Rice Science, 2004, 11(5-6): 261-268 261 http://www.ricescience.org

Cold Tolerance of Core Collection at Booting Stage Associated with Eco-geographic Distribution in Rice Landrace (Oryza sativa), China

1,2 1 1 1 LI Shen-chong , ZENG Ya-wen , SHEN Shi-quan , PU Xiao-ying (1Biotechnology and Genetic Resources Institute, Yunnan Academy of Agricultural Sciences, 650205, China; 2College of Agronomy and Biotechnology, Yunnan Agricultural University, Kunming 650201, China)

Abstract: Four hundred and seventy-seven accessions of the second core collection of rice landrace from five rice cropping regions (16 prefectures) of Yunnan Province, China, were evaluated for cold tolerance at booting stage. The results showed as follows: 1) there was a significant positive correlation (0.588**) between anther length and seed setting rate under natural low temperature conditions but was not significant in greenhouse (0.080). 2) there were significant differences in cold tolerance among core collections from different cropping regions under natural low temperature conditions while a negligible cold damage in greenhouse (with a seed setting rate approaching or exceeding 70%) for cold tolerance evaluation. Cold tolerance of core collection from Northwest Yunnan cold highland japonica region was the strongest, and that from south marginal paddy-upland rice region was the most sensitive, suggesting that the breeding goals for cold tolerance should be different in various rice cropping regions. 3) there were remarkable differences in cold tolerance of core collections from different prefectures of Yunnan Province under natural low temperature conditions. Based on the reduction of seed setting rate and characteristics of natural climate, the 16 prefectures could be divided into three categories, i.e. serious cold damage , cold damage and slight cold damage regions. 4) Difference of cold tolerance between different rice cropping regions and prefectures revealed further that temperature change caused by elevation and latitude was not only a dominant factor for differentiation of japonica and indica but also the basic reason that the genetic diversity and six ecological group of indica and japonica were being developed and, even the critical factor leading to the formation of the cold tolerance gene as well. The cold tolerance at booting stage could be believed to be resulted from the long term co-evolution between Yunnan rice landrce and cold stress in rice cropping regions. Key words: Yunnan rice landrace; core collection; cold tolerance; rice cropping region; geographical distribution

Rice is a staple food crop in the world, especially damage is a serious problem not only in the in Asia, and its consistent and stable production is high-latitude regions, such as Hokkaido in Japan, but vital for food supply security. Most rice-growing also in high-elevation regions of low-latitude area, e.g. countries are facing low temperature stresses that Yunnan Province in China. Cold tolerance of rice is a severely reduce the rice production. Low temperature complex quantitative trait controlled by multi-genes. is a major climatic problem for rice growing over 20 In recent years, much work has been conducted on countries, including Japan, Korea, China, USA and screening, evaluation and gene mapping for cold Australia, and even tropical countries such as the tolerance of rice at booting stage, and remarkable Philippines and Thailand [1]. Booting stage is the most progress has been achieved by many domestic or sensitive time for rice to chilling injury, particularly foreign researchers. Wang et al[4] proved that there during 10 days before heading phase. It might result was a significant correlation between anther length in panicle degeneration and empty grains at harvest and seed setting rate, and regarded the anther length due to cold damage. Yoshida and Satake [2, 3] found as one of the evaluation indices for cold tolerance at that low temperature affect significantly the spikelet booting stage. Futsuhara et al [5] estimated the number development at the young microspore stage about 10 of cold tolerance genes to be four or more. It has been or 11 days before heading. Sterile panicle due to cold reported that they are linked with the genes Pr (purple

hull), Rc (brown pericarp), d2 (dwarf), gh (gold hull), Received: 20 July 2004; Accepted: 25 October 2004 nl (neck leaf) and bc (brittle culm) on chromosomes 3, [5-7] Corresponding author: ZENG Ya-wen ([email protected]) 4, 5 and 7 . So far QTLs responsible for cold

262 Rice Science, Vol. 11, No. 5-6, 2004 tolerance, have been detected on each of rice October). The depth of water was maintained about chromosomes in Japan, USA and China. However, 20 cm. At heading stage, three anthers per main the relationship between geographical distribution and panicle and three main panicles per accession in cold tolerance of the second core collection for rice greenhouse while one anther per main panicle and ten landrace resources in Yunnan has never been reported main panicles per accession in paddy field were taken in domestic or abroad to date. for measurement of anther length with 50 times Yunnan Province is a center of genetic and amplification through a versatile projector. The ecological diversity of rice cold tolerance in China [8]. corresponding average anther length and anther length Cold damaged tract constituted one second (463–533 shortening rate (ALS) were calculated. The ALS was thousand hectares) of all rice cropping areas in calculated by the following formula: Yunnan Province [9]. As a result of the cold ALS=(Mean anther length in greenhouse－Mean acclimation for hundreds or thousands of years, anther length under natural low temperature)/Mean Yunnan rice landrace are ranked the first in the anther length in greenhouse. abundance for their cold tolerant germplasms in China, After ripening stage, cold tolerance was evaluated and their cold tolerance is stronger than the rice based on the mean seed setting rates of three and five cultivars in Japan, generally. Therefore, we conducted sample plants from greenhouse and field, respectively. this study to investigate the cold tolerance at booting According to filled or unfilled grains, total grains per stage and geographical distribution of Yunnan rice panicle, and corresponding seed setting rate reduction landrace, to disclose the evolution and biodiversity of (SSRR). SSRR was calculated as follow: rice species, giving a probable insight into the rice SSRR=(Mean seed setting rate in greenhouse－ genetics and breeding for cold tolerance and Mean seed setting rate under natural low temperature) production. /Mean seed setting rate in greenhouse. The SSRR and ALS were regarded as evaluation MATERIALS AND METHODS indices for cold tolerance at booting stage. The variation in cold tolerance was indicated by standard Rice materials deviation (SD) and coefficient of variation (CV) of the second core collection. Four hundred and seventy-seven accessions (265 In terms of administrative regional division, japonica and 212 indica) of the second core collection Yunnan rice cropping is divided into five regions, or were selected based on 31 morphological traits of sixteen prefectures by administrative division [11]. 6121 accessions, 41 morphological traits and 12 polymorphic isozyme loci of 912 accessions, which RESULTS represent more than 90 percent genetic diversity of Yunnan rice landrace[10]. Correlation analysis between seed setting rate and Methods anther length

The cold tolerance of rice was evaluated in All the accessions of the second core collection of greenhouse (average temperature 23℃) and under Yunnan rice landrace were damaged severely by cold natural low temperature conditions (average 18℃). at booting stage under natural low temperature (1910 The rice materials were sown on March 19, and the m above sea level and 18–20℃ in Kunming) in 2002. seedlings were transplanted to greenhouse and paddy There was a significant positive correlation (0.588**) field at the same time on 8 May, 2002. Twenty between seed setting rate and anther length under seedling of each accession was planted in one line, natural low temperature condition but non-significant with a 10 cm × 17.5 cm spacing. The cold tolerance in greenhouse (0.080) (Table 1). In addition, there was evaluated after cold-water (18–19℃) irrigation was a remarkable correlation between seed setting from 20 days before heading till maturity (1 July to 31 rate in greenhouse and seed setting rate (0.214**), as

LI Shen-chong, et al. Cold Tolerance of Core Collection Associated with Eco-geographic Distribution in Yunnan Rice 263 well as anther length under natural low temperature CV is relatively as small as 15.04 to 34.00%, and the (0.312**). The results showed that there was a close anther length of core collection from five rice relationship between anther length and cold tolerance cropping regions except Northeast Yunnan plateau in rice in accordance with Wang et al [4]. japonica rice region all exceed 2.00 mm. Therefore, the cold damage of core collection is severe under Difference in cold tolerance at booting stage natural low temperature conditions but little or no among the second core collection from five damage occurred in greenhouse. The order of seed Yunnan rice cropping regions setting rate reduction was as follows: South marginal The results revealed that there was significant paddy-upland rice region( Ⅲ ) (0.90) ＞ South difference in cold tolerance at booting stage of 477 Yunnan single/double season rice region (Ⅱ)(0.84)＞ accessions among the five rice-cropping regions in Northeast Yunnan plateau japonica rice region(Ⅳ) Yunnan (Table 2). Under natural low temperature (0.74) ＞ Central Yunnan single season japonica- conditions, there was relatively low mean seed setting indica region(Ⅰ) (0.67) ＞ Northwest Yunnan cold rate (from 7.11 to 42.72%) and short anther length highland japonica rice region(Ⅴ) (0.49). The lesser (1.63 to 1.94 mm) (Table 2) of core collection in the seed setting rate reduction was, the stronger cold different rice cropping regions, with coefficient of tolerance of core collection was indicated. It was clear variation (CV) of 81.95 to 221.24% and 13.81 to that cold tolerance of the second core collection 18.23%, respectively. Conversely, in greenhouse the acclimated in Northwest Yunnan cold highland mean seed setting rate approached to or over 70%, japonica rice region is the strongest, followed by

Table 1. Correlation analysis between seed setting rate and anther length for core collection in Yunnan rice landrace.

Seed setting rate in Seed setting rate under low Anther length in Anther length under low Character greenhouse temperature condition greenhouse temperature condition

Seed setting rate in greenhouse 1.000 0.214** 0.080 0.218** Seed setting rate under low temperature conditions 0.214** 1.000 0.312** 0.588** Anther length in greenhouse 0.080 0.312** 1.000 0.517** Anther length under low temperature conditions 0.218** 0.588** 0.517** 1.000

** Significant at 0.01 level (2 tailed), r0.05=0.098 (df=475), r0.01=0.128 (df=475).

Table 2. Difference of cold tolerance at the booting stage among core collections from different rice cropping regions in Yunnan Province.

Rice cropping Accessions of core collection Experimental Seed setting rate(%) Anther length(mm) SSRR ALS region japonica indica Total place Mean SD CV(%) Mean SD CV(%)

Ⅰ 053 0 38 0 91 Greenhouse 79.63 15.25 19.15 2.04 0.27 13.24 0.67 0.11 Paddy field 26.06 30.52 117.11 1.81 0.33 18.23

Ⅱ 120 83 203 Greenhouse 74.69 19.19 25.69 2.07 0.29 14.00 0.84 0.15 Paddy field 11.65 20.88 179.23 1.75 0.29 16.57

Ⅲ 173 111 284 Greenhouse 68.82 23.40 34.00 2.04 0.30 14.71 0.90 0.20 Paddy field 7.11 15.73 221.24 1.63 0.27 16.56

Ⅳ 0 21 0 30 051 Greenhouse 79.64 18.66 23.43 1.81 0.25 13.81 0.74 0.05 Paddy field 20.32 27.78 136.71 1.72 0.28 16.27

Ⅴ 021 004 025 Greenhouse 83.72 12.59 15.04 2.13 0.33 15.49 0.67 0.09 Paddy field 42.72 35.01 81.95 1.94 0.32 16.49

SSRR, Seed setting rate reduction value; ALS, Anther length shortening rate. Rice cropping region:Ⅰ, Central Yunnan single cropping region of indica-japonica; Ⅱ, South Yunnan single/double rice cropping region; Ⅲ, South marginal paddy-upland rice region; Ⅳ, Northeast Yunnan plateau japonica region; Ⅴ, Northwest Yunnan cold highland japonica region.

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Northeast Yunnan plateau japonica rice region and cold damage was relatively severe and the cold Central Yunnan single season japonica-indica region. tolerance variation was relatively low. The growth of South marginal paddy-upland rice region is the indica and japonica rice in the second core collection weakest. Rice cropping region Ⅳ is located in the was poor in this region. Due to the lagging of cold northeast with higher altitudes whileⅠlies in the tolerance breeding for indica rice in this region for central region with lower altitude, however the seed recent two decades, a tremendous change in rice setting rate of the former was lower than that of the production occurred, in which indica and japonica latter, because the former included 30 indica varieties rice interlaced cropping has been almost replaced by from Jinshajiang River dry-hot valley belt (＜1500 m japonica rice. So the breeding for cold tolerance of above sea level) in rice cropping region Ⅳ. In all the indica rice should be considered as priority. It rice cropping regions, the order of anther length revealed that rice cropping regionⅠis the ideal base shortening rate was as follows: Ⅲ(0.20) ＞Ⅱ(0.15) for breeding rice variety with cold tolerance at ＞Ⅰ(0.11) ＞Ⅴ(0.09) ＞Ⅳ(0.05). Obviously, a booting stage and near isogenic lines (NILs) in China certain degree of difference occurred on the [8], as japonica in Kunming and indica in evaluation of core cold tolerance by anther length Prefecture. The cold damage was relatively slight but shortening and seed setting rate reduction, because the variation of cold tolerance in core collection of anther size and spikelet fertility of rice were affected rice germplasm was particularly high in Northeast by different ecological environmental conditions. The Yunnan plateau japonica rice region (Ⅳ) and South former could be regarded as an obstacle index in cold Yunnan single/double season rice region (Ⅱ). There tolerance screening when rice can’t naturally develop is a larger differentiation of indica and japonica rice under low temperature during heading and flowering and a great difference of elevation between the above period, and the latter is influenced by the low two regions. The former is located in Jinshajiang dry temperature after fertilization which restrains natural and hot river valley belt, mainly including Yanjing, photosynthesis of leaves and transportation of its Daguan, Wenxin, Yiliang, Zhenxiong and Qiaojia products. Therefore, we considered the cold tolerance counties in Prefecture and in evaluation being based on the seed setting reduction Prefecture. The latter includes region of indica in this experiment. and japonica rice interlaced and region of indica and In addition, there was a pronounced difference in japonica differentiated. The slightest cold damage and coefficient variation (CV) of seed setting rate under the greater variation of cold tolerance occurred in low temperature in different rice cropping regions, South marginal paddy-upland rice region(Ⅲ), a center such as Ⅲ(221.24%)＞Ⅱ(179.23%)＞Ⅳ(136.71%) of genetic diversity of Yunnan rice. As a result of ＞Ⅰ(117.11%)＞Ⅴ(81.95%). It has been elucidated humid and hot weather, indica and japonica, paddy that the cold damage in Northwest Yunnan cold and upland, glutinous and non-glutinous rice types are highland japonica rice region (Ⅴ) was extremely distributed in this area. Therefore, high production, serious and the variation of cold tolerance in this high quality and diseases resistance should be the region was the least. Considering that the core rice main objective for breeding programs there. The germplasms included 21 accessions of japonica and difference in cold tolerance of the second core only 4 accessions of indica, japonica rice should be collections from different rice cropping regions the primary breeding objective for cold tolerance. So further illustrated that temperature changing with this rice cropping region, especially Prefecture, elevation is not only a dominant factor for the is the ideal breeding base for cold tolerance at booting differentiation of japonica, but the main factor for that stage of japonica rice in China. In Central Yunnan the genetic diversity and six ecological groups of single season japonica-indica rice region (Ⅰ), the rice indica and japonica were developed.

LI Shen-chong, et al. Cold Tolerance of Core Collection Associated with Eco-geographic Distribution in Yunnan Rice 265

Difference in cold tolerance at booting stage of the respectively (see Table 3). Variation of cold tolerance second core collection among prefectures in in Xishuangbanna was the most pronounced followed Yunnan Province by Dehong, Licang, Simao, and Lijiang in a The cold tolerance at booting stage in 477 descending order. Among them, Xishuangbanna, accessions of core collection among prefectures in Dehong, and Simao constitute a center of [13] Yunnan is displayed in Table 3. Under natural low genetic diversity of minorities . temperature conditions, a large variation of the In addition, anther length was relatively short chilling injury was observed among rice varieties in under low temperature conditions, with the anther different prefectures, and the seed setting rates were length of core collection from Qujing Prefecture being relatively low and variable compared with those of the longest (2.03 mm), while that of the core the core collection in greenhouse. The highest collection from Dehong Prefecture being the shortest. (50.50%) and the least (3.20%) seed setting rates of Co-efficient of variation (CV) of anther length from core collection occurred in Kunming and Qiqing, Chuxiong was the biggest, followed by Kunming,

Table 3. Difference of cold tolerance at the booting stage for core collection in different prefectures in Yunnan Province.

Accessions Seed setting rate Anther length Prefecture Place Mean SD CV Mean SD CV SSRR ALS Japonica Indica Total (%) (%) (%) (mm) (mm) (%) Kunming 3 1 4 Greenhouse 89.66 3.62 4.04 2.15 0.31 14.42 0.44 0.21 Paddy field 50.52 40.00 79.18 1.70 0.44 25.88 Lijiang 13 20 33 Greenhouse 79.14 18.72 23.65 1.81 0.25 13.81 0.75 0.06 Paddy field 19.65 27.94 142.19 1.71 0.29 16.96 Nujiang 11 3 14 Greenhouse 83.68 8.88 10.61 2.24 0.26 11.61 0.53 0.09 Paddy field 38.98 29.97 76.89 2.03 0.30 14.78 Qujing 13 6 19 Greenhouse 74.62 20.52 27.50 2.04 0.28 13.73 0.62 0.10 Paddy field 28.47 31.09 109.20 1.83 0.29 15.85 Dali 59 37 96 Greenhouse 72.59 18.28 25.18 2.02 0.25 12.38 0.85 0.16 Paddy field 10.57 20.40 192.99 1.70 0.27 15.88 Chuxiong 48 29 77 Greenhouse 72.05 23.90 33.17 2.13 0.29 13.62 0.87 0.20 Paddy field 9.41 18.61 197.77 1.70 0.26 15.29 Yuxi 24 9 33 Greenhouse 77.14 17.51 22.7 1.94 0.21 10.82 0.85 0.14 Paddy field 11.39 21.18 185.95 1.67 0.28 16.77 Zhaotong 14 5 19 Greenhouse 87.37 8.04 9.2 2.09 0.29 13.86 0.46 0.06 Paddy field 46.99 33.88 72.10 1.97 0.33 16.75 Baoshan 12 15 27 Greenhouse 75.84 13.09 17.26 2.09 0.30 10.35 0.77 0.11 Paddy field 17.82 23.80 133.56 1.87 0.34 18.18 Wenshan 18 16 34 Greenhouse 76.82 16.20 21.09 2.02 0.23 11.39 0.89 0.17 Paddy field 8.26 15.69 189.95 1.68 0.29 17.26 Simao 28 27 55 Greenhouse 67.16 24.32 36.21 2.13 0.27 12.68 0.95 0.23 Paddy field 3.48 9.13 262.35 1.64 0.25 15.24 Lincang 4 1 5 Greenhouse 68.68 24.09 35.08 2.07 0.19 9.18 0.55 0.18 Paddy field 31.19 35.09 112.5 1.69 0.45 26.63 Honghe 5 2 7 Greenhouse 76.72 15.28 19.92 2.10 0.34 16.19 0.56 0.04 Paddy field 33.94 32.39 95.43 2.01 0.34 16.92 XSBN 18 25 43 Greenhouse 65.10 28.72 44.12 1.91 0.41 21.47 0.90 0.20 Paddy field 6.27 15.78 251.67 1.52 0.27 17.76 Dehong 5 4 9 Greenhouse 86.62 13.90 16.05 2.08 0.35 16.83 0.59 0.10 Paddy field 35.17 37.85 107.62 1.87 0.25 13.37 Diqing 2 0 2 Greenhouse 78.96 - - 1.84 - - 0.96 -0.04 Paddy field 3.20 - - 1.91 - -

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Wenshan, Dehong and Honghe in a decreasing order. and Dehong as well as the river valley zone in Deqing Among them, Dehong and Whenshan is one of the Prefecture. When the rice was planted under natural centers of genetic diversity in Yunnan rice landrace low temperature conditions in Kunming in 2002, the [12]. However, the core collection among prefectures seed setting rate of rice core collection among in greenhouse were not significantly affected by low prefectures except Diqing was relatively as lower as temperature, the seed setting rate approaching or 3.48% to 11.39%, and the CV was as relatively higher exceeding 65%, the CV being relatively small, at 4.04 as 185.59% to 262.35%. It revealed that genetic to 44.12%, and the anther length being relatively diversity for cold tolerant rice resources almost stable with small CV. corresponds to the centre of genetic diversity for rice The seed setting rate reduction among 16 resources in Yunnan. prefectures showed the following sequence: Diqing On the other hand, a large variation of anther (0.96) ＞ Xishuangbanna (0.95) ＞ Dehong (0.90) ＞ length shortening rate among prefectures was found. Honghe (0.89)＞Lincang (0.87) ＞Simao (0.85) = The order was as follows: Xishuangbanna (0.23) ＞ Baoshan (0.85) ＞Wenshan (0.77) ＞Zhaotong (0.75) Kunming (0.21) ＞ Dehong (0.20) = Licang (0.20) ＞ ＞ Yuxi (0.62) ＞Nujiang (0.59) ＞ Dali (0.56) ＞ Chuxiong (0.18) ＞Honghe (0.17)＞Simao (0.16) ＞ Chuxiong (0.55)＞Qujing (0.53)＞Lijiang (0.46)＞ Baoshan (0.14) ＞ Wenshan (0.11) ＞Yuxi (0.10) ＞ Kunming (0.44). According to cold tolerance at Nujiang (0.10) ＞Qujing (0.09) ＞Lijiang (0.06) = booting stage in the second core collection from Zhaotong (0.06) ＞ Dali (0.04) ＞ Diqing (－0.04). Yunnan rice landrace, sixteen prefectures can be Obviously, different results should be obtained from divided into three regions, i.e. strong cold tolerance the evalution of cold tolerance for core germplasm (the seed setting rate reduction value is below 0.60), mainly based on the seed setting rate reduction and intermediate cold tolerance (0.60–0.80), and weak anther shortening length rate. However, the cold cold tolerance (over 0.80) regions. They could be tolerance evaluated with seed setting rate reduction classified into serious cold damage, cold damage and had proven that temperature change is not only a slight cold damage regions, correspondingly. dominant factor responsible for the differentiation of Serious cold damage regions included Kunming, indica and japonica rice, but also the basic reason for Lijiang, Qujing, Chuxiong, Dali and Nujiang, where the difference among the six ecological groups of cold damage was extremely serious, especially in the indica and japonica and large genetic diversity for rice areas with altitude at 1800–2700 m above sea level. resources in Yunnan. Cold tolerance of core When accessions from these six places was planted collection at booting stage reflected indirectly the under natural low temperature conditions in Kunming whole tendency of cold damage in rice cropping in in 2002, they showed a seed setting rate of 31.19% to these prefectures throughout the years. 50.52% and CVs as low as 72.10% to 112.50%. In addition, some areas with altitude over 1900 m above DISCUSSION sea level in Zhaotong Prefecture and regions with altitude over 2000 m above sea level in Diqing There exist significant variation in anther length Prefecture belonged to serious cold damage region. and seed setting rate in the second core collection Cold damage regions mainly involved Yuxi, among rice cropping regions or prefectures. An Zhaotong, and Wenshan. When the rice was planted extremely remarkable correlation (0.588**) was under natural low temperature conditions in Kunming established between anther length and seed setting in 2002, the seed setting rate and CV% of the second rate under natural low temperatures but not significant core collection among the three prefectures were in greenhouse (0.080). Therefore, anther size and cold 17.82% to 28.47% and 109.20% to 133.56%, tolerance of rice disclosed a close relationship, strong respectively. and weak cold tolerance of core collection could be Slight cold damage region mainly comprised directly reflected by anther length shortening rate Baoshan, Simao, Lincang, Honghe, Xishuangbanna, among rice cropping regions and prefectures. It is

LI Shen-chong, et al. Cold Tolerance of Core Collection Associated with Eco-geographic Distribution in Yunnan Rice 267 verified that the stability degree of anther size of the roughly categorized into central diversity, scattering core collection, in indica rice region, indica and diversity and lacking diversity regions[15]. japonica rice interlaced regions and warm-cool The cold damage difference of rice among japonica rice region, could be regarded as an index of different cropping regions and prefectures was a screening for cold tolerance [4]. dominant factor by which the genetic diversity for There is a large difference of cold tolerance at cold tolerance was established. Its distribution was booting stage in the second core collection from not only correlated with cold damage zones and different rice cropping regions in Yunnan. intensity of cold atmosphere, but also related to the Temperature is highly variable throughout Yunnan relative weak or strong cold tolerance of the second Province in China, because of variable altitudes core collection in Yunnan rice landrace. CV of the especially in northwest Yunnan cold highland seed setting rate and anther length in the core japonica rice region and central Yunnan single season collection was closely related to the genetic diversity japonica-indica region. Therefore, developing cold of rice resources in Yunnan. Therefore, the tolerant varieties and suitable cultivation practices are temperature changing with altitude was the dominant of great concern for the future strategies because these factor by which the ecological groups of indica and will lead to produce consistently high yield in cold japonica differentiated and genetic diversity were regions, particularly in rice cropping region V (e.g. formed [16]. Lijiang and Nujiang) and I (e.g. Kunming, Qujing and Dali). The cold tolerance at booting stage of Yunnan ACKNOWLEDGEMENTS rice landrace has been developed by cold acclimation for hundreds or thousands of years. In addition, Zeng This research was supported by the Natural found that cold tolerance of hybrids at booting stage Science Foundation of China (30160043, 30260060), could be obtained and strengthened after acclimatized and a grant from the Yunnan Natural Science for 2 to 3 years [13]. It was forcefully proved that the Foundation of China (2002C0077M). pressure of selectivity under low temperature played a REFERENCES dominant role for accumulation of cold tolerant [8,13] gene . Since 1975, about 3000 varieties and 1 Kaneda C, Beachell H M. Breeding rice for cold tolerance. breeding lines have been tested, 25 of 40 varieties Saturday Seminar Paper 9. Los Banos, Philippines: IRRI, with stronger cold tolerance were originated from 1974. Yunnan Province in China [14]. Cold tolerance at 2 Yoshida S. Fundamentals of Rice Crop Science. Los Banos, Philippines: IRRI, 1978. booting stage of Yunnan rice landrace, especially in 3 Satake T. Determination of the most sensitive stage to Northwest Yunnan cold highland japonica rice region sterile-type cold injury in rice palnt. Res BullHokkaido Natl and Central Yunnan single season japonica-indica Agric Exp Sta, 1976, 113: 1–43. region is well known all over the world. Sixteen 4 Wang H Y, Xiong J H. Relation of anther length and cold prefectures in Yunnan could be divided into three tolerance in rice. J Southwest Agric, 1988, 1(2): 65–67. 5 Futsuhara Y, Toriyama K. Genetic studies on cool tolerance regions, i.e. strong, intermediate and weak cold in rice. Ⅲ. Linkage relations between genes controlling cool tolerance regions, or in other words, serious cold tolerance and marker gene of Nagao and Takahashi. Jpn J damage region, cold damage region and slight cold Breeding, 1966, (4): 231–242. damage region. It revealed that cold tolerance of 6 Takahashi M. Functioning of major genes of rice as an aid in Yunnan rice landrace at booting stage was closely understanding genetic phenomena of agronomic importance. related to the cold tolerance of core collection among Indian J Genet, 1974, 34A: 1104–1116. 7 Sawada S. Studies of sterile-type cool injury in rice plants rice cropping regions and prefectures. These results with special reference to the mechanism and inheritance of were certainly related to the ecological and genetic sterility. Res Bull Obihiro Zootech, Uni Ser, 1978, 1(10): diversity of Yunnan rice resources, which could be 837–883.

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