Oryza Rufipogon

Blackwell Science, LtdOxford, UKPSBPlant Species Biology0913-557XThe Society for the Study of Species Biology, 2005August 20052028392Original ArticleCOMMON WILD RICE BIODIVERSITYZ. SONG Et al. http://www.paper.edu.cn Plant Species Biology (2005) 20, 83–92 Genetic diversity and conservation of common wild rice (Oryza rufipogon) in China ZHIPING SONG, BO LI, JIAKUAN CHEN and BAO-RONG LU Ministry of Education Key Laboratory for Biodiversity and Ecological Engineering, Institute of Biodiversity Science, Fudan University, Handan Road 220, Shanghai 200433, China Abstract Common wild rice (Oryza rufipogon Griff.), known as the ancestor of Asian cultivated rice (Oryza sativa L.), is the most important germplasm for rice improvement. The first male sterility gene was found in the wild rice, and introduced to the cultivated rice, which launched the fast development of the high-yielding hybrid rice. Other agronomically beneficial traits in the wild rice, such as rice tungro virus resistance, bacterial leaf blight (Xa21 gene) resistance and acid sulfate soil tolerance, have played important roles in rice breeding. China has the northernmost distribution area of wild rice possessing great genetic diversity. However, most of the populations of this species have disappeared in China over the last three decades, mainly caused by habitat loss, fragmentation and other human disturbances. Unfortunately, the decline of existing populations still continues. In the present study, we reviewed studies on genetic diversity and conservation of this wild rice in China, concentrating on population structure, pollen competition, pollen/ gene flow from cultivated rice to wild rice, and ecological restoration in relation to in situ conservation. The relatively high genetic diversity of populations of O. rufipogon in China suggests that there is great value for conservation. Considerable gene flow from cultivated rice to wild rice may alter the genetic structure of natural populations of O. rufipogon and eventually lead to its genetic erosion. Pollen competition between wild and cultivated rice has caused a low rate of crop-to-wild gene flow, but it does not completely prevent gene flow from the crop. Effective isolation measures should be undertaken in the regions where in situ conservation of O. rufipogon is carried out. Reintroduction is an important alternative for the in situ conservation of wild rice species. As wild rice is an important genetic resource, both in situ and ex situ conservation strategies are needed. Keywords: common wild rice, conservation, gene flow, genetic diversity, genetic resource, Oryza rufipogon, restoration. Received 7 January 2005; revision received 22 March 2005; accepted 5 April 2005 Introduction crop species, particularly those in the gene pool of wild relatives of crop species, will provide many more oppor- The continuous increase of the global population, the tunities. Through millions of years of evolution and reduction of farming land, the increasing shortage of genetic adaptation to environments, the wild relatives water and the loss of rural labor to the urban centers have accumulated abundant genetic diversity. Many traits profoundly challenge the world’s food supply. To meet are unique to the wild relatives and might be beneficial to the increasing demands for food supply, the human race the improvement of cultivated species. Serving as a vast has to significantly enhance crop productivity, for which genetic reservoir, wild relatives provide elite germplasm fuller exploitation and utilization of genetic resources in for improving crop varieties by transferring beneficial genes to the crops (Lu 1996, 1998). Correspondence: Bao-Rong Lu The Asian cultivated rice, Oryza sativa L., and African Email: [email protected] cultivated rice, Oryza glaberrima Steud., are classified in © 2005 The Society for the Study of Species Biology 转载中国科技论文在线 http://www.paper.edu.cn 84 Z. SONG ET AL. the genus Oryza, which includes over 20 wild species that turbances to its habitats (Gao 2003). Conservation and are widely distributed in the pan-tropics and subtropics, related studies of O. rufipogon have been extensively car- particularly in Asian countries (Khush 1997). The wild ried out in China. Here we briefly summarized some of species in the genus Oryza and in the related genera in the the progress made over the past decades. tribe Oryzeae constitute an exceptionally valuable gene pool for rice improvement (Lu 1996; Bellon et al. 1998; A brief description of common wild rice Zhong et al. 2000). There are many successful examples of utilizing biodiversity in the rice gene pool, particularly in Common wild rice is here referred to as the perennial wild the wild Oryza gene pool for rice improvement. The most rice O. rufipogon, although this taxon is also thought to successful example of utilizing the wild Oryza species is include the annual wild O. nivara by some authors (e.g. hybrid rice, where the male sterility (MS) gene was intro- Chang 1976; Matsuo & Hoshikawa 1993) and was once duced from the perennial common wild rice (CWR, Oryza named as Oryza perennis by Oka (1988) because the plant rufipogon Griff.) found in Hainan Province (formerly has species-specific characteristics compared with other Hainan Island, a part of Guangdong Province), China, Oryza species. O. rufipogon has short to long rhizomes and subsequently the most essential MS system of hybrid from which tillers can emerge far from the main stalk. The rice was developed (Yuan 1993). Another prominent period for its vegetative growth is quite long (Matsuo & example is the varieties of grassy stunt virus-resistant Hoshikawa 1993). rice, where the virus-resistant gene was incorporated The ligule is long and split into two at its sharp tip. The from one accession of the annual CWR (Oryza nivara panicles are open and the spikelets are slender. The anther Sharma et Shastry) collected from India (Khush 1977). of O. rufipogon is usually long and is of a yellowish-white Recently, many disease-resistant and insect-resistant color. The stigma is colored from white to dark, but genes, high-yielding genes and abiotic stress-tolerant mainly pale purple; it appears out of the glume at flow- genes have also been found in wild Oryza species (Khush ering time (Fig. 1). The grain is usually slender with a long et al. 1990; Jena & Khush 1990; Brar et al. 1996; Xiao et al. awn (unhusked), is of a dark purple color at maturity and 1996). Some of these genes have successfully been trans- falls naturally. The color of the husked grain is red. The ferred to varieties of cultivated rice. Conserving the biodi- flowering time is basically the same as that of O. sativa, versity of the wild Oryza species is therefore essential for which is responsive to photoperiods. The cross-fertility is the world’s sustainable food supply and becomes increas- high in this species. ingly important for continued availability and sustainable Oryza rufipogon is widely distributed in the tropics and use of these valuable genetic resources. subtropics of Asia (Vaughan 1994). This species is The perennial CWR, Oryza rufipogon Griff., known as reported to occur in 113 counties of eight provinces in the ancestor of Asian cultivated rice (O. sativa L.), is the south China, including Guangdong, Guangxi, Hainan, most important germplasm for rice improvement (Oka Yunnan, Hunan, Jiangxi, Fujian and Taiwan (Taiwan 1988). The collected samples of this wild rice species have O. rufipogon populations disappeared in 1978; Kiang et al. been extensively used by scientists and breeders from 1979; Fig. 2). The range of CWR in China stretches from agricultural research stations and universities for breed- 18∞09¢N to 28∞14¢N and 100∞40¢E to 121∞15¢E (Pang & ing and research. The well-known Chinese rice variety Chen 2002). ‘Zhongshan no. 1’, which is tolerant of cold tempera- tures and other abiotic stresses, was bred by Profes- Exploration and collection of common wild rice sor Ding Ying in 1931 through wide hybridization with in China O. rufipogon, except for the famous hybrid that incorporated the MS trait identified in O. rufipogon in the early The exploration and collection of wild Oryza species in 1970s (Yuan et al. 1989; Yuan 1993). Other agronomically China can be traced back to as early as 1917 when Dr E. beneficial traits, such as high-yielding, rice tungro virus D. Merrill and colleagues first found the perennial CWR resistance, elongation ability and tolerance of acid sulfate (O. rufipogon) at Lofu Mountain and the Shilong Plain in soil, found in the wild rice are of great potential for rice Guangdong Province (Wu 1990). It was Professor Ding breeding (Xiao et al. 1996; Bellon et al. 1998). China is the Ying who initiated the systematic exploration and collec- northern boundary of O. rufipogon’s natural range, where tion of wild Oryza species in China. In 1926, he found great genetic diversity has been found in its populations O. rufipogon and collected its samples in many more sites, (Wu 1990; Zhou 1995; Wang & Sun 1996; Gao 1997; Ge such as those in Guangzhou, Heiyang, Zhengcheng, et al. 1999; Song et al. 2003a). However, this species has Qingyuan and Sashui in Guangdong Province, on Hainan been under serious threats in China over the past decades Island, and in the Xijiang River Basin in Guangxi Prov- because of the changes in farming systems, economic ince. These findings and collections had significantly development, rapid urbanization and other human dis- enriched the knowledge of Chinese wild Oryza species © 2005 The Society for the Study of Species Biology Plant Species Biology 20, 83–92 中国科技论文在线 http://www.paper.edu.cn COMMON WILD RICE BIODIVERSITY 85 spikelet stigma anther awn Fig. 1 A photo showing part of an opening panicle of Oryza rufipogon. After 1949, the exploration and collection of wild Oryza germplasm in China was further emphasized and came to a new era.

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