KU 12162A. KU 12163A. KU 12163B. KU 12073A. KU 12078A. KU 120788. KU 12092A. KU 120928. KU 12100A. KU 12100B. KU I2104A. KU 121049. Rhodes.
Hereditas 116: 247-251 (1992)
Intraspecific hybrid sterility in Aegilops caudata L. SHOJI OHTA Plant Germ-plasm Institute, Faculty of Agriculture, Kyoto University, Mozume, Muko, Kyoto 61 7, Japan
OHTA, S. 1992. lntraspecific hybrid sterility in Aegilops caudata L. - Hereditas 116: 247-251. Lund, Sweden. ISSN 0018-0661. Recevied August 2, 1991. Accepted February 10, 1992
Ae. caudata L. is an annual, diploid species distributed over the eastern Mediterranean. Morphologically, it is divided into two varieties, var. typica and var. polyathera Boiss. In the present work, two series of crossing experiments were carried out. Firstly, reciprocal crosses between the two varieties co!lected from sympatric populations were made. All F, hybrids showed normal fertility. Secondly, crosses between accessions collected from different geographical regions were made. F, hybrids from the crosses between most Aegean accessions and the accession from Syria (Tester A) or the accession from northern Turkey (Tester B) showed complete sterility. However, those from the crosses between the Aegean accessions and the accession from Olympia in Greece (Tester D) showed normal fertility. Contrary to this, F, hybrids from crosses between the accession from northern Iraq and those from Syria and northern Turkey showed high fertility, while complete sterility was observed in hybrids between the Iraqi accession and the accessions from Greece and northwestern Turkey (Testers D and C). Accordingly, it is concluded that the intraspecific hybrid sterility in Ae. caudata is not a characteristic of intervarietal hybrids but is due to geographical differentiation: The factors responsible for genetic differentiation in Ae. caudata causing intraspecific hybrid sterility are not correlated with morphology but with geography. Shoji Ohta, Plant Germ-plasm Institure, Faculty of Agriculture, Kyoto University, Momme, Muko, Kyoto 617, Japan
Aegilops caudata L. is an annual, diploid species distributed over the eastern Mediterranean from Greece to the northern part of Iraq. EIG (1929) described two varieties, var. typica and var. polyathera Boiss. The former has no awn on the empty glumes of the lateral spikelets whereas the latter has an awn on them. TANAKA et al. (1967) investigated some accessions of Ae. caudata cytologically. They found that the intraspecific F, hybrids between the two varieties were highly sterile. The present author collected many accessions of Ae. caudata, including both varieties, on four of the Aegean islands (Crete, Rhodes, Samos, and Lesbos). The two varieties often grow sympatrically on the Aegean islands, and plants raised from seeds collected at such sympatric stands often showed segregation in spike morphology. From these observations, it was suspected that the sterility of the intraspecific F, hybrids observed by TANAKA et al. (1967) is not a characteristic of the intervarietal hybrids, but is a phenomenon indicating geographical differentiation of the species irrespective of morphology. The aim of the present study is to obtain further evidences on intraspecific hybrid sterility in order to elucidate the pattern of intraspecific genetic differentiation of Ae. caudata.
Material and methods The material used in the present study is listed in Table 1. All accessions of Ae. caudata are maintained by self-pollination at the Plant Germ-plasm Institute, Kyoto University. Four accessions were chosen as tester strains (Testers, see Table I). The four Testers were collected from marginal localities of the distribution area of Ae. caudata. Testers A, B, C and D were from the southern, the northern, the northwestern and the western margins of the distribution area, respectively. Testers A, C and D belong to var. typica and Tester B to var. polyathera. TANAKAet al. (1967) used the same accessions in their crossing experiment. The other accessions were collected on the four Aegean islands, except one accession collected in northern Iraq. The Iraqi accession (KU 5475) is from the southeastern margin of the distribution area of the species. All accessions from the Aegean islands and northern Iraq were from mixed stands of the two varieties. Two series of crossing experiments were carried out in the present study. Firstly, the two varieties from each sympatric stand on the Aegean islands were crossed reciprocally. Secondly, nine accessions from the Aegean islands and one from north-
248
Hered,lrror 116 (1992)
S.OHTA
Table 1. The accessions of Aegilops caudata L. used in the present study
Accession No.
Variety
Collection locality
Tester strains KU 6-2 (Tester A) KU 5852 (Tester 8 ) KU 5864 (Tester C) KU 5871 (Tester D)
typica polyarhera typica typica
I 1 km S of Ma’aret el Nu’man (Aleppo-Hama), Syria 16 km W of Amasya (Corum-Amasya), Turkey 17 km W of Karacabey (Bursa-Bandirma), Turkey
In the ruins of Olympia, Greece
Aegean accessions Crete KU 12040A KU 120408 K U 120558 K U 121558 KU 12162A K U 12163A K U 12163B
fypica polyathera polyathera polyathera typica typiea polyathera
Zaros Zaros 18.5 km W from Sfaka to Ag. Nikolaos 19.7 km S from Vrises to Chora Sfakion 6.0 km NE from Selia to Rethimnon 12.1 km NE from Selia to Rethimnon 12.1 km NE from Selia to Rethimnon
Rhodes K U 12073A K U 12078A KU 120788 KU 12092A K U 120928
typica typica polyathera rypica polyathera
9.9 km N from Eleoussa to Soroni Western outside of Laerma Western outside of Laerma 22.4 km NE from Arhangelos to Rhodes 22.4 km NE from Arhangelos to Rhodes
12100A 12100B I2104A 121049
typica polyathera typica polyathera
12 km 12 km 6 km 6 km
-esbos K U 12117A K U 12117B K U 12121A K U 121218
typica polyarhera typica polyathera
Samos
KU KU KU KU
Iraqi accession K U 5475
palynthera
S from Platanos to Pirgos S from Platanos to Pirgos E from Hora to Possidonio E from Hora to Possidonio
5.7 km 5.7 km 3.7 km 3.7 km
E E E E
from from from from
Skala Eressou to Kaloni Skala Eressou to Kaloni Vatera to Plomari Vatera to Plomari
Sarsang (29.5 km WSW from Amadiyah to Dohuk)
ern Iraq were crossed with the four Testers. Seeds were sown in the autumn. Plants were grown under a vinyl roof and under the natural conditions. Chromosome pairing at the first metaphase (MI) of meiosis in pollen mother cells (PMCs) was observed by the aceto-carmine smear technique. Pollen fertility was estimated according to OHTA (1991). Seed set after open-pollination was estimated based on at least 10 spikes in the second crossing experiment.
and in the reciprocal F, hybrids was normal, and seven bivalents were observed in the PMCs. As shown in Table 2, the pollen fertility in the parental strains was normal, and ranged from 71.5 % to 98.0 %. The F ., hybrids also showed . normal pollen fertility, ranging from 69.9 YO to 98.6 %. Thus, no sterility was found in the F, hybrids between two varieties from sympatric stands.
F, hybrids involving different geographical regions
Results Parental strains and F, hybrids involving sympatric stands Accessions from eight sympatric stands of vars. typica and polyathera on the four Aegean islands were used in this crossing experiment (Table 2). The chromosome pairing in the parcntal strains
F, hybrids between the four Tester strains The pollen fertility and the seed set after open-pollination in the F, hybrids obtained from crosses between tester strains are shown in Table 3. All the F, hybrids showed complete pollen sterility (from 0 to 0.1 %) and low seed set (from 3.8 YO to 46.6 %), while the four tester strains showed normal pollen fertility and seed set. The anthers of the
INTRASPEClFlC HYBRID STERILITY IN AEGfLOPS
ffrredirm 116 (1992)
249
Table 2. Pollen fertility in percent in the two varieties o f Aegilops caudara collected at sympatric stands in the Aegean islands, and their reciprocal F, hybrids ________________
~
Geographical region
Accession No (KU)
Pollen fertility (%) Parental strains')
F , hybrids
T
P
TxP
PxT
Crete
12040A,B 12 163A,B
82.6 96.3
88.2 95.8
90.6 98.5
94.1 97.9
Rhodes
12078A,B 12092A,B
90.5 71.5
89.9 90.6
93.8 89.4
96.5 89.8
Samos
12100A,B 12104A.B
-
98.0
84.7 96.9
98.3 98.6
98.6 98.2
I21 17A,B 121 21A,B
95.7 75.6
97.4 83.4
96.8
97.7 69.9
Lesbos
')
-
T: var. typica, P: var. polyalhera
Table 3. Pollen fertility and seed set in percent in the F, hybrids between the four Tester strains of Aegilops CRUdRla above and below the diagonal, respectively Tester
A B C D
A KU6-2 Hama
6. I
B KU5852 Corum
C KU5864 Bandirma
D KU5871 Olympia
Table 4. Pollen fertility in percent and dehiscencel' of the anthers in F, hybrids obtained from the crosses o f the Aegean and the Iraqi accessions of Aegilops caudata with the four Tester strains Parental strains
F, hybrids between accessions from diSferent geographical regions and the Tester strains A total of 10 accessions from the four Aegean islands and northern Iraq were crossed with the four Tester strains. The parental strains showed normal pollen fertility and seed set. The pollen fertility of the F, hybrids from these crosses is shown in Table 4. The F, hybrids between all the Aegean accessions and Tester A from Hama in Syria showed complete pollen sterility and the anthers never dehisced. The F, hybrids between eight of the nine Aegean accessions and Tester B from Corum also showed complete pollen sterility and no dehiscence of the anthers. The F, hybrid between the accession from Samos (KU 12100B) and Tester B showed slightly higher pollen fertility ( 1 5.1 YO)and its anthers dehisced partially. The F,
D
0 14.5; 0 0 0.8
25.0* 83.5.1 69. I ** 72.2** 96.3**
Accession A No. (KU)
Crete
120408 120558 121558 12162A 12163A
0 0 0 0 0.1
0
Rhodes
l2073A
0
0.1
Samos
12100B
0
15.1*
42.6"
86.3.'
Lesbos
12117B I2121A
0 0
0.1 0.3
8.91 0.2
56.0**
Iraq
5475
')
B
C
Geographical region
14.6
F, hybrids did not dehisce at all. These observations almost coincided with the results reported by TANAKA et al. (1967). Chromosome pairing in the four tester strains and the F, hybrids was normal.
Tester strains
0 0 0 0
72.8** 43.0'
0
0
0
0. I 0
* and ** indicate partial and normal dehiscence of the anthers,
respectively
hybrid between the Samos accession and Tester C from Bandirma showed pollen fertility as high as 42.6 % and its anthers dehisced normally. The F, hybrids between two of the other eight Aegean accessions (KU 12055B and K U 12117B) and Tester C produced a few normal pollen grains (14.5 % and 8.9 %, respectively), and their anthers dehisced partially. However, complete or almost complete pollen sterility was observed in the F, hybrids between the other six Aegean accessions and Tester C. Four of the five accessions from Crete, the accession from Samos and one of the two accessions from Lesbos produced F, hybrids showing high pollen fertility when crossed with Tester D, originating from Olympia in Greece. The F,
250
S.OHTA
Hrrrdirns 116 (1993
Tuhk 5. Seed set in percent after open-polhation in the F , hybrids obtained from the crosses of the Aegean and the Iraqi accessions of Aegilops caudafa with the four Tester strains
Parental strains
Tester strains
8
C
D
0 10.0 14.1 13.0 8.6
22.5 38.9 21.4 23.5 14.8
31.5 37.1 27.3 50.7
74.1 75.9 78.6 82.4 81.2
12073A
22.7
42.9
40.0
43.8
12100B
31.8
62.9
63.2
89.6
121178 12121A
5.3
7.1
52.8
0
1.821.5
77.5 2.0
Geographical region
Accession A No. ( K U )
Crete
120408 120558 121558 12162A 12163A
Rhodes Samos Lesbos Iraq
5475
69.7
50.0
~
3.1
21.2
hybrids between one of the Cretan accessions ( K U 12040B) and Tester D showed lower pollen fertility (25.0 X)and partially dehisced anthers. Complete pollen sterility was observed in the F , hybrids between Tester D and the accessions from Rhodes (KU 12073A) and Lesbos (KU 12121A). Contrary to the F, hybrids involving the Aegean accessions, those between the Iraqi accession (KU 5475) and Testers A and B showed high pollen fertility, 72.8 % and 43.0 YO,respectively. The anthers of the former hybrid dehisced normally and those of the latter dehisced partially. The hybrids between the Iraqi accession and the other Testers ( C and D) showed complete pollen sterility and their anthers never dehisced. The results obtained with the Iraqi accession formed a great contrast to those with the Aegean accessions mentioned above. The seed set after open-pollination in the F, hybrids is shown in Table 5. This result was correlated with that from pollen fertility mentioned above. The F, hybrids between six of the nine Aegean accessions and Tester D, showing high pollen fertility, also showed high seed set. In addition, one of the Cretan accessions (KU 12040B) also produced F, hybrids showing normal seed set (74.1 %), when crossed with Tester D. The F, hybrids between one of the two accessions from Lesbos ( K U 12121A) and all four Testers, which showed complete pollen sterility, also showed very low seed set, ranging from 0 to 21.5 YO.The F, hybrids between the other Aegean accession ( K U 12073A) and all Testers showed low seed set. The F, hybrids between the Iraqi accession and Testers A and B showed high seed set, whereas those
involving the other Testers ( C and D) showed low seed set. It was quite different from the result with the F, hybrids involving Aegean accessions. Thus, the results from pollen fertility and seed set were apparently correlated. All parental strains and the F, hybrids showed normal chromosome pairing in their PMCs.
Discussion TANAKA et al. (1967) reported that the distribution areas of the two varieties were different and that var. typica occurs in Crete, western Turkey, and Syria, whereas var. polyathera occurs in central Turkey. Based on their own results, TANAKA et al. (1967) concluded that the intervarietal F, hybrids between vars. typica and polyathera were highly sterile. Later, TANAKA (1983) referred to the presence of a single mixed population of the two varieties a t Sarsang in northern Iraq. However, according to EIG (1929), var. polyathera is distributed in Greece, the Aegean islands, Syria and northern Mesopotamia. RECHINGER( 1943) also reported that var. polyathera occurs in the Aegean region in addition t o var. typica. Mixed populations of the two varieties were observed by the present author on four of the Aegean islands, Crete, Rhodes, Samos, and Lesbos. All the F, hybrids from the crosses between the two varieties collected from sympatric stands showed normal fertility. This clearly indicates that the sterility observed in the intraspecific F, hybrids of Ae. caudata is not a characteristic of the intervarietal hybrids. The material used by TANAKA et al. (1967) was derived from rather restricted areas and the accessions of the two varieties originated from different geographical regions. In the present crossing experiment, materials originating from widely different geographical regions were used. The F, hybrids between most Aegean accessions and the Tester strain collected at Olympia in Greece (Tester D) showed high fertility. However, F, hybrids between these Greek accessions and the Testers from the other geographical regions (Turkey and Syria) were highly sterile. Contrary to this, the F, hybrids between the accession from northern Iraq and Tester A from Syria showed high fertility. High fertility was also observed in a F, hybrid between the Iraqi accession and Tester B from Corum in northern Turkey. These results indicate that the present distribution area of Ae. caudata may be divided into a t least two parts according to in-
HFredilos I16 (1992)
traspecific hybrid sterility: A western part composed of Greece, including the mainland and the Aegean islands, and an eastern part composed of Turkey (mainly the Anatolian plateau), Syria and Iraq. Based on hybrid sterility among the four Tester strains, it is also suggested that the eastern part of the distribution area may be further subdivided into a northern and a southern part. The F, hybrids between some Aegean accessions and all the four Testers showed high sterility. This suggests that the western part of the distribution area may also be subdivided. Based on these results, it is concluded that the intraspecific hybrid sterility observed in Ae. caudata is due to genetic differentiation correlated with gebgraphical areas but not with morphology. KIHARA( 1968) suggested that the intraspecific hybrid sterility in Ae. caudata was cytoplasmic, based on his own backcrossing experiment and cytological observation. Later, KIHARAand OHTA ( 1970) repeatedly backcrossed both parental strains to the intervarietal, sterile F, hybrids, and found that the hybrid sterility was not cytoplasmic. In the present work, chromosome pairing was normal both in highly sterile F, hybrids and in fertile ones. This suggests that the hybrid sterility may be genic. However, an alternative explanation is that cryptic structural hybridity causes the sterility. STEBBINS ( 1945) defined cryptic structural hybridity as chromosomal sterility due to heterozygosity
INTRASPECIFICHYBRID STERILITYI N A E G I L O P S
25 1
for structural differences too small to materially influence chromosome pairing at meiosis. Detailed observations during gametogenesis in sterile Fl hybrids and data on fertility in tetraploids artificially induced from sterile, diploid F, hybrids are necessary to elucidate the mechanisms of the sterility. Acknowledgements. - The present study was supported by a grant-in-aid from the Kihara Memorial Yokohama Foundation for the Advancement of Life Science.
References EIG, A. 1929. Monographisch-kritische Uebersicht der Gattung Aegilops. - Repert. Spec. Nov. Regni Veg. 55 1-228 KIHARA, H. 1968. Cytoplasmic relationships in the Triticinae. Proc. 3rd Int. Wheat Genet. Symp.: 125-166 KIHARA, H. and OHTA,Y. 1970. Intraspecific genome differentiation in Aegilops caudata. - Seiken Ziho 2 2 99-106 OHTA, S. 1991. Phylogenetic relationship of Aegilops mutica Boiss. with the diploid species of congeneric Aegilops-Triticum complex, based on the new method of genome analysis using its 8-chromosomes. - Mem. CON. Agric. Kyoro Univ. 137: 1-116 RECHINGER, K. H. 1943. Flora Aegaea. - Denkschr. Akad. Wiss. Wien, Muth.-Nat. KI. lOS(I): 1-924 STEBBINS, G . L. JR. 1945. The cytological analysis of species hybrids. 11. - 301. Rev. I I : 463-486 TANAKA, M. 1983. Geographical distribution of Aegilops species based on the collections at the Plant Germ-plasm Institute, Kyoto University. - Proc. 6th Int. Wheat Genet. Symp.: 1009- 1024 TANAKA, M., SUEMOTO,H. and ICHIKAWA, S. 1967. The awn characters and sterility in Aegilops caudata L., 1. - Jup. 1. Breed. 17, Suppl. 2: 155 - 156
