Agriculture Reference
In-Depth Information
the same report projected an increase of 33% to $20 billion. Actual igures for 2005 showed that seed
sales totaled $25 billion, exceeding expectations, and are likely to exceed $37 billion by the end of 2008
(International Seed Federation, 2008). According to the International Service for the Acquisition of Agri-
Biotech Application (2009), the global area of biotech crops continued to grow strongly, reaching 134 mil-
lion hectares (335 million acres) in 2009, up from 125 million hectares in 2008 and 114 million hectares
in 2007. The nations growing GM plants on the largest areas are the United States (64 million hectares),
Brazil (21.4), Argentina (21.3), India (8.4) and Canada (8.2). In 2009, the global market value of biotech
crops was US $10.5 billion, representing 30% of the US $34 billion 2009 global commercial seed market.
Recognizing the importance of these new markets and genetically modiied products, seed technology will
necessarily be at the forefront of ensuring the genetic purity of the new biotechnology products. Moreover,
the increasing value of seeds in the future indicates that high quality seeds will be paramount to avoid litiga-
tion concerning inaccurate identiication of varieties.
It is clear that an array of more sophisticated genetic purity tests will be needed as a result of the revo-
lution in biotechnology. In some cases, this may be a relatively simple process such as germinating seeds
in herbicide solution to determine their tolerance to the compound. In most cases, however, when only a
single gene is modiied, more powerful genetic purity tests may be required. These may include the use
of immunoassays to detect the proteins produced by the inserted genes. Other approaches include newer
DNA-based technologies such as restriction fragment length polymorphisms (RFLP) and methods that use
the polymerase chain reaction (PCR) to allow even more discrimination and faster identiication of variet-
ies. At the moment, this area is rapidly changing and it is dificult to anticipate which of these tests will
provide the greatest beneit in genetic purity testing. However, the following represents an evaluation of the
most promising of these DNA-based technologies, their strengths and limitations (McDonald, 1998a; Smith
and Register, 1998). There are two categories of tests to be considered. The irst utilizes highly sophisticated
analytical techniques made possible through the biotechnological revolution. These are collectively known
as DNA marker techniques. The second utilizes less sophisticated techniques to easily distinguish between
non-genetically modiied and genetically modiied varieties.
AnALyTICAL METHodS AnALyzInG dnA-MArkEr TECHnIQuES
DNA marker methods are quickly becoming the standard for varietal identiication. DNA proiling tech-
niques offer many advantages over traditional morphological descriptions. These techniques are more
objective, speciic, allow testing at all stages of development, and have become more cost effective. DNA
tests require a level of expertise and equipment not usually part of the common seed testing laboratory.
However, with the increasing availability of kits for part or all of a test procedure, the skills required
for each test are diminishing. DNA testing is not limited to varietal identiication (Henry, 2001; Weising,
2005). Other applications include GMO screening, genotyping, DNA sequencing and pathogen detection.
The PCR (polymerase chain reaction) technique facilitated the development of simple, low-cost molecular
marker techniques. PCR-based techniques for variety testing include RAPD (Random Ampliication of
Polymorphic DNA) analysis and microsatellite markers. RAPDs are used to generate DNA ingerprints
used to identify varieties. Microsatellite markers, also known as Simple Sequence Repeats (SSRs), act like
a molecular barcode to identify varieties, in addition to their common usage in genome mapping. These and
other molecular techniques will be described in the following sections.
restriction fragment Length Polymorphism (rfLP)
Restriction fragment length polymorphism was one of the irst DNA marker techniques used to identify
varieties. RFLPs have also been used for other purposes, including human DNA screening for presence of
genetic disorders and forensic DNA ingerprinting.
