Aluminium toxicity and problems concerning tolerance and ecological performance are discussed briefly. Differential tolerance of plant genotypes to aluminium stress is a more promising approach to increase our understanding of aluminium tolerance in plants. Induction of Al tolerance and its characterization are also reviewed. The cytogenetic effects of aluminium on plants are discussed in depth. Efforts have been made to compare the relative sensitivity of various plant species including micro-and macro-flora to aluminium, and uptake and transport of aluminium are taken into account with phytotoxicity and their interactions with nutrients. Present knowledge concerning the physiology and biochemistry of aluminium with regard to phytotoxicity is discussed and offers some ways for increasing the Al tolerance. This review shows the complexity of the toxicity mechanisms of trace elements. aluminium / phytotoxicity / tolerance / Al stress Résumé-Toxicité de l'aluminium pour les plantes : mise au point. L'article fait le point sur la toxicité de l'aluminium, la tolérance des plantes à cet élément et leur performances écologiques. La tolérance au stress provoqué par l'aluminium varie d'un génotype de plante à l'autre et cette approche est prometteuse pour améliorer notre compréhension de la tolérance à l'aluminium. L'induction de la tolérance à l'aluminium et sa caractérisation sont également passées en revue. Les effets cytogénétiques de l'aluminium sur les plantes font l'objet d'une discussion approfondie. On compare la sensibilité relative à l'aluminium des diverses espèces de plantes, de la macroflore à la microflore. On traite de l'absorption et du transport de l'aluminium, ainsi que de sa phytotoxicité et de ses interactions avec les nutriments. La connaissance actuelle concernant la physiologie et la biochimie de l'aluminium en relation avec la phytotoxicité est discutée et offre certaines possibilités pour accroître la tolérance à l'aluminium. Cette mise au point montre la complexité des mécanismes liés à la toxicité des éléments traces.
Rice blast disease caused by Magnaporthe oryzae is one of the most destructive disease causing huge losses to rice yield in different parts of the world. Therefore, an attempt has been made to find out the resistance by screening and studying the genetic diversity of eighty released rice varieties by National Rice Research Institute, Cuttack (NRVs) using molecular markers linked to twelve major blast resistance (R) genes viz Pib, Piz, Piz-t, Pik, Pik-p, Pikm Pik-h, Pita/Pita-2, Pi2, Pi9, Pi1 and Pi5. Out of which, nineteen varieties (23.75%) showed resistance, twenty one were moderately resistant (26.25%) while remaining forty varieties (50%) showed susceptible in uniform blast nursery. Rice varieties possessing blast resistance genes varied from four to twelve and the frequencies of the resistance genes ranged from 0 to 100%. The cluster analysis grouped the eighty NRVs into two major clusters at 63% level of genetic similarity coefficient. The PIC value for seventeen markers varied from 0 to 0.37 at an average of 0.20. Out of seventeen markers, only five markers, 195R-1, Pi9-i, Pita3, YL155/YL87 and 40N23r corresponded to three broad spectrum R genes viz. Pi9, Pita/Pita2 and Pi5 were found to be significantly associated with the blast disease with explaining phenotypic variance from 3.5% to 7.7%. The population structure analysis and PCoA divided the entire 80 NRVs into two sub-groups. The outcome of this study would help to formulate strategies for improving rice blast resistance through genetic studies, plant-pathogen interaction, identification of novel R genes, development of new resistant varieties through marker-assisted breeding for improving rice blast resistance in India and worldwide.
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