...From the pages of Agricultural Research magazine
Reforestation efforts may get a lift thanks to a new advance in plant-tissue
culturing at ARS's National Center
for Agricultural Utilization Research, Peoria, Illinois. Plant physiologist
Brent Tisserat has devised an automated plant culture system (APCS),
coupled with enhanced CO2 treatments, that bolsters yield
and survival of delicate shoots.
In reforestry operations, budding shoots are cultured inside small
glass tubes or in Magenta vessels and nourished on an agar gel. Tissue
culturists treat these shoots, originally derived from leaves, with
growth regulators to coax them into multiplying secondary shoots. Transplanted
to soil, these shoots eventually root and become whole, free-living
plantlets that can then be put in the field.
With this technique, known as micropropagation, forest-product companies
can restock plantations with millions of genetically identical tree
plantlets. The yield of trees clonally derived from these plantlets
is much more predictable than that from fertilized seed, says Tisserat.
Even so, not all micropropagated shoots survive transplantingespecially
"vitrified" shoots, the source of axillary branches that do
not readily root. In contrast, nonvitrified shoots readily form roots
but produce few axillary branches.
Tisserat's tree micropropagation involvement began in 1996, when Union
Camp contacted him about tackling the yield problem in sweetgum trees.
The Savannah, Georgia-based company, since merged with International
Paper, grew sweetgum for making bags and other paper products. Like
other forest-product companies, Union Camp used traditional micropropagation
techniques to produce shoots and plantlets. The company wanted a method
to mass-produce clonal sweetgum shoots and a way to root these shoots
at high percentages. Tisserat observed that only 40-60 percent of Union's
vitrified shoots survived transplantation.
The standard approach to solving the problem would have involved tweaking
the agar medium's nutritional composition. But Tisserat changed the
way nutrient medium is applied to the shoots, modified the physical
environment in which they are grown, and switched from Magenta vessels
to larger growth chambers, which provide the tender shoots with much
more space and media.
Tisserat's APCS uses an automated pump to microirrigate the shoots
with liquid medium piped in from a separate tank. The medium is applied
and removed several times over a 24-hour period. In trials, this resulted
in a 10-fold increase in shoot yields compared to traditional culture
methods and a 14-fold increase in fresh weight.
To root these sweetgum shoots into soil, Tisserat subjected them to
high CO2 levels under high humidity, and they were able to
survive, photosynthesize, and make roots. By pumping the gas directly
into the chamber, ultra-high CO2 levels can be achieved.
For example, instead of an ambient CO2 concentration of 350
ppm of CO2 (0.03 percent), Tisserat's system uses 10,000
ppm (1.0 percent).
The CO2 treatments resulted in a 94-percent survival rate
for transplanted sweetgum shoots (including vitrified ones). The APCS
also speeds seedling growth of loblolly pine, a chief lumber resource
in the southeastern United States. Tisserat and co-investigators had
earlier success micropropagating and rooting peas, lettuce, tomatoes,
beans, and spearmint.By Jan
Suszkiw, Agricultural Research Service Information Staff.
This research is part of Quality and Utilization of Agricultural
Products, an ARS National Program (#306) described on the World Wide
Web at www.nps.ars.usda.gov.
Brent Tisserat is in the USDA-ARS Fermentation Biotechnology Research Unit, National Center for Agricultural Utilization Research, 1815 University St., Peoria, IL 61604; phone (309) 681-6289, fax (309) 681-6427.
"Micropropagation Technique May Speed Reforestation Efforts" was published in the December 2004 issue of Agricultural Research magazine.