genome relationships among elytrigia (= agropyron ) elongata , e . stipifolia , " e . elongata...
TRANSCRIPT
GENOME RELATIONSHIPS AMONG ELYTRZGZA (= AGROPYRON) ELONGATA, E . STZPZFOLZA, "E.
ELONGATA 4x," E . CAESPZTOSA, E . ZNTERMEDZA, AND "E. ELONGATA 1Ox9'
Department of Agronomy and Range Science, University of California, Davis, Califor7mia 95616, U.S.A.
Hybrids were obtained from the crosses Elytrigia elongata (Host) Holub X "E. elongnta 4x", E . stipifolia Czern. ex Nevski X "E. elongata 4x," "E. elongata 4x" X E . caespitosa ( C . Koch) Nevski, and E. intermedia (Host) Nevski X E. caespitosa. "Elytrigia elongata 10x" was crossed with four ditelosomic additions of E. elongata telosomes to Triticum aestivum L. em. Thell. Elytrigia intermedia was crossed with ditelosomic addition of "E. elongata 10x" telosome 7e1,a to T. aestivum. The S genome of E. stipifolia appears to be related only very remotely to the E genome of E. elcmgata. "Elytrigia elongata 4x" has two modified E genomes, which are designated E" and ESC. The genomes of E. caespitosa, tentatively designated XI, and XI,', are related to each other; both are considered to be distantly related to the E genome. Elytrigia intermedia has two genomes, designated N and Nk, that are distantly related to the E genome and one genome of an unknown origin tentatively designated XI. It is suggested that "E. elongata lox" has at least two genomes that are related to the E. genome.
On a produit des hybrides en croisant Elytrigia glongata (Host) Holub x E. elongata 4x, E. stipifkilia Czem. ex Nevski x E. elongata 4x, E. elongata 4x x E . caespitosa (C. Koch) Nevski, et E, intermedia (Host) Nevski X E . caespitosa. On a croist Elytrigia elongata 10x ainsi que 4 additions ditClosomiques des tilosomes de E. ekongata avec Triticum aestivum L. em. Thell. On a croisk Elytrigia intermedia et l'addition ditCloiomique du tClosome 7el,cr de E. elongata 10x avec T . aestivum. Le gtnome S de E. stipqolia semble ne s'apparenter que de t&s loin au genome E de E. elongata. Elyrrigia elongata 4x a deux ginomes E modifiks, connus sous la disignation ES et ESc. bas gCnomes de E. cuespitosa, connus tentativement comme X,, et Xc15, s'apparentent %'un i l'autre; on considkre que les deux s'apparentent de loin au gCnome E. Elytrigia intermedia a deux gCnomes, connus comme N et N1, qui s'apparentent de loin au ginome E, et un ginome d'origine inconnue que l'on dCsigne tentativernent comme X4. On suggere que E. elongata 10x posskde au moins deux gCnomes qui s'apparentent au ginome E.
[Traduit par le journal]
Most of the species of the genera Elytrigia (= Agropyron in broad sense), Ebymus, and Sitanion are affiliated in a single large polyploid complex (Stebbins, 1956). A conspicuous feature of this complex is that it is built from a remarkably low number of basic genomes, even though it involves over 100 polyploid species occurring throughout the Old World and the Americas. The most widespread genome among the polyplsids is the S genome that has been identified in the Old World diploid species Elytrigia stipifolin (Czern. ex Nevski) Nevski, E . libanotica Hack., and E . fauri (Boiss. et Bal.) Tzvelev, and in the New World diploid species E. spiccktu (Pursh) Love (Dewey, 1974, 1975; Stebbins and Pun, 19531). The second genome most widespread among the polyploids is the J genome of Elymus junceus Fisch. The third basic genome identified in the complex is the E genome that occurs in E!yfrigia elongafa (Host) Holub, 2n - 2x - 14. Another genome, unfortunately designated J as that of Ebynau.~ jllnceus (Cauderon and Saigne, 1961; Cauderon,
Manuscript received August 1, 1981.
Can. J. Genet. Cytol. 23: 481-492, 1981.
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1966), is found to occur in the species of Elytrkgiea .g'ut.mc.eu complex, diploid E. hessartahica (Savul. et Rayss) Holub (= A. besst~aa&fc.u?n Savul. et Rayss, E / ~ Y B ~ U S striarufus Runemark), tetraploid Elytrigin juncsi$or-mis L@ve et L ~ v e (= '4. juncsun~ L. ssp. boreo-utlanticuraa Sirnsnet et Guinochet), and hexaploid E. juncsca (L.) Nevski (= A . junc-rum L. ssp. medirerr~lnssrm Sirnonet). The complex also involves at least one genome of Hordeurn (Stebbins et a!., 1946; Stebbins and Vaarama, 1952, 1954; Stebbins and Snyder, 1956; Dewey, 1968, 1971).
Stebbins and Pun (1953a) obtained a hybrid from a cross between E. libancatica, which they emoneously called A . cc~espi~osum C. Koch (= E . cas,~pitnsa (C. Koch) Nevski), and E. .gakratu. The hybrid had almost complete chromosome pairing, suggesting that the two species have very similar genomes. Stebbins and Pun (1953a) further speculated that the E genome of E . elongatla may actually be a modification of the S genome present in these two species. If that is the case, the number of basic genomes involved in the construction of the polyploid complex will be further reduced. However, no hybrid involving any of the S genome diploids and E. elongala has yet been produced, so the relationship between the % genome and the E genorne is not known.
Likewise, the involvement of the E genome in the origin of polyploid species of the complex has not been experimentally tested. Stebbins and Bun (195389) and later Cauderon (1958, 1966) concluded that the E genome must be present in E. I'n~er~nedia (Host) Nevski., 2n = 6 x = 42, and ' T . elongata B O x . ' '
The present author developed Qisomic and ditelosomic additions in which chro- mosomes of E. elnngata were added to the chrsmosome complement of Tra'tisum a~stivrlm L. em. Thell. and determined the homoeology between the added E. s~lo~agcata chromosomes and wheat chromosomes (Dvoihk and Knott, 1974; Dvo"rk, B 980). These additions were then crossed with additions involving hornoeologous chromosomes of " 'E. ekongata 10x ' ' sand E. a'rzrs~nnediu, and pairing frequencies between Elylrigic~ chromosomes were determined. The pairing was invariably low or absent, suggesting that " E . elongara 18x" and E. intermedia do not share homologous genomes with E. ~longuta (Dvo'i.hk, 16375, 198 I ) .
To learn more a b u t the relationship of E. eCongatu with diploid and polyploid species of the complex, interspecific hybrids involving E. elongutu, " E . elongata 4x, " E. s~ipi$ipliu, E . ~ ' u e ~ p i t o ~ ~ ~ (C. Koch) Nevski, and E. i~2fsrmedia were produced m d their meiotic behavior was evaluated.
Materials and Methods Elyfrigia elongntci was obtained from L. E. Evans, University of Manitoba. Winnipeg;
the accession originated from Tunisia (G. L. Stebbins, personal communication). Elytrigicl stipijolia and ' X . elongatsa 4x" were received from D. R. Dewey, University of Utah, Logan. ECyfrigia C ( E C S ~ ~ ~ O S ( I accession A-62-62 was supplied by Dr. Dewey who received it from V. Jaaska, Institute of Zoology and Botany, Tartaa, Estonian S.S.R. Dr. Jaaska also supplied " ' E . slolagcnfu 10x" accessions 24 and 28 which he collected in Crimea. Accessions PI 206259 and PI 281863 of E . in~errnecbia were received from Dr. S. Dieaz, Regional Plant Introduction Station, Pullman, Washington. Accession PI 281 863 was erroneously designated A . junceuna (L.) P.B.
Interspecific crosses were made in the greenhouse. Two-week-old seeds were surface- sterilized, and embryos were excised and placed on a filter-paper platform in a vial with a liquid medium. The medium (Table I) was a modification of B-5 medium developed by Gamborg eb al. (1968). Seedlings obtained by embryo culture were transplanted directly into pots and covered with glass jars for several days to prevent their dessication. Slides for cytological analyses were prepared by the standard acetocarmine method. A minimum of 50 pollen mother cells (PMCs) were analyzed in each hybrid. except for the combination E. infernzedia x E. caespitoscz, for which only ten cells could be analyzed completely.
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GENOME RELATIONSHIPS AMONG ELURIGM
TABLE I
Modified B-5 liquid medium for embryo culture
Compound mg per one liter
NaH2W,. H20 150.Q KN03 2,500.00 (NH412SOd 134.00 MgSO, - HzO 250.00 Fe-EDTA 35.00 CaCB2 - 2H20 150.00 MnSO, . H,O 10.00 H3BO3 3 .oo ZnSf.3,. 7H20 2.00 Na4Mo04 2H20 0.25 CuSO4 0.03 Co612 - 6H20 0.03 KI 0.75 Nicotinic acid 1 .OO Thiamine 10.00 Pyridoxine 1 .OO Inositol 2,00Q.00 Glutarnine 400.00 Sedne 80.00 Cy steine 10.00 Sucrose 60,000.00
Adjust pH to 5.5 with 1 N NaOH and filter-sterilize.
To assess the relationship of the E. elongata genome with genomes of " E . elongata IOx," Triticum aestivum cv. Chinese Spring and several ditelosomic additions of E. elangcttca telosomes to the chromosome complement of Chinese Spring wheat, were hybridized with "E. elongnta 10x." A hybrid was also obtained from a cross between ditelosomic addition 7e1,a and E. intermedia. In this ditelosomic addition, a telosome derived from an "E. elorsgata BOX" chromosome designated 7e1, was added to the chromosome complement of T. aes t i~wn cv. Thatcher (Sharma and Knott, 1966). Embryos from these crosses were also artificially cultured. Slides were scanned systematically, and the pairing behavior of the telosome and overall chromosome pairing were recorded in at least 50 cells.
The reasons for abandoning the name A. varnense in favor of 'T . elongata 1Qx" and the use of Eiytrigia instead of Agropyron in broad sense are explained elsewhere (Dvoiak, 1981).
Results Elytrigia rlongata x ' 'E. e!ongata 4x": A maximum of one quadrivalent per
cell was observed at metaphase I (MI) in "E. elongata 4x" (Table 11), which implies that "E. elorzgata 4x" is an alloploid. A single hybrid plant was obtained by crossing E. elczngata with " E . elongntu 4x. " The plant had 22 instead of the expected 2% chromosomes, which was presumably due to disomy in one of the parental gametes. The chromosome pairing in the hybrid is recorded in Table 11. A high frequency of trivalents, with a mean of 2.2 per cell and a range from 0 to 5 per cell, showed that ""E eelongata 4x" chromosomes in the hybrid paired both autosyndetically and allosyndetically. Both "'E. elongata 4x" genomes appeared to be related closely to the genome of E. elongata. A single quadrivalent or quin- quevalent, which were observed in several cells, suggested that at least one trans- location among the genomes was present.
Elytrigia stip?bliu x " E . ~longatn 4x": The former species was hybridized with both E . elongata and " E . elongnta 4x." Both crosses yielded hybrids. Two
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GENOME, RELATIONSHIPS AMONG E L ~ R I G I A 485
seedlings that were obtained from the cross involving E. elongata stopped growing after several months and eventually died. No hybrid lethality occurred in the cross involving " E . elongata 4x. "
Meiosis of the E . stipifolia x " E . elongata 4x" hybrids was characterized by a high number of ring bivalents but a low number of trivalents (Table 11). This, plus the uniformly high number of univalents (Table 11), clearly showed that most of the pairing was between chromosomes of the genomes of "E. elongata 4x." Elytrigia stipifolia paired very rarely with the chromosomes of "E. elongcita 4.x ,' ' indicating that the two species have different genomes that are only distantly related phylogenetically .
"Elytrigiu eloragata 4x" x E. caespitosu: Two plants of E . caespitosa were analyzed meiotically. They differed from each other in the number of multivalents per cell. One plant had a maximum of two quadrivalents, had a hexavalent regularly, and had an octavalent occasionally (Table 11). The other plant had only a single trivalent or quadrivalent. The difference in the meiotic behavior and particularly the high frequency of the hexavalent in the former plant indicated that most of the multivalents in the former plant resulted from translocation heterozygosity rather than from heterogenetic chromosome pairing.
Chromosome pairing at MI in the hybrids was characterized by a high number of ring bivalents (Fig. 1) and multivalents; univalents were rare (Table 1%). Dvoiak (I98B) crossed a number of T. nestivnm-E. elongata ditelosomic additions with E. caespitosa, and observed that the E. elonguta telosomes paired very seldom with E. caespitosu chromosomes. In the same hybrids, E. caespitosu chromosomes paired autosyndetically at frequencies that were substantially higher than were those of the allosyndetic pairing of the E. elongata telosomes with the E. caespitosa chromo- somes. This suggests that E . elongata and E. caespitosu do not have a common genome and that most of the pairing in the " E , elonguta 4x" x E. cae.~pitosa hybrid was autosyndetic. In spite of the relatively regular ehromosome pairing resulting in frequent normal tetrads (Pig. 2), the hybrids had very low pollen fertility. Of two hybrids for which pollen fertility was determined, one had 1.8% and the other 0.3% stainable pollen. Obviously, the two genomes constituting the chromo- some complement of "E. elongutu 4x " are differentiated structurally and genetically from each other. The same is true of the two genomes of E . caespitosu.
Elytrigia intermedin x E. caespitosa: Chromosome pairing at MI in two E. inteamedia plants was investigated. Multivalents occurred in both plants (Table 1).
Hybrids E. inter-anedia x E. caespitosa were rhizomatous and tall and had long spikes, spikelets had five or more florets. Both glumes were obtuse (like those of E. caespitosa) without the point present in the E. intermedia parent. Except for being rhizomatous, the hybrids resembled "E. elongata 4x" and " E . elongatn lox." Since only ten cells in a single hybrid were analyzed (although more cells were inspected), the results of meiotic analysis must be considered preliminary. The cells had numerous multivalents (Table 11). A pentavalent, consisting of two rings joined by the fifth chromosome, was often observed. Presumably both autosyndesis and allosyndesis occurred. The E , intermedia x E. caespitosa hybrids had non- dehiscent anthers and were sterile.
Crosses invollting addition lines: The hybrid Chinese Spring x " E . elongata 10x" had an average of 15.1 univalents per cell (Table 111). In haploid Chinese Spring, the average number of univalents per cell is close to 21 (Miller and Chapman, 1946; Dvoi-ak, 8977). Even if all "E. elongata IOx" chromosomes paired auto- syndetically in the hybrid, an average of five Chinese Spring chromosomes must
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GENOME RELATIONSHIPS AMONG EEYTRIGIA 487
have paired as well. Thus, the hybrid had increased heterogenetic pairing. In spite of high overall chromosome pairing in the hybrids between Chinese Spring-E. clnngata ditelosomic additions and "E. elonguta lQx," the pairing frequencies of E. elongcrta telosomes, with a possible exception of telosome 7EL, were %ow (Table HI), suggesting that " E . elorzguta 1Qx" does not have a genome completely ho- mologous to that of E . elonguta.
" E . elorzgatcp 10x" telosome 7e1,cr paired in 20.2% of the cells in a hybrid involving E. inrerrnedda (Table 111). The activity of the wheat diploidizing genes was at the normal level in T. aestivum x E. intermedia hybrids if the hybrids had an average of two to three chiasmata per cell (Dvoihk, 1981). Since the present hybrid had 9.5 chiasmata per cell, the activity of the wheat diploidizing genes had to be partially suppressed by the Elytrigin genotype.
Discussion Chromosome pairing in the E. rloizgatu x " E . elongatw 4x" hybrid showed
that the genomes of "E. elongata 4.r" are very closely related to the genome of E. elongatu. A similar conclusion was made from karyotype analysis by Heneen and Runemark (1 972b) and by Breton-Sintes and Cauderon (1978). From the pairing frequencies of individual E. elongatn telosomes with the "'E. elorzgata 4.x" chro- mosomes, it was concluded that slight differentiation has occurred in every chro- mosome of the two species (DvoYr&, 1981). Both genomes of "E. eloagnta 4x" appear to be modified versions of the E. elongnta genome and will therefore be designated EQnd ES' (Table IV).
Chromosome pairing of 3.4' + 4.5" -i- 2.8" ' -i- 8.11'" in a triploid hybrid E , eloizgata x E . .junseiformis f i v e et Love (Cauderon and Seigne, 1961) was essentially identical to that in the hybrid E. rlongata X ' 'E . elongata 4x. ' ' Moreover, E. 1~essurabic.u~ a diploid relative of A . j u n ~ e ~ ~ r r n i s , has a karyotype very similar to that of E. plsngatu (Heneen and Runemark, 1972a). It appears, therefore, that the species of the j u n c ~ n complex - E. bessc~rubicu, E . ,juracuiformks, and E. jzincea (L.) - also possess an E genome. It is proposed that the genome of E. hesscrmhicn be designated E' and those of E . juncei$orme be designated Ea and Eb (Table IV). The high number of trivalents of autosyndetic origin in the hybrid E. .y'uncea x E. ibztermedia (Cauderon, 1958) suggests that E. juncea has three modified E genomes. The proposed genome formula for E. juncea is EaEaE''EhECEC.
The poor pairing that occurred between the chromosomes of "E. elongutu 4x" and E. stipifdplia revealed that the E genome is related only remotely to the genome of E. stdpifolia, hence the designation of the two genomes by different letters - E for E. ~longcpta and S for E. stipifolia - is upheld. The S genome has been further detected in diploid species E. l ik~~nstdca, E. tauri, and E. spicatu (Stebbins and Pun, 1953a; Dewey, 1974, 1975). High or complete sterility of the hybrids among these species suggests that the genomes of E. libunotica, E. stigifoliu, and E. spicatu are modified with respect to each other, It is proposed that the genome of E. ldhunotica be designated S, that of E. stipkfolia S" and that of E. sgicata SP (Table IV). The exact relationship of the E. rauri genome to these genomes is unknown.
It was concluded that E. cuaLsgirosa, in spite of its morphological similarity to E. elortgata, does not have homologous genomes with E. elongata. Multivalents observed in the "E. elongata 4x" >( E . ~ u e ~ p i t o s ~ ~ hybrids suggest that the chro- mosomes of the two species occasionally pair allosyndetically. Since no extant species is known that would qualify to be the diploid ancestor of E. cuespitosa, the E. cs~rspltosa genomes will be designated tentatively as unknown genomes X,,. The genome formula of E. caespitosa will be X,,XI5X~,XCl5.
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GENOME RELATIONSHIPS AMONG ELYTRICiIA
Proposed genome designations for some of the species of the genus Elytrigia
Ploidy Species ( 2 n ) Genome formula Remarks
E . elongnta (Host) Holub. 2x EE "E. edongata 4x" 4x ESESESCESC C'
"E. elongatn 10x" 1 Ox ? E . bessarabica (Savul. et Rayss) Lij ve 2x EGE' E. junceiformis Love et Love 4x E"EaEhEb E . juncea (L.) f i v e 6~ E ~ E ~ E " E " E C E C
E . caespitosa ( C . Koch) Nevski 4x X,,X,5C15XCl,** XIS may equal to N. E. intermedirt (Host) Nevski 6x NNN1NiX,X4 N and XIS are related to E E. libanutica (Hack.) Holub. 2x SS E. stipifolia (Czern. ex Nevski) Nevski 2x SSSS E. spicatu (Pursh) Liive 2x SPSp
*Genomes differing by superscripts are modified with respect to each other. **Genomes differing by subscripts are different from each other.
Lyubimova (1970), who studied chromosome pairing in a hybrid E. intermedia x "E . elongata lOx", concluded that " E . elongata lox' ' originated from hybrid- ization of E . intermedia with E . caespitosa. Jaaska (1972) upheld Lyubimova's hypothesis on the basis of comparison of six allozyme systems in E . intermedia and " E . elorlgata 10x". There are several reasons, however, why this hypothesis seems unlikely. Elytrigia elongata, ' ' E . elongata 4x9', and ' ' E . elongatcc 10x" have similar ecological requirements. All are adapted to saline soils, unlike E. intermedia and E . caespitosa, which appear to be intolerant of salinity (McGuire and Dvoiak, 1981). Furthermore, the former three species are caespitose, whereas E. intermedia is rhizomatous. The rhizomatous growth habit persisted in the E. intermedia x E. caespitosa hybrid. Thus, E . elongata, " E . elungata 4x," and " E . elongata /Ox" appear to be affiliated with each other more than with E. intermedia or E . caespitosa.
Jaaska (1972) speculated that E. caespitosa contributed two of the three genomes of E. intermedia. It was shown here that E . caespitosa chromosomes pair with E . intermedia chromosomes. This finding supports Jaaska's hypothesis. However, since the extent of this allosyndesis in the E. intermedia x E . caespitosa hybrid could not be evaluated reliably, the assessment of the relationship between the genomes of E. caespitosa and those of E. intermedia will require additional work.
A hypothesis suggesting that a genome of E . intermedia and " E . elongata 10x" may be present in T. aestivum, originally proposed by Vakar (1935), was recently resurrected by Konarev (1979). Konarev concluded by immunochemical analysis of ethanol-soluble seed proteins that the D genome present in Aegilops squarrosa L. and T . aestivum may be present in " E . elongata 4x," and that the D and B genomes of T. aestivum may be present in "E. elongata lox." Dvoiik (1971) obtained a hybrid from a cross between E. elongata and Aegilops squarrosa. Not only did the hybrid not resemble "E. elongata 4x," but pairing between the chromosomes of E. elongata and Ae. squarrosa was poor which contrasts with the high autosyndesis occurring among the " E . elongata 4x" chromosomes (DvoIak, 1981). Clearly, "E. elongata 4 x ' A o e s not have a D genome but does have two E genomes. Genome homology between T. aestivum and " E . elongata lox" seems equally unlikely (Dvoiak, 1975, 1976, 198 1).
Stebbins and Pun (1953b) and later Cauderon (1958, 1966) suggested that E. intermedia has at least one genome homologous to, or closely related to, that
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of E. ekongceta. The former authors also speculated that the E genome may be present in " E . ehngata BOX." In a hybrid between addition lines, E. intermedia telosome 7in,a paired with E. elsngntw homseologue 7E in 4.3% of the cells (Dvoiak, 1981). In a similar manner, some of the added " E . elongatu IOx" chromosomes paired with added E. elongata homoeologues. The frequencies of pairing between specific added homoeologous chromosomes of these two species ranged from 0.0 to 13.6% of the cells (Dvoihk, 1975, 198%). In the hybrids obtained from crosses between E. elongnta ditelosomic additions and " E d elongatn 1Ox" studied here, the E. ehngata telosomes paired from 0.0% to 25.0% of the PMCs. Thus, in all cases the pairing between chromosomes of E. rlongafa, and those of "'E. elongata 10x" and E. interrnedicr was low.
"Elytrigka eloragcrta BOX" telosome 7e1,a paired in 20.2% of the cells in the hybrid ditelosomic addition 7e1,cu x E . intermedia. The pairing frequency of the 7e1,a telosome was similar to the pairing frequencies of wheat and E. elongata telosomes in T. aestivurn x E. Entermedin hybrids which had an average number of chiasmata ger cell similar to that of the hybrid involving telosome 7e1,a - 9.5 chiasmata per cell. Trkthc~m ~zestii'adrn telosomes 7AL and 7DS paired in 16.0% and 17.1% of the cells in the hybrids which had 7.4 and 7 . 8 chiasmata per cell, respectively (DvoEhk, 198 1). Elytrigin elongata telosome 4EL paired in 7.7% and 17.7% of the cells in hybrids having 7.6 and 11.2 chiasmata per cell, respectively; telosome 6Ea paired in 15.8% and 30.0% of the cells in hybrids having 8.5 and 9.2 chiasmata per cell, respectively; and telosome 7EE paired in 5.4% and 8 1.1% of the cells in hybrids having 7.9 and 7.0 chiasmata per cell, respectively (Bvo?&, 1981). This suggests that the "E. elangata BOX" genome that contributed chro- mosome 7e1, is no more related to the genomes of E. intermedia than is the genome of E. elongarn. Using the pairing frequencies of the two wheat telosomes as a reference the degree of relatedness between the genome of E . elr~rzgaec~ and the specific genome of "E. elongata 10.~" on one hand and the genomes of E. intermeciia on the other is of a similar magnitude as is the degree of relatedness between the A and D genomes of T. aestivum. Hence, it appears that the genomes of E. edongata, E. intermedkca, and "E . elongata B0.x9' are too differentiated to be considered homologous or modified genomes.
Dvoiak (1981) showed that E. elongata telosomes paired with E. internzsdiu chromosomes in monotelobivalents and monotelotrivalents. This suggests that E . injerrnedin has two genomes that are phylogenetically related to the E genome. The two genomes will be designated N and Ki. The third genome, of an unknown origin, is related only distantly to the two genomes (Stebbins and Pun, 195%; Dewey, 1962; Cauderon, 1946). This unknown genome will be tentatively designated X,. The genome formula of E. intermedia then is NNN'NiX4X4.
' 'Ejytrigia elongata 1 Ox' ' has considerable heterogenetic pairing (Peto. 1936). "Elytrigiu elongatce IOx9' appears to have owe group of three closely related genomes and another group of two closely related genomes, as suggested by the high frequencies of bivalents and trivalents, but relatively low frequencies of quadrivalents and quinquevalents in hybrids from a cross between tetraploid and hexaploid wheat and "E. elongnta 10n" reported here and by Peto (1934). In the hybrids of E. elongata ditelosomic additions with " E . elsngatn 18.xU, the E . elongaba telosomes paired mostly in monotelobivalents; they seldom paired in monotelotrivalents and never paired in larger multivalents, although trivalents, quadrivalents, quinquevalents, and larger multivalents were present (Table 11). This probably means that E. elongata chromosomes are related more closely to the doublet of the "'E. ~longata BOX" genomes than to the triplet.
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G E N O M E R E L A T I O N S H I P S A M O N G I%JT'RIGIA 49 1
The relationships among E. elongata, "E. elongatn 4x," E. caespitosa, E. intermedia, and " E . elongatn lox" illustrate that the existence of a polyploid series of closely related taxa is in itself insufficient reason for concluding that a species at one specific level of ploidy is a component of a species at a higher ploidy level. Of the species considered here, tetraploid "E. elongata 4x" is clearly not an ancestor of the decaploid "E. eloizgata 10x" since the chromosomes of the tetraploid are more closely related to those of E , elorzgata than to the chromosomes of the decaploid species. Nor does it appear that tetraploid E. caespitosa and hexaploid E . intermedia are the ancestors of " E . elongata 10x". Elytrigia caespitosa E . intermedia, " E . elongata 1 Ox" and ' 'E. elonguta 4x" presumably originated from evolving diploid populations which gave rise to the extant E . elongata and E . bessarabica. "Elydrigia elongata 4x" is a product of a more recent speciation event than the E. caespitosa, E. intermedia, and " E . elongata 10.u" .
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