Blast disease caused by the fungal pathogen
Magnaporthe oryzae
is the most severe diseases of rice. Using classical plant breeding techniques, breeders have developed a number of blast resistant ...cultivars adapted to different rice growing regions worldwide. However, the rice industry remains threatened by blast disease due to the instability of blast fungus. Recent advances in rice genomics provide additional tools for plant breeders to improve rice production systems that would be environmentally friendly. This article outlines the application of conventional breeding, tissue culture and DNA-based markers that are used for accelerating the development of blast resistant rice cultivars. The best way for controlling the disease is to incorporate both qualitative and quantitative genes in resistant variety. Through conventional and molecular breeding many blast-resistant varieties have been developed. Conventional breeding for disease resistance is tedious, time consuming and mostly dependent on environment as compare to molecular breeding particularly marker assisted selection, which is easier, highly efficient and precise. For effective management of blast disease, breeding work should be focused on utilizing the broad spectrum of resistance genes and pyramiding genes and quantitative trait loci. Marker assisted selection provides potential solution to some of the problems that conventional breeding cannot resolve. In recent years, blast resistant genes have introgressed into Luhui 17, G46B, Zhenshan 97B, Jin 23B, CO39, IR50, Pusa1602 and Pusa1603 lines through marker assisted selection. Introduction of exotic genes for resistance induced the occurrence of new races of blast fungus, therefore breeding work should be concentrated in local resistance genes. This review focuses on the conventional breeding to the latest molecular progress in blast disease resistance in rice. This update information will be helpful guidance for rice breeders to develop durable blast resistant rice variety through marker assisted selection.
Submergence or flood is one of the major harmful abiotic stresses in the low-lying countries and crop losses due to waterlogging are considerably high. Plant breeding techniques, conventional or ...genetic engineering, might be an effective and economic way of developing crops to grow successfully in waterlogged condition. Marker assisted selection (MAS) is a new and more effective approach which can identify genomic regions of crops under stress, which could not be done previously. The discovery of comprehensive molecular linkage maps enables us to do the pyramiding of desirable traits to improve in submergence tolerance through MAS. However, because of genetic and environmental interaction, too many genes encoding a trait, and using undesirable populations the mapping of QTL was hampered to ensure proper growth and yield under waterlogged conditions Steady advances in the field of genomics and proteomics over the years will be helpful to increase the breeding programs which will help to accomplish a significant progress in the field crop variety development and also improvement in near future. Waterlogging response of soybean and major cereal crops, as rice, wheat, barley, and maize and discovery of QTL related with tolerance of waterlogging, development of resistant variety, and, in addition, future prospects have also been discussed.
In the development of new varieties, physicochemical properties such as grain quality, milling, and chemical content are important. Twenty rice hybrids were tested in various environments in this ...study. Using multivariate and univariate models, the major goal is to identify rice hybrids with acceptable physicochemical properties and high stability. According to the ANOVA, variance due to season×genotype×location revealed a significant difference in length to width ratio, head rice recovery, and amylose content. Milled grain length and width varied from 6.64 to 7.32 mm and 1.78 to 2.06 mm, respectively, throughout the environments. The head rice recovery and amylose content, on the other hand, varied from 84.83 to 94.68% and 16.51 to 22.21%, respectively. The stability analysis for head rice trait using genotype superiority, static stability, Wrickie ecovelance, Nassar and Huehn, AMMI stability value, and coefficient of variation stability analysis, revealed that hybrids G2, G13, G8, G16, G7, G9, G6, G17, and G18 were the most stable. For Amylose content, hybrids G7, G4, G19, G10, G5, G17, G3, G12 and G11 were significantly stable. Except for G5, all hybrids demonstrated stable performance in the multivariate stability analysis for head rice recovery. Similarly, hybrids G3, G4, G5, and G7 responded in minimum GE interaction in multivariate analysis for amylose content. This discovery can help breeders pick potential hybrids by identifying the physicochemical attribute expression that was examined in different conditions.
One of the most valuable traits in high-quality rice is aroma or fragrance, which is important for consumer preference and global trade. Aromatic rice is unique and recognized as a badge of honor and ...an asset in many countries. Among more than 100 volatile components, 2-acetyl-1-pyrroline (2AP) is believed to be the main aromatic compound in rice. The principal gene contributing to 2AP is badh2, which was mapped on chromosome 8 by map-based cloning. A deletion in this gene truncates and makes non-functional the BADH2 protein. Thus, the mutant badh2 transcript leads to 2AP accumulation in aromatic rice. The discovery of the gene has led to the clarification of the biochemistry, molecular genetics and evolution of fragrant rice. The breeding of fragrant rice is now faster because of marker assisted selection (MAS), which is based on recognized genes. For a more extensive elucidation of all effective and fundamental factors contributing to rice fragrance, it is essential to further explore target quantitative trait loci (QTLs) and their inheritance and locations.
This study was conducted to determine the combining ability and heritability of rice grain quality traits. Some grain quality traits such as grain length, grain width, milled grain length, milled ...grain width, length to width ratio, milled rice recovery, head rice recovery, amylose and gel consistency were analyzed using a full diallel mating design in Malaysian rice varieties. This study was commenced by crossing the selected rice varieties based on a full diallel mating design. The F1 was harvested at the end of the season. In the following season, the crossed, reciprocal and parental lines were planted in randomly complete block design with three replications. Analysis of variance indicated that genotypes were significantly different for all traits evaluated except for milled rice recovery. Mean square values for general combining ability were significant for the evaluated grain quality traits which indicated the importance of additive gene effects in inheritance of these traits. The specific combining ability effects were significant for several populations derived from crosses involving MR 263, MR 267, MRQ 74, Q 85 and MRQ 76. Reciprocal effects were significant for eight combinations for grain quality traits. Broad sense heritability showed that the AMYL and GC had the lowest value. The GL showed moderate value while GW, MGL, MGW, LW and HRR were the highest. The narrow sense heritability for grain physical properties was higher than grain chemical properties. The highest heritability was observed for LW, MGL, HRR, MGW, GW and GL.
This study was conducted to determine the combining ability and heritability of rice grain quality traits. Some grain quality traits such as grain length, grain width, milled grain length, milled ...grain width, length to width ratio, milled rice recovery, head rice recovery, amylose and gel consistency were analyzed using a full diallel mating design in Malaysian rice varieties. This study was commenced by crossing the selected rice varieties based on a full diallel mating design. The F1 was harvested at the end of the season. In the following season, the crossed, reciprocal and parental lines were planted in randomly complete block design with three replications. Analysis of variance indicated that genotypes were significantly different for all traits evaluated except for milled rice recovery. Mean square values for general combining ability were significant for the evaluated grain quality traits which indicated the importance of additive gene effects in inheritance of these traits. The specific combining ability effects were significant for several populations derived from crosses involving MR 263, MR 267, MRQ 74, Q 85 and MRQ 76. Reciprocal effects were significant for eight combinations for grain quality traits. Broad sense heritability showed that the AMYL and GC had the lowest value. The GL showed moderate value while GW, MGL, MGW, LW and HRR were the highest. The narrow sense heritability for grain physical properties was higher than grain chemical properties. The highest heritability was observed for LW, MGL, HRR, MGW, GW and GL.
This study was conducted to investigate the genotype by environment (G×E) interaction of 20 rice hybrids tested in eight environments which include four locations and two different cropping seasons ...in Malaysia. The parameter was observed on yield per ha, number of panicles per plant, number of filled grains per panicle, and thousand-grain weight. Data analysis was used by ANOVA and stability measurement according to AMMI and GGE biplot graph. The ANOVA indicated that all studied phenotypic showed significantly different in variance genotypes, season, location, location × season, genotype × season, genotype × location × season. The most promising hybrids were G19, G3, G18, G13, G8, G7, and G14, resulting in a higher mean yield per ha. The multivariate stability analysis defined those hybrids divided into three categories. The first category is hybrids with high mean yield and wide adaptability (G19, G18, G3 and G4), the second category is the hybrid exhibiting high mean yield and is suitable for a specific environment (G12) and lastly, a hybrid with low yield and high stability (G9, G11 and G1). Hybrids with high yield and stable performance could be further evaluated in large-scale planting for prior release for commercial.
Rice is staple food and Malaysia is net importer of rice. Import is increasing yearly and after a drastic increase in price experience 2008, the government has set up a policy is to ensure supply at ...reasonable price. To stabilise and reduce price, rice production must be increased. Among the strategies recommended are: 1) prevention of crop failure due to outbreak of pest and diseases as well as climatic variations, 2) increase average yield through adoption of technologies and development of new technologies 3) increase production in marginal area through development of new varieties. In breeding for new varieties, it is important to have a good germplasm collection, conservation and documentation.
With the ever-increasing global demand for high quality rice in both local production regions and with Western consumers, we have a strong desire to understand better the importance of the different ...traits that make up the quality of the rice grain and obtain a full picture of rice quality demographics. Rice is by no means a ‘one size fits all’ crop. Regional preferences are not only striking, they drive the market and hence are of major economic importance in any rice breeding / improvement strategy. In this analysis, we have engaged local experts across the world to perform a full assessment of all the major rice quality trait characteristics and importantly, to determine how these are combined in the most preferred varieties for each of their regions. Physical as well as biochemical characteristics have been monitored and this has resulted in the identification of no less than 18 quality trait combinations. This complexity immediately reveals the extent of the specificity of consumer preference. Nevertheless, further assessment of these combinations at the variety level reveals that several groups still comprise varieties which consumers can readily identify as being different. This emphasises the shortcomings in the current tools we have available to assess rice quality and raises the issue of how we might correct for this in the future. Only with additional tools and research will we be able to define directed strategies for rice breeding which are able to combine important agronomic features with the demands of local consumers for specific quality attributes and hence, design new, improved crop varieties which will be awarded success in the global market.
After yield, quality is one of the most important aspects of rice breeding. Preference for rice quality varies among cultures and regions; therefore, rice breeders have to tailor the quality ...according to the preferences of local consumers. Rice quality assessment requires routine chemical analysis procedures. The advancement of molecular marker technology has revolutionized the strategy in breeding programs. The availability of rice genome sequences and the use of forward and reverse genetics approaches facilitate gene discovery and the deciphering of gene functions. A well-characterized gene is the basis for the development of functional markers, which play an important role in plant genotyping and, in particular, marker-assisted breeding. In addition, functional markers offer advantages that counteract the limitations of random DNA markers. Some functional markers have been applied in marker-assisted breeding programs and have successfully improved rice quality to meet local consumers' preferences. Although functional markers offer a plethora of advantages over random genetic markers, the development and application of functional markers should be conducted with care. The decreasing cost of sequencing will enable more functional markers for rice quality improvement to be developed, and application of these markers in rice quality breeding programs is highly anticipated.
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