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.

Conservation of Traditional Rice Varieties in a Globally Important Agricultural Heritage System (GIAHS):Rice-Fish Co-Culture

The traditional rice-fish farming system is selected as a ＂globally important agricultural heritage system＂ （GIAHS） by the Food and Agriculture Organization （FAO）,United Nations Development Programme （UNDP）,and Global Environment Facility （GEF）,etc.In Zhejiang Province of China,where the pilot site for this GIAHS farming system is located,we compared the use of traditional rice varieties in rice-fish co-culture and rice monoculture.Further,we determined how traditional rice varieties were performed in this rice-fish system.Only 19% of the farmers who practiced rice monoculture planted traditional varieties while 52% of farmers who practiced rice-fish co-culture planted traditional varieties.Traditional varieties represented 13% of the total land cultivated under rice in the rice-fish system but only 2% in the rice monoculture system.In the rice-fish system,yield was lower for traditional rice varieties than hybrid varieties but application of fertilizers and pesticides was also lower.In a field experiment in the rice-fish system without pesticides,rice planthopper numbers and sheath blight incidence were lower from three traditional varieties than one hybrid variety;yields were 8 to 32% lower from the traditional varieties than the hybrid.Our results showed that traditional rice varieties can be preserved through conserving GIAHS rice-fish co-culture.Our study also indicated that traditional rice varieties can survive in the rice-fish system because these varieties are helpful to the whole system and beneficial to the farmers.

Evaluation of Chinese rice varieties resistant to the root-knot nematode Meloidogyne graminicola

The root-knot nematode Meloidogyne graminicola, which is distributed worldwide, is considered a major constraint on rice production in Asia. The present study used the root gall index and number of nematodes inside the roots to evaluate resistance/susceptibility to M. graminicola in different subpopulations of Oryza sativa （aus, hybrid aus, indica, hybrid indica, temperate japonica, tropical japonica）. Nematode development in highly resistant varieties was also evaluated. Analyses of randomly selected 35 varieties showed the number of M. graminicola nematodes inside the roots correlated very strongly （r=0.87, P≤0.05） with the nematode gall index, and the results from pot and field experiments revealed similar rankings of the varieties for resistance/susceptibility. Among the 136 tested varieties, temperate japonica displayed the highest gall index, followed by tropical japonica, indica, hybrid indica, aus, and hybrid aus. Zhonghua 11 （aus）, Shenliangyou 1 （hybrid aus） and Cliangyou 4418 （hybrid indica） were highly resistant to M. graminicola under both pot and field conditions. Further examination of nematode development suggested that compared to susceptible rice, M. graminicola penetrated less often into highly resistant varieties and more frequently failed to develop into females. The promising varieties found in the present research might be useful for the breeding of hybrid rice in China and for the further development of practical nematode management measures.

Relationship Between the First Base of the Donor Splice Site of Waxy Gene Intron 1 and Amylose Content in Yunnan Indigenous Rice Varieties

There exists a single nucleotide polymorphism, G or T, at the first base of the donor splice site of waxy gene intron 1 in rice. In order to study the relationship between the first base of the donor splice site of waxy gene intron 1 and amylose content in rice, the one-step PCR method was used to determine whether it is G or T in 220 Yunnan indigenous rice varieties from 14 districts, 55 towns/counties of Yunnan Province, and 101 varieties of which were validated by the PCR-Acc I method. According to the G/T polymorphism, 164 rice varieties showed GG-genotype, while the other 56 fell into TT- genotype, accounting for 74.5% and 25.5% of all the test varieties, respectively. When all the rice varieties were divided into indica and japonica subspecies, it was found that 80.5% of indica rice and 67.0% of japonica rice belonged to GG-genotype. The rice varieties with GG-genotype had significantly higher amylose content （18.95% on average） than those with TT- genotype （all below 16%）, but 33 rice varieties with GG-genotype still had low amylose content ranging from 3.91% to 15.93%, and most of them came from the Dai minority area in the Southwest of Yunnan Province. However, there was no significant difference in the mean amylose content of the same GG or TT genotypes between indica and japonica rice, suggesting that different genetic backgrounds, indica or japonica, had no effect on amylose content. The coefficient of correlation between the genotype and amylose content was 0.733 （P〈0.01）.

Tolerance evaluation of rice varieties to the brown planthopper,Nilaparvata lugens feeding

The brown planthopper,Nilaparata lugens(Stl)(BPH)is one of the most important insect pests of rice in China and other east-southern Asian countries.Untilization of rice resistance varieties is one of the most econnomic and effective ways for

Effect of nitrogen fertilizer on the uptake and utilization of potassium by various rice varieties in purple soil

Nitrogen and potassium are important nutrientelements for rice.Besides supplied by the or- ganic manure,potassium nutrition of ricecomes dominantly from purple soils in Sichuanbasin.Potassium exists abundantly in mineralforms in the purple soils.Availability of soilpotassium for crop depends on the potassiumforms,the uptake ability of crops,and fertiliz-er practices.A pot culture experiment wasconducted to study the kinetics of potassiumuptake in the purple soil(total N 22.64g·kg,total K 24.36g·kg,available N 102.6mg·kg,available K 140.6mg·kg,acidsoluble K 936.0mg·kg,and pH 6.8).Ma-terials used were three Fhybrid rices,Eryou

Cultivar Mixture Cooperation(CMC)of rice varieties(lines) with different blast resistant gene

We studied Cultivar Mixture Cooperation(CMC)of rice varieties(lines)by screening mixture ofrice varieties which possess different genes,1983-1996.

Breeding for multiresistant rice varieties

From 1977 to 1987, new rice varieties Xiangkang 32xuan 5, Xiangzaoxian 3 and HA79317—4 were bred. They had resistance to bacterial blight (BB), rice blast (BL), brown planthopper(BPH), whitebacked planthopper (WBPH), with high-yielding and good rice quality.

Use AMMI model to analyze adaptability of rice varieties

The adaptability of rice varieties is one of themost concerned questions to rice breeders.Inrice breeding,combined variety test and re-gional trials which included multiple genotypesand environments were conducted to identifythe adaptability of new rice varieties.In mostregional trials,interaction between genotypeand environment is significant,so it is impor-tant to analyze the interaction for estimating

The location of 5′-nucleotidase in seedling cells in Yunnan rice varieties and the change of enzyme activity after chilling injury

The seedlings of three rice varieties (Damagu,Ligeng 2, and Xiuzinuo) were cultivated at 25 ±1℃. After chilling injury (at 2~C), blacksediments of lead phosphate appeared on plas-

Varied responses to copper for plant regeneration from calli of different rice varieties

Enrichment of copper to the culture mediumcould enhance the plant regeneration from cal-lus of indica rice variety Qiugui’ai 11. Westudied the effect of copper on plant regenera-tion of other rice varieties.Calli of 14 indica and 2 japonica varietieswere induced from disinfected mature embryoson an agar-gelled medium containing Nbasal

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.

Susceptibility to Insecticides and Ecological Fitness in Resistant Rice Varieties of Field Nilaparvata lugens Stl Population Free from Insecticides in Laboratory

A population of rice brown planthopper （BPH） Nilaparvata lugens collected from a paddy field in Hangzhou was successively reared on susceptible rice Taichung Native 1 （TN1） in a laboratory free from insecticides for more than 14 generations. The changes in susceptibility to insecticides and ecological fitness on different resistant rice varieties were monitored in each generation. The resistance ratio to imidacloprid sharply declined with the succession of rearing generations without insecticides from 359.94-fold at F1 to 6.50-fold at F14 compared with the susceptible strain, and the resistance ratio to chlorpyrifos was from 9.90-fold at F1 to 5.94-fold at F14. Nymphal duration and weights of newly hatched female adults were significantly affected by rice variety, generation and their interactions, but nymphal survival was significantly affected by the generation only. The ratio of brachypterous adults in males was affected by the generation and generation × variety interaction, whereas no difference was found in females. Nymphal duration extended with increasing generations, and the female nymphal duration was shorter in the susceptible variety TN1 than those in the resistant varieties IR26 and IR36. In addition, the female adult weight in TN1 was higher than those in IR26 and IR36. These results indicated that the resistance of field BPH population to insecticides was reversed after several generations of no-exposure to insecticides, and the ecological fitness in TN1 was higher than those in IR26 and IR36. These findings suggested the rational and reduced use of insecticides in combination with the manipulation of resistant rice varieties would be effective for BPH management.

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.

Simulation of Potential Productivity of Early Season Rice Varieties in Different Reqions of South China

Rice is a staple food crop in China.Since the 1950’s,many new varieties havebeen used and resulted in great increase ofyield.However there were still some barriersin the nationwide extension of new varietiesdue to the insufficient information about thecharacteristics of varieties.So,it is impor-tant to find ways of determining the potential

Field Evaluation of Growth and Yield of Two Local Rice Varieties (Tox-728-1 and Madjitolngar) in Response to Indogenous Mycorrhizal Inoculation in South-Chad

This study was carried out to find out how dependent are two local rice varieties (Magitolngar and Tox-728-1) to inoculation with selected endogenous arbuscular mycorrhizal fungi (AMF) in a field where they were isolated. The multi-indigenous endomycorrhiza spores previously isolated and identified were the active ingredient in the production of bioinoculants used for this purpose. Spores massively multiplied from the rhizosphere of each rice variety in each of the four locally collected soils substrates were harvested to constitute 08 AMF inoculants (Kema = T1;Lama = T2;Latox = T3;Ndjatox = T4;Koloma = T5;Kolotox = T6;Ndjama = T7;Ketox = T8). These inoculants were field tested on the two rice varieties at Kelo, under a complete randomized block design, comprising 10 treatments (8 inoculants, 01 positive control = T9, 01 negative control = T10), each of which was repeated thrice. The analysis of data indicates that AMF-inoculated plants were taller, developed more tillers/plant, and produced more rice grains/panicle than non-AMF-inoculated plants for both studied rice varieties. The rice variety Madjitolngar yielded more grains (7.5 t/ha) than the Tox-728-1 variety (5.8 t/ha). Moreover, inoculants Koloma (T1), Latox (T3) and Kolotox (T6) on the one hand, Koloma (T1) and Ketox (T8) on the other hand, were best suited for the improvement of growth and yield of the rice varieties Madjitolngar and Tox-728-1 respectively, tested under field conditions at Kelo. In this study, the two rice varieties have shown a dependency to endomycorrhizal symbiosis at Kelo, and therefore, an industrial-scale production of efficient endomycorrhal inoculants is necessary to sustainably boost the productivity of this important crop in Chad.

Effect of Combined Application of Subsurface Drainage and Mineral Fertilization on Iron-Reducing Bacterial Populations’ Developments and Fe2+ Uptake by Two Rice Varieties in an Iron Toxic Paddy Soil of Burkina Faso (West Africa)

Rice is one of the staple crops in Burkina Faso. However, the local production covers only 47% of the population demands. One of the main reasons of the poor productivity in Burkina Faso is iron toxicity which is related mainly to the activity of Iron Reducing Bacteria in the rice field’s ecosystems. In order to control the harmful effects of Iron Reducing Bacterial populations and to improve rice productivity, a pots experiment was conducted at the experimental site of the University Ouaga I Pr. Joseph KI-ZERBO. An iron toxic soil from Kou Valley (West of Burkina Faso) and two rice varieties, BOUAKE-189 and ROK-5, sensitive and tolerant to iron toxicity, respectively, were used for the experiment. The pots were drained for 14 days (D2) and amended with chemical fertilizers (NPK + Urea and NPK + Urea + Ca + Mg + Zn complexes). Control pots without drainage and fertilization (D0/NF) were prepared similarly. The kinetics of Iron Reducing Bacterial populations and ferrous iron content in soil near rice roots were monitored throughout the cultural cycle using MPN and colorimetric methods, respectively. The total iron content was evaluated in rice plant using a spectrometric method. Data obtained were analyzed in relation to drainage and fertilization mode, rice growth stage and rice yield using the Student’s t-test and XLSTAT 2014 statistical software. The experiment showed that the combined application of subsurface drainage and NPK + Urea + Ca + Mg + Zn fertilization, reduced significantly the number of IRB in the soil near rice roots for both rice varieties (p = 0.050 and p = 0.020) increased the leaf tissue tolerance to excess amounts of Fe, and rice yield.

Generation of new glutinous rice by CRISPR/Cas9-targeted mutagenesis of the Waxy gene in elite rice varieties

In rice, amylose content （AC） is controlled by a single dominant Waxy gene. We used Clustered Regularly Interspaced Short Palindromic Repeats （CRISPR）/CRISPR-associated 9 （Casg） to introduce a loss-of-function mutation into the Waxy gene in two widely cultivated elite japonica varieties. Our results show that mutations in the Waxy gene reduce AC and convert the rice into glutinous ones without affecting other desirable agronomic traits, offering an effective and easy strategy to improve glutinosity in elite varieties. Importantly, we successfully removed the transgenes from the progeny. Our study provides an example of generating improved crops with potential for commercialization, by editing a gene of interest directly in elite crop varieties.

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.

QTL editing confers opposing yield performance in different rice varieties

Grain yield is one of the most important and complex trait for genetic improvement in crops; it is known to be controlled by a number of genes known as quantitative trait loci（QTLs）. In the past decade, many yield-contributing QTLs have been identified in crops.However, it remains unclear whether those QTLs confer the same yield performance in different genetic backgrounds. Here, we performed CRISPR/Cas_9-mediated QTL editing in five widely-cultivated rice varieties and revealed that the same QTL can have diverse, even opposing, effects on grain yield in different genetic backgrounds.