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
1999-08-19
2003-12-02
Fox, David T. (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
C800S269000, C800S275000, C435S412000, C435S424000, C435S430000, C435S430100
Reexamination Certificate
active
06657110
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
This invention relates to a novel maize plant having a nuclear genome of maize chromosomes, and an extranuclear genome of
Tripsacum floridanum
extranuclear genes.
2. Description of the Prior Art
Each year, an estimated 71 million acres of maize are planted in the seventeen major corn producing states of the U.S. alone, as reported by the National Agricultural Pesticide Impact Assessment Program (NAPIAP) (Biologic and Economic Assessment of Pesticide Use on Corn and Soybeans, NAPIAP Report No. 1-CA-95). The principal use of field maize is for livestock feed (60%). Significant amounts of the maize crop are also used for human consumption as sweet maize, sweeteners, cooking oil, margarine, processed meal, starches, and syrups, and for the production of ethanol.
Scientists have traditionally used cross-breeding and hybridization techniques to produce maize plants having desirable traits such as increased yields, resistance to disease and pests, increased hardiness, improved nutritional value, and taste.
Breeding programs have also included attempts to cross maize or its wild relatives with perennial gama grass,
Tripsacum dactyloides
. Kindiger and Sokolov (U.S. Pat. No. 5,710,367) disclosed the production of apomictic maize and apomictic maize/Tripsacum hybrids. These apomictic plants, which reproduce asexually, were produced by intercrossing maize (
Zea mays
) with the above-mentioned
Tripsacum dactyloides
. Eubanks (U.S. Pat. No. 5,750,828) has also disclosed the production of a new species, designated Tripsacorn, produced by crossing two perennials,
Zea diploperennis
with
Tripsacum dactyloides
. Tripsacorn is disclosed as being a fertile perennial having a diploid chromosome number between 18 and 20, and which is cross-fertile with maize.
SUMMARY OF THE INVENTION
We have now discovered novel maize plants having a nuclear genome of maize chromosomes with no Tripsacum chromosomes, but with extranuclear genes or cytoplasmic DNA from
Tripsacum floridanum
. These novel maize plants are fertile and may be readily crossed as the female parent with any maize (as the male parent) and the progeny thereof will retain the Tripsacum extranuclear genes. Moreover, by using an inbred maize line as the male parent in such a cross, followed by repeatedly backcrossing the progeny thereof as the female parent with the same inbred line, the inbred line may be placed in a,
Tripsacum floridanum
cytoplasm. In other words, the resultant inbred maize will possess a nuclear genome substantially identical to the parent inbred maize line but it will have the extranuclear genes of
Tripsacum floridanum
rather than those of the parent maize.
Maize plants having these Tripsacum extranuclear genes will exhibit modified traits which are controlled by the extranuclear genes or influenced by the interaction of the extranuclear genes with the maize nuclear genome. Traits which may be exhibited include one or more of increased disease and insect resistance, particularly increased resistance to the corn rootworm complex, and the production of aerenchyma in the roots.
In accordance with this discovery, it is an object of this invention to provide maize plants having a nuclear genome of maize chromosomes with no Tripsacum chromosomes, but with the extranuclear genes of
Tripsacum floridanum.
Another object of this invention is to provide maize plants and methods which may be used to transfer the extranuclear genes of
Tripsacum floridanum
into any maize line.
It is also an object of this invention to provide maize plants which exhibit increased disease and insect resistance, and/or the production of aerenchyma in the roots.
Still another object of this invention is to provide maize plants which may be used to restore male fertility in maize lines.
Other objects and advantages of this invention will become readily apparent from the ensuing description.
DETAILED DESCRIPTION OF THE INVENTION
In producing the maize plants of this invention we have conveyed the extranuclear genes of
Tripsacum floridanum
into maize without introducing any Tripsacum chromosomes or nuclear DNA into the maize nuclear genome. Thus, the nuclear genome of this maize retains a full complement of maize chromosomes (2n=20 or 20+) with no Tripsacum chromosomes, while its extranuclear genes are from
Tripsacum floridanum
, not maize. As used herein, extranuclear genes, which are also referred to as the plasma genes or the cytoplasmic genome or genes, include the organelle genome, specifically the genomes of the mitochondria and chloroplast.
Because the maize plants of this invention possess a nuclear genome of only maize chromosomes, they resemble normal maize in appearance and growth, including but not limited to properties such as chromosome number, plant height, ear height, no. of ears per stalk, ear size, no. of kernel rows per ear, kernel color, size, weight, and shape, and leaf blade properties such as size and color. The precise characteristics of the maize will of course vary with its parent maize lines, with expressed traits generally being derived from each parent.
Although the maize plants having the Tripsacum extranuclear genes appear as normal maize, they will nonetheless exhibit modified traits which are controlled by the extranuclear genes or influenced by the interaction of the extranuclear genes with the maize nuclear genome. For instance, without being limited thereto, traits which may be exhibited include one or more of the following: increased disease and insect resistance, particularly increased resistance to the corn rootworm complex, better developed and substantially increased numbers of aerenchyma in the roots.
The maize of this invention, which may also be considered a maize cybrid, were produced by first crossing two Tripsacum species to produce an interspecific hybrid. The interspecific hybrid was then hybridized with different maize lines (
Zea mays
) in a series of crosses to transfer the extranuclear genes of the Tripsacum into the maize. The progeny from each cross were selected which exhibited successively reduced numbers of Tripsacum chromosomes, eventually producing a maize plant which possessed a nuclear genome comprising maize chromosomes with no Tripsacum chromosomes, but which retained the Tripsacum extranuclear genes. With each cross it was necessary to use the plants containing the Tripsacum extranuclear genes as the female parent, because the extranuclear genes of these plants always convey with the female parent during sexual reproduction.
As described in greater detail in Example 1, a first cross was made between two Tripsacum species,
T. floridanum
as the female parent and
T. dactyloides
as the male parent, to produce an interspecific hybrid having
T. floridanum
extranuclear genes. This interspecific hybrid was then crossed as a female parent with a first maize line as a male parent to produce an F
1
hybrid having a nuclear genome composed of a combination of maize chromosomes and Tripsacum chromosomes, and having the
T. floridanum
extranuclear genes. The resultant F
1
hybrid was then crossed as a female parent with a second maize line as a male parent to produce a second hybrid, referred to as BC
1
, with a nuclear genome having a full complement of maize chromosomes in combination with Tripsacum chromosomes, while retaining the extranuclear genes from the Tripsacum parent. BC
1
was crossed as a female parent with a third maize line, producing a third hybrid, BC
2
, having a nuclear genome of maize chromosomes and a variable, reduced number of Tripsacum chromosomes, with the Tripsacum extranuclear genes. BC
2
plants having lowest numbers of Tripsacum chromosomes were selected and crossed with a fourth maize line, producing a fourth hybrid, BC
3
, all of which retained the Tripsacum extranuclear genes, with further reduced numbers of Tripsacum chromosomes in the nuclear genome. Some members of the BC
3
generation possessed no Tripsacum chromosomes, and those individuals were selected and selfed, producing progeny,
Dewald Chester L.
Sims Phillip L.
Deck Randall E.
Fado John D.
Fox David T.
The United States of America as represented by the Secretary of
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