Mapping loci controlling vernalization requirement in Brassica rapa

Brassica cultivars are classified as biennial or annual based on their requirement for a period of cold treatment (vernalization) to induce flowering. Genes controlling the vernalization requirement were identified in a Brassica rapa F₂ population derived from a cross between an annual and a biennial oilseed cultivar by using an RFLP linkage map and quantitative trait locus (QTL) analysis of flowering time in F₃ lines. Two genomic regions were strongly associated with variation for flowering time of unvernalized plants and alleles from the biennial parent in these regions delayed flowering. These QTLs had no significant effect on flowering time after plants were vernalized for 6 weeks, suggesting that they control flowering time through the requirement for vernalization. The two B. rapa linkage groups containing these QTLs had RFLP loci in common with two B. napus linkage groups that were shown previously to contain QTLs for flowering time. An RFLP locus detected by the cold-induced gene COR6.6 cloned from Arabidopsis thaliana mapped very near to one of the B. rapa QTLs for flowering time.     

Development of genetic markers in celery based on restriction fragment length polymorphisms

Summary Linkage relationships are reported for 34 markers in celery (Apium graveolens L. var dulce) including 21 RFLP, 11 isozyme, and 2 morphological traits. The mapping was carried out in a cross between celery and an annual accession from Thailand, A143, and based on F₂ segregation of 136 plants. A total of 318 centiMorgans (cM) are covered by the markers distributed in 8 linkage groups. Probes for the identification of RFLPs were isolated from a celery cDNA library and were also obtained from heterologous sources. EcoRV, EcoRI, and HindIII were the most useful restriction enzymes in uncovering polymorphism. In our cross, 18% of the cDNA probes were found to be polymorphic for at least one of the enzymes used. Six of the markers showed significant deviations from expected F₂ ratios.     

Plasmon divergence in peanuts (Arachis hypogaea): A third plasmon and locus affecting growth habit

Summary In a series of reciprocal crosses between peanut (Arachis hypogaea L.) cultivars from different regions and known testers, the cultivar HG1 from India was shown to have a third plasmon type, designated [G]. HG1 also has a third locus, Hb₅ , which interacts with the plasmons and the loci described earlier. In the [G] plasmon, Hb₁ and Hb₅ are additive: plants having three or four dominant alleles have a trailing habit while the other nuclear genotypes produce in [G] erect plants. In the [V4] plasmon, Hb₂ and Hb₅ are complementary, [V4] Hb₂-, Hb₅-plants being trailing, the others erect. In the [G] plasmon, Hb₂ and Hb₅ are complementary, while in the [O] plasmon they are additive.     

Intergeneric hybridization between Brassica napus and Sinapis pubescens,and the cytology and crossability of their progenies

The cytological possibility of gene transfer from Sinapis pubescens to Brassica napus was investigated. Intergeneric hybrids between Brassica napus (2n = 38) and Sinapis pubescens (2n = 18) were produced through ovary culture. The F₁ hybrids were dihaploid and the chromosome configurations were (0–1) _III + (2–11) _II + (5–24) _I . One F₂ plant with 38 chromosomes was obtained from open pollination of the F₁ hybrid. Thirty-one seeds were obtained from the backcross of the F₂ plant with B. napus. Five out of seven plants had 38 chromosomes, and the pollen stainability ranged from 0% to 81.4%. In the B₂ plants obtained from the backcross of B₁ plants with B. napus, 66.7% of the plants examined had 38 chromosomes. S. pubescens may become a gene source for the improvement of B. napus.     

The influence of the genes An1, An2, and An4 on the activity of the enzyme UDP-glucose:Flavonoid 3-O-glucosyltransferase in flowers of Petunia hybrida

A relation between gene dosage and UDP-glucose:flavonoid 3-O-glucosyl-transferase (UFGT) activity was found in homozygous dominant and recessive parental lines and their F₁ progeny for both of the genes An1 and An2. In both F₂ crosses, progeny plants could be classified as belonging to groups showing either a low or a medium to high UFGT activity. Test crosses showed that heterozygous and homozygous dominant plants were present throughout the medium- to high-active group. The dosage relation in F₂ plants is most probably confounded by the segregation of modifiers. Thermal inactivation experiments indicated that structurally different UFGT enzymes are formed in homozygous dominant lines as well as in lines homozygous recessive for either An1 or An2. Lines homozygous recessive for the gene An4 contain a UFGT with a half-life time at 55° C of less than 8 min, whereas UFGTs from lines homozygous dominant for An4 show a half-life time of 25 min or above, with one exception. This relation was confirmed in the F₂ progeny; heterozygotes for An4 showed an intermediate half-life time. It is concluded that An4 might be the structural gene for the enzyme; An1 and An2 are both regulatory genes. UFGT activity in flowerbuds of An4/An4 plants seems to be lower than in an4/an4 plants. Anthers of flowers of an4/an4 lines, however, are virtually devoid of UFGT activity.     

Transactivation of Ds elements in plants of lettuce (Lactuca sativa)

The maize transposable element, Activator (Ac), is being used to develop a transposon mutagenesis system in lettuce, Lactuca sativa. In this paper, we describe somatic and germinal transactivation of Ds by chimeric transposase genes in whole plants. Constructs containing either the Ds element or the Ac transposase open reading frame (ORF) were introduced into lettue. The Ds element was located between either the 35S or the Nos promoter and a chimeric spectinomycin resistance gene (which included a transit peptide), preventing expression of spectinomycin resistance. The genomic coding region of the Ac transposase was expressed from the 35S promoter. Crosses were made between 104 independent R₁ plants containing Ds and three independent R₁ plants expressing transposase. The excision of Ds in F₁ progenies was monitored using a phenotypic assay on spectinomycin-containing medium. Green sectors in one-third of the F₁ families indicated transactivation of Ds by the transposase at different developmental stages and at different frequencies in lettuce plants. Excision was confirmed using PCR and by Southern analysis. The lack of green sectors in the majority of F₁ families suggests that the majority of T-DNA insertion sites are not conducive to excision. In subsequent experiments, the F₁ plants containing both Ds and the transposase were grown to maturity and the F₂ seeds screened on medium containing spectinomycin. Somatic excision was again observed in several F₂ progeny; however, evidence for germinal excision was observed in only one F₂ family.     

Distribution of the genes causing F2 chlorosis in rice cultivars of the Indica and Japonica types

Summary Chlorotic plants were segregated in F₂ populations in varietal crosses of common rice. The genetic basis and distribution of the genes causing F₂ chlorosis in native cultivars were studied to examine the role of the F₂ chlorosis in varietal differentiation of rice. It was proven that this F₂ chlorosis was controlled by a set of duplicate genes, hca-1 and hca-2. The hca-2 gene was widely distributed in native cultivars of the Japonica type, while many Indica types carried its dominant allele hca-2 ⁺. Japanese cultivar J-147 carried hca-2. The hca-1 gene was frequently distributed in cultivars containing the Hwc-2 gene for F₁ weakness. We concluded that F₂ chlorosis does not cause or promote varietal differentiation in rice.     

Inheritance of resistance to the two-spotted spider mite from L. pimpinellifolium (Jusl.) Mill. accession ‘TO-937’

The two-spotted spider mite (Tetranychus urticae Koch) is an important pest of tomato (Lycopersicon esculentum Mill.) crops in temperate regions as this spider mite has a very large capacity for population increase and causes severe tomato yield losses. There is no described tomato cultivar fully resistant to this pest, although resistant accessions have been reported within the green-fruited tomato wild species L. pennellii (Corr.) D’Arcy and L. hirsutum Humb. & Bonpl. We observed a L. pimpinellifolium (Jusl.) Mill. accession, ‘TO-937’, which seemed to be completely resistant to mite attacks and we crossed it with the susceptible L. esculentum cultivar. ‘Moneymaker’ to obtain a family of generations consisting of the two parents, the F₁, the F₂, the BC₁ to L. esculentum, and the BC₁ to L. pimpinellifolium. This family was evaluated for mite resistance in a polyethylene greenhouse using an experimental design in 60 small complete blocks distributed along 12 double rows. Each block consisted of five F₂ plants in one row and one plant of each of the two parents, the F₁, the BC₁ to L. esculentum, and the BC₁ to L. pimpinellifolium in the adjacent row. Plants at the 10–15 leaf stage were artificially infested by putting on them two pieces of French bean leaf heavily infested with T. urticae. After two months, evaluations of infestation were made by visual observation of mite nets and leaf damage. Plants that were free of signs of mite reproduction on the top half were considered as resistant, plants with silky nets only on their basal leaves, intermediate, and plants with mite reproduction on both basal and top canopies were scored as susceptible. Dominance for resistance appeared because all the ‘To-937’, BC₁ to L. pimpinellifolium, and F₁ plants were resistant. Not all ‘Moneymaker’ plants behaved as susceptible because 35% of plants were intermediate. In the BC₁ to L. pimpinellifolium and the F₂, most plants were scored as resistant, only 7 % BC₁ and 3 % F₂ plants were intermediate, and a single F₂ plant (0.3 %) was susceptible. With these figures, resistance seemed to be controlled by either four or two genes according to whether segregation in the BC₁ or in the F₂, respectively, were considered. These results could in part be explained because of appearance of negative interplot interference due to the high frequency of resistant genotypes within most of the generations. Therefore, the family was evaluated again but using a different experimental design. In the new experiment, 16 ‘TO-937’, 17 ‘Moneymaker’, 17 F₁, 37 BC₁ to L. pimpinellifolium, 38 BC₁ to L. esculentum, and 125 F₂ plants were included. Each of these test plants was grown besides a susceptible ‘Moneymaker’ auxilliary plant that served to keep mite population high and homogeneous in the greenhouse. Negative interplot interference was avoided with this design and all the ‘TO-937’, F₁, and BC₁ to L. pimpinellifolium plants were resistant, all ‘Moneymaker’ test plants were susceptible, and 52 % BC₁ to L. esculentum and 25 % F₂ plants were susceptible, which fitted very well with the expected for resistance governed by a single dominant gene. The simple inheritance mode found will favour sucessful introgression of mite resistance into commercial tomatoes from the very close relative L. pimpinellifolium.     

Establishment of an enhancer trap system with<Emphasis Type="Italic"> Ds</Emphasis> and GUS for functional genomics in rice

To develop an efficient means of enhancer trapping, a two-element system employing Ds and an Ac transposase (AcTPase) gene was tested in rice. We generated 263 transgenic rice plants, each of which harboured the maize transposable element Ds together with a GUS coding sequence under the control of a minimal promoter ( Ds-GUS), and a gene that confers resistance to the herbicide chlorsulfuron. Among the 263 lines generated, 42 were shown to have a single copy of the Ds-GUS element. Four single-copy lines were crossed with each of six transgenic plants that carried the AcTPase gene. Excision of the Ds-GUS in leaves of F₁ plants was detected in eight combinations out of seventeen examined. The frequency of transposition of Ds-GUS in germ cells in the F₁ plants was examined using 10,524 F₂ plants, and 675 (6%) were judged to be transposants. Their frequencies differed among F₁ plants depending on the AcTPase x Ds-GUS cross considered, and also among panicles on the same F₁ plant. This suggests that Ds-GUS tends to transpose during panicle development. Southern analysis with a GUS probe showed different band patterns among transposants derived from different panicles. Therefore, the transposants derived from different panicles must have arisen independently. Transposants showing tissue-specific GUS activities were obtained, and enhancers thus trapped by the Ds-GUS element were identified. These results demonstrate that the system is suitable for the isolation of large numbers of independent Ds-GUS transposants, and for the identification of various tissue-specific enhancers. The Ds-GUS lines generated in this study offer a potentially powerful tool for studies on the functional genomics of rice.Communicated by M.-A. Grandbastien     

Interspecific hybrids between Brassica napus L. and B. oleracea L. developed by embryo culture

Summary Interspecific hybrids between Brassica napus and B. oleracea are difficult to produce, and previous attempts to transfer economic characters from one species to the other have largely been unsuccessful. In these studies, oilseed rape cv. Tower (2n38) (B. napus) was crossed with broccoli and kale (2n18) (B. oleracea), and hybrid plants were developed from embryos in culture by either organogenesis or somatic embryogenesis. In rape × broccoli, F₁ plants were regenerated from hybrid embryos and the plants produced viable selfed seeds. F₅ plants (2n38) homozygous for white flower colour were selected for high oil content (47%) and Line 15; a selection from these plants produced fertile hybrids with rape, broccoli and kale without embryo culture. In reciprocal crosses between oilseed rape cv. Tower and an aphid resistant diploid kale, 28 and 56 chromosome F₁ hybrid plants were regenerated from somatic embryos. The 56 chromosome plants were self-fertile and it was concluded from F₂ segregation ratios that a single dominant gene controls resistance to cabbage aphid in kale. The 28 chromosome F₁'s were self-sterile, but these and the 56 chromosome F₁'s could be backcrossed to rape and kale. A cross between the F₁ (2n56) and a forage rape resulted in the selection of a cabbage aphid (Brevicoryne brassicae L.) resistant line (Line 3). Both Line 15 and Line 3 can serve as bridges for gene interchange between B. campestris, B. napus and B. oleracea, which has not been possible hitherto. Hybridisations between rape and tetraploid kale produced F₁ plants with 37 chromosomes. One F₂ plant possessed coronal scales and the inheritance was shown to be controlled by a single recessive gene unlinked to petal colour.This paper is dedicated to Mr. T. P. Palmer, a colleague and close friend who retired from the DSIR as Assistant Director of the Crop Research Division in September 1984     

Characterization and mapping of <Emphasis Type="Italic">Rpi1</Emphasis>, a gene that confers dominant resistance to stalk rot in maize

The maize inbred lines 1145 (resistant) and Y331 (susceptible), and the F₁, F₂ and BC₁F₁ populations derived from them were inoculated with the pathogen Pythium inflatum Matthews, which causes stalk rot in Zea mays. Field data revealed that the ratio of resistant to susceptible plants was 3:1 in the F₂ population, and 1:1 in the BC₁F₁population, indicating that the resistance to P. inflatum Matthews was controlled by a single dominant gene in the 1145×Y331 cross. The gene that confers resistance to P. inflatum Matthews was designated Rpi1 for resistance to P. inflatum) according to the standard nomenclature for plant disease resistance genes. Fifty SSR markers from 10 chromosomes were first screened in the F₂ population to find markers linked to the Rpi1 gene. The results indicated that umc1702 and mmc0371 were both linked to Rpi1, placing the resistance gene on chromosome 4. RAPD (randomly amplified polymorphic DNA) markers were then tested in the F₂population using bulked segregant analysis (BSA). Four RAPD products were found to show linkage to the Rpi1 gene. Then 27 SSR markers and 8 RFLP markers in the region encompassing Rpi1 were used for fine-scale mapping of the resistance gene. Two SSR markers and four RFLP markers were linked to the Rpi1 gene. Finally, the Rpi1 gene was mapped between the SSR markers bnlg1937 and agrr286 on chromosome 4, 1.6 cM away from the former and 4.1 cM distant from the latter. This is the first time that a dominant gene for resistance to maize stalk rot caused by P. inflatum Matthews has been mapped with molecular marker techniques.     

Genetic studies of yield contributing traits in Amaranthus

Summary Genetical studies on grain yield and its contributing traits were made in a six parent complete diallel in the F₁ and F₂ generations of one of the most widely grown grain species of grain amaranths (Amaranthus hypochondriacus L.). Graphical analysis indicated that epistasis exists for 1,000-grain weight in the F₁. Grain weight/panicle, yield/plant and harvest index indicated absence of non-allelic gene interaction. The harvest index in the F₁ and F₂ and grain weight/ panicle, 1,000-grain weight, yield/plant in the F₂ appeared to be controlled by overdominance effects. Higher grain yield appeared to be associated with dominant genes. Both additive and non-additive gene effects were responsible for the genetic variation in the diallel population. However, dominance variance was more important than additive variance in grain yield/ plant and harvest index in the F₁ and F₂. For 1,000-grain weight additive genetic variance was more important in the F₁ and non-additive in F₂. There was overdominance of a consistent nature in the two analyses for harvest index in the F₁ and F₂, grain weight/ panicle, 1,000-grain weight and yield/plant in the F₂ and partial dominance for 1,000-grain weight in the F₁.     

The inheritance of organogenic response in melon

Previous studies have demonstrated variation in organogenic competence among plants within a population ofCucumis melo. In order to determine if leaf explant response is under genetic control, we investigated the distribution of the shoot regeneration frequency in F₁ and F₂ generations from parents representing extreme values forin vitro organogenic response. Results suggest a genetic model with two genes, partial dominance, independent segregation and similar effects for both genes.     

Mapping loci controlling flowering time in Brassica oleracea

The timing of the transition from vegetative to reproductive phase is a major determinant of the morphology and value of Brassica oleracea crops. Quantitative trait loci (QTLs) controlling flowering time in B. oleracea were mapped using restriction fragment length polymorphism (RFLP) loci and flowering data of F₃ families derived from a cabbage by broccoli cross. Plants were grown in the field, and a total of 15 surveys were made throughout the experiment at 5–15 day intervals, in which plants were inspected for the presence of flower buds or open flowers. The flowering traits used for data analysis were the proportion of annual plants (PF) within each F₃ family at the end of the experiment, and a flowering-time index (FT) that combined both qualitative (annual/biennial) and quantitative (days to flowering) information. Two QTLs on different linkage groups were found associated with both PF and FT and one additional QTL was found associated only with FT. When combined in a multi-locus model, all three QTLs explained 54.1% of the phenotypic variation in FT. Epistasis was found between two genomic regions associated with FT. Comparisons of map positions of QTLs in B. oleracea with those in B. napus and B. rapa provided no evidence for conservation of genomic regions associated with flowering time between these species.     

<Emphasis Type="Italic">Lr41, Lr39,</Emphasis> and a leaf rust resistance gene from<Emphasis Type="Italic"> Aegilops cylindrica</Emphasis> may be allelic and are located on wheat chromosome 2DS

The leaf rust resistance gene Lr41 in wheat germplasm KS90WGRC10 and a resistance gene in wheat breeding line WX93D246-R-1 were transferred to Triticum aestivum from Aegilops tauschii and Ae. cylindrica, respectively. The leaf rust resistance gene in WX93D246-R-1 was located on wheat chromosome 2D by monosomic analysis. Molecular marker analysis of F₂ plants from non-critical crosses determined that this gene is 11.2 cM distal to marker Xgwm210 on the short arm of 2D. No susceptible plants were detected in a population of 300 F₂ plants from a cross between WX93D246-R-1 and TA 4186 (Lr39), suggesting that the gene in WX93D246-R-1 is the same as, or closely linked to, Lr39. In addition, no susceptible plants were detected in a population of 180 F₂ plants from the cross between KS90WGRC10 and WX93D246-R-1. The resistance gene in KS90WGRC10, Lr41, was previously reported to be located on wheat chromosome 1D. In this study, no genetic association was found between Lr41 and 51 markers located on chromosome 1D. A population of 110 F₃ lines from a cross between KS90WGRC10 and TAM 107 was evaluated with polymorphic SSR markers from chromosome 2D and marker Xgdm35 was found to be 1.9 cM proximal to Lr41. When evaluated with diverse isolates of Puccinia triticina, similar reactions were observed on WX93D246-R-1, KS90WGRC10, and TA 4186. The results of mapping, allelism, and race specificity test indicate that these germplasms likely have the same gene for resistance to leaf rust.Contribution number 03-348-J from the Kansas Agricultural Experimental Station, Manhattan, KansasCommunicated by J. Dvorak     

Meiotic restriction in emmer wheat is controlled by one or more nuclear genes that continue to function in derived lines

Highly fertile F₁ hybrids were made between Triticum turgidum L. ssp. turgidum (2n = 28, AABB) and Aegilops tauschii Coss. (2n = 14, DD) without embryo rescue and hormone treatment. The F₁ plants had an average seed set of 25%. Approximately 96% of the F₂ seeds were able to germinate normally and about 67% of the F₂ plants were spontaneous amphidiploid (2n = 42, AABBDD). Cytological analysis of male gametogenesis of the F₁ plants showed that meiotic restitution is responsible for the high fertility. A mitosis-like meiosis led to meiotic restitution at either of the two meiotic divisions resulting in unreduced gametes. Test crosses of the T. t. turgidum–Ae. tauschii amphidiploid with Ae. variabilis and rye suggested that the mitosis-like meiosis is controlled by one or more nuclear genes that continue to function in derived lines. This discovery indicates a potential application of such genes in producing double haploids.     

Inheritance of cell size in wheat (Triticum aestivum L.) and its relationship to the vernalization loci

Reduced cell size is an important adaptive feature in plant response to environmental stresses. The objectives of the present study were to determine the inheritance and location of genes controlling cell size and to establish the relationship between cell size, low-temperature (LT) tolerance, and growth habit as determined by the Vrn loci in wheat. Guard cell length was measured in F₁, F₂, andF₂-derived F₃ populations from parents ranging widely in cell size and in the Chinese Spring/ Cheyenne (CS/CNN) chromosome substitution series. The cell size of F₁ hybrids was similar to the parental midpoint and the F₂ frequency distribution was symmetrical about the mean indicating that cell size was determined by additive gene action with little or no dominance. It appears that there are several genes involved since none of the F₂ progeny had a cell size as large or as small as the parental mean range. The cell size of the homozygous spring and winter lines from F₂-derived F₃ populations fell into two distinct groups that were related to plant growth habit. Large cell size was associated with the spring-habit alleles (Vrn-A1) and small cell size was associated with the winter-habit alleles (vrn-A1) on chromosome 5A. Analyses of the CS/CNN chromosome substitution series showed that CNN chromosomes 5A and 5B both reduced cell size without changing the growth habit, indicating that growth habit per se does not determine cell size. The group-5 chromosomes therefore appear to carry homoeologous alleles with major effects on cell size in wheat. This places cell-size control and many other low-temperature (LT) tolerance associated characters in close proximity to the vrn region of the group-5 chromosomes. Received: 17 August 2000 / Accepted: 20 November 2000     

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.     

Inheritance and tagging of gene regulating flowering time in the green manure crop <Emphasis Type="Italic">Sesbania rostrata</Emphasis> (Bremek. &; Obrem.)

This is the first report on genetic studies and molecular tagging of a gene regulating flowering time in the stem nodulating legume crop Sesbania rostrata (Bremek. & Obrem.). An F₂ segregating population was developed from a cross between Trombay Sesbania rostrata-1 (TSR-1, a radiation induced late flowering mutant) and S. rostrata. A phenotypic segregation ratio of 3 (normal flowering):1 (late flowering) in the F₂ generation indicated that the late flowering is governed as a monogenic recessive trait. A genotypic ratio of 1:2:1 in the F₂ generation, determined from phenotypic segregation patterns in 73 F₃ families, confirmed the monogenic inheritance of the late flowering trait. Inter Simple Sequence Repeat (ISSR) and Amplified Fragment Length Polymorphism (AFLP) marker techniques were evaluated for their applicability as genetic marker systems in this green manure crop. Using the F₂ segregating population, an ISSR marker (UBC 881₁₀₀₀) tightly linked to the trait was identified. Two linked AFLP markers GCTG₅₀₀ and CCAT₃₅₀ were also identified. They were found to be at a distance of 1.4 ± 0.034 cM and 8.0 ± 0.047 cM flanking the flowering locus respectively. The ISSR marker UBC 881₁₀₀₀ was converted into a Sequence Characterized Amplified Region (SCAR) marker. The single recessive mutation regulating the late flowering trait and the availability of tightly linked, flanking markers will help in identification and isolation of the gene controlling the flowering time trait.     

Analysis of dominant spring mutations in rye

The dominant mutant genes responsible for the spring habit were studied in seven rye plants according to the developed scheme of two-step crosses and analysis of the F₂ progeny. The genotypes with a particular genetic formula (heterozygote) were obtained by crossing the studied plants with the winter rye Korotkostebel’naya 69 carrying the recessive genes that control the winter habit of plants. Heterozygotes yielded by different combinations were crossed with each other. The F₁ hybrids were either self-pollinated to obtain F₂ progeny or crossed with the winter rye. Analysis of the progeny suggests that all seven plants carry the same gene.