RESPONSE OF SUB1 INTROGRESSION LINES OF RICE TO VARIOUS FLOODING CONDITIONS

Two types of floods can be happen in rice crops, i.e. flash floods and  stagnant floods. Flash floods cause complete submergence for up to 2 weeks, while stagnant floods (SF) could partially submerge part of rice  plant. To overcome yield loss due to the floods, introgression of SUB1 gene, known as a gene suppressing cell elongation and carbohydrate  metabolism, to rice genotype can increase plant tolerance to complete submergence for 10 days or more. The study aimed to evaluate the response of 18 rice genotypes, including the recently developed sixth pair SUB1 near isogenic lines (NILs) of mega-rice varieties (Swarna, Sambha Mahsuri, IR64, TDK1, BR11, and CR1009), to various flooding conditions. The rice genotypes were planted at field ponds at Los Banos, Philippines, in the wet season (WS) of 2009. The treatments were 15 days  submergence, SF, SF follows submergence and normal conditions. Each treatment was arranged in completely randomized block design with threereplications. The results showed that the SUB1 introgression rice lines had higher survival compared to the non-SUB1 and did not much elongate their shoots during submergence. Nevertheless, under SF the rice genotypes should elongates their shoots to allow restoring contact with the air. SF and SF follows submergence decreased the panicle number, grainnumber per panicle and panicle fertility. Consequently, the yield declined. It suggests that sensitive genotypes are mostly sourcelimited during grain filling. The SUB1 introgression lines had higher chlorophyll concentration and less depletion in soluble sugar and starch after submergence. Under SF, soluble sugar and starch contents between the SUB1 NILs and  non-SUB1 lines were not significantly different. Introgression of the SUB1 into high-yielding varieties improved submergence tolerance without affecting yield potential. The study indicates that introgression of the SUB1 into taller type rice varieties should be done to compensate the effect of suppressed elongation

Genetic Parameters of Some Characters and Their Correlation with Rice Grain Yield in Relation to the Plant Adaptability to Semi-Deep Stagnant Flooding Condition

Stagnant flooding (SF) is a major problem in floodprone rice ecosystem where the depth of flood water ranging from 20-50 cm in the entire seasons. In Indonesia this kind of water stress can be found in swampy basin area or Rawa Lebak. A study was conducted to determine the genetic parameters related to rice plant adaptability to SF. Eighteen rice genotypes including the recently developed 6 pairs of SUB1 near isogenic lines (NILs) of widely planted varieties and checks were tested under 50 cm depth of SF in the 2009 wet season at Los Banos, Philippines. The results showed that most of genotypes showed different responses on morphological and agronomical characters under SF and normal conditions. Most of the SUB1 NILs had lower grain yields than their respective parents. This was because SUB1 suppressed shoot elongation and less restoring contact with the air. Some SUB1 lines such as PSBRc68 and IR70181-32, however, produced high grain yields under this condition. Under SF condition, rice genotypes required shoot elongation to allow restoring contact with the air, therefore the traits that related to growth attributes such as shoot weight, leaf weight, LAI, stem diameter, plant high, and tiller number were strongly correlated with the grain yields. These traits also had broad genetic variability, high heritability, and strong correlation with grain yields. Selection under real stress SF conditions was effective to obtain high yielding genotypes and also tolerant

Rice Molecular Breeding Laboratories in the Genomics Era: Current Status and Future Considerations

Using DNA markers in plant breeding with marker-assisted selection (MAS) could greatly improve the precision and efficiency of selection, leading to the accelerated development of new crop varieties. The numerous examples of MAS in rice have prompted many breeding institutes to establish molecular breeding labs. The last decade has produced an enormous amount of genomics research in rice, including the identification of thousands of QTLs for agronomically important traits, the generation of large amounts of gene expression data, and cloning and characterization of new genes, including the detection of single nucleotide polymorphisms. The pinnacle of genomics research has been the completion and annotation of genome sequences for indica and japonica rice. This information—coupled with the development of new genotyping methodologies and platforms, and the development of bioinformatics databases and software tools—provides even more exciting opportunities for rice molecular breeding in the 21st century. However, the great challenge for molecular breeders is to apply genomics data in actual breeding programs. Here, we review the current status of MAS in rice, current genomics projects and promising new genotyping methodologies, and evaluate the probable impact of genomics research. We also identify critical research areas to “bridge the application gap” between QTL identification and applied breeding that need to be addressed to realize the full potential of MAS, and propose ideas and guidelines for establishing rice molecular breeding labs in the postgenome sequence era to integrate molecular breeding within the context of overall rice breeding and research programs

IR64: a high-quality and high-yielding mega variety

Abstract High-yielding varieties developed in the 1960s and 1970s at the International Rice Research Institute (IRRI) and elsewhere benefited farmers and the public, ultimately increasing yields and reducing the cost of rice to consumers. Most of these varieties, however, did not have the optimum cooking quality that was possessed by many of the traditional varieties they replaced. In 1985, the IRRI-developed indica variety IR64 was released in the Philippines. In addition to its high yield, early maturity and disease resistance, it had excellent cooking quality, matching that of the best varieties available. These merits resulted in its rapid spread and cultivation on over 10 million ha in the two decades after it was released. It has intermediate amylose content and gelatinization temperature, and good taste. It is resistant to blast and bacterial blight diseases, and to brown planthopper. Because of its success as a variety, it has been used extensively in scientific studies and has been well-characterized genetically. Many valuable genes have been introduced into IR64 through backcross breeding and it has been used in thousands of crosses. Its area of cultivation has declined in the past 10 years, but it has been replaced by a new generation of high-quality varieties that are mostly its progeny or relatives. Continued basic studies on IR64 and related varieties should help in unraveling the complex genetic control of yield and other desirable traits that are prized by rice farmers and consumers