Adoption of Improved Rice Varieties in the Global South:A Review

Improved rice varieties(IRVs)play a significant role in establishing food security and improving livelihood in the Global South since its introduction in the 1960s.However,the adoption of new IRVs has remained relatively low.This low adoption poses a challenge to rice-producing and consuming countries as they are increasingly threatened by production shortages,malnutrition,and poor rice quality.Many empirical studies have attempted to identify the determinants influencing the adoption of IRVs by distinguishing the characteristics between adopters and non-adopters.This review showed a consensus on the important determinants influencing the adoption of IRVs in the Global South.Findings synthesized from 99 studies suggested that variables(farm size,education,information access and farm location)examined extensively are not necessarily the most important determinants of adoption when undertaking a weighted analysis.Terrain,source of seed and technology-related attributes(perceived yield,maturity,ease of use,marketability and technical efficiency)are more important determinants of adoption,with determinants changing according to adoption type(probability or intensity of adoption),variety type and region.The recommendations for future adoption studies include:incorporating more technology-specific variables,increasing research for overlooked regions and variety types,shifting away from predominant static analysis by capturing the dynamics of the adoption process,and considering the potential biases in analyses.This review will facilitate the development of targeted interventions and policies that promote IRV adoption in the Global South.

Factors Affecting Adoption of Improved Rice Varieties among Rural Farm Households in Central Nepal

The use of improved high yielding crop varieties is an important avenue for reducing hunger and food insecurity in developing countries. Using cross-sectional data obtained from a survey conducted during 2013 crop season, we performed a probit model （plot-level analysis） to determine the probability of adopting new improved rice varieties （NIRVs） by smallholder farmers particularly from two main agro-ecological regions （hills and tropical plain terai regions） of Central Nepal. The results revealed that education, extension services and seed access play significant roles in adoption decisions. Additionally, farm and field characteristic variables such as farm size, endowment of favorable land type （e.g. lowlands）, and animal power （e.g. oxen） are the key factors influencing the probability of adopting NIRVs. The results showed that technology specific variables （e.g. yield potential and acceptability） are significant for explaining adoption behavior, implying that it is important to take farmers＇ preferences to varietal characteristics into consideration in the design of a research and development program. Given the significant role played by extension and access related variables, increased emphasis on information dissemination, field demonstration, and farmers＇ participatory research and training programs to popularize new rice varieties and enhance their adoption rate are required. This also suggests that policy intervention should be made on improving the educational status of farming households, and developing programs on varietal package of rice seed which offer farmers a variety of choices among the appropriate pools of germplasm. Such programs ultimately help farmers develop more profit-oriented behavior which are necessary to enhance adoption rate, production and food security in the long run.

Analysis of Genetic Similarity for Improved Japonica Rice Varieties from Different Provinces and Cities in China

To provide a genetic basis for japonica rice breeding, the genetic similarity and cluster of 139 accessions of improved japonica rice varieties from 12 provinces and cities of China were analyzed using 34 SSR markers. Totally 198 alleles were detected among these improved japonica rice varieties with the average number of alleles per pair of primers was 5.3235. RM320, RM531, RM1, RM286, and RM336 showed more alleles, which were 15, 12, 11, 9, and 9, respectively. RM320, RM336, RM286 and RM531 showed higher genetic diversity indexes; which were 2.3324, 2.0292, 1.8996, and 1.7820, respectively. The range of genetic similar index among improved japonica rice varieties from different provinces was from 0.321 to 0.914, with the average of 0.686. There was a high genetic similarity among improved japonica rice varieties from Heilongjiang, Jilin, Liaoning, Ningxia, and Yunnan, which were located in similar latitude or similar ecological environment, while there was a low genetic similarity between improved japonica rice varieties from Guizhou and Jiangsu, and other provinces which were located in more different latitudes and ecological environments. The markers of RM320, RM531, RM1, RM286, and RM336 fit to be used in analysis of genetic diversity for improved japonica rice variety. The genetic similarity among improved japonica rice varieties from different provinces was closely associated with genetic basis of parents, and was also correlated with latitude and ecological environment where the varieties were bred.

Changes in starch quality of mid-season indica rice varieties in the lower reaches of the Yangtze River in last 80 years

Rice (Oryza sativa L.) quality depends mainly on the characteristics of starch stored in kernels. Understanding the changes in starch characteristics in kernels during variety improvement would have great significance to improve rice quality. This study was designed to investigate the starch characteristics in the kernels and associated physiological traits of indica rice varieties in the lower reaches of the Yangtze River in China in last 80 years. Eight representative mid-season indica rice varieties were grown in the field. The results showed that the grain yield was significantly increased with the improvement of varieties and such an increase was mainly attributed to the increase in total number of spikelets. The tall varieties applied in the 1940s–1950s had higher protein content, relative crystallinity and infrared (IR) ratio of 1 045/1 022 cm^–1. The semi-dwarf varieties applied in the 1980s–1990s had higher gel consistency, amylopectin content, IR ratio of 1 022/995 cm^–1, and breakdown value. With the improvement of varieties, the amylose content, large-sized starch granule number and volume distribution, onset and peak of gelatinization temperature, gelatinization and retrogradation enthalpy, setback value, pasting temperature, viscosity of peak, hot and final, and 1-aminocycopropane-1-carboxylic acid (ACC) concentrations in panicles and root bleeding were gradually decreased, whereas the medium-sized starch granule number and volume distribution, activities of key enzymes in grains, and zeatin (Z)+zeatin riboside (ZR) contents in panicles and root bleeding at grain filling stage were gradually increased. Correlation analysis showed that starch thermodynamic characteristics were closely related to starch structure and components, key enzymes and hormones. The results suggest that starch quality was enhanced through the optimization of starch components, structure, thermodynamics, and the regulation of key enzymes in grains and hormones in panicles and root bleedings at grain filling stage during the improvement of mid-season indica rice.

Morphological and physiological traits of large-panicle rice varieties with high filled-grain percentage

financed by the Special Program of Super Rice of Ministry of Agriculture, China （02318802013231）;the National Public Services Sectors （Agricultural） Research Projects, Ministry of Agriculture, China （201303102）;the Great Technology Project of Ningbo, China （2013C11001）

Assessing indica-japonica differentiation of improved rice varieties using microsatellite markers

To assess the indica-japonica differentiation of improved rice varieties, a total of 512 modem varieties including 301 indica and 211 japonica accessions were analyzed using 36 microsatellites. The Fst coefficients ranged from 0.002 to 0.730 among the loci with an average of 0.315. Significant differentiation was detected at 94.4% of the loci studied （P 〈 0.05, pairwise Fst tests）, indicating that there was a high level of indica-japonica differentiation within the improved varieties. At 18 loci, about 74%-98% of the alleles of indica and japonica accessions were distributed in two ranges of amplicon length. Linkage disequilibrium analysis showed that the distribution trends were significantly nonrandomly associated. Using the differentiation trends at the 18 loci, microsatellite index （MI） was proposed for discrimination of the two subspecies. When rice accessions with MI value greater than zero were classified as indica, and those with MI value smaller than zero were classified as japonica, about 96.1% of the accessions could be classified. This result agrees with the classification based on morphological-physiological characters, indicating that this method is feasible and effective.

Rice variety improvement and the contribution of foreign germplasms in China

The introduction and use of foreign germplasms have played an important role in the improvement of crop varieties in China. Based on published materials and scientist interviews, we collected data on the sown area, morphological characteristics, and pedigree of the popular rice varieties grown in the 15 major rice production provinces and 1 autonomous region in China, from 1982 to 2011. Results showed that China＇s scientists developed the largest number of rice varieties worldwide, and that rice yield potential and grain quality have substantiality improved during the studied period. In contrast, resistance of newly-released varieties to diseases and insect pests has decreased since the 1990s. Germplasms from the Interna- tional Rice Research Institute （IRRI） and from Japan have contributed 16.4 and 11.2% of genetic materials to China＇s rice varieties developed between 1982 and 2011, respectively. While IRRI＇s materials contributed to the improvement of yield potential, growth duration, and blast and bacterial blight resistance, Japanese materials contributed to the improvement of grain quality. Materials from other countries contributed to the improvement of resistance to diseases and insect pests, particularly to rice blast disease, brown planthoppers, white-backed planthoppers, and striped stem borers.

Genetic Improvement in Juglans mandshurica and Its Uses in China:Current Status and Future Prospects

Juglans mandshurica is an economically and ecologically valuable species that is used for various construction purposes,making luxurious furniture,as food and sources of medicinal substances and landscaping because of its excellent wood,edible fruits and rich in various types of chemical compounds.In the past few decades,several genetic improvements of J.mandshurica were made,with a focus on the selection of improved varieties and on breeding technology.Many elite provenances and families were selected based on growth traits or wood properties.In recent years,with the increasing demand for high-quality seedlings in Chinese forestry production,the breeding goals of genetic improvement for J.mandshurica were redefined to include other traits,such as fruit yield and contents of medicinal component.However,the improvement processes were still slow due to the long breeding cycle and the limited use of advanced breeding technologies,resulting in the selection of fewer improved varieties.In this review,we summarized the research progresses on genetic improvements of J.mandshurica and other related works,and discussed research gaps and suggested future directions for genetic improvement of the species.The review provides valuable insight for the selection of improved varieties and production of excellent germplasms.

Molecular bases of rice grain size and quality for optimized productivity

The accomplishment of further optimization of crop productivity in grain yield and quality is a great challenge.Grain size is one of the crucial determinants of rice yield and quality;all of these traits are typical quantitative traits controlled by multiple genes.Research advances have revealed several molecular and developmental pathways that govern these traits of agronomical importance.This review provides a comprehensive summary of these pathways,including those mediated by G-protein,the ubiquitin–proteasome system,mitogen-activated protein kinase,phytohormone,transcriptional regulators,and storage product biosynthesis and accumulation.We also generalize the excellent precedents for rice variety improvement of grain size and quality,which utilize newly developed gene editing and conventional gene pyramiding capabilities.In addition,we discuss the rational and accurate breeding strategies,with the aim of better applying molecular design to breed high-yield and superior-quality varieties.