EP-3518658-B1 - PARTHENOCARPIC WATERMELON PLANTS

Inventors

• SIRIZZOTTI, Alberto
• BERENTSEN, Richard, Bernard
• VRIEZEN, HENDRIK, WILLEM

Dates

Publication Date

20260506

Application Date

20170929

Claims (10)

1. A watermelon plant or plant part or seed comprising at least one copy of a mutant allele of a gene name WOP1, said gene encoding a wild type WOP1 protein of SEQ ID NO: 32 or a protein comprising at least 95% sequence identity to SEQ ID NO: 32 and wherein said protein comprises a myb-like DNA binding domain SHAQKYF-class of SEQ ID NO: 35 wherein said mutant allele encodes a mutant WOP1 protein and wherein said mutant WOP1 protein comprises at least one amino acid of amino acids 47 to 54 of SEQ ID NO: 35 being replaced by another amino acid, preferably amino acid 47 not being a Serine, said mutant allele conferring facultative parthenocarpy when the mutant allele is in homozygous form, and wherein said plant or plant part is not exclusively obtained by means of an essentially biological process.
2. The plant or plant part or seed according to claim 1, wherein said plant or plant part or seed is diploid and is homozygous for the mutant allele.
3. The plant or plant part or seed according to claim 1 wherein the watermelon plant or seed is diploid, triploid or tetraploid.
4. The plant or plant part or seed according to claim 3, wherein the diploid plant or plant part or seed comprises two copies, the triploid plant or plant part or seed comprises three copies and the tetraploid plant or plant part or seed comprises four copies of the mutant allele.
5. A fruit produced by a plant according to claims 2 or 4, wherein the fruit is seedless and is produced in the absence of pollination and is not exclusively obtained by means of an essentially biological process.
6. The plant or plant part or seed according to any one of claims 1 to 4, wherein said plant or plant part or seed further comprises a gene conferring male sterility or a gene conferring stenospermocarpy.
7. The plant part according to any one of claims 1 to 4 wherein the plant part is a cell, a flower, a leaf, a stem, a cutting, an ovule, pollen, a root, a rootstock, a scion, a fruit, a protoplast, an embryo, an anther.
8. The plant according to any one of claims 1 to 4, wherein the plant is a vegetatively propagated plant.
9. A method of producing seedless watermelon fruits, said method comprising growing a triploid watermelon plant comprising three copies of mutant allele according to claim 1 and harvesting the fruits produced by said plants.
10. The method according to claim 10, whereby in said method no pollenizer plant is present and the fruits develop without pollination of the female flowers.

Description

FIELD The present invention is directed to facultative parthenocarpic watermelon plants, producing seedless fruits without pollination of the female flowers, due to the presence of a mutant allele of a recessive gene referred to as WOP1 (for WithOutPapa 1). The present invention also discloses methods for production of said plants and comprises the use of the mutant allele, referred to as wop1, for the production of seedless watermelon fruits. BACKGROUND Most commercial seedless fruits have been developed from plants whose fruits normally contain numerous relatively large hard seeds distributed throughout the flesh of the fruit. Seedless fruits are e.g. known for watermelon, tomato, cucumber, eggplant, grapes, banana, citrus fruits, such as orange, lemon and lime. As consumption of seedless fruits is generally easier and more convenient, they are considered valuable. Fruit development normally begins when one or more egg cells in the ovular compartment of the flower are fertilized by sperm nuclei from pollen. Seedless fruits can result from two different phenomena. In some cases fruit develops without fertilization of the ovule by pollen, a phenomenon known as parthenocarpy. In other cases seedless fruits occur after pollination when seed (embryo and/or endosperm) growth is inhibited or the seed dies early, while the remainder of the fruit continues to grow (stenospermocarpy). In contrast to parthenocarpy, stenospermocarpy requires pollination for initiation of fruit growth. Seedless orange fruits are an example for parthenocarpy. Some orange varieties (e.g. Navel) do not produce viable pollen. They however can be cross-pollinated with pollen from other varieties. In case only the male sterile variety is grown in an orchard, there will be no pollination and parthenocarp seedless fruits will be produced. Propagation of the respective orange trees is commonly done by cuttings followed by grafting to another rootstock. Seedless bananas are triploid. Although pollination in some cases can be normal the vast majority of fruits is seedless. This is explained by the uneven sets of chromosomes (3x) leading to improper division of chromosomes during meiosis and as a consequence to the production of non-viable pollen. Without fertilization, triploid bananas are also able to set and develop seedless fruits. Even when pollination takes place, at most one in three hundred fruits comprises a few seeds. This may be due to the triploid pollen being non-viable, for the reasons explained. Therefore, banana plants can in general be seen to be parthenocarpic. Banana plants are commonly propagated asexually from side shoots or suckers at the base of the main stalk, which can be removed and replanted to continue the cultivar. Growers also propagate bananas by means of tissue culture, in particular for producing disease free material. Seedless cucumber, seedless squash and seedless eggplant are examples for crops which can produce seedless fruits without pollination (parthenocarpy), e.g. under conditions where pollination is impaired (e.g. low temperatures). Nevertheless, commercial quality fruit can be produced under these conditions. All these crops however can produce seed bearing fruits upon pollination. Therefore, these crops are facultative parthenocarpic. Propagation of the crops can be done by self- or cross pollination, in vitro propagation, and grafting. From tomato mutants it is also known that they can produce seedless fruits under conditions where normal pollination/fertilization is impaired (e.g. under circumstances of low temperature). Thus, these mutants are also facultative parthenocarpic. Mutants known for showing this phenotype are pat, pat-2 and the pat-3/pat-4 system. The genes underlying these mutations are not known and the pat-3/pat-4 system seems to depend on multiple loci. Parthenocarpy has also been introduced into several plant species by means of genetic modification. Expression of a bacterial tryptophan monooxygenase (iaaM) conferring auxin synthesis under control of the ovule and placenta specific DefH9 promoter did induce parthenocarpy in cucumbers (Yin et al., 2006, Clular & molecular Biotech. Letters 11, 279-290), eggplant (Acciarri et al., 2002, BMC Biotech. 2(4)), tomato (Rotino et al., 2005, BMC Biotech. 5(32)) and tobacco. These transgenic plants demonstrate the importance of plant hormones in seed and fruit development. That seed and fruit development are besides other factors strongly under control of several plant hormones is well known in the art. Parthenocarpy, including the logical consequence of fruit's seedlessness, can also be induced e.g. by exogenous application of plant hormones, in particular auxin or gibberellin (Ruan et al., Trends in Plant Sci. 17(11), 1360-1385). Seedless watermelons produced currently by breeders are examples for stenospermocarp crops. Normal watermelon plants are diploid (2n). Seedless fruit producing watermelons are hybrids produced by crossing a male dipl