Multicellular living organisms and unmodified parts thereof and – Plant – seedling – plant seed – or plant part – per se – Higher plant – seedling – plant seed – or plant part
Reexamination Certificate
1997-03-07
2002-04-23
McElwain, Elizabeth F. (Department: 1638)
Multicellular living organisms and unmodified parts thereof and
Plant, seedling, plant seed, or plant part, per se
Higher plant, seedling, plant seed, or plant part
C800S260000, C800S298000, C800S278000, C800S300000, C435S415000, C435S419000
Reexamination Certificate
active
06376754
ABSTRACT:
The present invention relates to a seed, a plant, a variety, an inbred, and a hybrid which contain a level of resistance to more than one herbicide. Such plants have advantages over plants having a single gene for herbicide resistance, especially with respect to prevention of resistance development in the target weed plants.
BACKGROUND OF INVENTION
The features of a commercially competitive plant varieties generally include more than high yield with excellent standability. While yield is the single most critical input which affects the crop producer's profit, producers expect consistency of yield from year to year, disease resistance, other value-added traits, and—more recently—herbicide resistance. The addition of herbicide resistance has created both opportunities as well as tremendous challenges in production agriculture.
Historically, herbicide treatments have been an integral part of modern agriculture because they provide cost-effective increases in agricultural productivity. Increased yields result from reduced weed competition for water, light, and nutrients. In addition, crop quality often improves in the absence of contaminating weed seeds. Herbicides can also aid soil conservation efforts through no-till agricultural practices, wherein herbicides rather than tillage are used to reduce weed populations prior to planting.
Herbicides generally give more consistent weed control compared to tillage in many environments. Consequently, there is increasing use of both non-selective herbicides for weed control prior to crop establishment and selective herbicides for crop weed control while a crop is growing. Non-selective herbicides kill or inhibit the growth of all actively growing plant material. Selective herbicides are those herbicides generally used for the suppression of growth of certain plant species (usually weeds), while leaving another species (usually a crop) unaffected. In North America and many other countries, these herbicides have benefitted the farmer by enabling the earlier planting of short-season crops, and by improving weed control in many cropping systems.
Herbicide development programs have always assessed the crop safety of a given herbicide in a weed control system, so that no crop yield reduction results from herbicide application. In fact, crop safety has been a focus of chemical herbicide discovery and plant breeding for the last 30 years, and thousands of chemical analogues have been screened to allow identification of herbicides that control target weeds and are safe to crops minimizing yield loss due to chemical stress. Nevertheless, while several classes of herbicides possess a broad spectrum of efficacy, many of the herbicides lack selectivity and severely injure or kill crop plants at the application rates required for effective weed control.
Examples of widely used herbicides are chlorimuron and thifensulfuron, which belong to the sulfonylurea class. They inhibit the plant enzyme acetolactate synthase (also called ALS), and soybeans which are resistant to these herbicides are referred to as STS (also called sulfonylurea tolerant) soybeans. These herbicides are the active ingredients in Classic and Pinnacle, respectively, and are registered for control of broadleaf weeds in soybeans as described in Weed Science Society of America, Herbicide Handbook, 7th edition (1994). While chlorimuron and thifensulfuron are registered for use in non-STS soybeans, they can cause significant crop injury, especially if applied post-emergence as described in Fielding and Stoller, Weed Technol. 4:264-271 (1990); Fielding and Stoller, Weed Sci. 38:172-178 (1990); Newsom and Shaw, Weed Sci. 42:608-613 (1994); and Ahrens, Weed Technol. 4:524-528 (1990). Factors which influence the extent of herbicide injury are physiological stresses from poor seed quality, delayed emergence in cold and wet soils, seedling diseases, etc.; soil pH and climatic conditions (i.e. temperature and humidity) when applications are made; and injury from prior applications of chemicals (e.g. insecticides and other herbicides).
When these herbicides are combined, either intentionally or unintentionally, positive and negative interactions can result. Chlorimuron and thifensulfuron are sold pre-mixed at elevated rates under the trade names Synchrony and Reliance, and act cooperatively to broaden the spectrum of weeds controlled. On the other hand, thifensulfuron interacts synergistically with imazethapyr (the active ingredient in the herbicide Pursuit) at normal use rates to severely injure non-STS soybeans; this combination causes less injury to STS soybeans but injury can exceed 20% which is commercially unacceptable and is discussed in Simpson and Stoller, Weed Technol. 9:582-586 (1995).
Glyphosate, which belongs to a different class of herbicide and is the active ingredient in both Roundup (also called RR) and Roundup Ultra, complements activity of the other herbicides (e.g. 2,4-D and dicamba). In some cases, glyphosate interacts synergistically with these other herbicides when they are applied in combination, as shown in Moshier, Weed Sci. 28:722-724 (1980) and Flint and Barrett, Weed Sci. 37:12-18 (1989). Tank mixing Classic at 0.5 oz/A or Pinnacle at 0.125 oz/A with Roundup at 16 fl oz/A increases control of broadleaf weeds but, in the case of Pinnacle, injury of Roundup Ready soybean is greater with the combination than with Roundup alone as discussed in Lich and Renner, Proc. NCWSS 50:124 (1995). Combination of Roundup Ultra with Synchrony (premix of chlorimuron plus thifensulfuron at elevated rates) effectively controls a broad spectrum of weeds.
Combining glyphosate with Synchrony or Reliance has the potential of increasing the spectrum of weeds (e.g. annual and perennial grasses, smartweeds, nightshade, pigweed spp., morningglory spp., etc.) that are controlled. Consequently, combining or “stacking” a level of resistance to both glyphosate and ALS in soybeans will allow these herbicide combinations to be used for effective weed control without crop injury.
With the development of chemical crop protection and the increasing availability of effective selective herbicides, monocultures of crops have become common. This has led to repeated application of the same or similar herbicides to these crops. More recently, in conservation or zero-tillage crop establishment systems, cultivation for weed control has largely been replaced by the use of selective and non-selective herbicides. Thus, two prevailing conditions are present in these cropping systems: (i) the frequent use of a limited range of effective herbicides and (ii) reliance upon these herbicides to the exclusion of other forms of weed control. Where these conditions prevail, herbicide-resistant weeds will increase in frequency (i.e. evolve) if there is heritable variability in response to herbicide application in weed populations and selective mortality from the herbicides.
Given the existence of genetic variation, the rate of evolution will be determined by the mode of inheritance of resistance traits, together with the intensity of selection. The evolution of resistance under persistent applications of herbicide may be considered as an example of recurrent selection in which there is a progressive, and sometimes rapid, shift in average fitness of populations of weeds exposed to herbicide. Once established, gene flow via seed distribution has probably contributed to the spread of resistant weeds. A major determinant in the selection of herbicide-resistant biotypes is the effective selection intensity that differentiates resistant individuals (more fit) from susceptible one (less fit) in the face of selection (the application of herbicide).
There are two ways in which resistance traits may arise within a weed population. A major gene, or genes may be present at low frequency, or mutate, so that selection acts to change a population which is initially susceptible. Alternatively, recurrent selection may act on continuous (quantitative) variation and achieve a progressive increase in average resistance from generation to gen
Byrum Joseph R.
Schillinger John A.
Walker Alan K.
Asgrow Seed Company
McElwain Elizabeth F.
Rothwell Figg Ernst & Manbeck
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