II. 16. Origin and evolution of cultivated barley: Wild barley from Western Szechuan and Tibet, China.
Shao, Qiquan, Institute of Genetics, Academia Sinica, Beijing, China. Li Chang-sen and Baschan Chiren, Institute of Agronomy, Xizang (Tibet) Autonomous Region.
This report is based on the results of field expedition and laboratory identification of the comprehensive scientific expedition corps of Ching Tsang (Chinghai Province and Tibet Tsang Autonomous Region), Academia Sinica in 1974. The expedition indicated that there were many types and wide distribution of wild barley in the south western part of China. This is of theoretical importance in barley evolution. It is also of practical importance since wild barley is highly disease-resistant which is a valuable original material for disease-resistant breeding.
1. Two-rowed wild barley (Hordeum spontaneum C. Koch.)
Two-rowed wild barley, first found in 1848, is the most original species
of cultivated forms. The known distribution area of two-rowed wild barley
is Afghanistan, Turkey, Jordan, Syria, Iraq, Iran, Pakistan, individual
parts of North Africa (i.e. Silania, Marmarika), outer Caucasus, USSR,
and the southern part of Middle Asia. Normally it is grown from 350-1500
m above sea level. Since wild barley is cold tolerant, it is occasionally
found above 1500 m. Some workers argued that two-rowed wild barley was
the direct ancestor of the cultivated form. The importance of wild barley
of China in the origin of cultivated forms has often been neglected, since
there was no original report of Chinese two-rowed wild barley. This is
a first one. Our expedition verified that two-rowed wild barley not only
occurred in the southwestern part of China, but was widespread from the
east Daofu County, Ganze Autonomous Prefecture, Shichuan Province to the
west Xigaze County, Xigaze Prefecture; from the south Cona County, Shan-nan
Prefecture to the north Dolongdequen County, Lhasa, lengthwise and crosswise
about 1500 Km, from 2800-4050 m above sea level, involving the agricultural
areas of the Yalong River Valley, Jinsha River Valley, Lancang River Valley,
Nu River Valley, Yarlong Zonbo River, Nianchu River and Lhunze River. It
is assumed that the real distribution area will be even wider. Wild barley,
like any naturally occurring species, is apparently polymorphic. The three
major varieties, identified by the results of two-rowed wild barley research
during the past 120 years throughout the world, all are also grown in the
above-mentioned areas. They are: H. spontaneum Var. ithaburense
(Boiss) Nabelek, the basic difference taxonomically being a blunt-rounded
tip of the lateral inefficient spikelet of the triplets H. spontaneum
Var. Ischnatherum (Cosson) Thell, with a sharp angled tip of lateral inefficient
spikelets; H. spontaneum Var. pro-Skowetzii Nabelek, with
awn-shaped tip. The two-rowed wild barley plants were grown as weeds in
fields of wheat, barley and peas and not as wild populations since fields
in the valley have been exploited fully for agricultural production or
pastures.
2. Six-rowed wild barley (Hordeum agriocrithon Åberg)
Some workers claimed that there was significant difference between
two-rowed wild barley and present cultivated forms, especially cultivated
six-rowed forms. There should be intermediary types in the barley evolution
process, but none has so far been found. Åberg reported six-rowed
wild barley, seeds of which he obtained indirectly, was found in Daofu
County, Ganze Prefecture in the western part of Tzechuan Province. Scholars
of foreign countries in this field were impacted by the discovery, and
investigation enthusiasm was stimulated for a period of time. Discovery
of six-rowed wild barley was followed successively in the southern and
eastern parts of Tibet by Freisleben and Schiemann after Åberg. Six-rowed
wild barley found in the southwestern part of China was argued as the ancestor
of cultivated six-rowed forms by Vavilov et al. Schiemann et al. indicated
the cultivated two-rowed type was from the six-rowed wild form with the
reduction of the lateral spikelets to nonfruited ones.
The fact that six-rowed wild barley was found in the southwestern part of China is doubted by a number of workers, such as Bachteev et al. Their views might be summed up as follows: (1) the six-rowed wild barley is a spontaneous hybrid; for example, several types similar to the six-rowed wild barley could be obtained in the progenies of the hybridization from two-rowed wild and cultivated six-rowed barley; (2) the six-rowed wild barley is not very stable; for example, two varieties had been segregated by Åberg; (3) no natural distribution from investigations is seen by Bachteev as unconvincing. First, evidence is lacking to ascertain that similar types are the same, since "similarity" is not "equivalent". According to the opinion mentioned above the flowering date of wild barley and the cultivated type must be similar, otherwise they could not be crossed. Native farmers generally indicated that wild barley matured about half a month earlier than cultivated naked type spikelets. In our expedition, it was seen that spikelets of the black six-rowed wild barley were fallen on the ground by the wind in a naked barley field in Changzhu Commune, Naidong County, Shannon Prefecture, Tibet, on July 31, 1974, while the cultivated naked barley was only in the initial waxy maturity. According to field observation in the agricultural and pastural experiment station, Shannan Prefecture, the maturity date of native naked barley varieties was uniformly between August 9 and 17, and was about half a month later than the wild form. In our opinion the difference in flowering period between wild and cultivated barley is exactly the interspecific isolating mechanism to maintain the independence of the species. Second, is the consideration of whether six-rowed wild barley is homozygous or not. We have made examined progenies from one ear for 12 families (Table 1). The results verify that they are fully stable. About a dozen varieties and forms of six-rowed wild barley were collected in 1974. Exhibited here are the yellow six-rowed wild barley of Daofu and black six-rowed wild barley of Tzedang.
Table 1. Identification results of stability of wild barley from Tibet.
The polymorphisism within the species showed that the species is a naturally occurring one. Third, wide distribution of the six-rowed wild barley is similar or even surpasses that of the two-rowed wild forms. Two-rowed wild forms could not be found in some places, while there were a lot of six-rowed wild types. The six-rowed wild barley is not easily identified, since it has a close relation to the cultivated species. Nowadays natural populations of wild barley will be eliminated rapidly by cultivation.
From the context, the six-rowed wild barley is the immediate ancestor of the cultivated six-rowed type, and even is the possible primitive cultivar. A Tibetan Commune member said that barley with a brittle rachis was grown in ancient times. Wild barley was used for milling flour and making wine in Yangda Commune, Dueilong-deqing County, and Jiula District, Cuona County. The native farmers knew it well, and gave it a special Tibetan name "Tzeda", the English equivalent of which is the "wild thing". The facts indicated further that six-rowed wild barley is grown inherently in the southwestern part of China, and is closely related to the cultivated types.
3. The bottle-shaped wild barley (Hordeum lagunculiforme Bacht.)
Six-rowed wild barley was discovered by Bachteev in Middle Asia. This
form is very similar to that found in the southwestern part of China. Only
one difference occurred, i.e. the lateral spikelet has its own stalk, like
a bottle placed upside down. Apart from middle Asia, Zohary also reported
the bottle-shaped wild barley, and it was claimed as the ancestor of cultivated
forms by Bachteev. Whether the bottle-shaped wild barley occurs in other
parts of the world, has not yet been reported. Bottle-shaped wild barley
was found in many places in southwestern China for the first time, and
grown simultaneously with six-rowed wild type.
Bottle-shaped wild barley is morphologically stable. Wide distribution of the bottle-shaped wild barley is similar to that of the six-rowed wild barley.
4. Intermediate forms of wild barley.
It appeared that two-rowed, bottle-shaped and six-rowed wild barley
occurred as different forms at various times in barley evolution. From
these forms it is shown that a real evolution process did occur in which
intermediate forms must be produced. It is of significant importance to
these forms in evolution, although they are not so stable and are often
neglected taxonomically. Many intermediate wild forms of barley have been
found in the southwestern part of China. One of them is with single ear,
i.e. six-rowed and two-rowed spikelets are grown on the different position
of the same ear; the other is with different rows in the main and tiller
ears of the same plant, i.e. six-rowed ear, and two-rowed tillers. Complete
radicle and original episperm are kept for these plant specimens; they
are fully proved of one seed origin. All the intermediate forms are similar
to bottle-shaped wild barley, i.e. a stalk or one smaller than that of
bottleshaped forms on the lateral spikelets. These characters indicate
that six-rowed bottle-shaped barley is an intermediate form in evolution
from two-rowed to six-rowed wild barley. No stalk is seen on the lateral
spikelets of the triplet in six-rowed wild and cultivated forms. This indicates
further that the six-rowed wild form in the southwestern part of China
is the ancestor of the six-rowed cultivated naked type. From practical
materials, significant variation of the row character occurred in wild
form, and the evolution of the row character was completed first. When
wild barley is grown in cultivated environments, it may change to six-rowed
forms.
5. Cytological and genetical identification.
Since the number of chromosomes of cultivated and wild barley is the
same, i.e. 2n = 14, it is necessary to carefully analyze the chromosome
morphology from the evolutionary standpoint. The chromosome configuration
has been identified by Oinuma (1952)(1, 2, see below) in two-rowed and
six-rowed wild barley and 86 cultivars. It showed that the first and the
longest chromosome pair of the wild form with a microsatellite on one terminal
is of the a1 a1 type of karyotype, and that of approximately
half of the cultivars is aiso of the a1 a1 type,
thus indicating that these wild barleys are closely related to the cultivated
forms. Cytological studies of several forms of wild barley (i.e. H.
spontaneum var. ithaburense, var. ischnatherum, var.
proskowetzu;
H. logunculiforme Bacht., H. agriocrithon Åberg)
showed that their first and longest chromosomes are all of the Oinuma's
a1 a1 type, while similar results were lacking in
the bottle-shaped wild forms. The first and longest chromosomes of bottle-shaped
forms is also of a1 a1 type in our experience, and
it showed further from the chromosome morphology that six-rowed bottle-shaped
barley is possibly one of the intermediate forms in barley evolution. In
addition, their meiosis is normal.
(1) Oinuma, T. 1952. Karyomorphology of cereals. Biol. J. Okayama Univ.
1:12-71.
(2) Oinuma's results have not been substantiated by other workers.
Also his identification and designation of barley chromosomes are considerably
different from presently accepted system.
Literature and comments are added by T. Tsuchiya.
For identification of position of every specie of wild barley in the evolutionary system crosses were made between different species of wild barley. The results of this crossing experiment are shown in Table 2. These verified the dominance of two-rowed wild barley to six-rowed wild barley and dominance of bottle-shaped wild barley from two-rowed wild barley, through bottle-shaped wild barley and six-rowed wild barley to cultivated one.
Table 2. Characteristics of F1 from crosses between wild barley.
6. Evolution system of cultivated barley.
Different hypothesis on the evolution system of cultivated barley were
drawn (Table 3). It was generally considered, before 1938, that cultivated
barley evolved directly from two-rowed wild barley. Since 1938, there were
different views: Some investigators think that cultivated barley originated
from Tibetan six-rowed wild barley but the others did not think so. They
have proposed that two-rowed cultivated barley has originated from two-rowed
wild barley and six-rowed cultivated barley has originated from six-rowed
wild barley. After 1962, there was a new hypotheses of origin of cultivated
barley from bottle-shaped wild barley.
Table 3. Hypothesis on evolution system of cultivated barley.
We are presenting in this paper a new consideration concerning the origin and evolution system of cultivated barley. It is based on the results of morphological, cytological and genetical investigations. The main point of this hypotheses is that the origin and evolution of cultivated barley is a kind of process both periodic and continuous. The two-rowed wild barley is the oldest ancestor, the bottle-shaped wild barley represents the second stage and six-rowed wild barley, the third stage, while the cultivated barley denotes the final stage of evolution.
