Search

The resistance of rice to its bacterial blight pathogen Xanthomonas oryzae pv. oryzae (Xoo) has both qualitative and quantitative components that were investigated using three near-isogenic line sets for four resistance (R) genes (Xa4, xa5, xa13, and Xa21) and 12 Xoo races. Our results indicate that these two resistance components of rice plants were associated with the properties of the R genes. The qualitative component of the R genes was reflected by their large effects against corresponding avirulent Xoo races. The quantitative component of the R genes was their residual effects against corresponding virulent races and their epistatic effects, which together could lead to high-level resistance in a race-specific manner. Our results revealed important differences between the different types of R genes. Two R genes, Xa4 and Xa21, showed complete dominance against the avirulent Xoo races and had large residual effects against virulent ones. They acted independently and cumulatively, suggesting they are involved in different pathways of the rice defensive system. The third R gene, xa5, showed partial dominance or additivity to the avirulent Xoo races and had relatively small but significant residual effects against the virulent races. In contrast, xa13 was completely recessive, had no residual effects against the virulent races, and showed more pronounced race specificity. There was a strong interaction leading to increased resistance between xa13 and xa5 and between either of them and Xa4 or Xa21, suggesting their regulatory roles in the rice defensive pathway(s). Our results indicated that high-level and durable resistance to Xoo should be more efficiently achieved by pyramiding different types of R genes.

A 2275-marker genetic map of rice (Oryza sativa L.) covering 1521.6 cM in the Kosambi function has been constructed using 186 [F.sub.2] plants from a single cross between the japonica variety Nipponbare and the indica variety Kasalath. The map provides the most detailed and informative genetic map of any plant. Centromere locations on 12 linkage groups were determined by dosage analysis of secondary, and telotrisomics using >130 DNA markers located on respective chromosome arms. A limited influence on meiotic recombination inhibition by the centromere in the genetic map was discussed. The main sources of the markers in this map were expressed sequence tag (EST) clones from Nipponbare callus, root, and shoot libraries. We mapped 1455 loci using ESTs; 615 of these loci showed significant similarities to known genes, including single-copy genes, family genes, and isozyme genes. The high-resolution genetic map permitted ns to characterize meiotic recombinations in the whole genome. Positive interference of meiotic recombination was detected both by the distribution of recombination number per each chromosome and by the distribution of double crossover interval lengths.

Secondary trisomics and telotrisomics representing the 12 chromosomes of rice were isolated from the progenies of primary trisomics. A large population of each primary trisomic was grown. Plants showing variation in gross morphology compared to the primary trisomics and disomic sibs were selected and analyzed cytologically at diakinesis and pachytene. Secondary trisomics for both arms of chromosomes 1, 2, 6, 7 and 11 and for one arm of chromosomes 4, 5, 8, 9 and 12 were identified. Telotrisomics for short arm of chromosomes 1, 8, 9 and 10 and for long arms of chromosomes 2, 3 and 5 were isolated. These secondary and telotrisomics were characterized morphologically and for breeding behavior. Secondary trisomics 2n + 1S [center dot] 1S, 2n + 1L [center dot] 1L, 2n + 2S [center dot] 2S, 2n + 2L [center dot] 2L, 2n + 6S [center dot] 6S, 2n + 6L [center dot] 6L and 2n + 7L [center dot] 7L are highly sterile, and 2n + 1L [center dot] IL, 2n + 2L [center dot] 2L and 2n + 7L [center dot] 7L do not set any seed even upon backcrossing. Telotrisomics are fertile and vigorous. Genetic segregation of 43 marker genes was studied in the [F.sub.2] or backcross progenies. On the basis of segregation data, these genes were delimited to specific chromosome arms. Correct orientation of 10 linkage groups was determined and centromere positions on nine linkage groups were approximated. A revised linkage map of rice is presented.

Abstract The major scientific advances of the last century featured the identification of the structure of DNA, the development of molecular biology and the technology to exploit these advances. These breakthroughs gave us new tools for crop improvement, including molecular marker-aided selection (MAS) and genetic modification (GM). MAS improves the efficiency of breeding programs, and GM allows us to accomplish breeding objectives not possible through conventional breeding approaches. MAS is not controversial and is now routinely used in crop improvement programs. However, the international debate about the application of genetic manipulation to crop improvement has slowed the adoption of GM crops in developing as well as in European countries. Since GM crops were first introduced to global agriculture in 1996, Clive James has published annual reports on the global status of commercialized GM crops as well as special reports on individual GM crops for The International Service for the Acquisition of Agri-biotech Applications (ISAAA). His 34th report, Global Status of Commercialized Biotech/ GM crops: 2011 [1] is essential reading for those who are concerned about world food security.

Ground water tables in Punjab are declining at alarming rates in most districts of Punjab. One of the major causes of declining water tables is the increased cropping intensity. Whereas cropping intensity in Punjab was only 120% until about 50 years ago, it is now 190%. With one crop per year, a balance was maintained between water extraction and aquifer recharge. With two crops per year, this balance has been altered. Homogenization of crops in the state has also exacerbated the problem. Even more serious threat to nation’s agriculture is climate change. Himalayan glaciers, which are water towers for our rivers, are retreating. This will reduce the water flow in our rivers. While the climate-change impact on our water availability is several years away, we must address immediate problem of declining water tables in the state. Suggested interventions include crop diversification, precision agriculture, including water saving technologies, and developing crop varieties with improved water-use efficiency. [ABSTRACT FROM AUTHOR]

Rice is the most important food crop. Worldwide, more than 3.5 billion people depend upon rice for more than 20% of their calories. Global rice demand is estimated to rise from 676 million tons in 2010 to 763 million tons in 2020 and to further increase to 852 million tons in 2035. This is an overall increase of 176 million tons in the next 25 years. To meet this challenge rice production on existing land must be increased. Grain production is largely influenced by the yield potential of rice varieties. Therefore, improvement in the yield potential of rice is the major strategy to increase world rice production. Various strategies to increase the yield potential include; (1) conventional hybridization and selection, (2) ideotype breeding, (3) hybrid breeding, (4) exploitation of wild species germplasm, (5) enhancement of photosynthesis, (6) genomic approaches and (7) physiological approaches. Rice has become a model plant for genetics and breeding research. Advances in molecular biology and genomics, proteomics and metabolics have opened new avenues to apply innovative approaches to rice breeding. Molecular-assisted selection (MAS) has become an integral component of germplasm improvement. A large number of genes/QTLs for various traits have been tagged with molecular markers to apply MAS for trait improvement. Genome sequence data have become an important source for detecting allelic variation. It is now possible to precisely understand the role of epigenetic changes in gene expression, thus understanding the stability of various stresses under changing environments. All these advances when integrated with conventional breeding will result in designer rice varieties to meet the challenges of rice food security in 21th century. [ABSTRACT FROM AUTHOR]

Primary and secondary trisomics as well as telotrisomics have been well characterized in rice morphologically and the transmission rates of extra chromosomes have been investigated. Primary trisomics have been utilized for associating genes and linkage groups with respective chromosomes. Secondary trisomics and telotrisomics were employed to associate genes with respective chromosome arms. As a result the positions of centromeres on the linkage maps could be pinpointed. Monosomic alien addition lines (MAALs) have a complete chromosome complement of Oryza sativa and a single chromosome of a wild species in genus Oryza. All the MAALs of O. officinalis and O. punctata have been produced. A partial set of MAALs of 5 other wild species of rice have also been produced. These aneuploid stocks of rice are useful not only for genetic study such as gene dosage analysis but also for rice breeding. [ABSTRACT FROM AUTHOR]

The author shares his journey from wheat fields of Punjab to orchards of California. His journey from a small Punjabi village and took him all over the world in pursuit of his passion-higher education and scientific achievement. He explains how sheafs of wheat were spread on the threshing floor and pairs of bullocks with a contraption called Phalla joked to them, were made to walk on them in a circular motion.

Changes in global biodiversity at the genetic level have proved difficult to determine for most organisms because of lack of standardized, repeated or historical data; this hampers the attempts to meet the convention on biological diversity (CBD) 2010 targets of reducing loss of genetic diversity, particularly of crop species. For rice, where germplasm and genetic data have been collected throughout South and Southeast Asia over many decades, contrary to popular opinion, we have been unable to detect a significant reduction of available genetic diversity in our study material. This absence of a decline may be viewed positively; over the 33-year timescale of our study, genetic diversity amongst landraces grown in traditional agricultural systems was still sufficiently abundant to be collected for ex situ conservation. However, if significant genetic erosion does take place in the future as a result of accelerating global warming and/or major changes in land use or agricultural practices, will it be catastrophic or gradual, and how will it be detected? We have shown a strong link between numbers of landraces collected (and therefore extant) and genetic diversity; hence, we have a clear indicator to detect loss of genetic diversity in the future. Our findings lend considerable support for ex situ conservation of germplasm; the more than substantial genetic resources already in genebanks are now safe. On the other hand, it is the germplasm growing in farmers' fields, continually adapting genetically to changing environmental conditions and evolving novel genetic forms, whose future has been much less certain but can now be effectively monitored using our criteria. [ABSTRACT FROM AUTHOR]