Download B. nigra

Brassica nigra – Black Mustard
 Black 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 unpublished.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
http://www.giftpflanzen.com/armoracia_rusticana.html
90-95% 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.
http://www.pharm.kumamoto-u.ac.jp/flower/H1904.html
“Toxic to many herbivores, bacteria and
mycorrhizal fungi.” Direct impact on other
plants?
First Hypothesis
• “Because of sinigrin’s 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 quadrat
 Estimated the % ground cover of
four functional groups:

B. nigra

heterospecific forbs

grasses

bare ground
 Measured sinigrin concentration of
target B. nigra species.
Target B. nigra
 Final fitness for each individual
“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.
“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.”
“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.”
•
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 fiddleneck
Sonchus oleraceus (Asteraceae) – Common sowthistle
Malva parviflora (Malvaceae) – Cheeseweed mallow
•
•
•
3 community types
1) High-sinigrin B. nigra monocultures
2) Low – sinigrin B. nigra monocultures
3) A 3-species mixed heterospecific
community
Each community consisted of 24
neighbor plants, surrounding a
target invader.
Target Invader
-High sinigrin B. nigra
-Low sinigrin B. nigra
Or 1 of the heterospecifics:
Amsinckia menziesii
Sonchus oleraceus
Malva 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 caveat
• Mycorrhizal fungal communities may be playing a role.
• Mycorrhizal fungal communities may be altered by
sinigrin, a known antifungal substance, or it’s 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 communities
Invaded by High-sinigrin
B. nigra
Invaded by
heterospecific species.
Low-sinigrin B. nigra community
Invaded by low-singrin B. nigra
High-sinigrin B. nigra community