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311.
L A Denner N L Weigel B L Maxwell W T Schrader B W O'Malley 《Science (New York, N.Y.)》1990,250(4988):1740-1743
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Kossi Lorimpo Adjah Maxwell Darko Asante Aboubacar Toure Mawuli Aziadekey Francis Osei Amoako-Andoh Michael Frei Yacouba Diallo Komi Agboka 《水稻科学》2022,29(6):512-521
Rice plays a paramount role in food and nutrition security in many West African countries. Despite the doubling of production during the last decade, rice consumption has grown faster, creating a deficit between the demand and supply. Although the West African sub-region remains the main rice-producing centre on the continent, production is severely hampered by biotic and abiotic stresses. Drought is one of the factors that most severely reduce grain yields of rice. Systems of production need to be established in order to mitigate yield loss as a result of drought. This review discusses the effects of drought on rice production in West Africa and its mitigation with an emphasis on the improvement of tolerance to drought stress. Yield stability can be achieved by developing drought-tolerant varieties through several processes encompassing profiling of known QTLs and identification of new ones, marker-assisted selection, genomic selection, and extensive multi-locational yield trials. We suggest a comprehensive strategy for breeding drought-tolerant rice varieties in West Africa. 相似文献
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The rhodium porphyrin-catalyzed cyclopropanation of alkenes by ethyl diazoacetate (EDA) is representative of a number of metal-mediated cyclopropanation reactions used widely in organic synthesis. The active intermediate in these reactions is thought to be a metal carbene complex, but evidence for the involvement of metal-olefin pi complexes has also been presented. Low-temperature infrared and nuclear magnetic resonance spectroscopies have been used to characterize a rhodium porphyrin-diazoalkyl adduct that results from the stoichiometric condensation of the catalyst and EDA. Optical spectroscopy suggests that this complex is the dominant steady-state species in the catalytic reaction. This compound decomposes thermally to provide cyclopropanes in the presence of styrene, suggesting that the carbene is indeed the active intermediate. Metal-alkene pi complexes have also been detected spectroscopically. Kinetic studies suggest that they mediate the rate of carbene formation from the diazoalkyl complex but are not attacked directly by EDA. 相似文献
316.
Crampton JS Beu AG Cooper RA Jones CM Marshall B Maxwell PA 《Science (New York, N.Y.)》2003,301(5631):358-360
To interpret changes in biodiversity through geological time, it is necessary first to correct for biases in sampling effort related to variations in the exposure of rocks and recovery of fossils with age. Data from New Zealand indicate that outcrop area is likely to be a reliable proxy of rock volume in both stable cratonic regions, where the paleobiodiversity record is strongly correlated with relative sea level, and on tectonically active margins. In contrast, another potential proxy, the number of rock formations, is a poor predictor of outcrop area or sampling effort in the New Zealand case. 相似文献
317.
David G. Fisher Kenneth L. Deahl Maxwell V. Rainforth 《American Journal of Potato Research》2002,79(4):281-293
Horizontal resistance (HR) was assessed as a strategy to reduce potato defoliation by the Colorado potato beetle (CPB). Hybrids amongSolanum tuberosum varieties grown in Iowa were first evaluated with a detached leaflet feeding bioassay. Beginning in 1998, resistance was increased annually over three years by intermating and selecting the most resistant l%–2% of each generation of 300–400 plants using the bioassay. When C (= mg leaf tissue consumed* neonate larva-1 over 48 h) was measured for the 1% most-resistant genotypes of all generations grown side by side in 2000, it ranged from 6.1 mg* larva-1 in the parents to 2.3 for progeny of the F3 generation compared to 2.7 in ND2858-1, a resistant check. Field trials in Wisconsin showed less defoliation in the F1 and F2 selected genotypes than in the parents. A second breeding program using moreS. tuberosum parents with greater genetic diversity, and much larger breeding populations, resulted in significantly faster accumulation of resistance, further suggesting that recurrent mass selection is effective. Foliar glycoalkaloid analyses revealed low levels of solanine and chaconine in the F3 selections; no leptines or leptinines were detected. Because the parents wereS. tuberosum varieties in which vertical resistance to CPB is unknown, and because the resistance to feeding from parents to the F3 resistant plants was linear and gradual while ranging from initially very low to considerably higher in the third year, horizontal resistance is strongly implicated. The development of a significant degree of resistance after three rounds of breeding using relatively small breeding populations suggests that HR can be developed from varieties ofSolanum tuberosum lacking initial high levels of resistance to CPB. 相似文献