Genetic Control of the Diagnostic Morphology of the Two Varieties

Two varieties collected at the nine sympatric stands on the Aegean Islands were crossed reciprocally with each other. All the F1 hybrids had awnless lateral spikelets and their pollen fertility was normal (Ohta 1992). The segregation of the awn character in the F2 generation did not significantly deviate from 3 (awnless): 1 (awned) ratio (Table 6.3). This result indicates that a dominant inhibitor controls awnless lateral spikelets characteristic of var. typica.

Further, 13 typica accessions including Testers A (KU6-2), C (KU5864) and D (KU5871) were crossed with a common polyathera Tester B (KU5852) (Table 6.1)

Table 6.3 The segregation of the awn character on lateral spikelets in the F2 populations derived from fertile reciprocal F1 hybrids between two varieties collected at their sympatric stands (Ohta 2001)

Population no.

No. of F2 plants observeda

Total

Awnless

Awned

χ2 (3:1)

1982-6-11-1

48

33

15

1.00

1982-6-12-2

86

63

23

0.13

1982-6-12-4

49

35

14

0.82

1982-6-12-7

72

59

13

1.85

1982-6-14-7

89

71

18

2.03

1982-6-14-8

63

49

14

0.26

1982-6-14-9

48

35

13

0.11

1982-6-17-1

69

55

14

0.82

1982-6-23-1

71

53

18

0.04

aData from reciprocal crosses were pooled

Fig. 6.3 Geographical distribution of the dominant and recessive typica accessions (Ohta 2001). Solid circles: dominant typica accessions, open circles: recessive typica accessions, and an open triangle: a common polyathera accession (Tester B: KU5852) used in the crosses. The figures indicate the accession numbers of Kyoto University

(Ohta 1992, 2000). These 13 typica accessions could be divided into the dominant and recessive typica accessions based on the spike morphology of the F1 hybrids (Fig. 6.3). The F1 hybrids involving the eight accessions from the western region were var. typica, while those involving the five accessions from the eastern region were var. polyathera. It is suggested that dominant typica accessions in the western region are controlled by a dominant inhibitor of the awns on lateral spikelets, while recessive typica accessions in the eastern region are controlled by recessive allele(s) for awn development on lateral spikelets.

Geographical Differentiation and Establishment of the Present Geographical Distribution in Ae. caudata

The present distribution area of Ae. caudata can be divided into the western and eastern regions with the border in the mountains lying between West Anatolia and Central Anatolia. And the western and eastern accessions are isolated not only geographically by the mountains but also reproductively by hybrid sterility caused by gametocidal-like genes. The morphology of var. typica is controlled by two different genotypes in the western and eastern regions, so the division of the two taxonomic varieties based on the awn character on lateral spikelets is not so significant for the phylogeny of the species.

The distinct genetic differentiation between the western and eastern groups strongly suggests that the two geographical groups were isolated for a long term in the past. In the maximum glacial period from 18,000 BP to 16,000 BP, steppe and desert-steppe with Artemisia and Chnopodiaceae covered the greater part of the Near East (van Zeist and Bottema 1991), which is now the primary diversity center of the wild Triticum and Aegilops species. Ae. caudata did not occur in Central Anatolia and East Anatolia in that period, and its distribution area might be divided into the two isolated refuges. One was the region surrounding the Aegean Sea where the climate was affected by the sea and was not excessively cold or dry, and the other was the western Levant or some sheltered habitats in the East Taurus/Zagros mountain arc. As the climate became warmer after the last glacial period, Ae. caudata penetrated Central Anatolia and East Anatolia with the spread of oak woodland from the latter refuge region, and now occupies the eastern region of the distribution. Variety polyathera with many awns on spikes might be advantageous to such a rapid colonization to new open habitats. The western region of the present distribution was established by the populations in the Aegean Sea region during the last glacial period.

Acknowledgments The authors thank the Plant Germ-plasm Institute, Kyoto University for the materials. These materials are now preserved and provided by the National BioResouce Project (NBRP)-WHEAT, Japan.

 
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