Brassica nigra – Black Mustard  Black mustard is cultivated for its seeds, the source of...

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Transcript of Brassica nigra – Black Mustard  Black mustard is cultivated for its seeds, the source of...

  • Brassica nigra Black MustardBlack mustard is cultivated for its seeds, the source of commercial table-mustard, used as a condiment and medicine. Seeds contain both a fixed and an essential oil, used as a condiment, illuminant, lubricant, and soap constituent. Black mustard is mixed with white mustard (Sinapis alba) to make mustard flour, used in various condiments as "English Mustard" when mixed with water and "Continental Mustard" with vinegar. Mustard flowers are good honey producers. Mustard is agriculturally used as a cover crop. Mustard oil (allyl isothiocyanate) is used in cat and dog repellents. Source: James A. Duke. 1983. Handbook of Energy Crops. unpublished. Center for New Crops & Plant Products, at Purdue University

  • Toxic to many herbivores, bacteria and mycorrhizal fungi. Direct impact on other plants? of the glucosinolates in B. nigra are in the form of sinigrin, hence selection for glucosinolate conc. is really selection for sinigrin. Because sinigrin is a heritable trait, it is easier to track the selective advantage of glucosinolates.

  • First HypothesisBecause of sinigrins effects on heterospecific plants and mycorrhizal fungi (mutualists that benefit most plant species but not members of the Brassicaceae), we hypothesize that investment to sinigrin should benefit B. nigra genotypes competing with heterospecifics but not conspecifics.

    To look for possible feedback effects due to sinigrin concentrations, the authors sampled naturally occurring populations along a gradient of monocultures to mixes with heterospecific species.

  • 1 meter diameter quadratEstimated the % ground cover of four functional groups:B. nigraheterospecific forbsgrassesbare ground Measured sinigrin concentration of target B. nigra species.Final fitness for each individualTarget B. nigra

  • We found that the selective value of sinigrin increased as the community became dominated by heterospecfics.

  • Abundance of heterospecific species correlated with the sinigrin concentration of the target species.

  • Our observations suggest that cyclic dynamics between selection pressures and community composition could lead to the simultaneous maintenance of both genetic diversity in sinigrin genes and species diversity in the plant community.

    To test this hypothesis rigorously, we performed a community invasibility experiment.Thus, not only does the selective value of sinigrin concentration seem to depend on community composition, but the community composition may also depend on the sinigrin concentration of individual plants.

  • Created genetic lines of high- and low sinigrin B. nigra. Selected 3 abundant, co-occuring, phylogenetically diverse competitor species. (Which presumable have mychorrizal associations.)Amsinckia menziesii (Boraginaceae) Common fiddleneckSonchus oleraceus (Asteraceae) Common sowthistleMalva parviflora (Malvaceae) Cheeseweed mallow

  • 3 community types1) High-sinigrin B. nigra monocultures2) Low sinigrin B. nigra monoculturesA 3-species mixed heterospecific communityEach community consisted of 24 neighbor plants, surrounding a target invader.Target Invader-High sinigrin B. nigra-Low sinigrin B. nigraOr 1 of the heterospecifics: Amsinckia menziesii Sonchus oleraceusMalva parviflora

  • Thus the fitness of a B. nigra genotype depends on the community composition (diverse vs. monculture) that it invades.

  • The observed differences in heterospecific invader fitness in seed production persisted into the next generation in the field, resulting in higher seedling densities in low-sinigrin communities.

  • Caveats to this experiment.

    The effects seen in this experiment could be pleiotropic effects or genes closely linked to sinigrin concentrations.

  • Caveats to this experiment.

    The effects seen in this experiment could be pleiotropic effects or genes closely linked to sinigrin concentrations.

    Pleiotropy when many effects are produced from a single gene.

  • Another caveatMycorrhizal fungal communities may be playing a role.

    Mycorrhizal fungal communities may be altered by sinigrin, a known antifungal substance, or its metabolic breakdown products.

    To explore this possibility, we estimated the mycorrhizal infection potential (MIP) of soils taken from 10 plots of each community type (high- & low-sinigrin B. nigra and a mix of the 3 heterospecfics), using Sorghum bicolor as an indicator species.

  • Brassicaceae are nonmycorrhizal. The heterospecific species are mycorrhizal.

  • Heterospecific communitiesInvaded by High-sinigrin B. nigraHigh-sinigrin B. nigra communityLow-sinigrin B. nigra communityInvaded by heterospecific species.Invaded by low-singrin B. nigra