Agronomic Evaluations of Transgenic Cotton Varieties
J.C. Silvertooth, Plant Sciences Department
E.R. Norton, Plant Sciences Department
Several field experiments were conducted in many of the cotton growing areas of Arizona in 1997 for the purpose of
evaluating agronomic characteristics of many new transgenic Upland cotton varietie. In many cases, the new transgenic
lines were compared directly with their recurrent (non-transgenic) parents. Evaluations were carried out by collecting
plant mapping data from each variety on a regular 14 day interval throughout the season and relating the resultant
information to established baselines for Upland cotton in Arizona. Lint yield measurements were also taken on each variety
at all locations. Results indicate that all transgenic lines tested are very similar to their recurrent parents in terms of
growth, development, and yield. Some subtle differences were noted but they were very slight and should impact management
of the varieties significantly in comparison to their recurrent parents.
The cotton plant is the centerpiece to a cotton production system.
Accordingly, the variety being grown is extremely important. Transgenic
varieties can possess tremendous potential by providing unique tools to the
farmer, being delivered directly in the plant system. However, it is important
that the variety carrying the transgenic property is a strong variety for the
situation in which it is being used. It is also important to note that although
statements may be made relative to a new transgenic variety being "the same as"
it's non-transgenic parent variety; the new transgenic variety is
actually a separate and unique variety. Under these circumstances it becomes
even more critical to have access to objective, well documented information
regarding the agronomic nature (growth, development and yielding potentials in
response to soil and environmental factors) of the variety in question. This
point was illustrated quite dramatically in 1997 with concerns and reports of
problems associated with several Roundup Ready (RR) cotton varieties in some of
the mid-south states.
As an example, the most critical difference associated with a Bt variety is
that it contains some genetic information that was extracted from a
naturally-occurring soil bacteria called Bacillus Thuringiensis, or Bt, which
has insecticidal properties. Essentially, this genetic information was spliced
into the cells of cotton plants and crossed back into favorable varieties through
conventional breeding techniques. Accordingly, it is important to note that the
Bt varieties that we are dealing with in the field are very similar to their
non-Bt counterparts, but they are unique varieties in themselves. With or
without internally controlled insecticidal properties, the variety of cotton
plants grown in a field has a tremendous impact on the yield potential of the crop.
Therefore, monitoring the agronomic characteristics of a Bt variety, as with any variety,
is an important part of the variety evaluation. This is true not only for Bt cotton, but also
for any new transgenic variety that is developed (i.e. Roundup Ready or Buctril
To be competitive and to maintain economic sustainability in either a short-
or long-term sense, it is important that cotton growers in Arizona have access
to the best and latest in technology. To use this technology effectively, it is
equally important to have a complete understanding of what the technology offers
and what it can and cannot do. To utilize transgenic varieties effectively and
to provide appropriate management, it is very important to understand the
agronomic characteristics of them.
The purpose of this study was to compare the crop growth, crop development,
and yield of several new transgenic varieties against both their recurrent
parents and also against established crop growth and development baselines for
A group of field experiments were conducted at several locations across Arizona in 1997 containing numerous transgenic
cotton lines that are being evaluated for introduction into the commercial market in 1998
(Table 1). Lines
include varieties with Bt genes and Roundup Ready (RR) genes. Several
of these lines are being prepared for possible release in 1998 (i.e. DP 20b, 50b, 90b, and 32b).
For each primary site (seven) in this project, a complete battery of crop growth and development
parameters were conducted
on all pertinent varieties throughout the season on approximately 14 day intervals
The following measurements were made in each plot on all dates of sampling:
plant height, number of mainstem nodes, node of
the first fruiting branch, aborted sites at positions one and two, the number of
nodes above the top white flower (NAWF),
and petiole nitrate-N concentrations. From these measurements we calculate the
height to node ratio (HNR) and percent fruit
retention (% FR), which is plotted along with petiole NO3- -N and NAWF
values for each treatment relative to established
baselines for these parameters. Harvest and lint yield estimates were conducted
at all locations (13 locations total).
In each case, seedcotton yields, turnout, lint yields, and HVI measurements were
conducted for each set of
Results are shown in figures 1-34
Basic features evident from this data include the following points:
- Most transgenic lines are very similar to their recurrent parents.
- The problems associated with RR varieties reported from several locations
in the mid-south in 1997 were not apparent in any of these studies.
- Misshapen bolls and lower rates of fruit retention were not detected for
- Slight differences were detected between some varieties in terms of vigor and in-season fruit retention.
- Most of the new varieties are sensitive to stress, which is commonly expressed by low vigor and reduced fruit retention.
- Differences in yield were not attributed to agronomic properties.
- DP 33b does not have greater growth/vegetative tendencies than 5415 (vigor / HNR).
- DP 33b was consistently a high yielding variety across locations. DP 32b also yielded very well and demonstrated good consistency.
- Agronomic evaluation of transgenic lines without a direct comparison to the recurrent parent is possible in Arizona due to the availability of regional baselines for vigor (HNR, FR, NAWF, etc.).
- Transgenic lines of this type are commonly not placed in advanced strain studies. Therefore, studies of this type are needed for the evaluation and comparison of transgenic lines.
This is a part of publication AZ1006:
"Cotton: A College of Agriculture Report," 1998, College of Agriculture, The University of
Arizona, Tucson, Arizona, 85721.
Any products, services, or organizations that are mentioned, shown, or indirectly
implied in this publication do not imply endorsement by The University of Arizona.
The University is an Equal Opportunity/Affirmative Action Employer.
This document located at http://ag.arizona.edu/pubs/crops/az1006/az10063j.html
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