Hereditus 116: 207-212 (1992)

Biosystematic research in Aegilops and Triticum J. GILES WAINES and DAVID BARNHART

Department of Botany and Plant Sciences, University of California, Riverside, C A 92521, U.S.A.

WAINES, J. G. and BARNHART, D. 1992. Biosystematic research in Aegilops and Trificum. - Heredifas 116 207-212. Lund, Sweden. ISSN 0018-0661. Received August 21, 1951. Accepted February 12, 1992

As Kihara had only I to 3 accessions of each diploid analyzer species in his germplasm collection, W E conclude the genome formulae for Aegilops and Triticum published by him between 1920 and 1960 were largely based on the typological concept applied to cytogenetic research. The same restriction applies to his concept of “modified genomes” in the tetraploid Aegilops species, which therefore may not actually be modified. Genome analysis by itself is not a very fine-tuned experimental technique. A biological specier concept based on several different biosystematic studies in Aegilops and Trificurn is preferable to a species concept based only on genome analysis in meiocytes of F , hybrids. Biosystematic studies recognize Aegilopa sharonensis, Ae. peregrinu, and Triticum urarfu as valid species distinct from other species. Our attempts tc resynthesize tetraploid wheats using Ae. spelfoides and Ae. searsii as female parents and T. monococcum and T. urarfu as male parents met with little success. There may be an embryo lethality mechanism operating in these F, hybrid combinations. Sterile hybrid plants were obtained with Ae. longissima, Ae. shuronensis. and Ae. bicornis as female parents in crosses with the two Trificum species as males. Amphidiploid seed was obtained with the use of colchicine.

J . G . Wuines, Deparfment of Bolunv and Planf Sciences, University of California, Riverside, California. 92.521-0124. U.S.A

Although there has been some recent molecular genetic research in the Aegilops-Triticum group, and cladistic research into possible phylogenies and classification, basic biosystematic research in this group is still largely lacking, or what has been published is often ignored. There is a mistaken assumption on the part of most modern re- searchers that biosystematic research was carried out thoroughly by EIG (1929) and Kihara and his co-workers between the 1920’s and 1960’s, and that there is no need for further work. This is not true. Some of the reasons for this view were set forth in the literature review and the discussion of WAINES (1969), and others will be mentioned here.

Genome formulae and modified genomes Most botanists are not aware that Kihara’s gen- ome formulae, while they consitute a monumental work, were largely based on the typological con- cept applied to cytogenetic research. Kihara had only a few ( I -3) accessions of each diploid ana- lyzer species (KIHARA 1937, Table 3) and it is doubtful because of the 1939-1945 war that he tested many more before the formulae reached their final form (KIHARA 1954, 1963). Nothing

approaching the total morphologic nor geographic variation was present in Kihara’s species collec- tion. Kihara realized this, for he said one possible explanation of what he called the “modified genomes” was that the appropriate diploid had not yet been found. This limitation on the validity of Kihara’s genome formulae was not appreciated by ZOHARY and FELDMAN (1962) nor by most people interested in evolution in Aegilops L. and Triticum L. since that time. The important point with regard to the “modified genomes” is that these genomes can only be thought of as modified in comparison with the accessions of the diploid analyzer genomes in Kihara’s collection that he actually used in crosses with the polyploids. ZOHARY and FELD- MAN (1962) did not check Kihara’s genome formu- lae, nor have many people after them. Thus, the “modified genome” concept is also based on one to three accessions, which again suffers from being typological.

Recently, we proposed that the female genome should be listed first in the genome formulae (WAINES and BARNHART 1990). Thus, the for- mula for tetraploid wheat Triticum turgidum L. would be BBAA, rather than AABB. The work of SUEMOTO (1973) suggested that the B genome donor contributed the cytoplasm of tetraploid wheat, and this was supported by more recent

208 J. G . WAINES AND D. BARNHART

Table 1. Genome and plasma type symbols for diploid Aegilops and Triticum species (after KIMBER and TSUNEWAKI 1988)

Species Symbol Synonyms

N* P*

T. monococcum L. T. urartu Turn. Ae. speltoides Tausch Ae. bicornis (Forsk.) Jaub. et Sp Ae. longissima Schw. et Muschl. Ae. sharonensis Eig Ae. searsii Feldman et Kislev Ae. mutica Boiss. Ae. tauschii Coss. Ae. comosa Sibth. et Sm. Ae. uniaristata Vis. Ae. caudata L. Ae. umbellulata Zhuk.

A A s Sb S1 S'

A A S,G S b S1 S' S' T , T ~ D Ae. squarrosa Tausch M Ae. heldreichii Boiss. N C Ae. markgrafi (Greuter) Hammer U

T. boeoticum Boiss., T. aegilopoides (Link) Bal.

Ae. Iiguslica Savign., Ae. aurheri Boiss.

~

*N = nuclear; P = plasma

Table 2. Genome and plasma type symbols for polyploid Aegilops and Triticum species. The so-called "modified" genomes are underlined (after KIMBER and TSUNEWAKI 1988)

Species Symbol Synonyms

N' P*

T. rurgidum L. BA B T. dicoccoides Korn, T. dicoccon Schrank,

T. aestiuum L. em. Thell.

T. timopheeuii Zhuk. GA G T. araraticum Jakubz. T. zhukouskyi Men. et Er. GAA G Ae. kolschyi Boiss. su S2 Ae. peregrina (Hakel) Maire et Weil. SU S' Ae. variabilis Eig Ae. cylindrica Host DC D Ae. uentricosa Tausch DN D Ae. crassa (4x) Boiss. DM D2 Ae. crassa (6x) Boiss. DDM D2 Ae. uauilouii (Zhuk.) Chen. DMS D2 Ae. juuenalis (Thell.) Eig DMU D2 Ae. ouata L. MU Mo Ae. geniculata Roth Ae. triaristata Willd. UM U Ae. neglecfa Req. ex Bertol. Ae. recta (Zhuk.) Chen. U M N U Ae. triaristara (6x) Willd. Ae. biuncialis Vis. UM U Ae. lorentii Hochst.

Ae. triuncialis L. uc U ssp. rriuncialis Ae. rriuncialis L. cu C ssp. persica (Boiss.) Zhuk.

*N = nuclear; P = plasma

T. carthlicum Nevski, T. durum Desf.

Men., T. sphaerococcum Perc., T. uauilouii Jakubz. EAD B T. spelta L., T. compactum Host, T. macha Dek. et

Ae. columnaris Zhuk. UM U2

chloroplast DNA studies (OGIHARA and TSUNE- W A K I 1988). As plant breeders, we have to list the female parent first. The genome and plasma type symbols for diploid and polyploid Aegilops and Triticum species are listed in Tables 1 and 2.

Placing the female genome first in the polyploid genome formulae allows us to group those poly- ploids together which have the same or similar

female genomes. Thus, the four Trificum poly- ploids have the B or G genomes which have many similarities with the S genome of Ae. kotschyi Boiss. and Ae. peregrina (Hakel) Maire et Weil. which, in turn, is derived either from Ae. searsii Feld. et Kis. (SIREGAR et al. 1988) or from Ae. longissima Schw. et Muschl. or Ae. sharonensis Eig ( Z H A N G et al. 1992).

Heredilas 116 (1992) BIOSYSTEMATICS IN AEGILOPS AND TRITICUM 209

Biological species concept

We recently stressed the need for a biological spe- cies concept in Aegilops and Triticum (WAINES and BARNHART 1990) as against a species concept based only on the genome formula (KIMBER and FELDMAN 1987; KIMBER and SEARS 1987). This will tend to stabilize the number of species in Aegilops and Triticum, and it will be of use to plant breeders and taxonomists. If chromosomes pair in F, hybrids then, according to KIMBER and FELDMAN (1987) and KIMBER and SEARS (1987), the parents have the same genome and are considered the same species. This view may be all right if the F, hybrid is fully fertile, but if it is sterile, it has the effect of lumping together species that are reproductively isolated. Genome analysis is not a very finely tuned experimental technique because it does not take into account the effects of pairing control gene polymorphisms at the diploid and tetraploid levels (SHANG et al. 1989). Thus KIMBER and FELDMAN (1987) and KIMBER and SEARS (1987) do not recognize that T. urartu Tum. is reproductively isolated from T. monococcum L. ssp. boeoticum Boiss. even though the F, hybrid is sterile and there is consid- erable published evidence which supports their isolation (JOHNSON and DHALIWAL 1976; SHARMA and WAINES 1981; SHANG et al. 1989). The work of KIMBER and FELDMAN (1987) and KIMBER and SEARS (1987) appears to be unaware of these biosystematic studies on diploid Triticum species.

A similar state of affairs exists for the validity of Ae. sharonensis as being biosystematically dis- tinct from Ae. longissima (KIMBER and SEARS 1987). The biosystematic evidence for separating the two species was presented by WAINES and JOHNSON (1972) and WAINES et al. (1982). The work of KIMBER and SEARS (1987) cites only the genome formulae ot' KIHARA (1954), and they appear to be unaware of later biosystematic studies.

There is need for further research as to whether Ae. kotschyi is biosystematically distinct from ,?e. peregrina. KIMBER and FELDMAN (1987) treat them as two separate species, but KIMBER and SEARS (1987) do not. The reasons for this different treatment by the same senior author in the same year are not explained. We think that these two species are biosystematically distinct and that they should be recognized as separate species.

Attempts to synthesize Triticurn turgidum Any botanist who travels in southern Turkey soon realizes that wild wheat (Triticum) populations oc- cur mostly on islands of basaltic soil and that they are largely absent from the red clay and limestone derived soils that surround these dark basaltic soils (HARLAN and ZOHARY 1966). These basaltic is- lands often contain populations of Triticum urartu, T. monococcum ssp. boeoticum and T. turgidum L. ssp. dicoccoides KOrn and/or T. timopheevii Zhuk. ssp. araraticum Jakubz., as well as Aegilops spel- toides Tausch ssp. speltoides Tausch and ssp. ligus- tica (Savign.) Zhuk. Other Aegilops diploids and polyploids may also be present, as they often grow in the vicinity on the red clay and Iimestone derived soils where Triticum species are absent.

If the B and G genomes of T . turgidum and T. timopheeoii Zhuk., respectively, are derived from an S genome species, for which there is consider- able published evidence (DVORAK and ZHANG 1990), the question is which S genome species was it, and how easy is it to resynthesize the tetraploids today? The only S genome species known to oc- cur in Turkey is Ae. speltoides for which there is present considerable morphological variation. However, to the south in southern Syria, Lebanon, Israel, and Jordan, the four other S genome species occur: Ae. searsii, Ae. longissima, Ae. sharonensis, and Ae. bicornis (Forsk.) Jaub. et Sp. The Triticum diploids rarely occur south of Mt. Hermon; T. monococcum ssp. boeoticum has been collected in western Jordan. The tetraploid T. turgidum ssp. dicoccoides is more common and grows in northern Israel, southern Syria, and western Jordan.

During the last few years, we have attempted to cross accessions of the five S genome species as females with T. monococcum ssp. boeoticum and ssp. monococcum L., and T. urartu as males. The results of our work in 1988 are shown in Table 3. They suggest that Ae. speltoides may possess an F, hybrid embryo lethality mechanism in crosses with diploid Triticum species, for no hybrid seed was obtained. The one exception with T . monococcum ssp. monococcum produced seed that did not ger- minate. Thus, we did not obtain any amphiploid with Ae. speltoides as the female parent. KIHARA and LILIENFELD (1932) and RILEY et al. (1958) were more successful, for they each report one hybrid of Ae. speltoides x T. monococcum ssp. monococcum. Other possible hybrids are reported by MANN and GORDON (1988). Clearly, however,

210 J. G. WAINES A N D D. BARNHART Heredims 116 (1992)

Table 3. Results of diploid Argilops x Triricum crosses in glasshouse, 1988

Female parent Male parent Trrticum Aegilops

boeog. hoeot. hoeor. hoeor. mono. mono. urarfu urariu G642 G643 GI174 GI215 GI560 GI561 (33197 G3206

ligusricu GI936 liguslicu G201 I ligusricu G2020 spelroides G2148 searsii G 14 1 3 searsii G3068 searsii G3525 longissirnu G I305 longissirnu GI 307 longissirnu GI415 shuronensi.s G946 birornis GI425

0 0 0 0 0 0 0 0 0 0 C C

0 0 0 0 0 NG 0 0 C C C C

0 0 0 0 0 0 0 0 0 0 C C

0 0 0

C 0

0 0 0 0 0 NG

0 C C C 0

0 0 0 NG 0 NG 0 C NG NG C C

0

0 0 0 SH C 0 0 0 0 C

NG

~ = cross not made 0 = no hybrid seed obtained from at least 10 crosses NG = hybrid seed obtained but no germination SH = sterile F , hybrid plant obtained C =sterile F, hybrid plant produced C, seed with colchicine treatment

the hybrid is not an easy one to make. The results of crosses with Ae. searsii were a little better and were genotype dependent. Ae. searsii G3068 pro- duced nongerminable F, hybrid seed in four com- binations and a sterile hybrid plant with T. urartu G3197, from which we have not yet obtained seed with colchicine treatment. Ae. searsii G3525 pro- duced a sterile F, hybrid plant with T. urartu G3197 from which C, seed was obtained by col- chicine treatment.

Aegilops longissima produced sterile F, hybrid plants and C, seed in five combinations with T. monococcum ssp. boeoticum and ssp. monococcum, after colchicine treatment, but no F, hybrid plants were produced with T. urartu. The single acces- sions of Ae. sharonensis and Ae. bicornis produced many sterile F, hybrid plants and C, seed follow- ing colchicine treatment with both T. rnonococcum (both subspecies) and T . urartu. Although we need to make more crosses with S genome Aegilops species and diploid Triticum species, the trend from our 1988 season results suggests that if the diploid Aegilops species and Triticum species have overlap- ping distributions in the wild, they are unlikely to produce F, hybrid seed that geminates to produce a sterile hybrid plant. This is so with Ae. speltoides and, to a lesser extent, with Ae. searsii. On the other hand, Ae. longissirnu, Ae. sharonensis, and Ae. bicornis, which have no or minimal overlap in the wild with T. monococcum ssp. boeoticum and T. urartu, readily produce F, hybrid seeds which ger-

minate to produce sterile hybrid plants which are easily treated with colchicine to produce viable amphidiploid seed. Obviously, if Ae. speltoides or Ae. searsii was the B or G genome donor of tetraploid wheats, the tetraploids are not easily synthesized today.

Triticum urartu and T. turgidum ssp. dicoccoides and T. timopheeoii ssp. araraticum Jakubz. have relatively restricted distributions on the islands of basaltic soil relative to those of Ae. speltoides or T. monococcum ssp. boeoticum which are considerably more widespread (EIG 1929; HARLAN and Zo- HARY 1966). The question arises whether the te- traploids were made only once or a few times and were distributed by animals from basaltic island to basaltic island, or whether each tetraploid on the island was made from diploids also growing on that island. Our 1988 crossings did not take this question into account. We are now making cros- ses of Ae. speltoides and T . monococcum ssp. boeoticum and T. urartu collected from the same sites. These studies may shed light on whether T. urartu is less successful as a male parent than T . monococcum as our 1988 results might suggest.

Other tetraploid combinations According to Table 2, Aegilops triuncialis L. occurs in two forms, one with Ae. umbellulata Zhuk. as the female parent (ssp. triuncialir) and the other with

Heredim 116 (1992) BIOSYSTEMATICS IN AEGILOPS AND TRRITKL'M 21 1

Ae. caudata L. as the female parent (ssp. persica (Boiss.) Zhuk.). To what extent do these two forms interbreed in the wild, and what is the fate of their offspring? Do other Aegilops tetraploids exhibit a similar arrangement, where the female parent can be from either species. Anyone who has looked at sheets of polyploid Aegilops species in a large herbarium is aware that some specimens are difficult to classify.

Many years ago, it was suggested on the basis of seed protein electrophoretic evidence that one genome of Ae. ouata L. might be from Ae. squar- rosa Tausch (Ae. tauschii Coss.) rather than Ae. comosa Sibth. et Sm. (WAINES and JOHNSON 1975). No one since seems to have investigated this hypothesis and, unfortunately, KIMBER et al. (1988) did not cross Ae. squarrosa to Ae. ouata when they investigated this tetraploid species. Moreover, they only used one accession of Ae comosa. Partly to continue investigation of this hypothesis, and partly to ask why are there no known tetraploids involving Ae. squarrosa and Ae umbellulata, which are both very successful diploid species, we have attempted to make this cross. We found that we could make the cross only one way with Ae. umbellulata as the female parent. The F, hybrid plant is sterile, but the spike morphology is sufficiently encouraging for us to continue this line of investigation. We now have allotetraploid seed from colchicine treatment.

Another combination springs to mind. Why are there no known tetraploids involving Ae. speltoides and Ae. umbellulata? If we allow that the S genome in Ae. kotschyi and Ae. peregrina is from Ae. searsii, or from Ae. longissima or Ae. sharonensis

1988; ZHANG et al. 1992) then surely two success- ful species such as Ae. speltoides and Ae. umbellu- fata must sometime produce allotetraploids. Are we just not recognizing them? Why is weedy Ae. mutica Boiss. not involved in any polyploid combinations? If it were, what would they look like?

The need for continued biosystematic research and use of a biological species concept for the diploid species of Aegilops and Triticum was re- cently stressed by us (WAINES and BARNHART 1990). We now extend this call for more biosystem- atic research on the other polyploid taxa. Kihara was a first-rate scientist, but he did not ask nor answer all the questions about evolution and biosystematics in Aegilops and Triticum. Kihara would be the first to admit this, but unfortunately

(OGIHARA and TSUNEWAKI 1988; SIREGAR et al.

present-day botanists have forgotten that there is still a need for continued research in biosystematics.

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