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  • 1
    Electronic Resource
    Electronic Resource
    A “defeated” rice resistance gene acts as a QTL against a virulent strain of Xanthomonas oryzae pv. oryzae (1999)
    Springer
    Molecular genetics and genomics 261 (1999), S. 58-63 
    Details
    ISSN: 1617-4623
    Keywords: Key wordsOryza sativa L. ; Gene mapping ; Quantitative trait loci (QTLs) ; Host-pathogen co-evolution ; Stabilizing selection
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Abstract The genetic components responsible for qualitative and quantitative resistance of rice plants to three strains (CR4, CXO8, and CR6) of Xanthomonas oryzae pv. oryzae (Xoo) were investigated using a set of 315 recombinant inbred lines (RILs) from the cross Lemont (japonica) × Teqing (indica) and a complete linkage map with 182 well distributed RFLP markers. We mapped a major gene (Xa4) and ten quantitative trait loci (QTLs) which were largely responsible for segregation of the resistance phenotype in the RILs. The Teqing allele at the Xa4 locus, Xa4 T , acted as a dominant resistance gene against CR4 and CXO8. The breakdown of Xa4 T -associated resistance mediated by the mutant allele at the avrXa4 locus in the virulent strain CR6 results from significant changes in both gene action (lose of dominance) and the magnitude of gene effect (≈50% reduction). Nevertheless, Xa4 T still acted as a recessive QTL with a significant residual effect against CR6. The mutant alleles at the avrXa4 locus in CXO8 and CR6 that lead to a reduction in effect, or “breakdown”, of Xa4 T were apparently accompanied by corresponding penalties for their fitness. The quantitative component of resistance to Xoo in the RILs was largely due to a number of resistance QTLs. Most resistance QTLs mapped to genomic locations where major resistance genes and/or QTLs for resistance to Xoo, blast and sheath blight were identified in the same cross. Most QTLs showed consistent levels of resistance against all three Xoo strains. Our results suggest that a high level of durable resistance to Xoo may be achieved by the cumulative effects of multiple QTLs, including the residual effects of “defeated” major resistance genes.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/s004380050941
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  • 2
    Electronic Resource
    Electronic Resource
    Model simulations of spatial distributions and daily totals of photosynthesis in Eucalyptus grandis canopies (1991)
    Springer
    Oecologia 88 (1991), S. 494-503 
    Details
    ISSN: 1432-1939
    Keywords: Eucalyptus grandis ; Photosynthesis modelling ; Canopy light climate ; Nitrogen use efficiency ; Light use efficiency
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Summary A simulation model for radiation absorption and photosynthesis was used to test the hypothesis that observed nonuniform distributions of nitrogen concentrations in young Eucalyptus grandis trees result in greater amounts of daily assimilation than in hypothetical trees with uniform N distributions. Simulations were performed for trees aged 6, 9, 12 and 16 months which had been grown in plantations under a factorial combination of two levels of fertilization and irrigation. Observed leaf N distribution patterns yielded daily assimilation rates which were only marginally greater (〈5%) than for hypothetical trees with uniform distributions. Patterns of assimilation distribution in individual tree crowns closely resembled those for absorbed radiation, rather than for N. These conclusions were unaffected by three choices of alternative leaf area density distributions. The simulation model was also used to calculate hourly and daily rates of canopy assimilation to investigate the relative importance of radiation absorption and total canopy nitrogen on assimilation. Simulated hourly rates of carbon assimilation were often lightsaturated, whereas daily carbon gain was directly proportional to radiation absorbed by the tree crown and to total mass of N in the leaves. Leaf nitrogen concentrations determined photosynthetic capacity, whereas total leaf area determined the amount of radiation absorbed and thus the degree to which capacity was realized. Observed total leaf area and total crown N were closely correlated. The model predicted that nitrogen use efficiences (NUE, mol CO2 mol−1 N) were 60% higher for unfertilized than for fertilized trees at low levels of absorbed photosynthetically active radiation (PAR). Nitrogen use efficiency was dependent on fertilizer treatment and on the amount of absorbed PAR; NUE declined with increasing absorbed PAR, but decreased more rapidly for unfertilized than for fertilized trees. Annual primary productivity was linearly related to both radiation absorbed and to mass of N in the canopy.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00317711
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