JSTOR is a not-for-profit service that helps scholars, researchers, and students discover, use, and build upon a wide range of content in a trusted digital archive. We use information technology and tools to increase productivity and facilitate new forms of scholarship. For more information about JSTOR, please contact support@jstor.org. This content downloaded from 169.230.243.252 on Tue SUMMARY(1) The effects of clipping (simulated grazing) and grazing by a chrysomelid beetle, Gastrophysa viridula, on plants of two species of Rumex were investigated.(2) Although Gastrophysa viridula feeds on both Rumex obtusifolius and Rumex crispus in the field, the preference is for R. obtusifolius.(3) Moderate levels of grazing or clipping had no significant effects on plants of either species when competing intraspecifically.(4) In the conditions of the experiments, R. obtusifolius grew better when competing interspecifically with R. crispus than when competing intraspecifically, whilst the reverse was found for R. crispus.(5) This advantage of R. obtusifolius was removed by moderate levels of clipping or grazing. Clipping removed the competitive disadvantage of R. crispus but moderate grazing enhanced it.(6) Heavy grazing significantly reduced leaf area, leaf dry weight, root dry weight and whole plant dry weight of R. obtusifolius and R. crispus grown alone.(7) Rumex obtusifolius responded to heavy grazing by an increase in the root: shoot ratio, whereas R. crispus responded by a decrease in this ratio.(8) There was a significant interference interaction between interspecific competition and heavy grazing in R. crispus. This was especially marked below ground.(9) The possible relevance of these findings to observations on the distribution of the two Rumex species in the field is discussed. It is concluded that there may be circumstances in which grazing by Gastrophysa viridula may affect the distribution of Rumex crispus, and that this is more likely to be the case if it is growing in the presence of R. obtusifolius.

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Artemisinin concentration declined beyond an optimal point with increasing plant nitrogen concentration. Maximization of artemisinin yield (amount per plant) requires optimization of plant biomass via control of nitrogen nutrition.

The antimalarial drug artemisinin (ART) is commercially extracted from the medicinal plant Artemisia annua L. Here, we report the screening of 70 A. annua plants representing 14 diverse germplasm accessions sourced from around the world, and identify lines containing . 2% ART. These extremely high-yielding individuals have been maintained as vegetative clones, and they represent promising germplasm resources for future A. annua breeding programmes.

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Root research on field grown crops is hindered by the difficulty of estimating root biomass in soil. Root washing, the current standard method is laborious and expensive. Biochemical methods to quantify root biomass in soil, targeting species-specific DNA, have potential as a more efficient assay. We combined an efficient DNA extraction method, designed specifically to extract DNA from soil, with well-established quantitative PCR methods to estimate the root biomass of twenty-two wheat varieties grown in field trials over two seasons. We also developed an assay for estimating root biomass for black-grass, a common weed of wheat cultivation. Two robust qPCR assays were developed to estimate the quantity of plant root DNA in soil samples, one specific to wheat and barley, and a second specific to black-grass. The DNA qPCR method was comparable, with high correlations, with the results of root washing from soil cores taken from winter wheat field trials. The DNA qPCR assay showed both variety and depth as significant factors in the distribution of root biomass in replicated field trials. The results suggest that these DNA qPCR assays are a useful, high throughput tool for investigating the genetic basis of wheat root biomass distribution in field grown crops, and the impact of black-grass root systems on crop production.