Evaluation of Transgenes in Floral Crops for Arthropod Resistance Progress Report — June 1997
Date 6/1//97
Title of Project: EVALUATION OF TRANSGENES IN FLORAL CROPS FOR ARTHROPOD
RESISTANCE
Institute where work is being conducted: Cornell University
Amount of Endowment Grant: $22,824
Covering Period: 8/1/96 - 7/31/97
Anticipated Date of Project Completion/Final Report: 7/99
Individual Conducting Project:
(List Project Leader First)
John P. Sanderson - Assoc Professor
KC Bennett
Joan Miller
Review of Industry Needs/Project Objectives:
The ability to insert novel genes that code for
products that are toxic to arthropod pests into floral crops opens up a
promising way to exploit plant resistance as part of greenhouse IPM. Once
effective genes are discovered and plant regeneration techniques developed,
it is conceivable that these genes may be inserted into any number of crop
species and cultivars. Because floral crops are not eaten for food, there
is no need to determine food tolerances for the gene products. Transgenic
floral plants offer a revolutionary method for least-toxic pest control
on ornamentals. My lab has been collaborating with Sanford Scientific,
Inc. (SSI), based in nearby Waterloo, New York, to develop the first transgenic
floral crops with the ability to resist arthropod infestations, and to
evaluate their use within an IPM context. SSI is exclusively interested
in using gene-gun technology to transform ornamental crops.
The current project goal is to evaluate the use
of transgenes in floral crops for resistance to greenhouse arthropod pests,
initially using petunia and poinsettia as the model systems. The work began
with whiteflies, and we have now expanded our work to include other pests,
with encouraging results. Specifically, our goals (as stated in the original
proposal) include: 1. Screen gene products for biological activity against
whiteflies affecting greenhouse floral crops using artificial feeding assays;
2. Transform petunia and poinsettia with genes that code for the biologically-active
products (done at SSI); 3. Assess the transgenic plants for impact on whiteflies,
and determine correlations between gene expression levels and levels of
resistance; 4. Assess transgenic petunia for resistance to other greenhouse
arthropod pests, including spider mites, aphids, and thrips. 5. Assess
the effect of transgenic plants on appropriate natural enemies (e.g. Encarsia
formosa, Phytoseiulus persimilis).
Summary of Work to Date:
Objectives 1-3:
Our artificial feeding assays have demonstrated
that the amino acid known as tryptamine is acutely toxic to adult silverleaf
whiteflies (Bemisia argentifolii). A gene, known as TDC, causes the production
of tryptamine in plants, and has been licensed to Sanford Scientific, Inc..
SSI has developed several lines of petunia and poinsettia that contain
this gene. The transformed poinsettia lines were tested for resistance
to whiteflies, but the results did not show any significant amount of resistance.
Subsequent tests suggested that poinsettia did not accumulate any appreciable
tryptamine, but seemed to metabolize it all. However, poinsettia was clearly
the exception. Later tests have shown that all other plant species tested
are able to accumulate biologically active levels of tryptamine in their
tissues - including petunia, rose, vinca, and geranium. SSI is addressing
the problem of lack of tryptamine accumulation in poinsettia. We will resume
evaluations of whitefly resistance on transformed poinsettia as soon as
the new transformed plants are available, perhaps in late 1997 (transformation
and regeneration of poinsettia can take 6 mos.).
Objective 4:
Using several lines of transformed petunia as the
test crop, we next began to survey the effect of tryptamine on other greenhouse
pests. (The petunia lines proved to have too many sticky leaf hairs to
be good for whitefly tests). Three TDC petunia lines were tested for spider
mite resistance. In each of four separate tests, one of these lines has
consistently caused a significant reduction in spider mite population growth
(see 1997 proposal). We are currently examining the correlation between
gene expression level and mite abundance. Although preliminary, further
studies suggest that mite survival and reproduction are reduced. This is
the first report of transgene-mediated resistance to spider mites in agriculture.
SSI is developing plant lines with increased tryptamine expression, which
we will test for even greater mite resistance. Floral crops on which mites
are especially serious (e.g., roses, foliage) may be transformed with the
TDC gene in the future, given transformation and regeneration procedures.
The discovery of an effect on mites, coupled with
toxicity to whiteflies, suggest that tryptamine may affect a broader range
of greenhouse pests than we first expected. We have now begun our work
with western flower thrips, and will soon begin similar studies of aphid
resistance on these TDC petunia lines. As most entomologists know, doing
careful research with thrips can be a challenge, and it has taken us longer
than we hoped to generate repeatable results. Unfortunately, our current
results with western flower thrips are inconclusive and too preliminary
to report at this time, but the work is continuing.
Because petunia is attacked by several important
greenhouse pests and we have several TDC petunia lines available, it is
a good model plant to use in this study. However, we have recently developed
a simple way to expand the scope of this research project to include more
crops. We have recently developed a new test which bypasses the need to
have transformed plants in hand for insect tests. Because it takes a significant
amount of time and effort to generate transformed plants for testing, we
sought a way to speed up the process. By irrigating leaf or stem cuttings
of any given plant species in various concentrations of tryptarnine, we
have found that we can assess the plant’s ability to accumulate tryptamine
in its tissue, and assess impact on insects and mites. We are using this
new test this summer to screen a variety of pest/crop combinations. We
are particularly interested in screening those floral plant species for
which regeneration techniques are known. This screening process will help
to identify the best plant species to target for transformation with the
TDC gene.
Objective 5:
Evaluations of the impact of the transgenic plants on greenhouse natural
enemies will begin once insect/mite resistant plant lines are adequately
developed. Significance of Research: Transgenic floral plants offer a revolutionary
method for pesticide-free pest control on ornamentals. This research project
has now produced the first evidence of a gene which can be used for achieving
resistance against spider mites. This proposed project will evaluate the
effect of tryptamine against a variety of greenhouse pests, assess the
feasibility of generating transgenic floral crops with resistance to these
pests, transform the most promising crops, and screen several transgenic
lines of each crop for arthropod resistance.
