Multiple-Herbicide resistance in a 2,4-D–Resistant waterhemp (Amaranthus tuberculatus) population from Nebraska

A 2,4-D-resistant tall waterhemp population (FS) from Nebraska was evaluated for resistance to other TIR1 auxin receptor herbicides and to herbicides having alternative mechanisms of action using greenhouse bioassays and genetic markers. Atrazine, imazethapyr, lactofen, mesotrione, glufosinate, and glyphosate were applied in a single-dose bioassay, and tissue was collected from marked plants for genetic analysis. The FS population was not injured by atrazine or by imazethapyr. Approximately 50% of the plants survived lactofen and were actively growing 28 d after treatment. The population was susceptible to mesotrione, glufosinate, and glyphosate. Ametryn, chlorimuron-ethyl, 2,4-D, aminocyclopyraclor, aminopyralid, and picloram were applied in dose–response studies. The FS population was sensitive to ametryn, and the Ser-264-Gly substitution in the D1 protein was not detected, suggesting the lack of response to atrazine is not due to a target-site mutation. The FS population exhibited less than 50% injury to chlorimuron-ethyl at application rates 20 times the labeled use rate. The Ser-653-Asn acetolactate synthase (ALS) substitution, which confers resistance to imidazolinone herbicides, was present in the FS population. However, this does not explain the lack of response to the sulfonylurea herbicide, chlorimuron-ethyl. Sequencing of a portion of the PPX2L gene did not show the ΔG210 mutation that confers resistance to protoporphyrinogen oxidase–inhibiting herbicides, suggesting that other factors were responsible for waterhemp survival after lactofen application. The FS population was confirmed to be at least 30-fold resistant to 2,4-D relative to the susceptible populations. In addition, it was at least 3-fold less sensitive to aminopyralid and picloram, two other TIR1 auxin receptor herbicides, than the 2,4-D-susceptible populations were. These data indicated that the FS population contains both target and non–target site mechanisms conferring resistance to herbicides spanning at least three mechanisms of action: TIR1 auxin receptors, ALS inhibitors, and photosystem II inhibitors.EEA ParanáFil: Crespo, Roberto J. University of Nebraska–Lincoln. Department of Agronomy and Horticulture; Estados UnidosFil: Wingeyer, Ana Beatriz. Instituto Nacional de Tecnología Agropecuaria (INTA). Estación Experimental Agropecuaria Paraná; Argentina. Consejo Nacional de Investigaciones Científicas y Técnicas; ArgentinaFil: Kruger, Greg R. University of Nebraska–Lincoln. West Central Research and Extension Center; Estados UnidosFil: Riggins, Chance W. University of Illinois. Department of Crop Sciences; Estados UnidosFil: Tranel, Patrick J. University of Illinois. Department of Crop Sciences; Estados UnidosFil: Bernards, Mark L. University of Nebraska–Lincoln. Department of Agronomy and Horticulture; Estados Unido

Somatic mutations of SUZ12 in malignant peripheral nerve sheath tumors

Neurofibromatosis 1 is a hereditary syndrome characterized by the development of numerous benign neurofibromas, a small subset of which progress to malignant peripheral nerve sheath tumors (MPNSTs). To better understand the genetic basis for MPNSTs, we performed genome-wide or targeted sequencing on 50 cases. Sixteen MPNSTs but none of the neurofibromas tested were found to have somatic mutations in SUZ12, implicating it as having a central role in malignant transformation

Search Engine Competition with Network Externalities

The market for Internet search is not only economically and socially important, it is also highly concentrated. Is this a problem? We study the question whether "competition is only a free click away". We argue that the market for Internet search is characterized by indirect network externalities and construct a simple model of search engine competition, which produces a market share development that fits the empirically observed development since 2003 well. We find that there is a strong tendency towards market tipping and, subsequently, monopolization, with negative consequences on economic welfare. Therefore, we propose to require search engines to share their data on previous searches. We compare the resulting "competitive oligopoly" market structure with the less competitive current situation and show that our proposal would spur innovation, search quality, consumer surplus, and total welfare. We also discuss the practical feasibility of our policy proposal and sketch the legal issues involved.