Bremia lactucae resistant plants

#The foregoing applications, and all documents cited therein or during their prosecution (“appln cited documents”) and all documents cited or referenced in the appln cited documents, and all documents cited or referenced herein (“herein cited documents”), and all documents cited or referenced in herein cited documents, together with any manufacturer's instructions, descriptions, product specifications, and product sheets for any products mentioned herein or in any document incorporated by reference herein, are hereby incorporated herein by reference, and may be employed in the practice of the invention. More specifically, all referenced documents are incorporated by reference to the same extent as if each individual document was specifically and individually indicated to be incorporated by reference.

#The instant application contains a Sequence Listing which has been submitted electronically in ASCII format and is hereby incorporated by reference in its entirety. Said ASCII copy, created on Sep. 9, 2016, is named Y795402001.txt and is 3,984 bytes in size.

#The present invention relates to plants and plant parts, in particular lettuce plants (Lactuca sativa L.), which have a broad spectrum resistance to Bremia lactucae. The invention further relates to parts of these plants, to seeds, to propagation material, to the progeny of these plants, and use of the plants as germplasm in breeding for broad spectrum resistance to Bremia lactucae.

#The following detailed description, given by way of example, but not intended to limit the invention solely to the specific embodiments described, may best be understood in conjunction with the accompanying drawings.

#FIG. 1: Determining the percentage of sporulation on a leaf disc surface infected with Bremia lactucae. The illustration shown can be used as a guideline for estimating the percentage of sporulation on a leaf disc.

#Column A, shows examples of six leaf discs that differ in the percentage of the leaf surface covered by sporangiophores of Bremia lactucae. Column B, shows the same six leaf discs which have been sectioned in order to facilitate counting of the sporangiophores. The estimated percentage of sporangiophores on the leaf disc surface is indicated.

#In the research that led to the present invention, novel lettuce plants (Lactuca sativa L.) were developed such that they are resistant against Bremia lactucae, and in particular, have a broad spectrum resistance against this pathogen.

#The said resistance of the invention is controlled by a resistance allele on the bottom of linkage group 9, the inheritance of which is consistent with that of a monogenic dominant trait. The term “dominant” is to mean in this context that the fully achievable resistance is observable in plants which comprises the resistance allele in the homozygous or heterozygous state. The resistance allele according to the invention or an introgression fragment which comprises the resistance allele, is obtainable from the genome of a distantly related wild species, in particular from the genome of wild accessions of Lactuca saligna containing the bott_C9 resistance allele which confers broad spectrum Bremia lactucae resistance, including but not limited to, CGN 15705. While the resistance allele in the context of the invention is obtainable from e.g. L. saligna accession CGN 15705, it is not intended to preclude others to use this accession per se. Therefore, the invention relates only to the bott_C9 resistance allele when present in a L. sativa background.

#The present invention thus relates to a cultivated lettuce plant which comprises a resistance allele which confers a broad spectrum resistance to Bremia lactucae, wherein the resistance allele is located on the bottom of linkage group 9. The resistance allele is located on an L. saligna fragment between markers CLS_S3_4656 and CLS_S3_3349 or is located below CLS_S3_3349 (SEQ ID NO:1), towards the end of the chromosome as shown in FIG. 2. Thus, in one embodiment a cultivated lettuce plant is provided which comprises an introgression from L. saligna on the bottom of chromosome 9, wherein the introgression comprises the sequence of SEQ ID NO: 1 (identifiable using primers of SEQ ID NO: 6 and 7) and/or SEQ ID NO:3 (identifiable using primers of SEQ ID NO: 8 and 9) and/or any L. saligna-genome specific marker in between markers CLS_S3_4656 and CLS_S3_3349 or is located below CLS_S3_3349 (SEQ ID NO:1), towards the end of the chromosome as shown in FIG. 2. In one aspect of the invention, the resistance allele is as found in plants grown from seeds of which a representative sample was deposited under accession number NCIMB 42141. In another aspect of the invention, the resistance allele is introgressed from another Lactuca saligna accession containing the bott_C9 resistance allele which confers broad spectrum Bremia lactucae resistance. Such a Lactuca saligna accession may be identified using one or more molecular markers linked to the bott_C9 resistance allele, for example by one or more of the markers defined herein, such as the markers of SEQ ID NO:1 (marker CLS_S3_3349) and/or SEQ ID NO:3 (marker CLS_S3_4656) and/or any marker in between markers CLS_S3_4656 and CLS_S3_3349 or is located below CLS_S3_3349 (SEQ ID NO:1), towards the end of the chromosome as shown in FIG. 2, or any other marker linked to the resistance allele. Subsequently, those L. saligna accessions having been identified using one or more molecular markers linked to the bott_C9 resistance allele and which comprises the resistance allele of the invention, may be confirmed by phenotypically screening the progeny of a cross between the L. saligna accession and a cultivated lettuce plant for broad spectrum Bremia lactucae resistance. Thus, other L. saligna plants which comprises the resistance allele on the bottom of chromosome 9 can be identified by e.g. screening L. saligna plants for the presence of markers of SEQ ID NO: 1 and/or SEQ ID NO:3 and/or any L. saligna marker in between markers CLS_S3_4656 and CLS_S3_3349 or is located below CLS_S3_3349 (SEQ ID NO:1), towards the end of the chromosome as shown in FIG. 2, and/or for other markers linked to the bott_C9 allele, followed by crossing with a cultivated lettuce plant and phenotypically screening the progeny for broad spectrum Bremia lactucae resistance. Other L. saligna markers linked to the bott_C9 allele can be developed by e.g. sequencing the bott_C9 region or by analyzing a segregating population from a cross between a resistant plant and a susceptible plant and identifying other molecular markers that co-segregate with the resistance phenotype.