relative water content, and shoot and root dry weight. Twenty known metabolites were identified as most important by 2 different methods including significant analysis of metabolites and partial least squares discriminant analysis. The most pronounced increase in accumulation due to drought stress was demonstrated for allantoin, l ‐proline, l ‐arginine, l ‐histidine, l ‐isoleucine, and tryptophan. Metabolites that showed a decreased level of accumulation under drought conditions were choline, phenylalanine, gamma‐aminobutyric acid, alanine, phenylalanine, tyrosine, glucosamine, guanine, and aspartic acid. Aminoacyl‐tRNA and plant secondary metabolite biosynthesis and amino acid metabolism or synthesis pathways were involved in producing genetic variation under drought conditions. Metabolic changes in light of drought conditions highlighted pools of metabolites that affect the metabolic and physiological adjustment in chickpea that reduced drought impacts.     

Genetic differentiation between three ecological variants (‘type’, ‘mysorensis’ and ‘intermediate’) of malaria vector Anopheles stephensi (Diptera: Culicidae)

Abstract Anopheles stephensi is the main vector of urban malaria in South Asia. Three ecological variants (‘type’, ‘mysorensis’and‘intermediate’) of An. stephensi have been reported on the basis of ecology and egg morphology. However, it is unclear if there is any genetic isolation between the three variants. We analyzed the three variants of An. stephensi using eight microsatellite loci and found that large and significant genetic differentiation exists between them (mean F_ST= 0.393 and mean R_ST= 0.422). Pairwise estimates of genetic differentiation between the variants were ‘type’ versus ‘mysorensis’ (mean F_ST= 0.411 and mean R_ST= 0.308), ‘type’ versus ‘intermediate’ (mean F_ST= 0.388 and mean R_ST= 0.518) and ‘intermediate’ versus ‘mysorensis’ (mean F_ST= 0.387 and mean R_ST= 0.398) and all were statistically significant (P < 0.05). The greater sensitivity of R_ST in differentiation indicated that mutations and not genetic drift had generated the differences between three variants of An. stephensi. The present study indicated large genetic differentiation and presence of non-significant low level of gene flow between the three variants (‘type’, ‘mysorensis’and‘intermediate’) of An. stephensi.     

Comparative genetic linkage maps of <Emphasis Type="Italic">Eucalyptus grandis</Emphasis>, <Emphasis Type="Italic">Eucalyptus globulus</Emphasis> and their F<Subscript>1</Subscript> hybrid based on a double pseudo-backcross mapping approach

Comparative genetic mapping in interspecific pedigrees presents a powerful approach to study genetic differentiation, genome evolution and reproductive isolation in diverging species. We used this approach for genetic analysis of an F₁ hybrid of two Eucalyptus tree species, Eucalyptus grandis (W. Hill ex Maiden.) and Eucalyptus globulus (Labill.). This wide interspecific cross is characterized by hybrid inviability and hybrid abnormality. Approximately 20% of loci in the genome of the F₁ hybrid are expected to be hemizygous due to a difference in genome size between E. grandis (640 Mbp) and E. globulus (530 Mbp). We investigated the extent of colinearity between the two genomes and the distribution of hemizygous loci in the F₁ hybrid using high-throughput, semi-automated AFLP marker analysis. Two pseudo-backcross families (backcrosses of an F₁ individual to non-parental individuals of the parental species) were each genotyped with more than 800 AFLP markers. This allowed construction of de novo comparative genetic linkage maps of the F₁ hybrid and the two backcross parents. All shared AFLP marker loci in the three single-tree parental maps were found to be colinear and little evidence was found for gross chromosomal rearrangements. Our results suggest that hemizygous AFLP loci are dispersed throughout the E. grandis chromosomes of the F₁ hybrid.Communicated by O. Savolainen