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Abstract It has a long history of rice cultivating in Taihu Lake region， with abounds rice landraces resources. The research on the genetic diversity of rice landraces resources can provide some reference for the protection and utilization of highquality germplasm resources and breeding of new varieties. In this study， we reviewed the concepts of genetic diversity， research methods， genetic diversity of quality traits of rice landraces in Taihu Lake region and summarized the relevant utilization value of the rice landraces from Taihu Lake region.
Key words Taihu lake region; Landrace; Quality; Genetic diversity
Nearly half of the worlds population feeds on rice， and the southern part of China， especially Taihu Lake Basin， is dominated by rice. With the improvement of living standards， people have put forward higher requirements for rice quality. Studying the genetic mechanism of rice quality traits will be beneficial to the improvement of rice quality and the development of modern agriculture[1]. It has been clarified that starch synthase gene （Wx）， soluble starch synthase gene （Sss1）， isoamylase gene （Isa）， branching enzyme genes （Sbe1， Sbe3） and limit dextrinase or R enzyme gene （Pull） are related to rice quality[2]. However， the genetic basis of rice has become increasingly narrow in recent decades[3]. Therefore， studying the genetic diversity of rice， especially the quality traits of local cultivars， is of great significance for protecting and broadening the genetic background of rice.
According to historical records， Taihu Lake Basin began rice production as early as 8 000 years ago[4]. Longterm natural selection and artificial screening have accumulated abundant rice genetic resources in the region. In this paper， the rice landraces resources in Taihu Lake region were studied， and the research progress on the genetic diversity of quality traits was reviewed， which will provide a basis for rice quality research and resource conservation in Taihu Lake region.
Research Methods of Genetic Diversity
Generalized genetic diversity refers to the sum of genetic information carried by all living things on the earth， including genetic variation among different species and within species. The narrow genetic diversity mainly refers to the sum of genetic variation of different populations within species or different individuals within the same population. The richer the intraspecific genetic diversity， the greater the potential for species evolution and the greater the ability to adapt to environmental changes[5]. With the development of research techniques such as molecular biology and biochemistry， methods for studying biological genetic diversity have evolved from the initial morphological level through the cellular level （also known as chromosome level） and physiological and biochemical levels to the current molecular level. In order to explore the genetic diversity of rice germplasm resources， previous studies have used SRAP[6]， AFLP[7]， RFLP[8]， RAPD[9]， SSR[10]， SNPs[11]and isozymes[12]and other markers to conduct diversity research， from the polymorphic loci ratio， the effective number of alleles， the average expected heterozygosity， the polymorphism information content （PIC） of each locus， the genetic similarity coefficient between varieties （lines） （genetic similarity， GS）， Shannon information index and other aspects. In recent years， with the frequent occurrence of crossbreeding and interspecies gene drift， the genetic polymorphism of bred rice varieties has been significantly reduced. Therefore， the exploration of largescale highthroughput research methods of rice genetic diversity and the indepth understanding of rice genetic diversity formation mechanism and endangered mechanism has an important guiding role in the future research direction of rice[13].
Directing at the research on genetic diversity of rice， molecular biologists have developed a series of computer evaluation software， and more advanced and more powerful softwares are also being developed. Among them， POPGENE， STRUCTURES， NTSYSpc， PowerMarke and GenAlEx are widely used， and some of the computable genetic parameters of these softwares are shown in Table 1.
Study on the Diversity of Quality Traits of Rice Landraces in Taihu Lake Region
Rice cultivation in Taihu Lake region has a long history. Due to the small climate of Taihu Lake， unique geographical and ecological conditions and abundant water resources， there are a series of rice crops under the aquatic conditions and better plant diversity[14]. After longterm natural selection and artificial selection， rich local rice germplasm resources have formed， including many highquality， highyield and highphotosynthetic efficiency germplasm resources. Among them， japonica rice landraces are rich in polymorphism， which can provide more morphological basis for the selection of high quality japonica rice varieties in the future[15]. Since the 1950s and 1960s， rice landraces in Taihu Lake region such as Aininghuang， Laolaiqing and Wuzuinuo have been used as important parents of japonica rice resources in China through singleline selection and artificial breeding. In recent years， in order to fully exploit and utilize the excellent genes in rice resources in Taihu Lake region and expand the genetic basis of the bred varieties in the region， many researchers have studied the diversity of rice landraces in Taihu Lake Basin[16-18].
The phenotype is the combined result of the interaction between the expression of the gene and the environment， and is a morphological reaction in which the organism is subject to the environment. The differences indicated by the phenotypic traits are phenotypic diversity. Wang et al.[19]analyzed the phenotypic diversity of 10 foodquality traits in 161 wild rice varieties in Taihu Lake region. It was found that there were significant differences in the RVA profile between different rice lines， indicating that the taste quality of rice varieties is different. Chen et al.[20]used the phenotypic principal component analysis method to perform correlation cluster analysis on the main quality indexes of 44 aromatic rice varieties in Taihu Lake region， and found that there is certain correlation between the principal component factors affecting rice quality， which provided a basis for the quality breeding of aromatic rice in the future. Yao et al.[21]analyzed the RVA profiles of 494 early indica， japonica and late japonica rice in Taihu Lake region， and concluded that the RVA profile characteristics of different varieties were significantly different. Therefore， the indica and japonica rice can be divided into three different types. Shen et al.[22-23]evaluated the genetic diversity of japonica rice and glutinous rice germplasm resources in Taihu Lake region. They found that the RVA profiles of the rice were significantly different， and thus deemed that the plant and quality traits of the germplasm materials also had high genetic diversity.
At present， the research on the diversity of rice quality traits in Taihu Lake region has been developed to the molecular level. Jin[24]used microsatellite markers to analyze the polymorphism of 129 japonica rice landraces in Taihu Lake Basin at the DNA molecular level. It was found that the japonica rice landraces in Taihu Lake Basin were not only rich in genetic variation， but also retained a large number of rare allelic variations. Yu et al.[25]used 45 pairs of SSR primers to analyze the genetic diversity of 224 japonica rice landraces in Taihu Lake Basin， and concluded that the SSR diversity of japonica rice landraces in Taihu Lake Basin was low and there were more rare alleles. Luo et al.[16]used SSR primers to analyze the genetic diversity of 42 japonica rice varieties in Taihu Lake region. The results showed that the genetic similarity coefficient between the tested materials was 0.610 0， indicating a high similarity， and the PIC value of each polymorphic locus was 0.496 6， averagely. However， the markers selected in these studies were random and did not correlate with quality traits. Starch， as the most important organic substance in rice， accounts for about 90% of the composition of brown rice. The physical and chemical properties of starch affect many indicators of rice quality. Therefore， rice quality mainly refers to starch quality[26]. Based on previous studies， genetic equilibrium networks were constructed to explore the interaction effects between genes. Based on the determination of the gene sequences related to starch synthesis， selective marker design was performed for the specific binding sites of SNPs of each gene， and 22 markers were detected in total， namely， AGPsma1， Wx2， Wx3， GBSSII 1， SSI 1， SSI 2， SSII1t1， SSII2 t2， SSII3 1， SSII32， SSIII11， SSIII1t2， SSIV12， SSIV21， SSIV2t1， Sbe11， Sbe1 t3， Sbe3t1， Sbe41， Pul3， Isat1 and Isat2. There are genetic interaction effects during starch quality formation， and these interactions not only occur between genes encoding different types of enzymes， but also between different genes encoding similar enzymes. Liu et al.[27]systematically screened the genotypes of starch synthesisrelated genes among different rice varieties using molecular marker detection methods， and found that starch synthesisrelated genes showed good polymorphism among indica and japonica subspecies. In general， the genetic polymorphisms of local varieties and bred varieties are also significantly different. Ao et al.[17-18]used 22 internal markers of starch synthesisrelated genes to test 115 rice landraces and 87 bred varieties in Taihu Lake region， and found that the average genetic diversity and PIC values of rice landraces were slightly higher those of the bred varieties. Meanwhile， the alleles of the internal markers of the synthesisrelated genes in each rice variety were identified， and the rice in the region was evaluated according to the national evaluation standards for rice quality to find varieties that were excellent in various quality traits. Cui[28]selected 549 rice landraces in Taihu Lake region as test materials， and detected their starch quality genotypes using 23 internal molecular markers of starch synthesisrelated genes. They found that the average genetic diversity of rice landraces was 0.210 4， and the average PIC value was 0.184 7. Because the materials chosen by previous studies are different， the research results also have some differences.
Agricultural Biotechnology 2020
Utilization Value of Rice Varieties in Taihu Lake Region The Taihu rice area has a long history， and it has been a famous "granary in the world" since ancient times， which has made great contributions to the ancient agricultural civilization in China. The crossbreeding and distant hybridization technology that emergedin the 1950s and 1960s was based on the germplasm resources of the Taihu rice area. It has created a large number of genetic variations， improved the genetic characteristics of germplasms， and cultivated many excellent rice varieties， thereby playing a positive role in alleviating the food crisis at that time. In recent years， with the development of molecular biology and genetic technology， scientists have begun to perform breeding at the molecular level. Therefore， the rice landraces resources in Taihu Lake Basin will gradually attract attention and be used. Studies have also shown that rice landraces in Taihu Lake Basin still have rich genetic diversity and can still provide good resources for the research and utilization of rice germplasms in China[19]. The breeding of hybrid japonica rice is another time of largescale use of heterosis after hybrid indica rice. The rich japonica rice resources in Taihu Lake region have become one of the key fields of interest for breeders. However， traditional breeding has gradually been abandoned due to shortcomings such as long cycles， manpower consumption and difficult observation of good traits. In order to improve the screening efficiency， many researchers have also proposed the use of cytoplasm as a genetic tool to identify fertility， and through backcross breeding， free mating between parents with different ecological types will make the effect of heterosis more obvious[29].
Previous studies have detected some excellent starch synthesisrelated quality genes and rice varieties in Taihu Lake region[17]. Among them， the waxy gene （Wx） controls the synthesis of amylose in rice and is the most important gene that affects the cooking and eating quality of rice. Zhu et al.[30]summarized the types and benefits of different allelic variations of the Wx gene in rice， and successfully applied excellent Wx alleles to breeding work using molecular marker technology to achieve the effect of improving rice quality. From the current point of view， in addition to the Wx gene， more highquality genes of rice varieties or varieties in Taihu Lake region can be further used for rice quality breeding. In other words， there are still many excellent genes in most rice landraces in Taihu Lake region that have not been excavated and used， and rice landraces still have many genetic advantages. However， in recent years， due to the impact of global climate change and human activities， the homeland of rice germplasm resources have been severely damaged， genetic diversity is also rapidly disappearing， and some rice resources are even endangered. Therefore， it is particularly important to protect the diversity of rice germplasm resources. Wu[31]proposed that China should improve the supervision system and strengthen supervision and management in accordance with the law. And local governments should also build rice ecological environmental protection zones and strengthen ectopic protection efforts， and strive to establish a molecularlevel conservation protection system. Of course， traditional methods for protecting rice resources， such as planting and preservation， lowtemperature storage and preservation， are also worth our attention and reference[32]. In summary， only by adopting scientific and technological projects and setting up special funds to support the protection of rice resources at all levels can we meet the continuous demand for germplasm resources in scientific research， and integrate resources and establish a platform for shared use[33]. It is believed that in the near future， the combination of highquality rice genes and molecular markerassisted selection technology will greatly improve the quality of rice varieties and the nutritional function of rice， and will definitely become the focus of future breeders.
References
[1] DAI ML， SHAO LM， HU H， et al. Research progress on rice processing quality and its genetic basis[J]. Journal of Zhejiang Normal University： Natural Sciences， 2015， 12（9）： 5-8. （in Chinese）
[2] YAN CJ， TIAN SM， ZHANG ZQ， et al. The source of genes related to rice grain starch synthesis among cultivated varieties and its contribution to quality[J]. Scientia Agricultura Sinica， 2005， 39（5）： 865-871. （in Chinese）
[3] SHAH SM， ARIF M， ASLAM K， et al. Genetic diversity analysis of Pakistan rice （Oryza sativa） germplasm using multiplexed single nucleotide polymorphism markers[J]. Genetic Resources and Crop Evolution， 2015（19）： 1-14.
[4] WANG CL， ZOU JS， TANG LH， et al. Rice cultivation at the Neolithic age in Taihu Valley[J]. Jiangsu Journal of Agricultural Sciences， 2000， 16（3）： 129-138. （in Chinese）
[5] HU DD. Genetic diversity and population structure of maize inbred lines[D]. Beijing： Capital Normal University， 2009. （in Chinese）
[6] SHI LY， HOU JH， ZHANG YH， et al. Genetic diversity and population structure of maize inbred lines based on srap markers[J]. Crops， 2015（3）： 57-63. （in Chinese）
[7] ZAN FG， YING XM， WU CW， et al. Genetic diversity of 118 sugarcane germplasm using AFLP markers[J]. Scientia Agricultura Sinica， 2015， 48（5）： 1 002-1 010. （in Chinese）
[8] CHEN L， LIANG CY， SUN CQ， et al. Comparison between AFLP and RFLP markers in detecting the diversity of rice （Oryza sativa L.）[J]. Scientia Agricultura Sinica， 2002， 35（6）： 589-595. （in Chinese）
[9] XIAO M， LI Q， GUO L， et al. RAPD analysis of genetic diversity of an endangered species Sinopodophyllum hexandrum （Royle） Ying from Western Sichuan Province， China[J]. Acta Ecologica Sinica， 2015， 35（5）： 1 488-1 495. （in Chinese）
[10] TESHOME A， BRYNGELSSON T， DAGNE K， et al. Assessment of genetic diversity in Ethiopian field pea （Pisum sativum L.）accessions with newly developed ESTSSR markers[J]. BMC Genetics， 2015， 16（1）： 1-12. [11] SHI YX， LU BS， SONG W， et al. Genetic diversity analysis of waxy corn inbred lines by single nucleotide polymorphism （SNP） markers[J]. Acta Agriculturae BorealiSinica， 2015， 30（3）： 77-82. （in Chinese）
[12] DUAN ZG， ZHENG F， LIANG CY. Genetic diversity among different compatible varieties in rice （Oryza sativa L.） using isozyme markers[J]. Journal of Tropical and Subtropical Botany， 2006， 14（6）： 366-373. （in Chinese）
[13] YANG QW， HUANG J. Research progress on genetic diversity of Oryza rufipogon in China[J]. Acta Agronomica Sinica， 2013， 39（4）： 580-588. （in Chinese）
[14] WANG JG. The ecology of lakefarmlands along East Tai lake[J]. Social Science， 2012（1）： 142-151. （in Chinese）
[15] HUANG ZC， ZHANG XM， TANG H， et al. Genetic diversity analysis of japonica rice landraces （Oryza sativa L.） from Shanghai based on DUS testing [J]. Journal of Plant Genetic Resources， 2015， 16（3）： 451-159. （in Chinese）
[16] LUO B， XU GM， SUN HY， et al. Genetic diversity analysis of modern japonica rice （Oryza sativa L.） from Taihu Area based on simple sequence repeat （SSR） markers[J]. Chinese Journal of Agricultural Biotechnology， 2014， 22（12）1 502-1 513. （in Chinese）
[17] AO Y， CUI XF， LIU QQ， et al. Diversity of starch synthesisrelated genes in rice varieties in Taihu Region[C]//Proceedings of the 8th member congress and symposium of Jiangsu Genetics Society. Nanjing： Jiangsu Genetics Society， 2010. （in Chinese）
[18] AO Y， XU Y， CUI XF， et al. A genetic diversity assessment of starch quality traits in rice landraces from the Taihu Basin， China[J]. J Integr Agri， 2016， 15（3）： 493-501.
[19] WANG JP， QIAO ZY， AO Y， et al. Analysis on the eating quality of japonica rice varieties in Taihu Basin[J]. Jiangsu Journal of Agricultural Sciences， 2012， 28（4）： 691-696. （in Chinese）
[20] CHEN PF， WANG JP， HUANG J， et al. Correlation and cluster analyses for grain quality traits in aromatic rice from Taihu Lake area[J]. Jiangsu Journal of Agricultural Sciences， 2013， 29（1）： 1-7. （in Chinese）
[21] YAO YM， SHEN XP， SHEN MX， et al. Diversity of RVA profile in local rice from Taihu Lake Area[J]. Jiangsu Journal of Agricultural Sciences， 2009， 25（6）： 1 213-1 218. （in Chinese）
[22] SHEN XP， SHEN MX， GU L， et al. Diversity analysis of the RVA profile of glutinous rice in the Taihu Lake Area[J]. Scientia Agricultura Sinica， 2008， 41（8）： 2 513-2 519. （in Chinese） [23] SHEN XP， SHEN MX， GONG LP， et al. Analysis of RVA profile diversity in local late japonica rice at Taihu Lake Area[J]. Acta Agronomica Sinica， 2006， 32（12）： 1 902-1 908. （in Chinese）
[24] JIN WD. Heterosis and genetic diversity of japonica rice （Oryza sativa L.） in the Taihu Lake valley[D]. Nanjing： Nanjing Agricultural University， 2006. （in Chinese）
[25] YU P， LI L， LYU JZ， et al. SSR Analysis on japonica rice landraces from the Taihu Lake Region， China[J]. Chinese Journal of Rice Science. 2009， 23（2）： 148-152. （in Chinese）
[26] YOU SJ. Comparison of rice quality traits under water and dry conditions[J]. Modern Agricultural Science and Technology， 2011， 14（6）： 2-8. （in Chinese）
[27] LIU YQ， QIANG XT， ZHAO CF， et al. Screening and application of molecular markers for starch synthesisrelated genes in rice[J]. Jiangsu Journal of Agricultural Sciences， 2015， 31（3）： 471-476. （in Chinese）
[28] CUI XF. Study on the genetic diversity of starch synthesis related genes and association analysis of some starch quality traits with SSR makers of rice landraces in Tai Lake region[D]. Yangzhou： Yangzhou University， 2011. （in Chinese）
[29] HONG DL， YANG KQ， PAN EF. Heterosis of F1s derived from different ecological types and combining ability of their parents in japonica rice （Oryza sativa）[J]. Chinese Journal of Rice Science， 2002， 16（3）： 216-220. （in Chinese）
[30] ZHU JH， ZHANG CQ， GU MH， et al. Progress in the allelic variation of Wx gene and its application in rice breeding[J]. Chinese Journal of Rice Science， 2015， 29（4）： 431-438. （in Chinese）
[31] wu yc. Status and protection countermeasures of wild rice resources in Xiangzhou County， Guangxi[J]. Agriculture and Technology， 2015， 35（6）： 120. （in Chinese）
[32] ZHOU JM， ZHU ZB， CAO MX， et al. Technical specification of rice germplasm preservation of Taihu Lake Basin[J]. China Seed Industry， 2015（8）： 14-16. （in Chinese）
[33] WEI XH. Protection and utilization of rice seed resources in Zhejiang Province[J]. Journal of Zhejiang Agricultural Sciences， 2015， 56（5）： 727-729. （in Chinese）
Editor： Yingzhi GUANG Proofreader： Xinxiu ZHU
Key words Taihu lake region; Landrace; Quality; Genetic diversity
Nearly half of the worlds population feeds on rice， and the southern part of China， especially Taihu Lake Basin， is dominated by rice. With the improvement of living standards， people have put forward higher requirements for rice quality. Studying the genetic mechanism of rice quality traits will be beneficial to the improvement of rice quality and the development of modern agriculture[1]. It has been clarified that starch synthase gene （Wx）， soluble starch synthase gene （Sss1）， isoamylase gene （Isa）， branching enzyme genes （Sbe1， Sbe3） and limit dextrinase or R enzyme gene （Pull） are related to rice quality[2]. However， the genetic basis of rice has become increasingly narrow in recent decades[3]. Therefore， studying the genetic diversity of rice， especially the quality traits of local cultivars， is of great significance for protecting and broadening the genetic background of rice.
According to historical records， Taihu Lake Basin began rice production as early as 8 000 years ago[4]. Longterm natural selection and artificial screening have accumulated abundant rice genetic resources in the region. In this paper， the rice landraces resources in Taihu Lake region were studied， and the research progress on the genetic diversity of quality traits was reviewed， which will provide a basis for rice quality research and resource conservation in Taihu Lake region.
Research Methods of Genetic Diversity
Generalized genetic diversity refers to the sum of genetic information carried by all living things on the earth， including genetic variation among different species and within species. The narrow genetic diversity mainly refers to the sum of genetic variation of different populations within species or different individuals within the same population. The richer the intraspecific genetic diversity， the greater the potential for species evolution and the greater the ability to adapt to environmental changes[5]. With the development of research techniques such as molecular biology and biochemistry， methods for studying biological genetic diversity have evolved from the initial morphological level through the cellular level （also known as chromosome level） and physiological and biochemical levels to the current molecular level. In order to explore the genetic diversity of rice germplasm resources， previous studies have used SRAP[6]， AFLP[7]， RFLP[8]， RAPD[9]， SSR[10]， SNPs[11]and isozymes[12]and other markers to conduct diversity research， from the polymorphic loci ratio， the effective number of alleles， the average expected heterozygosity， the polymorphism information content （PIC） of each locus， the genetic similarity coefficient between varieties （lines） （genetic similarity， GS）， Shannon information index and other aspects. In recent years， with the frequent occurrence of crossbreeding and interspecies gene drift， the genetic polymorphism of bred rice varieties has been significantly reduced. Therefore， the exploration of largescale highthroughput research methods of rice genetic diversity and the indepth understanding of rice genetic diversity formation mechanism and endangered mechanism has an important guiding role in the future research direction of rice[13].
Directing at the research on genetic diversity of rice， molecular biologists have developed a series of computer evaluation software， and more advanced and more powerful softwares are also being developed. Among them， POPGENE， STRUCTURES， NTSYSpc， PowerMarke and GenAlEx are widely used， and some of the computable genetic parameters of these softwares are shown in Table 1.
Study on the Diversity of Quality Traits of Rice Landraces in Taihu Lake Region
Rice cultivation in Taihu Lake region has a long history. Due to the small climate of Taihu Lake， unique geographical and ecological conditions and abundant water resources， there are a series of rice crops under the aquatic conditions and better plant diversity[14]. After longterm natural selection and artificial selection， rich local rice germplasm resources have formed， including many highquality， highyield and highphotosynthetic efficiency germplasm resources. Among them， japonica rice landraces are rich in polymorphism， which can provide more morphological basis for the selection of high quality japonica rice varieties in the future[15]. Since the 1950s and 1960s， rice landraces in Taihu Lake region such as Aininghuang， Laolaiqing and Wuzuinuo have been used as important parents of japonica rice resources in China through singleline selection and artificial breeding. In recent years， in order to fully exploit and utilize the excellent genes in rice resources in Taihu Lake region and expand the genetic basis of the bred varieties in the region， many researchers have studied the diversity of rice landraces in Taihu Lake Basin[16-18].
The phenotype is the combined result of the interaction between the expression of the gene and the environment， and is a morphological reaction in which the organism is subject to the environment. The differences indicated by the phenotypic traits are phenotypic diversity. Wang et al.[19]analyzed the phenotypic diversity of 10 foodquality traits in 161 wild rice varieties in Taihu Lake region. It was found that there were significant differences in the RVA profile between different rice lines， indicating that the taste quality of rice varieties is different. Chen et al.[20]used the phenotypic principal component analysis method to perform correlation cluster analysis on the main quality indexes of 44 aromatic rice varieties in Taihu Lake region， and found that there is certain correlation between the principal component factors affecting rice quality， which provided a basis for the quality breeding of aromatic rice in the future. Yao et al.[21]analyzed the RVA profiles of 494 early indica， japonica and late japonica rice in Taihu Lake region， and concluded that the RVA profile characteristics of different varieties were significantly different. Therefore， the indica and japonica rice can be divided into three different types. Shen et al.[22-23]evaluated the genetic diversity of japonica rice and glutinous rice germplasm resources in Taihu Lake region. They found that the RVA profiles of the rice were significantly different， and thus deemed that the plant and quality traits of the germplasm materials also had high genetic diversity.
At present， the research on the diversity of rice quality traits in Taihu Lake region has been developed to the molecular level. Jin[24]used microsatellite markers to analyze the polymorphism of 129 japonica rice landraces in Taihu Lake Basin at the DNA molecular level. It was found that the japonica rice landraces in Taihu Lake Basin were not only rich in genetic variation， but also retained a large number of rare allelic variations. Yu et al.[25]used 45 pairs of SSR primers to analyze the genetic diversity of 224 japonica rice landraces in Taihu Lake Basin， and concluded that the SSR diversity of japonica rice landraces in Taihu Lake Basin was low and there were more rare alleles. Luo et al.[16]used SSR primers to analyze the genetic diversity of 42 japonica rice varieties in Taihu Lake region. The results showed that the genetic similarity coefficient between the tested materials was 0.610 0， indicating a high similarity， and the PIC value of each polymorphic locus was 0.496 6， averagely. However， the markers selected in these studies were random and did not correlate with quality traits. Starch， as the most important organic substance in rice， accounts for about 90% of the composition of brown rice. The physical and chemical properties of starch affect many indicators of rice quality. Therefore， rice quality mainly refers to starch quality[26]. Based on previous studies， genetic equilibrium networks were constructed to explore the interaction effects between genes. Based on the determination of the gene sequences related to starch synthesis， selective marker design was performed for the specific binding sites of SNPs of each gene， and 22 markers were detected in total， namely， AGPsma1， Wx2， Wx3， GBSSII 1， SSI 1， SSI 2， SSII1t1， SSII2 t2， SSII3 1， SSII32， SSIII11， SSIII1t2， SSIV12， SSIV21， SSIV2t1， Sbe11， Sbe1 t3， Sbe3t1， Sbe41， Pul3， Isat1 and Isat2. There are genetic interaction effects during starch quality formation， and these interactions not only occur between genes encoding different types of enzymes， but also between different genes encoding similar enzymes. Liu et al.[27]systematically screened the genotypes of starch synthesisrelated genes among different rice varieties using molecular marker detection methods， and found that starch synthesisrelated genes showed good polymorphism among indica and japonica subspecies. In general， the genetic polymorphisms of local varieties and bred varieties are also significantly different. Ao et al.[17-18]used 22 internal markers of starch synthesisrelated genes to test 115 rice landraces and 87 bred varieties in Taihu Lake region， and found that the average genetic diversity and PIC values of rice landraces were slightly higher those of the bred varieties. Meanwhile， the alleles of the internal markers of the synthesisrelated genes in each rice variety were identified， and the rice in the region was evaluated according to the national evaluation standards for rice quality to find varieties that were excellent in various quality traits. Cui[28]selected 549 rice landraces in Taihu Lake region as test materials， and detected their starch quality genotypes using 23 internal molecular markers of starch synthesisrelated genes. They found that the average genetic diversity of rice landraces was 0.210 4， and the average PIC value was 0.184 7. Because the materials chosen by previous studies are different， the research results also have some differences.
Agricultural Biotechnology 2020
Utilization Value of Rice Varieties in Taihu Lake Region The Taihu rice area has a long history， and it has been a famous "granary in the world" since ancient times， which has made great contributions to the ancient agricultural civilization in China. The crossbreeding and distant hybridization technology that emergedin the 1950s and 1960s was based on the germplasm resources of the Taihu rice area. It has created a large number of genetic variations， improved the genetic characteristics of germplasms， and cultivated many excellent rice varieties， thereby playing a positive role in alleviating the food crisis at that time. In recent years， with the development of molecular biology and genetic technology， scientists have begun to perform breeding at the molecular level. Therefore， the rice landraces resources in Taihu Lake Basin will gradually attract attention and be used. Studies have also shown that rice landraces in Taihu Lake Basin still have rich genetic diversity and can still provide good resources for the research and utilization of rice germplasms in China[19]. The breeding of hybrid japonica rice is another time of largescale use of heterosis after hybrid indica rice. The rich japonica rice resources in Taihu Lake region have become one of the key fields of interest for breeders. However， traditional breeding has gradually been abandoned due to shortcomings such as long cycles， manpower consumption and difficult observation of good traits. In order to improve the screening efficiency， many researchers have also proposed the use of cytoplasm as a genetic tool to identify fertility， and through backcross breeding， free mating between parents with different ecological types will make the effect of heterosis more obvious[29].
Previous studies have detected some excellent starch synthesisrelated quality genes and rice varieties in Taihu Lake region[17]. Among them， the waxy gene （Wx） controls the synthesis of amylose in rice and is the most important gene that affects the cooking and eating quality of rice. Zhu et al.[30]summarized the types and benefits of different allelic variations of the Wx gene in rice， and successfully applied excellent Wx alleles to breeding work using molecular marker technology to achieve the effect of improving rice quality. From the current point of view， in addition to the Wx gene， more highquality genes of rice varieties or varieties in Taihu Lake region can be further used for rice quality breeding. In other words， there are still many excellent genes in most rice landraces in Taihu Lake region that have not been excavated and used， and rice landraces still have many genetic advantages. However， in recent years， due to the impact of global climate change and human activities， the homeland of rice germplasm resources have been severely damaged， genetic diversity is also rapidly disappearing， and some rice resources are even endangered. Therefore， it is particularly important to protect the diversity of rice germplasm resources. Wu[31]proposed that China should improve the supervision system and strengthen supervision and management in accordance with the law. And local governments should also build rice ecological environmental protection zones and strengthen ectopic protection efforts， and strive to establish a molecularlevel conservation protection system. Of course， traditional methods for protecting rice resources， such as planting and preservation， lowtemperature storage and preservation， are also worth our attention and reference[32]. In summary， only by adopting scientific and technological projects and setting up special funds to support the protection of rice resources at all levels can we meet the continuous demand for germplasm resources in scientific research， and integrate resources and establish a platform for shared use[33]. It is believed that in the near future， the combination of highquality rice genes and molecular markerassisted selection technology will greatly improve the quality of rice varieties and the nutritional function of rice， and will definitely become the focus of future breeders.
References
[1] DAI ML， SHAO LM， HU H， et al. Research progress on rice processing quality and its genetic basis[J]. Journal of Zhejiang Normal University： Natural Sciences， 2015， 12（9）： 5-8. （in Chinese）
[2] YAN CJ， TIAN SM， ZHANG ZQ， et al. The source of genes related to rice grain starch synthesis among cultivated varieties and its contribution to quality[J]. Scientia Agricultura Sinica， 2005， 39（5）： 865-871. （in Chinese）
[3] SHAH SM， ARIF M， ASLAM K， et al. Genetic diversity analysis of Pakistan rice （Oryza sativa） germplasm using multiplexed single nucleotide polymorphism markers[J]. Genetic Resources and Crop Evolution， 2015（19）： 1-14.
[4] WANG CL， ZOU JS， TANG LH， et al. Rice cultivation at the Neolithic age in Taihu Valley[J]. Jiangsu Journal of Agricultural Sciences， 2000， 16（3）： 129-138. （in Chinese）
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Editor： Yingzhi GUANG Proofreader： Xinxiu ZHU