Evaluation of Transgenic Corn (Zea Mays L.) Resistant to Both Glyphosate and Western Corn Rootworm (Diabrotica Virgifera Virgifera LeConte) in Michigan PDF Download

Author: Kathrin Schirmacher
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ISBN:
Category : Corn
Languages : en
Pages : 212

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Author: Ted A. Wilson
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Languages : en
Pages : 216

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Monsanto Co. (St. Louis, MO) has received approval for the commercial sale of transgenic corn (Zea mays L.) modified to produce insecticidal protein (Cry3Bb1) from the soil bacterium Bacillus thuringiensis Berliner (Bt) for control of the western corn rootworm larvae, Diabrotica virgifera virgifera LeConte and northern corn rootworm, D. barberi Smith and Lawrence; southern corn rootworm. This new technology could help reduce the amount of pesticides applied to corn fields for control of these pests and provides an alternative management strategy. The first objective was to determine if the fitness of beetles surviving from transgenic corn was affected. Female adults emerging from transgenic treatments were the same size as females from terbufos and isoline treatments but laid fewer eggs. Transgenic corn did not affect percent egg hatch. Females from YieldGard Rootworm and terbufos flew significantly shorter distances than females from isoline and YieldGard Plus treatments. Virgin females did not fly sustained flights. Mated females from isoline and transgenic treatments flew farther than virgin females. The second objective was to examine similar questions but of adult beetles who had been exposed to the leaves and silks of transgenic plants. Beetles exposed to leaves or silks of transgenic plants did not fly significantly different than beetles exposed to nontransgenic plants. Beetles caged on leaves of transgenic plants for 5 days had higher mortality, consumed less leaf area, and laid fewer eggs than beetles caged on leaves of nontransgenic plants. Very little mortality occurred in beetles exposed to the silks of transgenic plants. Exposure to silks of transgenic plants did not affect egg laying or adult longevity. The third objective was to evaluate farmer perceptions and attitudes of transgenic corn using a survey. When asked if they would plant transgenic corn protected again the corn rootworm, 35.0% responded they would while 40.5% said they were unsure. The two biggest concerns farmers had of transgenic corn was the ability to sell harvested grain and additional technology fees. Farmers felt that less insecticide in the environment and less insecticide exposure to farmers were significant benefits of transgenic corn. The most common refuge-planting options farmers favored were adjacent fields and split fields.

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Languages : en
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Author: John S. Larsen
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Languages : en
Pages : 0

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This study examines the genetics and genetic variation of maize resistance to Diabrotica virgifera virgifera LeConte (rootworm). Rootworm resistance is a complex, multi-trait characteristic with inheritance mechanisms not fully understood or explained. In order to better understand the mechanisms of rootworm resistance and the genetic parameters that condition this trait, three studies were undertaken. The first study examined the genetic variation of components of resistance in twenty-three DEKALB Genetics Corporation hybrids. They were assessed for hydroxamic acid content under uniform greenhouse conditions and compared with field assessments over two growing seasons for resistance to the Western Corn Rootworm in terms of root pull resistance, root damage ratings and root lodging. Hydroxamic acid levels of all hybrids were found to be moderately low resulting in low antibiosis. It appears that rootworm resistance in these hybrids is achieved mainly through tolerance, not antibiosis. The study suggests an opportunity for improvement of resistance in commercial inbreds through selection for antibiosis and hydroxamic acid content. In the second study, the combining ability, additive and dominance effects and the heritability of several traits important to rootworm resistance in maize were determined. GCA and SCA effects were found to be significant in the inheritance of hydroxamate content, root weight and plant height. GCA effects were found to be significant in relation to low root damage ratings. Heritability in a narrow sense as determined by the midparent/offspring regression was found to be 0.34 for hydroxamate content, 0.26 for root damage ratings and 0.35 for plant height. Additive genetic effects were found to be significant in the inheritance of root damage ratings, both additive and dominance effects contribute to the inheritance of plant height and dominance effects were found to be most important in the expression of root weight. In the third study, two inbred lines were used to develop an F2 :F3 population to further investigate the genetic parameters governing some of the traits important to rootworm resistance. The inbred lines used were 93n445 (susceptible) and 118.31 (resistant). Dominance effects were found to be significant in the inheritance of plant height, additive effects were found to be significant in the inheritance of root size and additive and dominance effects were found to be significant in the inheritance of root damage ratings. Heritability in a narrow sense was found to be 54% for root size, 55% for root damage ratings, 84.7% for stalk circumference and 89% for plant height for the inbreds used in this study. (Abstract shortened by UMI.).

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Languages : en
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Author: Stephanie L Gorski
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Languages : en
Pages : 127

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Author: Michael James Forster
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Category : Corn
Languages : en
Pages : 140

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Author: Sarah N. Zukoff
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ISBN:
Category : Corn
Languages : en
Pages : 133

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The Environmental Protection Agency recently registered seed blend refuges for two of the transgenic Bt corn products targeting the western corn rootworm (WCR), Diabrotica virgifera virgifera LeConte. Larval movement between Bt and isoline plants can be detrimental to resistance management for high dose Bt products because the insect larvae will potentially be exposed to sublethal amounts of the Bt, however, the effect of this movement on low to moderate dose products is unknown. All current rootworm products are low dose. The main criteria for whether movement by WCR larvae between isoline and Bt corn plants will influence the development of resistance is whether or not selection for resistance is taking place. We found that movement between isoline and SmartStax[registered trademark] hybrid plants did occur in seed blend scenarios in our field study. The majority of plant damage to the SmartStax plants occurred when the larvae moved from surrounding infested isoline plants moved late in their development. These older, larger larvae are all able to tolerate the Bt in the plants, therefore resistance will likely not develop in these larvae. In a similar experiment, movement also occurred between Agrisure® Duracad[trademark] and isoline plants in seed blend scenarios, however the damage was low for all treatments. With isoline plants being mixed with Bt plants in seed blend refuges, host recognition behavior of the western corn rootworm on Bt and isoline plants is also important to understand. There were no differences between the host recognition behavior of WCR larvae after exposure to mCry3A, Cry3Bb1, Cry34/35Ab1, or their isoline corn hybrids, therefore all hybrids were perceived as hosts by WCR larvae. With all the hybrids on the currently registered being pyramided by different companies to control rootworms, the potential for cross resistance between these hybrids was evaluated using field resistant and susceptible populations. Based on the data from laboratory and greenhouse assays, the potential for cross resistance between mCry3A and Cry3Bb1 might be likely, but not between these hybrids and Cry34/35Ab1. Information gathered in this study provides important behavioral information on western corn rootworms that will aid in making decisions involving Bt corn hybrids.

Author: Ryan W. Geisert
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Category :
Languages : en
Pages : 102

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The western corn rootworm, Diabrotica virgifera virgifera LeConte, has developed resistance to most control tactics used to manage it. Transgenic corn varieties that express insecticidal proteins from the bacterium Bacillus thuringiensis Berliner (Bt), cause mortality to target pests when ingested. In an attempt to delay resistance formation to these Bt products, the Environmental Protection Agency mandates the development of an insect resistance management program prior to registration for commercial sale. Despite plans to delay resistance being in place, resistance has developed in the field for both Cry3Bb1 and mCry3A-expressing hybrids. Resistance to these products could be due to physiological adaptations or through behavioral avoidance of the toxin in the plant. For the first portion of this work, we investigated a behavioral avoidance hypothesis for resistance. We hypothesized that later hatching western corn rootworm larvae could utilize previous feeding damage on Bt corn roots by early hatching larvae as an entry point into the root cortex containing lower levels of the Bt protein. Field and greenhouse tests involving infestation staggering to facilitate previous feeding damage did not support our hypothesis and did not indicate any effect of previous root feeding on the ability of this pest to establish on Bt plants and cause damage. We also evaluated resistance dynamics in the western corn rootworm in response to the most recent Bt protein commercialized for rootworm management, eCry3.1Ab. For one experiment, an eCry3.1Ab-selected and a paired control western corn rootworm colony were utilized to determine the potential fitness costs associated with eCry3.1Ab resistance. Adult longevity, egg viability, and larval development time results indicated a lack of fitness costs associated with eCry3.1Ab resistance in the western corn rootworm. Reciprocally crossed colonies of the eCry3.1Ab-selected and control colonies were created in order to evaluate whether the resistance trait to eCry3.1Ab was recessive, dominant, or something in between. Each reciprocal cross and their parent colonies were evaluated in diet toxicity and plant assays. Results indicated that the eCry3.1Ab resistance trait we selected for under laboratory conditions is dominantly inherited.

Author: Peter Gacii Chege
Publisher:
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Category : Corn
Languages : en
Pages :

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With the increasing adoption of transgenic maize with resistance to rootworms, combined with glyphosate tolerance, as a control tactic for western corn rootworm, Diabrotica virgifera virgifera LeConte, an understanding of the effect of alternate host plants on rootworm population dynamics is critical to the formulation of effective IRM programs. Three studies were conducted to evaluate the effects of alternate host plant phenology on the survivorship, growth, development, and host searching behavior of larvae, as well as the effect of initial feeding of larvae on an alternate host followed by movement to rootworm resistant transgenic corn on beetle emergence and reproductive fitness of emerged female beetles. Initial feeding on alternate hosts followed by movement to Bt maize increased beetle emergence from Bt maize, fecundity of those that survived, and the number of viable eggs produced. In greenhouse trials, western corn rootworm larvae had significantly greater survival on younger grassy weeds (4 to 6 weeks old) versus older grassy weeds. In behavioral tests, western corn rootworm larvae recognized younger roots (4 week old) as hosts but did not recognize older roots (7 or 10 week old) as hosts. Phenological changes in grassy weeds could encourage movement of larvae from weeds to transgenic maize.