Abstract:In the past 20 years (1999-2019), the Ministry of Agriculture and Rural Affairs (MARA) had coordinated researchers in agricultural environmental protection agencies, universities and institutes to carry out the activities on the field surveys, collections, constructions and monitoring of in-situ conservation, information system establishment etc. Several major achievements have been made, including: (i) accomplishing national-wide survey of 80 crop wild relatives, such as discovering the distribution zones of wild orchid and wild tea trees; (ii) collecting 44737 germplasm accessions of 60 important wild relatives, which have subjected for the conservation in ex-situ Genebank and which are monitorable using a GPS/GIS information system; (iii) Establishing 205 in-situ conservation sites which refer 65 species in 28 provinces, as well as the technical monitoring and early warning system on the dynamic analysis of the collected data from 15 in-situ conservation sites. However, there are some problems remained in the conservation of agricultural wild plants. Only lower proportion of species/germplasm resources have been investigated without an overview coordinate. The technique issues on management have become the bottleneck restricting the in-situ conservation. Therefore, we suggest the development of management techniques of in-situ conservation sites to support local managers in application. The techniques should be feasible for different plants and different sites respectively, which indicates that the in-situ conservation will be changed from increasing the quantity to improving the quality.

Abstract:Wild rice is a strategic germplasm resource valuable for rice breeding and basic research, and its protection and practical use are important in Chinese food security. China is one of countries where abundant wild rice resources were found. Owing to the economic development over decades, the original habitat of wild rice had been seriously damaged, i.e. some populations were extinct. Since 1996, the Ministry of Agriculture and Rural Affairs initiated a serial of projects to support the survey, collection and conservation of wild rice germplasm resources in China. The article summarized the techniques, methods and achievements on investigation, collection and conservation of wild rice resources in China, especially with a focus on the implementation of in situ conservation. We proposed, by taking full consideration of the status on rice wild research as well as the prospective on breeding and bio-techniques, suggestions on future conservation and utilization of wild rice germplasm resources.

Abstract:Chinese wild soybean is the direct progenitor of cultivated soybean, having a self-pollinating reproduction system with a low outcrossing rate. This feature would make wild soybean have higher and lower amounts of genetic variation within and between geographical spaces or lower and higher amounts of genetic variation within and between populations. However, sometimes there are higher and lower amounts of genetic variation within and between populations, which may be caused by the stronger gene flow over the effects from environmental stresses, disturbance, and genetic drift or associated with the historical gene dispersal. Gene flow in the wild soybean is closely related to geographical distance. Chinese wild soybean has 4 clear genetic categories: small-seeded (100-seed weight under 2.0 g), medium-seeded (100-seed weight of 2.01–2.5 g), large-seeded (100-seed weight of 2.51–3.0 g) and semi-wild(100-seed weight over 3.0 g) types. The genetic differentiation between typical wild and semi-wild types is the main factor within the species. The genetic boundary of G. gracilis is at the range of 2.51–3.0 g 100-seed weight of Glicine soja, and therefore the classification of G. gracilis as over 3.0 g 100-seed weight against typical wild soybean is reasonable. Some medium-seeded plants and the majority of the large-seeded ones likely have originated from the segregation of hybrid progenies between wild and cultivated soybeans.

Abstract:This article focuses on the five major controversial issues regarding the origin of semi-wild soybeans. Based on our research experience over the past two decades and the expertise in studies of wild (G. soja) vs. semi-wild soybeans, we make an overview on the morphological evidence for the natural hybridization-origin of semi-wild soybean (big-seeded type) and the origin of some rare characters that were found in wild soybean. The results gained from the morphological and molecular evidences supported three grams in 100-seed weight as the cutoff of semi-wild soybean (G. gracilis). The abundant phenotypic variations were observed in wild soybean accessions that represent 2.5g-3.0g in 100-seed weight. By capturing the phenotypic variations of parental lines and derived hybridization progenies as well as the segregation ratios at each of traits, the origin of semi-wild soybean has been confirmed to result from natural hybridization between wild and cultivated soybeans. Meanwhile, our works have indicated that rare characters such as white flower, coloured seed coats (yellow, green and brown), no-seed-bloom, grey pubescence have been introgressed from cultivated soybean to its wild ancestor through the natural hybridization.

Abstract:In recent years, the research on soyasaponins in Chinese wild soybean has achieved some preliminary progresses, showing that Chinese wild soybeans were rich in the components and genetic variation of saponin composition. These progresses were as followings: identified a new sixth category of group-? in addition to the reported five groups of soyasaponin; found four new components A-αg, K-αg, KA-αg and HAb-αg, of which the A-αg component was first recognized to be the total precursor of the groups A, α and ?; discovered a Sg-7 locus controlling arabinose bonding to the C-22 position of the aglycone; identified a number of A0 mutants and rare accessions with AuAe phenotype and high-content Bd component and found the individuals with separate group α components in Chinese wild soybeans. Soyasaponin phenotypes and genes could be used as genetic markers of chemical composition, by which we analyzed the genetic diversity and geographical differentiation in Chinese wild soybeans. Chinese southern wild soybeans had the highest frequencies of AaBc phenotype and Sg-4 gene in eastern Asia, which implied that the southern wild soybeans were a regional population possessing more primitive ancestral characteristics, and that eastern Asian wild soybeans originally came from southern China.

Abstract:Thinopyrum intermedium, which is a perennial wheatgrass of Gramineae, is a wild relative species of common wheat. It generally develops stronger roots and shoots, larger spike and many flowers, and often represents good characters on biotic and abiotic stresses as well as higher protein content in the grains. Th. intermedium, as a target in breeding for perennial crops, has exhibited great potential in uses for grain and forage. In this paper, the achievements of direct domestication, distant hybridization with other crops, genomics-assisted breeding in Th. intermedium have been reviewed, and the future research focus and the breeding strategy have been prospected. This study can provide scientific basis for the improvement and utilization of Th. intermedium wild germplasm resources.

Abstract:China is the origin center of the Genus Fagopyrum Mill. and hosts the most abundant wild buckwheat germplasm resources in the world. This paper reviews the phylogenetic relationship and taxonomic status of the genus Fagopyrum Mill as well as discusses their origin and phylogenetic development. Meanwhile, we have introduced the main characteristics and utilization value of some important wild species, and have summarized the distribution, collection and preservation, as well as the variation of main agronomic traits and the evaluation of nutritional quality. Moreover, we have proposed suggestions for the incomplete survey, inadequate protection and insufficient utilization of wild buckwheat resources as follows: (1) Investigating the wild buckwheat germplasm resources, taking measures for in-situ conservation and establishment of resource nursery. (2) Establishing an identification and evaluation system and building up a database of cultivated and wild buckwheat germplasm resources. (3) Promoting the systematic development and innovative utilization of wild buckwheat resources, improving the adaptability, stability and high yield of cultivated buckwheat beneficial for breeding. (4) Analyzing the genomic variations of wild species and landraces and identifying the genetic loci underlying important agronomic characters, nutritional quality and abiotic stress responses, in order to improve the innovation efficiency of elite buckwheat.

Abstract:Vigna, a genus belonging to the tribe Phaseoleae (Leguminosae, Papilionoideae), consists of over 100 species, in which about 10 species have been domesticated. Previous studies showed that elite genes for tolerance of adverse conditions and resistance to pests and diseases are rich in the wild relatives of Vigna, which would be important sources for breeding of Vinga crops. In the present paper, we review the research progress in geographical distribution, characterization, cross-compatibility with cultivated species, genetics and its application in breeding of the wild relatives in Vigna, to provide useful information for people working with plant germplasm collection and breeding.

Abstract:Pea is one of the earliest domesticated crops. It is not only an important economic and grain-vegetable-forage crop widely grown globally, but also has significant ecological advantages in the sustainable development of agriculture. This article reviews the important research progress of the past decades in the aspects of the domestication of pea, systematic classification of Pisum, preservation status and research and utilization of germplasm resources of pea and its wild relative. Although there have been many studies, the domestication process of pea is still unclear and the systematic classification of Pisum has long been controversial. Combining the previous different classification views, phylogenetic research results, as well as our current research results, this article puts forward a comprehensive classification proposal on Pisum to make clear about pea wild relatives, thereby laying a foundation to better understanding of the domestication process of pea and make full use of the germplasm resources of pea wild relatives. In addition, in view of the current research status of pea wild relatives, relevant suggestions are made for their future research, so as to give full play to their huge potential in breeding improvement of pea.

Abstract:The wild germplasm resources of Phaseolus are abundant, and are important resources for genetic improvement of cultivated Phaseolus beans. In this paper, we provide an overview of the phylogenetic classification, morphological characters, geographical distribution, origin, population structure, genetic diversity, domestication traits and genetic mechanism of Phaseolus species, and put forward some suggestions for future investigation, which contribute to the utilization of wild resources of the genus.

Abstract:Broomcorn millet (Panicum miliaceum L.) is a representative crop in dryland agriculture and has been cultivated for over 10,000 years. Wild broomcorn millet, widely distributed in fields alongside the cultivated broomcorn millet and in woodland edges and grasslands across Eurasia, plays a crucial role in studies of broomcorn millet origin and domestication history. This review summarizes the research progresses achieved in China in germplasm collection and conservation, identification and evaluation, and genetic diversity analysis of wild broomcorn millet, and in the relationship between the wild broomcorn millet and cultivated broomcorn millet, and proposes further project development and the core mission of collection, utilization and research of wild broomcorn millet resources in China.

Abstract:The genus Cucumis includes about 70 species to date, and plants from this genus are found in 75 countries of Africa, Asia and Australia. The cultivated cucumber , which is important in daily diet, represented a narrow genetic diversity. The exploration and incorporation of elite and diversified genes, which were derived from wild relatives, are of great interest, in order to enrich the genetic basis of cultivated cucumber and the practical uses in breeding for new varieties. This review introduces the distribution and classification of Cucumis plants, the origin and discovery of the main wild relatives, the innovation of genetic resources between species, and finally emphasizes the research progress of the main wild species. Based on the expertise, the problems in the utilization of wild resources are summarized and the actions to improve and create novel cucumber varieties by incorporating wild resources are proposed. This work thus provides reference and guidance for the gene mining and genetic improvement of Cucurbits.

Abstract:Barbarea vulgaris as a cruciferous wild species is an elite germplasm resource on resistance against the pathogenic diseases and insects, and it is also recognized as a model to investigate the biosynthesis process of glucosinolate and saponin and the co-evolution between plant and insect. In 2015, our research group published the review paper ‘Advances on Research and Utilization of Elite Resistant Resource - Barbarea vulgaris’. Considering that the progresses regarding the studies of Barbarea vulgaris have been made worldwide in the past five years, this review summarizes recent advances and expects to provide updated information for the further study and effective use of this elite germplasm.

Abstract:Tomato, pepper and eggplant are the economically-imporant vegetables of Solanaceae cultivated worldwide. Natural evolution has resulted in abundant wild Solanaceae species adapted to the habitat of their origin zones. Over the long-term domestication and cultivation of Solanaceae wild plants, their yield and commodity quality have been continuously improved to meet the change of cultivation environments and the favors of people. However, the resistances upon biotic and abiotic stresses have been gradually decreased due to the losses of several functional components. The biologists and breeders have thus repeatedly turned their attention to the wild resources of Solanaceae in order to explore excellent characters or genes from wild species and break down the bottleneck of genetic improvement. In this paper, the theoretical research and applied utilization of wild resources of tomato, pepper and eggplant have been reviewed. We outlined the discovery of wild elite resources, gene localization and molecular cloning of important characters, genomics and functional genomics studies, distant hybridization, molecular assisted breeding, transgene and gene editing etc. Thus, this paper could provide guidance for the further excavation of wild Solanaceae resources and their utilization in genetic improvement of Solanaceae vegetables.

Abstract:Kiwifruit is one of the most successful examples in fruit domestication from wild to commercial cultivation, and nowadays this fruit plays an important role worldwide in the development of fruit industry. China is the origin site of kiwifruit and represented rich germplasm resources. To date, fifty-four species in genus kiwifruit have been identified in the world, and 52 of them are natively originated and distributed in China. The abundance on Kiwifruit germplasm resources played a crucial role in breeding and following industrial development in China. This paper reviews types of kiwifruit germplasm resource, geographical distribution, cultivation history, as well as survey, collection and conservation of the germplasm. Current research status in breeding, cytological study, resistance resource utilization, pharmacology and biotechnology, as well as breakthroughs of kiwifruit germplasm research over past four decades in China are summarized. We further propose suggestions in future studies of kiwifruit germplasm resources, in order to provide reference for sustainable utilization and supporting industrial development in China.

Abstract:China has the vast territory which contributes to the complexness of climate and landform, thus is rich of wild plant resources and regarded as the origin center of many important flowers such as Chrysanthemum ssp and Rosa ssp. How to effectively protect and utilize these germplasm resources has been concerned by policy makers, scientific research institutions and breeding companies. This paper mainly summarized the outstanding achievements in the investigation, protection, research and breeding of the important flower crops, such as rose, Chrysanthemum morifolium Ramat., orchid, peony, lily, etc., and discussed the current problems, possible suggestions and solutions of wild flowers resources. (1) The investigation, collection and conservation of wild flower resources had been carried out since 1980s. During the past decade, the investigation and protection of important flowers have been deepened rapidly, exemplified by the increase in research funds and in number of projects and the progress on conservation in vitro. (2) With the development of modern molecular biology, a series of flower crops have been sequenced and the regulatory networks of important ornamental traits have been revealed successfully. Research on genomics and functional gene play an important role in the accurate evaluation of wild flower resources; the utilization of wild flower resources has accelerated the breeding process of new varieties and promoted the development of special value of flowers. (3) There are still some problems on the conversation and utilization of wild flower resources, such as not many resource investigation systematically, lack of long-term sustainable support and in-depth basic research, inaccurate resource evaluation, etc. We suggest to establish a complete resource protection system and a stable support of flower resource innovation team to realize the real combination of scientific research and industry.

Abstract:The development and utilization of wild rice genetic resources are increasingly important given the fact that the genetic resources in cultivated rice (Oryza sativa L.) gene pool are insufficient to sustain the requirement in modern rice breeding. Although China hosts the world's largest collection of cultivated rice germplasm accessions, a large-proportion of stocks were domestically collected plus the alien wild germplasm accounting for only 10%. The wild rice germplasm resources, which are locally adapted to the diversified climates and habitats in countries from South and Southeast Asia, represented the high potential value in genetic development and breeding in China. In this paper, via summarizing the field surveys and the collections of wild rice (Oryza rufipogon and O. nivara) in 10 South and Southeast Asian countries from 2009 to 2019, 1166 samples from 66 populations were collected.Considering the ecotypes of Oryza rufipogon and O. nivara as well as environmental conditions in South and Southeast Asiancountries, we proposed suggestions for future collection of wild rice resources in this region.

Abstract:Oryza rufipogon Griff, which is recognized as the genetically closest wild species of cultivated rice (O. sativa L.), is an important resource valuable in rice improvement. In this study, 1777 O. rufipogon germplasm accessions, which were collected from China, were subjected for the genetic diversity analysis of five important agronomic traits including heading date, anther length, grain length, grain width and 100-grain weight. The principal component and variance analysis showed an abundant diversity, with the coefficient of variations on heading date, anther length, grain length, grain width and 100-grain weight of 0.06, 0.17, 0.07, 0.09 and 0.16, respectively. The diversity index of five phenotypic traits was 0.69, 0.72, 0.70, 0.65 and 0.71, respectively. By principal component analysis, the first and second components were found to be mainly associated with yield traits, with the cumulative contribution rate of 83.31%. The third principal component was mainly related to the heading date, with the cumulative contribution rate of 11.69%. The common wild rice collection was classified into three clusters, which were roughly explained by the collection sites. For examples, the samples of cluster1 were mainly collected from Jiangxi and Hunan; the samples of cluster2 were mainly collected from most areas of Guangxi and Guangdong and Fujian; the samples of cluster3 were mainly collected from Hainan and the southern part of Guangdong (Zhanjiang). The analysis of variance of five important agronomic traits based on geographical location showed that the variation of anther length, heading date and grain length among different geographical groups accounted for 69.09%, 57.98%, and 77.56% of the total variation, and Grain width variation accounted for 6.20%. Variations in anther length, heading date, and grain length played a decisive role in diversification among common wild rice geographic groups.

Abstract:In southern China, rice (Oryza sativa L.) grains are prone to field pre-harvest sprouting (PHS) due to high temperature and humid weather conditions, which seriously affects the yield, quality and storage of rice. Moderate seed dormancy prevents the adverse effects of the unfavorable environment and helps reduce or avoid PHS. Therefore, genetic studies of seed dormancy and breeding PHS-resistant varieties, are extremely important for rice production and development of seed industry. In this study, we used the indica cultivar ‘93-11’ as the recipient and recurrent parent, and Chaling common wild rice (CLCW) of O. rufipogon Griff. as the donor parent to develop an advanced backcross introgression population consisting of 812 lines. We assessed the seed dormancy of the population, and found five individual plants displaying strong dormancy with the germination rate ranging from 10.0% to 36.5%, while the control and recurrent parent ‘93-11’ had the germination rate of 89.5%. The germination rate of the selfed lines derived from the five strong-dormancy plants ranged from 3.1% to 17.4%. The plants with extremely strong seed dormancy selected from each of 3 selfed lines were crossed with ‘93-11’ to develop the F2 population. By combining the bulked segregant analysis (BSA) and 56K SNP chip data, 8 QTLs were detected, distributed on chromosomes 3, 5, 6, and10. This study will facilitate further map-based cloning of these QTLs and breeding PHS-resistant rice varieties.

Abstract:The geographic distance might contribute to the genetic differentiation of populations on the landscape. Understanding the mechanism of the geographic range that affects gene flow and genetic structure is beneficial to maintain the genetic diversity. Here we investigated the landscape genetic structure of sixteen natural populations of apricot representing two natural distribution ranges of wild common apricots (P. armeniaca) and siberian apricots (P. sibirica) using 18 microsatellite markers. The siberian apricots, which were originated from the North and northeastern China, represented the richer genetic variation and diversity than that of siberian apricots. We found that P. sibirica populations in the Northeast and Northwest of China likely belonged to discrete genetic clusters, while the northwestern populations seemed isolated on the edge. We speculate that this pattern could be a result of the currently complex ecological environment associated with their wide habitats range from west to east in China. While, Central Asian P. armeniaca populations showed a highly admixed structure which was probably due to the recent introgression in a limited geographic distribution region. Meanwhile, we also implemented Isolate by distance (IBD) study on the relationship between both genetic differentiation and related geographic gradients pattern. Our results showed asignificant association between geographical distance and genetic distance among wild populations of Chinese P. sibirica but in Central Asian P. armeniaca. Therefore, our results suggested that the genetic structure associated with eco-geographic patterns could affect the genetic differentiation and diversity, which varied differently in case of different Armeniaca plants, which might have an implication for establishing a conservationstrategy maintaininggenetic diversityinthesespecies.

Abstract:China is one of the major diversity centres of the grape genus Vitis and is therefore very rich in its germplasm resources. The diverse and elite genes of the wild relatives of grapes form an important gene bank for enrichment of the genetic composition of cultivated grapes. Owing to destruction of the ecological environment, some important wild grape populations have been threatened with extinction. Based on field investigation, specimen examination and literature survey, a total of 42 species, 1 subspecies and 13 varieties of wild relatives of geographical regionality, with the similarity of species composition of grape wild relatives between the Jiang-Han dispersal channels and provided a theoretical foundation for their resources protection. The results show that the grapes were recognized in China. The distribution of Chinese grape wild relatives were analyzed to reveal their distribution of Chinese grape wild relatives is complex and diverse. Endemics amount to 26.8% of the total number of species in China. Most of the Chinese grape wild relatives are concentrated in China-Japan forest plant subkingdom, and they are most abundant in the Eastern China region from which the number of Vitis species decrease gradually in all directions. The similarity level appears to be high, and the species do not show strong Plain Subregion and the Qinling-Bashan Subregion being the highest. V. heyneana Roem. et Schult. is the most widespread species, found in 29 regions and subregions, while some other grape wild relatives are narrowly distributed. It is suggested that the protection of Chinese grape wild relatives should be strengthened.

Abstract:In order to improve the exploration and utilization efficiency of wild tobacco germplasm resource, the genetic diversity of 30 wild tobacco accessions was accessed by phenotypic variations and SSR molecular markers. The results revealed abundant phenotypic variations at each of traits, with the genetic diversity index of 0.831 to 1.955. Among them, the diversity index of node distance was the highest, followed by leaf length and width. The marker analysis using 30 pairs of SSR primers detected 98 alleles with an average of 6.125. The mean value of Shannon information index (I), expected heterozygosity (He), observed heterozygosity (Ho) and Polymorphic information content (PIC) were 1.5425, 0.7596, 0.2404 and 0.8668, respectively. The cluster analysis and population structure analysis roughly suggested four groups, likely coincidence with the geographical collection sites. Sixteen SSR markers were used to construct the fingerprints of 30 wild tobacco accessions, which laid a theoretical foundation for the research on the identification system of wild tobacco accessions. Moreover, tests for disease resistance suggested seven accessions including N.exigua were resistant to black shank disease. The species N. nesophila were highly resistance to bacterial wilt, while N. debneyi and N.stocktonii were resistant. Five accessions including N. alata were immune to TMV. Nine accessions including N.alata were resistant to CMV, and 15 accessions including N. debneyi were resistant to PVY. This study established foundation for the identification and evaluation, germplasm resources innovation and explored excellent gene of wild tobacco resources.

Abstract:The field germination rate of maize seeds, which is controlled by the genetic factors that interact with environmental factors (i.e. temperature, water), directly affects yield production and severs as one of the important targets in maize breeding. In this study, we performed a high-resolution QTL mapping for field germination rate using the multiple QTL model implemented in R/qtl. The introgression line population including 866 lines was derived from a cross between a maize inbred line W22 and a typical accession of teosinte, the wild progenitor of maize, followed by genotyping with 19,838 SNP markers. Three QTL were detected including qFGR4-1, qFGR5-1 and qFGR8-1, which were flanked by the markers m20780 and m21277 on chromosome 4, m29418 and m29680 on chromesome 5, as well as m44383 and m44706 on chromosome 8, respectively. Three loci attributed to 11.2% of the phenotypic variation, with the phenotypic contribution rate and additive effect of each QTL ranged from 2.8% to 4.8% and from 4.5% to 7.4%, respectively. These results indicated that the field germination rate is a typical quantitative trait, which is controlled by multiple micro-effect genes. In addition, the W22 alleles at three loci showed positive additive effects, suggesting that field germination rate might have experienced a directional selection during maize domestication and improvement. Collectively, this study might provide important reference for future elucidating the genetic basis of field germination rate, cloning key genes and improving field germination rate using molecular marker-assisted selection in maize.

Abstract:This study investigated the changes in half lethal low temperature (LT50), the contents of flavonoid, non-structural carbohydrates and plant hormone, as well as the proteomics on the current-year branches of Rosa beggeriana during overwintering. The results showed that the freezing tolerance of the branches gradually increased and its LT50 value reached -54.7℃ in the coldest phase of the winter. No significance on the contents of starch and ABA were observed, whereas the contents of flavonoids, total soluble sugars including sucrose, glucose, fructose and raffinose were found to be significantly increased in the branches. However, SA contents in the branches decreased at the beginning phase of the winter, followed by an increase significantly in the coldest phase of the winter. The correlative analysis showed that the LT50 values were negatively correlated with the contents of flavonoids, total soluble sugars, glucose and fructose. The proteomic analysis showed that there were total 153 differentially expressed proteins (DEPs) accumulated in branches during overwintering. Of them, there were 92 DEPs at the beginning phase of the winter and 91 DEPs in the coldest phase of the winter. The DEPs, which are annotated to involve in starch and sucrose metabolism, flavonoids biosynthesis, antioxidant defenses, cell wall relaxation and extension, water transport channels as well as cell dehydration responses were significantly up-regulated, suggesting that the branches activated a series of physiological and biochemical responses to improve the long-term freezing tolerance. Moreover, the DEPs such as dehydrin, anti-freezing protein and aquaporin may play the important roles in the cell water balances of the branches in the coldest phase of the winter.

Abstract:In order to clarify the heat tolerance of F5 and F6 inbred lines derived from inter-specific hybrids of Cucurbita moschata (MO) × Cucurbita maximam (MA), the relative electrical conductivity (E) was measured before and after heat stress treatment, followed by the calculation of the rate of injury (RI), positive hyperparental advantage (PHA%) and negative hyperparental advantage (NHA%). The results showed that RI represented higher detection sensitivity and negative correlation with heat tolerance. The outcomes in tested inbred lines were coincident with the phenotyping results. The heat stress treatment resulted in elevated Evalue in inbred lines, suggesting a damage on the leaf cell membrane. The RI value of MO and MA were 0.24±0.10 and 0.65±0.29, respectively. Sixteen and 14 inbred lines showing heat tolerant and sensitive respectively, as well as six with moderate heat tolerance were identified. The heat tolerance trait was polarization among 36 tested inbred lines, and the tolerance enhance effective was obvious. The heat tolerance of three F4 lines were differing. The F5 offspring of 18SH and 18SE showed enhanced heat tolerance, whereas the F5 offspring of 18SF represented decreased heat tolerance. By taking the RI value of 0.15 as the threshold value, 13 heat tolerance inbred lines with higher PHA% value were selected, including ten F5 inbred lines derived from 18SH, two F5 derived from 18SE, and one F6 derived from 18FB. Collectively, these heat-tolerant lines might provide the germplasm basis in breeding for Cucurbita maximam cultivars breeding suitable for over-summer farming.

Abstract:Brasenia schreberi J. F. Gmel. of the family Cabombaceae is a perennial aquatic plant under first-level national protection in the wild in China. Its young stems and leaves are used as vegetables. It has been also cultivated in China for about 1800 years for its young stems and leaves as a vegetable, now widely grown in Leibo in Sichuan Province, Lichuan in Hubei Province, Shizhu in Chongqing Municipality, Taihu in Jiangsu Province, and Hangzhou in Zhejiang Province. In order to understand the current status of its wild populations in China, we carried out on-site investigation and collection in Hunan, Jiangxi, Yunnan, and Heilongjiang provinces. The genetic diversity of B. schreberi was then analyzed for six cultivars preserved in the National Germplasm Wuhan Aquatic Vegetable Collection and 27 samples newly collected from six wild populations, with the simplified genome-sequencing technology SLAF-seq. The wild populations of B. schreberi were more diverse than cultivated varieties in many phenotypic traits (such as the color of the rolling leaf, the color of the lower surface of the leaf, the leaf size, and the mucilage thickness). Molecular analysis revealed a rich genetic diversity in B. schreberi (π = 0.3456), with the wild populations (π = 0.3386) higher than the cultivated varieties (π = 0.2916), which is consistent with the phenotypic trait analysis. B. schreberi displayed great genetic differentiation (Fst = 0.2654) among the wild populations, with higher genetic variation within the populations (accounting for 76.99%) than among the populations (accounting for 23.01%), indicating that the within population variation was the main contributing factor. Using high-quality SNP loci, the nearest neighboring method was used to construct the clustering tree, with the total 33 samples divided into two groups. The first group contained two Mangshan populations. The second group included the other four wild populations and all the six cultivars. The samples from two Mangshan populations were mixed with each other, indicating relatively frequent gene exchange between the two groups and very low genetic differentiation. In the other group, wild samples from different populations were well separated, indicating that a certain genetic differentiation existed between those wild populations because of geographical isolation. The PCA and structure analysis all confirmed that the Mangshan samples gather together and were distant from the other samples, indicating an obvious differentiation between the Mangshan populations and the other populations. The genetic differentiation between cultivated varieties and wild populations is small (Fst = 0.0674), indicating a relatively low degree of artificial domestication of the cultivated varieties. This article puts forward some suggestions for the protection of B. schreberi resources in China.