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Genetic & Floral Community Diversity
Weed genetic biodiversity exists at several levels of plant organization:
all plants of the world all the way down to an individual plant of one species.
Below find a presentation of this type of genetic diversity:
Levels of Weedy Biodiversity within a Habitat
--->Floral Community
------>Species-Group
--------->Species
------------>Population
--------------->Variant: ecotype, biotype, mutant
--->Floral Community
Every agricultural field has, or has the potential, to produce a wide variety
of weeds from its seed and bud bank. Even when we control these weeds for
many years, they have the potential to come back because of the long soil
life they have, seed dormancy. Below are some extreme weed infestations.
------>Species-group
One of the best adapted and known weedy species-groups are the foxtails.
Take the Foxtail World Tour to learn
more about the biodiversity of this troublesome group.
The pigweeds are another infamous
species-group. There is considerable diversity within this superspecies,
maybe because promiscuous outcrossing between plants (and maybe species)
makes firm species identification problematic. Is it any wonder that most
weed management tactics miss at least some of these diverse pests?
The smartweed species-group consists of several species, including ladysthumb
and Pennsylvania smartweed. Below are a variety of leaf shapes and colors
from several plants in this group. They could be from the same or different
species, it is hard to tell from just this picture.
--------->Species
Much biodiversity exists within a single species, intra-specific diversity.
Below is a range of common lambsquarters leaves that could have come from
either the same plant or different plants in this species.
Hedge bindweed has several different colors of flowers within members of
the species:
------------>Population
Populations within a species can consist of one or many different genotypes.
Below are two different genotypes (and phenotypes) of quackgrass. The one
on the left is a prostrate growth habit type, the one on the right has upright
leaves. These two genotypes exist within the same field, forming the quackgrass
population of that field. Because the prostrate type exposes more leaf surface
to spray applications, often it is the first to get killed by foliar herbicide
applications.
Wild proso millet genotypes produce different colored seeds, some crop seed,
some weed seed. Below you can see this variation. Some fields have both,
or several different colored seed producing variants. Together they compose
the wild proso millet population.
--------------->Variant
Variants of a species can exist together in the same field and comprise
that field's population of that species. Variants can also exist in a field
all by themselves, in which case the population of that species in that
field is only one variant, or one genotype. Below is a collection of different
panicle (seedhead) variants of green foxtail. The panicles on the far left
are from the crop foxtail millet. Human selection for types with big fat
seedheads has produced these variants. The panicles on the middle left are
from robust purple green foxtail, very colorful. The picture on the middle
right was taken on a roadside near Madrid, Boone Co., Iowa. Several different
colored panicles make up that site's population. Some are purplish, maybe
on their way to being purple robust with time and selection. The panicle
on the far right is from a salt-tolerant green foxtail variant known as
pachy-stachys. It is located in a cozy cove in southern Japan on
the Sea of Japan. Quite a range of variants, don't you think?
--------------->Mutant
There is something dangerously exciting and appealing about mutants. Maybe
I feel this way because I saw too many 1950's science fiction movies in
my life, but weird and wild forms of an organism have an attraction to us
all, I am sure. Lets take a look:
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