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Several genetic maps of soybean [Glycine max (L.) Merr.] have been developed during the past decade. Different markers have been used to construct these maps including restriction fragment length polymorphism (RFLP), amplified fragment length polymorphism (AFLP), random amplified polymorphic DNA (RAPD), simple sequence repeat (SSR), and classical markers. However, virtually none of the maps and linkage groups developed has been associated with specific soybean chromosomes. For example, there are 13 single dominant resistance genes at 7 different loci that control Phytophthora sojae. These resistance genes (Rps genes) have not been located on any chromosomes, but several have been associated on classical and molecular maps. For example, the Rps1 locus is associated with molecular linkage group N. The objective of this study was to locate the Rpsl locus on a specific soybean chromosome using primary trisomic analysis. Crosses were made between 10 soybean trisomic lines and cv. Resnik (containing Rps1-k). The F 2 populations from trisomic parents were inoculated with race 3 of P. sojae to determine the ratio of resistant to susceptible plants. Nine of the F 2 populations tested segregated in a normal 3:1 ratio. The F 2 population of triplo 3 segregated in a 2:1 ratio, the expected segregation ratio for a single dominant gene if the gene is located on the extra chromosome, suggesting that the Rpsl locus is on chromosome 3. Thus, chromosome 3 corresponds to molecular linkage group N of the integrated genetic linkage map.

a complete set of primary trisomic individuals (each chromosome is trisomic in one member of the set) has Primary trisomics provide an excellent cytogenetic tool to associate allowed the establishment of cytogenetic maps. The trigenes and linkage groups with their respective chromosomes. A complete set of 20 primary trisomics (2x 1 41) has been established somic sets have been useful in positioning classical genes in soybean [Glycine max (L.) Merr.]. A linkage map of soybean with and molecular markers on specific chromosomes by the 20 consensus linkage groups has recently been defined. Because simple use of modified genetic ratios associated with trisomic sequence repeat (SSR) markers map to defined single positions in inheritance or by dosage effects from the extra chromothe soybean genome, the association of a SSR locus with a chromo- some (Tsuchiya, 1983; Carlson, 1988; Khush et al., 1984, some will provide an unambiguous association of a linkage group to McCouch et al., 1988; and Young et al., 1987). a specific chromosome. The objective of this work was to demonstrate In soybean [Glycine max (L.) Merr.], the complete the use of SSR markers to associate linkage groups with chromosomes set of primary trisomics (2x 1 41) has been difficult by means of primary trisomics. One population of F2 plants was devel- to establish because mitotic metaphase chromosomes oped from an F1 hybrid trisomic for chromosome 13 (Triplo 13) and are morphologically indistinguishable. Early attempts a second F2 population was obtained from a F1 hybrid trisomic for

A primary trisomic (2n = 2x + 1) is an excellent cytogenetic tool for locating Mendelian genes on a particular chromosome and for associating a conventional genetic linkage group with a specific chromosome. The objectives of this study were to produce and identify 20 primary trisomics (2n = 2x + 1 = 41) of soybean [Glycine max (L.) Merr.] and use them for associating linkage groups with specific chromosomes. Primary trisomics isolated from the progenies of asynaptic and desynaptic mutants, male sterile lines, neutron-irradiated plants, and tissue culture-induced sterile mutants were backcrossed (BC 4 ) with soybean cv. Clark 63. They were identified at pachytene on the basis of the diagnostic landmarks such as association of the extra chromosome with its normal homologues in a trivalent configuration, distribution of euchromatin and heterochromatin, total chromosome length, arm ratios, and by examining chromosome pairing at metaphase I in F 1 plants with 2n = 42 chromosomes isolated from crosses among primary trisomics. The F 1 plants from similar primary trisomics exclusively showed 21 II and those from dissimilar primary trisomics exhibited microsporocytes with 20 II + 2I, 1 III + 19 II + 1I, and 2 III + 18 II configurations. Thus, 20 primary trisomics were tentatively identified and were designated as triplo 1 through triplo 20. Female transmission of the extra chromosome in 20 primary trisomics ranged from 27.3% (triplo 20) to 58.5% (triplo 9). On the basis of the modification ratio (17:1) of a gene located on the extra chromosome in primary trisomic analysis, three marker genes Eul (seed urease), Lx1 (lipoxygenase-1), and P2 (puberulent) were located on chromosomes 5, 13, and 20, respectively. The ultimate aim of this project is to develop by means of primary trisomics a universal cytogenetic map of soybean by associating existing classical and several molecular maps with the specific chromosomes.

The formation of unreduced gametes in some hybrids between disomic D-genome substitutions (DS) of durum wheat cv. Langdon' and rye provides a convenient approach for the rapid introduction of D-genome chromosomes into hexaploid triticale. Meiotic pairing at metaphase I and seed fertility in spontaneous and colchicine-induced amphidiploids derived from F, hybrids between a set of Langdon' DS and 'Gazelle' rye were analysed. The purpose was to determine the effects of the substitution of D-genome chromosomes for their A- and B-genome homoeologues on hexaploid triticale and to select stable disomic D-genome substitutions of hexaploid triticale. The results showed that the disomic substitutions with D-genome slightly increased the frequency of univalents (1.0-3.13) compared with the 'Langdon' control primary hexaploid triticale (0.76). Substitutions 2D(2A) and 3D(3B) were partly desynaptic. The substitutions 1D(1A), 1D(1B) and 7D(7B) exhibited high seed fertility but the others had decreased fertility. Except for 2D(2A), 5D(5A), 3D(3B) and 5D(5B), 10 of the 14 possible hexaploid triticale D-genome disomic substitutions have been obtained. The results suggest that the poor compensation ability of some D-genome, chromosomes for their homoeologous A- and B-genome chromosomes is a major factor affecting meiotic stability and fertility in the hexaploid triticale D-genome substitutions.

An individual lacking one chromosome is called monosomic and is designated as 2n - 1. Monosomics are useful for locating genes to specific chromosomes and in the assignment of linkage groups. Monosomics are rare in diploid crops. The objective of this study was to determine the origin, morphology, cytology, fertility, and breeding behavior of two spontaneously produced monosomics (2n = 39) in soybean [Glycine max (L.) Merr., 2n = 40]. The two monosomic plants were identified among progenies of triplo 3 (BC3) and triplo 6 (BC 4 ) trisomic plants, backcrossed to 'Clark 63' as the recurrent parent. The two monosomics are designated as mono-3 and mono-6. The two monosomic and one disomic sibling plants were grown in the greenhouse to evaluate reproductive and morphological traits. Chromosome associations were examined at Metaphase I. F 1 hybrids from the crosses of monosomics with Clark 63 and selfed populations were used to evaluate breeding behavior. Morphologically, mono-6 was similar to the disomic, while mono-3 was smaller with reduced vigor. Both monosomics showed 19 II + 1 I chromosome assodation at Metaphase I. Pollen fertility in mono-3 was 8.8% and in mono-6 was 20.0%. Mono-3 and mono-6 produced 59 and 176 S 1 (first selfed generation) seeds. Female transmission (mono-3 Clark 63) in mono-3 was 6.5% and self-pollination yielded 3.5% 2n - 1 offspring. By contrast, mono-6 was not transmitted among 105 S 1 plants, although one plant with 39 normal chromosomes plus one acrocentric chromosome was found. This study demonstrates that monosomics in soybean are viable and fertile, but that the transmission rate is sporadic.

Durum wheat ‘Langdon’(LDN) caused a high frequency of first-division restitution (FDR) and partial fertility in hybrids with rye, Secale cereale L., and Aegilops squarrosa L. In order to determine the genetic control of FDR, a complete set of 14 Langdon durum D-genome disomic substitution lines (LDNDS) was crossed with ‘Gazelle’ rye and one accession (RL5286) of A. squarrosa. The microsporogenesis and fertility of the hybrids were studied. The results showed that most of the hybrids expressed a high frequency of FDR and partial fertility. However, the hybrids of 2D(2A), 4D(4A), 5D(5B) and 6D(6B) crossed with both rye and A. squarrosa, as well as 1D(1A) with A. squarrosa, had either little or no FDR and were completely sterile. These hybrids had different types of first meiotic divisions compared with LDN control hybrids. The hybrids with 2D(2A), 4D(4A) and 6D(6B) had a high frequency of random segregation of chromosomes at the first division. The hybrids with 5D(5B), as expected, showed high homoeologous pairing. The hybrid of 1D(1A) with A. squarrosa had a high frequency of equational division at first division. These results suggest that the reduced or absent FDR in such hybrids might be related to the substitution of chromosomes with an FDR gene and poor compensation ability of the D-genome chromosomes for their homoeologous A- or B- genome chromosomes. Cytological analysis suggested that chromosome 4A in LDN most likely carries a gene for high frequency of FDR in hybrids. In addition, some monads were observed at the end of meiosis in the hybrids of 3D(3A) and 6D(6A) crossed with rye. They were formed from FDR cells that failed to divide at second division, suggesting that the LDN 3A and 6A chromosomes might carry genes for normal second division of FDR cells in the rye crosses.

loids, a large number of triploid plants have been iso- lated from the progeny of different lines of homozygous Autotriploids (2n 5 3x ) are an excellent source of producing pri- 'Clark 63' and selfed population were used to evaluate breeding behav- soybean have not become useful sources for generating ior. Results revealed that the hypertriploid expressed more vigorous primary trisomics (2n 5 2x 1 1 5 41) in soybean. vegetative growth than the corresponding disomic sibling. At Meta- Recently, we obtained a spontaneous hypertriploid phase I, an average meiotic chromosome pairing was 0.10 IV 1 11.18 (2n 5 3x 1 1 5 61) in the progeny of a marker stock III 1 9.43 II 1 8.23 I, indicating that the four homologous chromo- T31 (glabrous, p2p2) and a primary trisomic line T190- somes mainly formed two bivalents. The hypertriploid showed 63% 47-3. The objectives of this study were to evaluate the pollen fertility and produced 98 seeds from self-pollination. Chromo- origin, morphology, cytology, fertility, and breeding be- some numbers in the selfed population of the hypertriploid ranged havior of a hypertriploid. from 2n 5 50 to 2n 5 69. However, the chromosome number in F1 plants from the cross of hypertriploid 3 Clark 63 ranged from 2n 5 44 to 2n 5 48 with an exception of one plant that contained 2n 5 56 MATERIALS AND METHODS chromosomes. Some plants with 2n 5 44 to 2n 5 47 had high seed One hypertriploid plant (2n 5 3x 1 1 5 61) in soybean fertility. The progenies of these aneuploid lines will segregate mostly was found among 10 F 1 plants from a cross T31 3 T190-47- into plants with 2n 5 41 chromosomes. This study suggests that soy- 3. T31 is a soybean line containing the homozygous recessive bean male and female spores tolerate a higher number of extra chro- glabrous (p 2p2 ) gene (Stewart and Wentz, 1926). T190-47-3 is mosomes than most true diploid plant species, corroborating the hy- an unidentified primary trisomic (2n 5 41). The T190-47-3 pothesis that soybean is a diploidized polyploid species. was originally produced by crossing soybean line T190 with Clark 63, and it has a pedigree of T190/Clark 63/F3/Clark63 (Xu et al., 1997). Soybean line T190 is a tissue culture-induced