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Wageningen Universiteit (2004)

Genetic, physiological and modelling approaches towards tolerance to salinity and low nitrogen supply in rice (Oryza sativa L.)

Manneh, B.

Titre : Genetic, physiological and modelling approaches towards tolerance to salinity and low nitrogen supply in rice (Oryza sativa L.)

Auteur : Manneh, B.

Université de soutenance : Wageningen Universiteit

Grade : PhD thesis 2004

Résumé
Meeting the world’s requirement for rice production in the future needs a dual approach : 1. the theoretical yield potential of rice should increase and 2.theyield gaps should be reduced especially in marginal areas where stresses such as salinity, low supply of plant nutrients, droughts and flooding often limit yields. Rice breeding used to be geared towards developing cultivars for high-input management conditions and these cultivars may not be suited to low input environments. In regions such asAfrica, where most of the rice is produced under low-input conditions, breeding should be targeted at rice cultivars that are tolerant to the main stresses encountered in the rice agro-ecosystems. Soil salinity and inadequate supply of plant nutrients (especially nitrogen) are two major stresses limiting rice yields in The Gambia where this study was undertaken. The aim of this study was to determine appropriate selection methods for rice across a range of environments and to identify options at the level of yield components and physiological traits to increase rice yield potentials under both high and low input conditions. For this purpose, a segregating population of rice comprising Recombinant Inbred Lines (RILs) developed from the cross of a high-yielding, semi-dwarf, salt-sensitive cultivar, IR29 and a tall, traditional, salt-tolerant cultivar, Pokkali, was grown in fresh water (EC of 0.15 dS m-1) and saline (EC of 8 dS m-1) conditions with 0 or 100 kg ha-1nitrogen. Analyses of variance revealed significant genotype × environment interaction for yield and for the four yield components, number of panicles m-2, total number of grains per panicle, thousand grainweightand percent spikelet fertility, across the range of test environments. Inter-environmental correlations for grain yield between the 0 and 100 kg ha-1N fertilizer regimes were high and significant in both fresh and saline water signifying that in the lowland, rice can be bred for general adaptability to different N fertilizer levels. However, the inter-environmental correlations for yield between fresh water and saline conditions, especially for the highest yielding cultivars in either environment, were low. This suggests that different sets of rice cultivars should be bred for cultivation in fresh water or saline environments. Analysis of the relationships between yield and yield components by means of regression revealed that generally in fresh waterenvironments,yield was sink-limited and that grain number attributes (comprising number of panicles m-2and total number of grains per panicle) of rice should be enhanced in order to boost yield potential under fresh water conditions. In saline environments, however, salt stress strongly limits assimilate production and translocation. To increase rice yield potential in saline environments, cultivars with better grain filling attributes (comprising grain weight and spikelet fertility) should be developed. The N fertilizer regime influenced the relative importance of panicles m-2and total number of grains per panicle in fresh water and of individual grain weight and spikelet fertility in saline environments, for yield determination. Through molecular marker analysis, putative quantitative trait loci (QTLs) were detected for grain yield and yield components in all four test environments. Overall, markers accounted for 23%-60% of the variation in yield and yield components. Markers associated with more than one trait had either similar or opposite effects on the traits. For all five traits studied, most markers were expressed in only one environment implying strong environmental specificity in expression of the QTLs for rice yield and yield components. Marker-assisted selection, based on AFLP markers, was successfully conducted for grain yield of rice in all four test environments over two years.

Mots clés : oryza sativa / rice / simulation models / salinity / plant physiology / nitrogen

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Page publiée le 24 mars 2007, mise à jour le 14 janvier 2018