Anyone doing this ? New to me.

I think of drought tolerant when I read

"The potential for selecting pathogen free plants, for selecting
stress-tolerant and pathogen-resistant clones of plants, and the novel
genetic combinations to be achieved through somatic hybridization are
all lines of research which can have a profound impact on the nursery
industry."

Sill looks like a pipe dream.

"The impact of obtaining pathogen-free nursery stock can only be
speculative, since little research documenting viral, bacterial, or
fungal diseases transmitted through propagation of woody ornamentals is
available."
.................................................. ........................

http://aggie-horticulture.tamu.edu/t.../pltissue.html

The Many Dimensions of Plant Tissue Culture Research
R. Daniel Lineberger
Professor of Horticulture
Texas A&M University
College Station, TX 77843
Webmaster of Aggie Horticulture (http://aggie-horticulture.tamu.edu/)

INTRODUCTION
The practice of plant tissue culture has changed the way some nurserymen
approach plant propagation. In the recent past, the applicability of
this technology to the propagation of trees and shrubs has been
documented. Some firms have established tissue culture facilities and
commercial scale operations are presently in operation for the mass
propagation of apples, crabapples, rhododendrons, and a few other
selected woody species. The intent of this research update is to briefly
examine "what is being done" and to explore "what can be done" with
regard to the tissue culture of ornamental plants. Such a consideration
necessarily includes an overview of tissue culture as a propagation
tool. The major impact of plant tissue culture will not be felt in the
area of micropropagation, however, but in the area of controlled
manipulations of plants at the cellular level in ways which have not
been possible prior to the introduction of tissue culture techniques.

THE ART AND SCIENCE OF MICROPROPAGATION
Of all the terms which have been applied to the process,
"micropropagation" is the term which best conveys the message of the
tissue culture technique most widely in use today. The prefix "micro"
generally refers to the small size of the tissue taken for propagation,
but could equally refer to the size of the plants which are produced as
a result.
Micropropagation allows the production of large numbers of plants from
small pieces of the stock plant in relatively short periods of time.
Depending on the species in question, the original tissue piece may be
taken from shoot tip, leaf, lateral bud, stem or root tissue (Fig. 1).
In most cases, the original plant is not destroyed in the process -- a
factor of considerable importance to the owner of a rare or unusual
plant. Once the plant is placed in tissue culture, proliferation of
lateral buds and adventitious shoots (Fig. 2) or the differentiation of
shoots directly from callus (Fig. 3), results in tremendous increases in
the number of shoots available for rooting. Rooted "microcuttings" or
"plantlets" of many species have been established in production
situations and have been successfully grown on either in containers or
in field plantings. The two most important lessons learned from these
trials are that this methodology is a means of accelerated asexual
propagation and that plants produced by these techniques respond
similarly to any own-rooted vegetatively propagated plant.
Micropropagation offers several distinct advantages not possible with
conventional propagation techniques. A single explant can be multiplied
into several thousand plants in less than one year. With most species,
the taking of the original tissue explant does not destroy the parent
plant. Once established, actively dividing cultures are a continuous
source of microcuttings which can result in plant production under
greenhouse conditions without seasonal interruption. Using methods of
micropropagation, the nurseryman can rapidly introduce selected superior
clones of ornamental plants in sufficient quantities to have an impact
on the landscape plant market.

PLANT IMPROVEMENT THROUGH TISSUE CULTURE
In introducing this research update, it was mentioned that the major
impact of tissue culture technology would not be in the area of
micropropagation, but rather in the area of controlled manipulations of
plant germplasm at the cellular level. The ability to unorganize,
rearrange, and reorganize the constituents of higher plants has been
demonstrated with a few model systems to date, but such basic research
is already being conducted on ornamental trees and shrubs with the
intent of obtaining new and better landscape plants.

SELECTION OF PLANTS WITH ENHANCED STRESS OR PEST RESISTANCE
Perhaps the most heavily researched area of tissue culture today is the
concept of selecting disease, insect, or stress resistant plants through
tissue culture. Just as significant gains in the adaptability of many
species have been obtained by selecting and propagating superior
individuals, so the search for these superior individuals can be
tremendously accelerated using in vitro systems. Such systems can
attempt to exploit the natural variability known to occur in plants or
variability can be induced by chemical or physical agents known to cause
mutations.
All who are familiar with bud sports, variegated foliage and other types
of chimeras have an appreciation for the natural variability in the
genetic makeup or expression in plants. Chimeras are the altered
cellular expressions which are visible, but for each of these which are
observed many more differences probably exist but are masked by the
overall organization of the plant as a whole. For example, even in
frost-tender species, certain cells or groups of cells may be frost
hardy. However, because most of the organism is killed by frost, the
tolerant cells eventually die because they are unable to support
themselves without the remainder of the organized plant. Plant tissues
grown in vitro can be released from the organization of the whole plant
through callus formation. If these groups of cells are then subjected to
a selection agent such as freezing, then those tolerant ones can survive
while all those which are susceptible will be killed. This concept can
be applied to many types of stress as well as resistance to fungal and
bacterial pathogens and various types of phytotoxic chemical agents. The
goal of selecting such resistant cell lines would be to reorganize whole
plants from them which would retain the selected resistance (Fig. 4).
Current research in this area extends across many interests including
attempts to select salt tolerant lines of tomato, freezing resistant
tobacco plants, herbicide resistant agronomic crops, and various species
of plants with enhanced pathogen resistance. Imagine, if you will, the
impact of a fireblight-resistant Bartlett pear, a clone of pin oak for
alkaline soils, or a selection of southern magnolia hardy to zone 4!

TISSUE CULTURE AND PATHOGEN FREE PLANTS
Another purpose for which plant tissue culture is uniquely suited is in
the obtaining, maintaining, and mass propagating of specific
pathogen-free plants. The concept behind indexing plants free of pests
is closely allied to the concept of using tissue culture as a selection
system. Plant tissues known to be free of the pathogen under
consideration (viral, bacterial, or fungal) are physically selected as
the explant for tissue culture. In most cases, the apical domes of
rapidly elongating shoot tips are chosen (Fig. 5). These are allowed to
enlarge and proliferate under the sterile conditions of in vitro culture
(Fig. 6) with the resulting plantlets tested for presence of the
pathogen (a procedure called indexing). Cultures which reveal the
presence of the pathogen are destroyed, while those which are indexed
free of pathogen are maintained as a stock of pathogen-free material.
Procedures similar to these have been used successfully to obtain
virus-free plants of a number of species and bacteria-free plants of
species known to have certain leaf spot diseases. The impact of
obtaining pathogen-free nursery stock can only be speculative, since
little research documenting viral, bacterial, or fungal diseases
transmitted through propagation of woody ornamentals is available.

SOMATIC HYBRIDIZATION
The ability to fuse plant cells from species which may be incompatible
as sexual crosses and the ability of plant cells to take up and
incorporate foreign genetic codes extend the realm of plant
modifications through tissue culture to the limits of the imagination.
Most such manipulations are carried out using plant "protoplasts".
Protoplasts are single cells which have been stripped of their cell
walls by enzymatic treatment. A single leaf treated under these
conditions may yield tens of millions of single cells, each
theoretically capable of eventually producing a whole plant. This
concept has fueled speculation as diverse as the possibilities of
obtaining nitrogen-fixing corn plants on the one extreme to discovering
a yellow-flowered African violet on the other extreme.
The observation that has provided the impetus for most of this research
is that when cells are stripped of their cell walls and brought into
close contact, they tend to fuse with each other (Fig. 7). This "somatic
hybridization" is not subject to the same incompatibility problems that
limit traditional plant breeding strategies. It is conceivable then that
one could hybridize a Juneberry with a crabapple or a plum, but the
fundamental research required to demonstrate such an event has yet to be
conducted.
The potential use of somatic hybridization to bring about novel
combinations of genetic material has been demonstrated in the genera
Petunia and Nicotiana. Research funded in part by the Horticultural
Research Institute at the University of Wisconsin is investigating the
feasibility of using such techniques with woody species. Brent McGown
and co-workers have succeeded in obtaining naked cells from tissue
cultures of Betula and Rhododendron, but as of yet, they have neither
obtained plants from single cells not achieved cellular fusion. However,
further research in this area promises to have a tremendous impact on
our concepts of woody plant diversity. Just as remarkable as the idea of
fusing plant protoplasts is the idea of incorporating foreign genetic
material into the genetic code of plant cells. Such transformations have
been carried out in the so-called "gene-splicing" experiments where the
information for making insulin was incorporated into bacteria. Not only
is the desired information transmitted to succeeding generations of
bacteria, but the bacterial cultures become synthesizers of insulin as
well. Plant cells can be made to take up foreign genetic codes, but
evidence that this can be transmitted into the daughter cells and serve
the intended function is lacking. What if, for example, the genetic
information for accumulating a very high sugar content is incorporated
into a clone of sugar maples? One could think of enough what ifÕs in
this category to fill several volumes!

SUMMARY
Plant tissue culture research is multi-dimensional. While most
nurserymen have been introduced to the techniques and advantages of
micropropagation, few have ventured to use it as a propagation tool. The
applicability of micropropagation for woody trees has been demonstrated
as feasible since all aspects of the technology have confirmed the fact
that trees produced by this method look like and grow like their
counterparts produced by traditional methods of cloning.
Other dimensions of tissue culture research have been less well
publicized. The potential for selecting pathogen free plants, for
selecting stress-tolerant and pathogen-resistant clones of plants, and
the novel genetic combinations to be achieved through somatic
hybridization are all lines of research which can have a profound impact
on the nursery industry.
http://aggie-horticulture.tamu.edu/t.../pltissue.html

--
Bill S. Jersey USA zone 5 shade garden
http://www.informationisbeautiful.ne...l-supplements/