Drought-Tolerant Rice at Molecular Breeding Eras:An Emerging Reality

Rice(Oryza sativa L.)stands as the most significantly influential food crop in the developing world,with its total production and yield stability affected by environmental stress.Drought stress impacts about 45%of the world’s rice area,affecting plants at molecular,biochemical,physiological,and phenotypic levels.The conventional breeding method,predominantly employing single pedigree selection,has been widely utilized in breeding numerous drought-tolerant rice varieties since the Green Revolution.With rapid progress in plant molecular biology,hundreds of drought-tolerant QTLs/genes have been identified and tested in rice crops under both indoor and field conditions.Several genes have been introgressed into elite germplasm to develop commercially accepted drought-tolerant varieties,resulting in the development of several drought-tolerant rice varieties through marker-assisted selection and genetically engineered approaches.This review provides up-to-date information on proof-of-concept genes and breeding methods in the molecular breeding era,offering guidance for rice breeders to develop drought-tolerant rice varieties.

Seed Storability in Rice: Physiological Foundations, Molecular Mechanisms, and Applications in Breeding

Long-term storage of crop seeds is critical for the conservation of germplasm resources, ensuring food supply, and supporting sustainable production. Rice, as a major food staple, has a substantial stock for consumption and production worldwide. However, its food value and seed viability tend to decline during storage. Understanding the physiological responses and molecular mechanisms of aging tolerance forms the basis for enhancing seed storability in rice. This review outlines the latest progress in influential factors, evaluation methods, and identification indices of seed storability. It also discusses the physiological consequences, molecular mechanisms, and strategies for breeding aging-tolerant rice in detail. Finally, it highlights challenges in seed storability research that require future attention. This review offers a theoretical foundation and research direction for uncovering the mechanisms behind seed storability and breeding aging-tolerant rice.

Artificial selection of the Green Revolution gene Semidwarf 1 is implicated in upland rice breeding

Semidwarf breeding has boosted crop production and is a well-known outcome from the first Green Revolution. The Green Revolution gene Semidwarf 1(SD1), which modulates gibberellic acid(GA) biosynthesis, plays a principal role in determining rice plant height. Mutations in SD1 reduce rice plant height and promote lodging resistance and fertilizer tolerance to increase grain production. The plant height mediated by SD1 also favors grain yield under certain conditions. However, it is not yet known whether the function of SD1 in upland rice promotes adaptation and grain production. In this study, the plant height and grain yield of irrigated and upland rice were comparatively analyzed under paddy and dryland conditions. In response to dryland environments, rice requires a reduction in plant height to cope with water deficits. Upland rice accessions had greater plant heights than their irrigated counterparts under both paddy and dryland conditions, and appropriately reducing plant height could improve adaptability to dryland environments and maintain high grain yield formation. Moreover, upland rice cultivars with thicker stem diameters had stronger lodging resistance, which addresses the lodging problem. Knockout of SD1 in the upland rice cultivar IRAT104 reduced the plant height and grain yield, demonstrating that the adjustment of plant height mediated by SD1 could increase grain production in dryland fields. In addition, an SD1 genetic diversity analysis verified that haplotype variation causes phenotypic variation in plant height. During the breeding history of rice, SD1 allelic mutations were selected from landraces to improve the grain yield of irrigated rice cultivars, and this selection was accompanied by a reduction in plant height. Thus, five known mutant alleles were analyzed to verify that functional SD1 is required for upland rice production. All these results suggest that SD1 might have undergone artificial positive selection in upland rice, which provides further insights concerning greater plant height in upland rice breeding.

Estimating Key Phenological Dates of Multiple Rice Accessions Using Unmanned Aerial Vehicle-Based Plant Height Dynamics for Breeding

Efficient and high-quality estimation of key phenological dates in rice is of great significance in breeding work. Plant height(PH) dynamics are valuable for estimating phenological dates. However, research on estimating the key phenological dates of multiple rice accessions based on PH dynamics has been limited. In 2022, field traits were collected using unmanned aerial vehicle(UAV)-based images across 435 plots, including 364 rice varieties. PH, dates of initial heading(IH) and full heading(FH), and panicle initiation(PI), and growth period after transplanting(GPAT) were collected during the rice growth stage. PHs were extracted using a digital surface model(DSM) and fitted using Fourier and logistic models. Machine learning algorithms, including multiple linear regression, random forest(RF), support vector regression, least absolute shrinkage and selection operator, and elastic net regression, were employed to estimate phenological dates. Results indicated that the optimal percentile of the DSM for extracting rice PH was the 95th(R^(2) = 0.934, RMSE = 0.056 m). The Fourier model provided a better fit for PH dynamics compared with the logistic models. Additionally, curve features(CF) and GPAT were significantly associated with PI, IH, and FH. The combination of CF and GPAT outperformed the use of CF alone, with RF demonstrating the best performance among the algorithms. Specifically, the combination of CF extracted from the logistic models, GPAT, and RF yielded the best performance for estimating PI(R^(2) = 0.834, RMSE = 4.344 d), IH(R^(2) = 0.877, RMSE = 2.721 d), and FH(R^(2) = 0.883, RMSE = 2.694 d). Overall, UAV-based rice PH dynamics combined with machine learning effectively estimated the key phenological dates of multiple rice accessions, providing a novel approach for investigating key phenological dates in breeding work.

Breeding and Seed Production Techniques of New Aromatic Danxiangyouzhenliang Rice Variety with Good Quality and High Yield

Danxiangyouzhenliang rice is a high-quality rice variety derived from the hybrid breeding of Danxiang 12A and Xianghuixiangmiao R133.Its unique temperature-sensitive three-line characteristics endow it with significant advantages of high and stable yield,and its rice fragrance is exquisite and its taste is delicate.Danxiangyouzhenliang rice showed good resistance to rice blast and bacterial blight.On June 10,2021,Danxiangyouzhenliang rice passed the Guangxi Crop Variety Approval(Guishendao 2021074).Danxiangyouzhenliang rice is suitable to be planted as early and late rice in southern,central and northern Guangxi.This study summarized the breeding process and high-yielding seed production techniques of Danxiangyouzhenliang rice,in order to provide useful reference for rice breeders and growers.

Breeding and Application Techniques of a New Rice Variety Liliang-you 3822 with High Yield and Disease Resistance

Liliangyou 3822 is a novel indica hybrid rice variety that exhibits disease resistance,high yield,lodging resistance,and late maturity.It employs a self-selected two-line sterile line,Li 38S,and a self-selected restorer line,R22.This variety was subjected to a regional test of indica late-maturing groups in the middle and lower reaches of the Yangtze River in 2020.The results demonstrated that the average yield of the variety was 9.95 t/hm 2,which was 10.67%higher than that of the control Fengliangyou 4,indicating a highly significant yield increase.In the continuous test in 2021,the average yield was 9.74 t/hm 2,representing a 6.52%increase over the control,which also exhibited a significant increase.Finally,the average yield of the two years regional test was 9.84 t/hm 2,which was 8.58%higher than that of the control.In the 2021 production test,the average yield of the variety was 9.32 t/hm 2,which was 12.19%higher than that of the control,indicating a remarkably significant yield increase.In 2022,the variety was validated by the National Crop Variety Approval Committee(GSD 20220143).

Dry Breeding and Dry Planting Techniques for Indica Hybrid Rice in Karst Mountain Areas of Gejiu City

Based on the arable land situation in Gejiu City,upland dry planting of indica hybrid rice is being expanded in Karst mountain areas with a rainfall of over 1400 mm and an altitude of 1100-1600 m to develop grain production.This paper gives a specific description of hybrid rice upland dry seedling technology,upland transplanting technology,fertilization technology,field management,weed prevention and control technology,and disease and pest control.

Rice3K56 is a high-quality SNP array for genome-based genetic studies and breeding in rice(Oryza sativa L.)

Single nucleotide polymorphism(SNP)genotyping arrays provide an optimal high-throughput platform for genetic research and molecular breeding programs in both animals and plants.In this study,a highquality and custom-designed Rice3K56 SNP array was developed with the resequencing data of 3024 rice accessions worldwide,which was then tested extensively in 192 representative rice samples.Printed on the Gene Titan chips of Affymetrix Axiom each containing 56,606 SNP markers,the Rice3K56 array has a high genotyping reliability(99.6%),high and uniform genome coverage(an average of 6.7-kb between adjacent SNPs),abundant polymorphic information and easy automation,compared with previously developed rice SNP arrays.When applied in rice varietal differentiation,population diversity analysis,gene mapping of 13 complex traits by a genome-wide association study analysis(GWAS),and genome selection experiments in a recombinant inbred line and a multi-parent advanced generation inter-cross populations,these properties of the Rice3K56 array were well demonstrated for its power and great potential to be a highly efficient tool for rice genetic research and genomic breeding.

Breeding of New Japonica-indica Hybrid Rice Combination——Chunyou 618

[Objective] The aim was to select and breed Chunyou 618 which is a novel combination among japonica-indica hybrid rice subspecies. [Method] Chunyou 618 is a japonica-indica hybrid rice combination developed from Chunjiang 16A, a late japonica CMS line with dwarfness and early anthesis time, and C18, an indicaclinous wide compatibility restorer line. In addition, the concerning characters were researched. [Result] Chunyou 618, which is japonica inclining, proved high in pro- duction and in resistance to lodging with Cheng＇s index at 15. It is of moderate re- sistance against Xanthomonas oryzae and stripe virus disease, of moderate susceptibility on rice blast, and of susceptibility on Nilaparvata lugens. The indices of rice quality achieved departmental standard 4 and grade 4 of Cooking Rice Variety Quality, respectively. [Conclusion] Chunyou 618 enjoys strong heterosis, strong stem, good lodging resistance, large panicles, good cold tolerance, high yield and wide adaptability, which is suitable to be grown in Zhejiang Province as single cropping late rice.

Key Techniques of an Ecological Pattern“Planting Rice in One Season and Breeding Red Swamp Crawfish in Three Seasons” for Green Production in Lixiahe Region of Jiangsu Province

Three big field projects, independent irrigation and drainage facilities, and a blocking net, which are auxiliary projects of a green planting and breeding pattern composed of rice and red swamp crawfish （Procambarus clarkii）, spatial and temporal coupling technology of ＂planting rice in one season and breeding red swamp crawfish in three seasons＂, green fertilization technology, green prevention and control technology, control technology of water level, and throwing technology of bait in Lixiahe region of Jiangsu Province were introduced successively, which can provide technical support for the development of ecological planting and breeding patterns and realization of green production in paddy fields.

Study on Breeding of Rice Gall Midge (Orseolia oryzae)

[ Objective ] The paper is to explore the breeding of rice gall midge. [ Method ] The morphological characteristics, living habits, breeding method and resistance identification of rice gall midge are introduced. [ Result] TN1 can be used as feedstuff to feed rice gall midge, and water should be sprayed to keep moisture during the breeding process. The damage caused by mice, rice planthopper, ants and spiders during the breeding process should be paid attention, mice and ants can be controlled by water insulation method, rice planthopper and spiders can be controlled by tap water rinsing method and artificial capture method, respec- tively. [ Conlcusion] The study provides reference for further study on rice gall midge.

Research Advances on Rice Root Breeding

Rice （Oryza sativa L.） roots pIay an important roIe in the deveIopment and yield of rice. Based on the present research situation of rice root breeding, this paper analyzes the significance of rice root breeding for improving yield and changing morphoIogical and physioIogical characteristics of rice. It also discusses research prospects of rice root breeding.

Great progress in molecular breeding of hybrid rice in CNHRRDC

Elite maintainer lines and restorer lines have been developed by genomic DNA transformation,Analyses of molecular markers, DNA sequences, and Southern blotting have revealed that high DNA polymorphism exists between new developed lines and its receptors, indicating that the special DNA fragment from distant relatives may be integrated into the genome of rice. And several combinations with the potential of super-high yield have been developed from these lines. Therefore, transformation of genomic DNA from distant relatives to the plant of a target receptor may open an avenue for breeding of super-hybrid rice.

The Purification and Rejuvenation and Breeding Technology of Rice Variety Yunjing 29 with Fragrant and Soft Rice

Yunjing 29 bred by Institute of Food Crops of Yunnan Academy of Agricultural Sciences is a new conventional japonica rice variety with fragrant and sof rice, it was examined and approved by Yunnan Provincial Variety Examination and Approval Committee in March of 2011. The variety is early-maturing, high-yield and good-quality, and has resistances to lodging, blast and bacterial leaf blight, its rice is sweet soft, goluptious and lucidus as well as not coarse when it is cold, so it is a good commodity. To further promote the popularization and cultivation of the variety, maintain its characteristics of high quality and high yield, and prevent commingling and degeneration, the purification and rejuvenation as well as breeding technology of high-quality seeds were proposed after continuous exploration and study.

Breeding of National Authorized Two-line Hybrid Rice Yanliangyou 2208

The breeding processes, characteristics and comprehensive characters of two-line hybrid rice Yanliangyou 2208 and its parents （Yan 220S and Yanhui 888） taking part in the national rice regional test of southern rice regions were introduced. Yanliangyou 2208 was approved by the National Crop Variety Appraisal Committee in 2013. The achievement has been transformed successfully and has been applied in production. It has good development and promotion prospects.

Breeding and Application of Indica PTGMS Line Yan 220S in Rice

Yan 220S, which is derived from a natural variant plant discovered among the population of Guangzhan 63S and developed by Jiangsu Agricultural Research Institute for Coastal Regions through pedigree selection over years, is an indica photo- and thermo-sensitive genic male sterile （PTGMS） line in rice. In 2013, it was technically identified by Jiangsu Crop Variety Appraisal Committee. Its hybrid Yan-liangyou 2208 （Yan 220S/Yanhui 888）, a new two-line hybrid rice combination with high yield and good grain quality, was subsequently developed and released for commercial production by the National Crop Variety Appraisal Committee in 2013.

Breeding and Application of WA-type Indica CMS Line Ningxian 2A in Rice

Ningxian 2A is a new Indica CMS line with WA type sterile cytoplasm in rice. It was developed from the testcross between WA type indica CMS line Jin 23A and the single plant selected from the F_4 population of the cross Wuxiang 2B×Jin 23B followed by successive backcross over years. In September, 2014, it was technically identified by Jiangsu Provincial Crop Variety Appraisal Committee. Ningxian 2A has the characteristics of complete pollen sterility, high outcrossing rate, good plant type, high combining ability and good grain quality. Among its hybrids, Ningxian you 8（ Ningxian 2A×R08） was registered and released for commercial production in Jiangsu Province in May, 2015.

Breeding and Application of Indica PTGMS Line Yan 161S and Its Hybrid Yanliangyou 1618 in Rice

In 2006, the indica photoperiod- and thermo-sensitive genic male sterile （PTGMS） line Yan 161S was successful y bred by crossing the Guangzhan 63S （♀） and the medium indica breeding material Yan 229 （♂）, which was bred by the Institute of Agricultural Sciences in Coastal Region of Jiangsu Province, after years＇ and generations’ selection in different areas. It passed the identification by Jiangsu Provincial Crop Variety Appraisal Committee in 2013. Crossing the Yan 161S with Yanhui 888, a new high-yielding and high-quality two-line hybrid rice combination Yanliangyou 1618 was developed, and it passed the variety identification in 2014. This paper introduced the breeding processes and characteristics of Yan 161S and Yanliangyou 1618 and the cultivation and seed production techniques of Yanliangyou 1618.

The Breeding of New Indica-japonica Intersubspecific Hybrid Rice Combination Chunyou 84

Chunyou 84 is an indica-japonica hybrid rice combination developed from Chunjiang 16A, a late japonica CMS line with early anthesis time, and C84, an indi-ca-japonica intermediate type restorer line with wide compatibility. It has the charac-teristics of high yield potential, high seed production, excel ent agronomic characters, good resistance and wide adaptability. It was registered and released by Zhejiang Provincial Crop Variety Appraisal Committee in March, 2013. The breeding proce-dure, characteristics, major techniques of cultivation and seed production of Chunyou 84 were introduced in this paper.

Inheritance of Aroma of Good-quality Indica Type Rice PTGMS Line GHS and Its Application in Hybrid Rice Breeding

The inheritance of aroma of GHS was studied by crossing GHS with non-aromatic lines 9311, Xianhui 207, Yuefengzhan, Taihuangzhan, Yuexiangzhan and aromatic lines Yuxiangyouzhan, Xiangwanxian 17, Tianlongxiang 103, Xinwanxiang and Chuangxiang 5. For the grains of F1 generation, the performance of aroma was tested by chewing method, while for the plants of generations of F1, F2 and BC1 F1, the performance of aroma was tested by KOH solution method. The results showed that the non-aroma of restorer line is a dominant trait, but the aroma of GHS line is a recessive trait; the aroma genes of GHS, Yuexiangzhan and Xiangwanxian 17 were non-al elic; the aroma genes of GHS, Yuxiangyouzhan, Tianlongxiang 103, Xin-wanxiang and Chuangxiang 5 may have the same al elic loci. Among the combinations of GHS and non-aromatic restorer lines, the non-aromatic to aromatic ratios of the F2 plants and the BC1 F1 plants were 3∶1 and 1∶1, respectively, and the inheritance of aroma of GHS was control ed by a pair of recessive nuclear genes. In hybrid rice breeding, using GHS, Qiongxiang S has been bred out, and a series of aro-matic hybrid rice combinations have also been selected. Among the hybrid combi-nations, Qiongxiangliangyou 1, Qiongxiangliangyou 2 and other high-yielding and high-quality combinations have been approved by provincial government, and they have good application prospects.