Methods for production of hybrid wheat

Details Methods for production of hybrid wheat Methods for production of hybrid wheat

1999-03-09

2002-06-18

Campell, Bruce R. (Department: 1661)

Multicellular living organisms and unmodified parts thereof and

Method of using a plant or plant part in a breeding process...

Method of breeding using gametophyte control

C800S260000, C800S266000, C800S267000, C800S320300, C800S320000

Reexamination Certificate

active

06407311

ABSTRACT:

FIELD OF THE INVENTION
The present invention concerns the production of hybrid seeds of common and durum wheat that yield hybrid plants that are highly heterozygous and phenotypically uniform. More specifically, the present invention concerns a new method, based on chromosome engineering, for maintaining a male-sterile female parental line for use in the production of hybrid wheat plants, which female line is homozygous for a recessive mutant male-sterility allele, for a recessive marker allele(s) and for a dominant pollen-killer allele, and a new maintainer line for maintaining the female parental line which is isogenic to the female line but has an additional alien engineered chromosome carrying a dominant male-fertility allele, a recessive pollen-killer allele susceptible for a pollen-killing of the dominant native pollen-killer allele, and a dominant selectable marker allele(s). All the alleles on the alien chromosome arm are permanently linked due to lack of pairing and recombination between the alien and the wheat chromosomes. The presence of the recessive pollen-killer allele on the alien engineered chromosome ensures that all the maintainer viable male gametes will lack this chromosome and consequently, the dominant male-fertility allele and the selectable marker allele. On one hand, about 20-50% of the female gametes will carry the alien engineered chromosome. When the selectable marker is an allele affecting plant height (plants carrying the engineered chromosome are taller by 8-10 cm from those not carrying it), it is possible to harvest the tall plants separately from the short plants. From the seeds that are developed on the tall plants about 20-50% carry the alien engineered chromosome and therefore, they will develop into male-fertile plants, and 50-80% lack this chromosome and will develop into male-sterile plants. The ability to harvest separately, each year, the seeds of the tall plants keeps constant the proportion of the male-fertile plants in the maintainer. When the selectable marker is a herbicide resistance gene (e.g., resistance to chlorotoluron), it is possible to apply the herbicide onto the progeny of the selfed maintainer, thereby to kill all the plants that lack the engineered chromosome (the male-sterile plants) while only the maintainer (the male-fertile) plants survive. This makes it possible to grow in each generation only the male-fertile plants from the progeny of the selfed maintainer. When the selectable marker is blue aleurone (an endosperm coloring trait), it is possible to separate the seeds that were developed on the maintainer line into blue seeds from which male-fertile plants (maintainer line) are developed, and natively colored (red/white) seeds from which male-sterile plants (female line) are developed. The possibility to sort out the seeds of the male-sterile female line directly from the progeny of the selfed maintainer line simplifies the system and reduces to a great extent the production cost of the hybrid seeds. The invention further provides new methods for producing the maintainer line, new methods for converting a desired cultivar into a male-sterile female line and a maintainer line for the female line, and a new method for hybrid wheat production in which the resulting hybrid plants are all heterozygous for the recessive mutant male-sterility allele and are, therefore, male-fertile.
BACKGROUND OF THE INVENTION
It has been well established that many hybrid plant lines have higher yields than pure, true breeding plant lines, and exhibit improved quality and greater tolerance to environmental and biotic stresses. Unlike corn in which male and female flowers are physically separated, common (bread) (
Triticum aestivum
var.
aestivum
) and durum (macaroni) (
T. turgidum
var.
durum
) are predominantly self-pollinating species and every flower contains both female and male organs. To produce hybrid seeds, it is therefore necessary to male-sterilize the female parent. Since hand emasculation is impractical in wheat, male-sterility may be brought about by application of chemical hybridizing agents (CHAs) or by genetic means. Utilization of a CHA to male-sterilize wheat plants is expensive, inefficient and pollutant. Indeed, the use of CHAs is currently mainly confined to scientific experiments.
The following conditions are required for the production of hybrid seeds by genetic means: 1) Complete and stable male-sterility of the female parent; 2) Complete and stable fertility restoration by the male parent; 3) Easy propagation of the female (male-sterile) parent by a maintainer line. Although these conditions are known to wheat geneticists there has, however, not been a breakthrough in hybrid wheat production during the 46 years since the first male-sterile wheat was described (Kihara, 1951).
There are two main types of genetic male-sterility that can be exploited for hybrid seed production: cytoplasmic male-sterility (CMS) in nuclear substitution or alloplasmic lines, caused by the incompatible interaction of an alien cytoplasm with the common wheat nucleus, and genic male-sterility (GMS) in euplasmic lines, caused by a recessive mutation or a deletion of a nuclear gene(s) which normally confers male-fertility in common wheat cytoplasm. It should be noted that CMS which involves an alien cytoplasm, usually reduces the yielding capacity of the hybrid, while GMS which involves a native cytoplasm should allow for a normal expression of the genome, and hence a full yielding capacity of the hybrid.
Whereas in many commercial crops (e.g. corn) it is the genic male-sterility which prevails, this type has not yet been fully exploited in common or durum wheat. Most attempts in common wheat have been directed to producing hybrid seeds on the basis of cytoplasmic male-sterility. In this respect, the cytoplasm (G cytoplasm) of another species of wheat,
Triticum timopheevii
, was widely used. Alloplasmic lines containing this cytoplasm are male-sterile. Another type of cytoplasm that was studied is that of
Aegilops variabilis
(the S
v
cytoplasm). This cytoplasm causes male-sterility in lines deficient for a S
v
restorer on chromosome arm 1BS. However, as noted above, the use of an alien cytoplasm as a sterilizing factor in common wheat has a major drawback since various important traits are negatively affected by the interaction between the common wheat nucleus and the alien cytoplasm. In addition, it has been difficult to find stable fertility restoration genes for such alloplasmic male-sterile lines, which are highly effective in a wide range of genotypes. Moreover, the system requires breeding of the male parent too (e.g. introduction of genes that can restore male-fertility to the alien cytoplasm), thus rendering hybrid seed production more expensive and limiting the number of male parents that can be tested for combining ability (contribution to a significant hybrid vigor).
Genic male sterility, on the other hand, is expressed in a normal common or durum wheat cytoplasm. Hence, no cytoplasm-induced deleterious effects on plant performance are expected. Further, using a female parent homozygous for a recessive male-sterility allele, any wheat cultivar which is by its nature homozygous for the dominant allele conferring male-fertility, can be used as a male parent that will restore complete fertility to the F
1
hybrids. There is no need to breed for male lines and no limitation exists for the number of males which can be crossed with the male-sterile females and evaluated for their combining ability.
Several chromosome arms have been described in common wheat which carry genes affecting male-fertility, e.g. chromosome arms of group 4: the long arm of chromosome 4A (4AL), the short arm of chromosome 4B (4BS) and the short arm of chromosome 4D (4DS), carrying the normal male-fertility Ms-A1, Ms-B1 and Ms-D1 genes, respectively, and the long arms of the group 5 chromosomes: 5A, 5B and 5D (5AL, 5BL and 5DL, respectively), carrying the Ms-A2, Ms-B2 and Ms-D2 genes, respectively. However, until now, only in the Ms-B1 locus, on the dis

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