BackgroundSoybean cyst nematode (Heterodera glycines, SCN) is the most economically damaging pathogen of soybean (Glycine max) in the U.S. The Rhg1 locus is repeatedly observed as the quantitative trait locus with the greatest impact on SCN resistance. The Glyma18g02680.1 gene at the Rhg1 locus that encodes an apparent leucine-rich repeat transmembrane receptor-kinase (LRR-kinase) has been proposed to be the SCN resistance gene, but its function has not been confirmed. Generation of fertile transgenic soybean lines is difficult but methods have been published that test SCN resistance in transgenic roots generated with Agrobacterium rhizogenes.ResultsWe report use of artificial microRNA (amiRNA) for gene silencing in soybean, refinements to transgenic root SCN resistance assays, and functional tests of the Rhg1 locus LRR-kinase gene. A nematode demographics assay monitored infecting nematode populations for their progress through developmental stages two weeks after inoculation, as a metric for SCN resistance. Significant differences were observed between resistant and susceptible control genotypes. Introduction of the Rhg1 locus LRR-kinase gene (genomic promoter/coding region/terminator; Peking/PI 437654-derived SCN-resistant source), into rhg1- SCN-susceptible plant lines carrying the resistant-source Rhg4+ locus, provided no significant increases in SCN resistance. Use of amiRNA to reduce expression of the LRR-kinase gene from the Rhg1 locus of Fayette (PI 88788 source of Rhg1) also did not detectably alter resistance to SCN. However, silencing of the LRR-kinase gene did have impacts on root development.ConclusionThe nematode demographics assay can expedite testing of transgenic roots for SCN resistance. amiRNAs and the pSM103 vector that drives interchangeable amiRNA constructs through a soybean polyubiqutin promoter (Gmubi), with an intron-GFP marker for detection of transgenic roots, may have widespread use in legume biology. Studies in which expression of the Rhg1 locus LRR-kinase gene from different resistance sources was either reduced or complemented did not reveal significant impacts on SCN resistance.

No abstract

There is increasing public concern to reduce nitrate pollution to groundwater, especially in sandy soils. Strategies to reduce nitrate leaching are developed to increase N use efficiency, reduce groundwater pollution, and increase tuber yield. A growing interest in N management should consider management strategies for N supply, soil moisture for transport, and crop N demand that are economical and compatible with local production systems. We present a review of the literature on conventional and innovative strategies for N, irrigation, and crop management for potato production in reducing N leaching in sandy soils. The amount of fertilizer-N should be decided based on an integrated evaluation of soil organic matter content, soil texture, residual soil N, crop residues, credit to organic N sources, crops to be grown including varieties and crop physiological needs, cropping systems, yield potential, water management, and N concentrations in irrigation water. Research advances have no quick fix for controlling NO 3 leaching to groundwater. However, the best combination of proven strategies can reduce leaching potential significantly.Resumen Existe una preocupación pública en aumento para reducir la contaminación de nitrato en el agua del subsuelo, especialmente en suelos arenosos. Se han desarrollado estrategias para reducir la lixiviación de nitratos para aumentar el uso eficiente de N, reducir la contaminación del agua del subsuelo, y para aumentar el rendimiento de tubérculo. Un interés en aumento en manejo de N debería de considerar estrategias de manejo para suministro de N, humedad del suelo para el transporte, y demanda de N del cultivo que sean económicas y compatibles con los sistemas locales de producción. Presentamos una revisión de la literatura en las estrategias convencionales e innovativas para el manejo de N, riego y del cultivo para producción de papa en la reducción de la lixiviación de N en suelos arenosos. La cantidad del fertilizante nitrogenado deberá decidirse con base a una evaluación integrada del contenido de materia orgánica en el suelo, textura, N residual, residuos de cosecha, reconocimiento a las fuentes de N orgánico, cultivos a sembrarse incluyendo variedades y necesidades fisiológicas del cultivo, sistemas de cultivo, potencial de rendimiento, manejo del agua, y concentraciones de N en el agua de riego. Los avances en investigación no tienen un remedio rápido para controlar la lixiviación de NO3 al agua del subsuelo. No obstante, la mejor combinación de estrategias probadas pueden reducir significativamente el potencial de lixiviación.

No abstract