The proceeding of the 8'''ISB:206-213(200l)
Discussion on the Origin of Cultivated Buckwheat in Genus Fagopyrum (Polygonaceae)
Qing-Fu CHEN
Laboratory of Genetics, Biology Department, Guizhou Normal University, Guiyang 550001, Guizhou, P.R.China; E-mail:
[email protected]
ABSTRACT Based on concerned reports and comparison among F. esculentum, F. tataricum F. megaspartanium and F. pilus the ancestral species and original places of cultivated buckwheat were discussed. It was concluded that F esculentum and F. tataricum have the hypothetic ancestral species --F megaspartanium and F. pilus, respectively and originate in the Yunnan and Tibet of southwestern China, respectively. Key world: ancestral species, buckwheat, words Fagopyrum, origin and evolution, original place, taxonomy SPECIES OF GENUS FAGOPYRUM NATIVE TO CHINA
Fagopyrum wild species native to China were systematically classified by Gross (1913, see Ye & guo,1992; Ohnishi & Matsuaka, 1996), with some species now recognized as Polygonum species also included. Later, Steward (1930) classified the Asian Polygonaceae and listed ten species in genus Polygonum sect. Fagopyrum. Ye & Guo (1992) classified and confirmed Steward's Fagopyrum species.Ohnishi & Matsuoka (1996) studied Fagopyrum species and proposed four new species native to China. Chen (1999a) described three new species native China. These species can be classified in two groups. The first group is called the large-achene group, including 7 species whose achenes are much longer than the perianths, these are: annual F esculentum Moench, F. tataricum (L.) Gaerth., F. homotropicum Ohnishi, perennial F. megaspartanium Q.F. Chen (big wild buckwheat), F. pilus Q.F Chen (pilous wildbuckwheat) and F cymosum Meissn, annual F. zuogogense Q.F Chen (Zuogong wild buckwheat). Among them, the former 5 species are diploid and the latter 2 species tetraploid. The small-achene group includes the others whose length oh achenes are almost equal to that of the perianths, these are: -F. gracilipes (Hemsl.) Dammer ex Diels, F leptopodum (Diels) hedb., F. gilesii (Hemsl.) Hedberg, F.lineare (Sam.) Haraldson, F. urophyUum Gross, F. statice. Gross, G. pleioramosum Ohnishi, F capillatum Ohnishi, and Fcallianthum Ohnishi et al. Studies on isozyme, Interspecific crossability and rbc L gene sequence analysis (Wang, 1987; Ohnishi & Matsuoka,1996; Chen, 1999a,b) suggested shat the interspecific relationship are close among the species in the same group and distant between the different groups. Most of species in the small-achene group were previously re-class from gunus Polygonum into Fagopyrum. Whether these species should remain in the genus Fagopyrum needs further study
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ANCESTRAL SPECIES OF CULTIVATED BUCKWHEAT
As the above stated, there are about 16 recognized buckwheat species native to China. Among them, which one is ancestor of cultivated buckwheat? There are four hypotheses as follows. The first hypothesis suggests that perennial F cymosum with the heterostyle type of flowers is the ancestor of cultivated buckwheat and that F cymosum, common buckwheat and tartary buckwheat are close in taxonomy (Hedberg, 1946; Campbell 1976). This hypothesis is supported in morphology. But, since most of the accessions of F cymosum previously reported are tetraploid (Alekseeva & Pausheva 1979, Zu et al.1984, Lin 1994) and the buckwheat is very different from cultivated buckwheat in isozyme (Ohnishi et al,1993; Wang 1987), the hypothesis has not been accepted widely as yet. The second hypothesis suggests that the characteristics such as heterostyle, well-developed nectary of F cymosum and common buckwheat should be the evolved properties and that there may be a primitive species with the homostyle type of flowers from which common and tartary buckwheat might have evolved respectively (Li et a1.1992). But the primitive species has not been found as yet. The third hypothesis holds that the relationships among F cymosum, common and tartary buckwheat are so distant that the F cymosum can not be the ancestor of cultivated buckwheat and thinks that wild F esculentum is the ancestor of common buckwheat (Ohnishi, 1991) But the relationship between the wild type and common buckwheat is so close that we think that there is more primitive wild ancestor of cultivated buckwheat. Recently, I (chen,1999a) proposed a new hypothesis that the diploid accessions of F megaspartanium and F pilus may be ancestors of common and tartary buckwheat, respectively. The evidence is as follows: F esculentum, F tataricum, F megaspartnium and F pilus are all diploid and similar in morphology (Chen, 1999a). Comparison of their achenes is given in Fig.I. It is clear that achenes of F tataricum and F pilus all have obvious grooves, and F magaspartnium in characteristics of achenes are more similar tocommon buckwheat than F pilus Studies of interspecific crossability(Hirose et ai, 1994,1995; Chen, 1996b) indicated that they are close in relationships. Sometimes some plants in accessions of F esculentum have frutescent knots and caudex (Chen, 1999a), indicating that there are certain relationships between annual and perennial species and that the perennial frutescent caudex may degenerate into an annual frutescent caudex or even or even into an annual herb. The comparison of esterase isozyme patterns of F esculentum, F tataricum, F megaspartnium and F pilus are given in Fig 2 and 3. It is clear that patterns of F magaspartnium and F pilus are similar to those of common and tartary buckwheat, respectively. In reproductional properties, F esculentum, F megaspartnium and F pilus are all completely or highly cross-pollinating and F tataricum completely self-fertile and ofen clestogamous, which lie on properties of styles. Some reports (Kovalenko, et aI., 1980) have suggested that the character of heterostyly is controlled by a super gene that consists of six closely-linked and related genes (/1, 12" G, 5, P, A). It was discovered very early that the super sgene can be broken (Lewis & Crowe, 1958; Chen,1999a). Since the super gene can be broken by gene mutation and reverting mutation is rare, Lewis & Crowe (1958) suggested that, in a genus that consists of both self-fertile and self-incompatible species, the self-fertile species evolve from self-incompatible species by mutation. Ohnishi (1989, see Ohnishi & Matsuoka, 1996) - 208-
Fig 1. Comparison of achenes among common buckwheat (=E), tartary buckwheat (=T), Fmegaspartnium (=M), and Fpilus (=P)
considered that the genus Fagopyrum was entirely heterostylous, and that the nonheterostylous species have arisen from heterostylous species by the loss of heterostyly and simultaneous development of self-fertilizing mechanisms. Ohnishi & Matsuoka (1996) have reported that there are both homostylous types in some populations of F. gracilipes. Chen (1999a) confirmed that there are also both types in some populations of F. pleioramousm, F. esculentum and F. pilus. These results indicated that the reproductional properties in genus Fagopyrum are easy to change. Based on the above analyses, F. megaspartanium and F. pilus may be ancestors of F. esculentum and F. tataricum, respectively. ORIGINAL PLACE OF CULTIVATED BUCKWHEAT
On the original place of cultivated buckwheat, there are two main hypothesis, these are: DeCandolle (1883)'s hypotheses that cultivated buckwheat originates in northern China or Siberia and Nakao (l960)'s hypotheses that cultivated buckwheat originates in the area of southwestern China close to Himalaya Mountain (see Matano & Ujihara, 1979). - 209-
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Ohnishi et aI. (1993) studied the allozyme variability of world-wide cultivated buckwheat resources, in order to find the center of variability related to the orgin of cultivated buckwheat. Their results suggested that at all loci of 12 enzymes allele frequency do not vary much among the populations and the center of allozyme diversity was not found. The notes of Chinese ancient books and poetries and the discovery of archaeological sites all suggest that buckwheat was cultivated in China 2000 years ago, which is the earlist in the world (Lin, 1994). The discovery of wild F. esculentum in Yunnan, China (Ohnishi, 1991) and the textual research of history of language and cultivation on buchyheat (Lin, 1994) in Yunnan, China, all support the Nakao (1960)'s hypotheses. So to speak, the opinion that cultivated buckwheat originates in southwestern China has been accepted by most scientists. But the problems such as whether common buckwheat and tartary buckwheat originate in the same place have not been solved as yet. 1. The original place of common buckwheat Cultivated F. esculentum is the type with the widest distribution among buckwheat species in the world. It distributes in Asia, Europe, America et al. But there is not great variability among populations native to various places in morphology and isozyme (Ohnishi et aI., 1993; Chen, - 210-
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1999a). The distribution of wild F. esculentum is very narrow, mainly in areas of Yunnan, southwestern China, such as Lijiang and Yongsheng (Ohnishi, 1991, Li & Yang, 1992). Among various populations there are certain variability. There are several reasons responsible for low variability of common buckwheat: (1) short history of cultivation and few variation accumulated. the earlist notes of buckwheat cultivation is in China ancient book - Shen Nong Shu (3-4 century B.C., 2000 years ago) (Lin, 1994). The earlist record of archaeology is in west Han Dynasty (206 B.C.,- A.D.8) (Lin, 1994). These suggest that the history of buckwheat cultivation is short, as comparison with wheat et al. (2) The effects of reproductional system of crosspollination and artificial factors such as artificial spreading et ai. These effects can make variations easily exchange among various populations and reduce divergence among different wasteland on hillside and extensive cultivation in rural area in China used to be reclaiming waste mountain and being missed into wild populations of F esculentum. These reduce the differences between cultivated and wild F. esculentum. The hypothetic ancestral species (F megaspartnium) of F esculentum widely distributes in southwestern China, where there are many related species such as most of small-achene group. According to the sensiveness to light and temperature, there are three ecotypes in common - 2lJ -
buckwheat (Matano & Ujihara, 1979), these are: autumn ecotype (sensitive, although the type may grow and blossom and bear fruit in both spring and autumn, it will do better in autumn), summer ecotype (insensitive) and middle ecotype. Matano & Ujihara (1979) thought that autumn ecotype is a primitive ecotype. The accessions of F. megaspartnium native to Chengdu, Sichuan, are the most sensitive to light and temperature in diploid species in the large-achene guoup, so that they make the differentiation of inflorescense and flowers only for a very short time of autumn (often August - September in Chengdu, Sichuan, China), indicating that the ecotype of F megaspartnium is strict autumn ecotype more primitive than that of F. esculentum. The accessions of F megaspartnium native to Yunnan and Guizhou are also the autumn ecotype whose plant and their achenes are more similar to F esculentum than those of Sichuan. Among the accessions native to Yunnan and Guizhou, some are strict autumn ecotype and others are not. Because of much more species of Fagopyrum in Yunnan (having more than 8 species) than Guizhou (having 4 species or more), Yunnan may be the center of variability of genus Fagopyrum. The above analyses indicate that common buckwheat may originate in Yunnan of southwestern China.
2. The original place of tartary buckwheat The distribution of cultivated tartary buckwheat is mainly in mountain area of southwestern China. There is certain variability of morphology among populations Tartary buckwheat is strictly selfpollinated. Its properties, such as nectaries and some stamens wi'th certain degenerations, small and green flowers often not opening and closefertilized, very short styles and stamens et al., indicate that tartary buckwheat evolves from crosspollinational species with heterostyle under the cooler conditions which are very unfavourable to entomophilous crosspollination. Wild tartary buckwheat often grows in banks of a ditch, riverside, woodlands, waste hillside and farmland as weeds, and have great variability among populations native to different places and is largely centralized in the cooler areas of the eastern Qing Zang Plateau, Chuan Xi Plateau and Yun Gui Platea at high altitude (often> 1500m above sea level), indicating that tartary buckwheat may originate in these areas. It is known that the hypothetic ancestral species (F pilus) of F tataricum mainly distributes in the eastern of Qing Zang Plateau such as Metuo, Bimi, Chayue, Linmang, Nielamu and MiEn, and Tibet, overlapping the area where the wild types of F tataricum are rich. According to the above analyses. tartary buckwheat may originate in Tibet of southwestern China.
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