Tomato plant resistant to tomato brown rugose fruit virus

Abstract

The present invention relates to a tomato, Solanum lycopersicum, plant that is resistant to Tobamovirus, wherein the plant comprises one or more genomic sequences conferring Tobamovirus resistance. More specifically the invention relates to a tomato plant that is resistant to Tomato Brown Rugose Fruit Virus (TBRFV). The present invention further relates to a genomic sequence or locus providing resistance to Tobamovirus. In addition, the present invention relates to methods for proving a tomato plant that is resistant to Tobamovirus.

Claims

1. A Tobamovirus resistant Solanum lycopersicum plant, wherein the plant comprises a Tomato Brown Rugose Fruit Virus (TBRFV) resistance gene encoding a TBRFV resistance protein comprising polypeptide sequence SEQ ID NO: 116.

2. The plant of claim 1, wherein the resistance gene comprises nucleotide sequence SEQ ID NO: 115.

3. The plant of claim 1, wherein the plant is resistant to Tobamovirus strains Tm0, Tm1, and Tm2.

4. The plant of claim 3, wherein the plant is resistant to Tobamovirus strain Tm0.

5. The plant of claim 3, wherein the plant is resistant to Tobamovirus strain Tm1.

6. The plant of claim 3, wherein the plant is resistant to Tobamovirus strain Tm2.

7. The plant of claim 1, wherein the plant is resistant to Tomato Brown Rugose Fruit Virus (TBRFV).

Description

(1) The present invention will be further detailed in the following examples and figures wherein:

(2) FIG. 1: Shows an overview of the mapping of the locus providing resistance against Tobamovirus, more specifically TRBFV in S. lycopersicum. F1 plants were created by crossing S. habrochaites line 90479-3 that was selected for resistance phenotype with S. lycopersicum lines OT9 and OT1317 to create two populations for mapping. Over 700 plants were tested on TRBFV resistance and several recombinant plants (21 plants) were selected and the results of the disease test were combined with the marker data. Several molecular markers (M1 to M42) have been used to determine the position and size of the genomic sequence providing resistance to TRBFV. A clear segregation was observed between resistant (R) and susceptible plants (S). The results indicated that a genomic region located between markers M16 and M17 was providing the TRBFV resistance; the corresponding locus (named LYC4943 R Locus) is 133.515 bp in length and comprises several putative genes. Based on further fine mapping, the size and location of the genomic sequence that was harbouring the TBRFV resistance was determined to be between markers M33 and M38 and was approximately 68.000 bp larger compared to the SL2.40 reference genome of S. lycopersicum (85.240 bp vs. 17.328 bp, respectively). It is therefore most likely that one or more genes that are located within this region, indicated as “TBRFV region”, are providing the TBRFV resistance.

(3) FIG. 2: Shows the results of a qPCR for the detection of TBRFV in infected and uninfected tomato plants (S. lycopersicum) of the present invention and plants that do not comprise the TBRFV resistance locus. Low Ct values (i.e. below 30) indicate the high presence of viral RNA present in the samples. OT9 is a tomato plant that does not comprise the TBRFV resistance locus. The control sample (OT9 uninfected) showed a Ct value of between 35 and 40 cycles and the infected control sample (OT9 infected) showed a Ct value of between 20 and 25. Plants that show a Ct value above 30 cycles, preferably around 35 cycles were considered resistant, whereas plants that show a Ct value below 30 were considered susceptible. Tomato plants comprising the TBRFV resistance locus, homozygous (B) or heterozygous (H) have a Ct value above 30 cycles and were considered as being resistant. Furthermore, the results showed that the resistance is dominant Plants that did not comprise the TBRFV resistance locus (A and OT9 infected) showed a Ct value of between 20 and 25, indicating that the plant was susceptible to TBRFV infection.

(4) FIG. 3: Shows a schematic overview of the genomic sequences SEQ ID No. 1 to SEQ ID No. 18 of the present invention that encode for one or more genes or genetic elements that provide resistance to Tobamovirus.

(5) FIG. 4: Shows an overview of a further mapping of the locus providing resistance against Tobamovirus in addition to FIG. 1. A further recombinant selection has been performed by further genotyping plants with M33 and M38 to identify recombinant plants in the identified TBRFV region and further limit this TBRFV region. Recombinant plants have been further genotyped with markers (M-SEQ 10, M-SEQ 11-1, M-SEQ 11-2, and M-SEQ 14) covering the TBRFV locus and were specifically designed to eliminate candidate regions in the TBRFV locus, i.e. the genomic sequences SEQ ID No. 1 to SEQ ID No. 18 of present invention that encode for one or more genes or genetic elements that provide resistance to Tobamovirus. Recombinant plants 15321-02, 15321-03 and 15321-07 were screened for resistance by inoculation with TBRFV isolate AE50. Based on these recombinant plants in combination with phenotyping, ELISA and qPCR data for the determination of TBRFV infection, it was concluded that the gene conferring resistance is part of genomic SEQ ID No 14. Plants 15321-02 and 15321-03 do not comprise SEQ ID No 14 and were shown to be susceptible to TBRFV, with high ELISA scores and low qPCR ct-values that correspond to the values obtained with the susceptible control line OT9, indicating virus infection. Plant 15321-07 comprises the SEQ ID No 14 and was shown to be resistant to TBRFV, with low ELISA scores and high qPCR ct-values.

(6) FIG. 5: Shows the TBRFV infection by ELISA in a homozygous TBRFV resistant line (15322-04) as well as a susceptible control line (OT9). Plants were infected with TBRFV (+TRBFV) and infiltrated with construct VIGS-01a that specifically targets the TRBFV resistance gene or with construct VIGS-01b which targets a different region within the identified TRBFV region. ELISA reading was done by measurement of absorption at 405 nm. Control plants OT9 infected by TBRFV resulted in absorption levels of 2000 abs or higher, whereas the resistant plant lines infected with TRBFV resulted in absorption levels of approximately 500 abs. In cases where the TRBFV resistance gene was silenced by VIGS-01a in the resistant plant lines, absorption levels of between 1500 and 2250 abs were measured, indicating viral infection. Silencing by VIGS-01b in the resistant plant lines, resulted in similar absorption levels as was observed in the infected resistant plant lines that were not silenced by VIGS.

(7) FIG. 6: Shows the TBRFV infection by qPCR in a homozygous TBRFV resistant line (15322-04) as well as a susceptible control line (OT9). Plants were infected with TBRFV (+TRBFV) and infiltrated with construct VIGS-01a that specifically targets the TRBFV resistance gene or with construct VIGS-01b which targets a different region within the identified TRBFV region. The infected control sample showed a Ct value of approximately 12 or 13. The resistant plant lines infected with TRBFV showed a Ct value of approximately 30, indicating TBRFV resistance. In cases where the TRBFV resistance gene was silenced by VIGS-01a in the resistant plant lines, Ct values were observed to drop to between approximately 12 to 20, higher than the infected control cells, and clearly indicating viral infection. Silencing by VIGS-01b in the resistant plant lines, resulted in similar Ct levels (Ct value of ˜30) as was observed in the infected resistant plant lines that were not silenced by VIGS.

EXAMPLES

(8) Inoculation of a tomato plant with TBRFV

(9) The TBRFV isolate AE050 (Origin: Saudi Arabia) was used to perform the disease assays. As plant material, the Line OT9, which is a plant line susceptible for TBRFV, was used for virus maintenance. Symptomatic leaves received from the original samples were used for sap-mechanical inoculation on the Line OT9. The virus was maintained on systemically infected tomato plants OT9 by monthly sap-mechanical inoculation on new 3 weeks-old seedlings.

(10) The tomato plants of the species of Solanum pennellii, S. peruvianum, S. chilense, S. habrochaites, S. pimpinellifolium, S. neorickii, S. corneliomulleri, S. chmielewskii, S. cheesmaniae, S. galapagense have been screened (˜800 out of 912 wild Solanum accessions in total). Twelve plants of each accession were infected with TBRFV isolate AE050.

(11) Seeds were sown in vermiculite, seedlings were transplanted in rockwool blocks and inoculated at 4 weeks after sowing. As starting material symptomatic leaves from infected-OT9 were collected and ground in a mortar and pestle in chilled demi water with carborundum (1 gr/100 mL). The oldest leaf from 3 weeks-old seedlings of each test plant was mechanically inoculated with AE050 by gently rubbing the leaf once with one finger.

(12) The plants were phenotyped by visual scoring of the plants and the leaves. Plants were scored for visual symptoms at regular time intervals. Symptoms were visually assessed at 2, 4 and 6 weeks after inoculation, and ELISA tests on remaining plants were done from 6 weeks onwards, with 1 month intervals. More than 50% of the plants showed already symptoms at 2 weeks after inoculation.

(13) Visual scoring was performed on a weekly basis. Plants were scored for visual symptoms. The presence of yellowing, mosaic pattern on leaves, leaf deformation (narrowing, mottling) was recorded on a weekly basis at the plant level. First symptoms were typically observed 12-14 days post-inoculation. Plants were categorized as “resistant” when no such symptoms on leaves were observed. Plants displaying any of the symptoms on leaves were categorized as “susceptible”. Leaf samples were collected from asymptomatic plants (i.e. resistant) to test for the presence of virus by ELISA.

(14) The screening allowed the selection of several candidates for resistance breeding, with the best candidate being LYC4943, a S. habrochaites accession from Peru. LYC4943 was symptomless and tested virus-free by ELISA for more than 15 weeks after inoculation.

(15) Determination of TBRFV Infection by ELISA

(16) Infection was determined by ELISA. One apical leaf (fully expanded) of every plant was collected. Leaves were crushed using a Type R302 D63N-472 machine (VECTOR Aandrijftechniek B.V., Rotterdam, The Netherlands) and sap was collected by adding 2 mL of PBS-Tween buffer. 100 μL of the extract was used for ELISA with antibodies against ToMV (supplier Prime Diagnostics, Wageningen, The Netherlands). ELISA reading was done by measurement of absorption at 405 nm with a FLUOstar Galaxy apparatus. Plants that gave absorption values more than 1.5 times of the clean control plants were considered infected (susceptible).

(17) Bioassays and Mapping of TBRFV Resistance Genomic Sequence

(18) The original LYC4943 (S. habrochaites) seed lot was segregating for the resistance. Nine different F1 families were sown for bioassay in order to identify the F1 families which were completely resistant (resistance is fixed) and which would be used for further backcrosses. Four F1 families germinated and were tested in bioassay. F1 plants created with LYC4943 plant 3 (90479-3) were selected for resistance phenotype to create two populations for mapping, choosing the S. lycopersicum lines OT9 and OT1317 as backcross lines. Markers M1 to M42 (respectively SEQ ID No. 19 to SEQ ID No. 102) that have been used in the mapping are listed in Table 1.

(19) 298 plants (OT9×90479-3)×OT9) and 484 plants (OT1317×90479-3)=total of 782 plants were inoculated with the TBRVF isolate AE050. Two to three weeks after inoculation the TBRFV symptoms were present and phenotyping by eye was done. A clear segregation was observed between resistant (R) and susceptible plants (S) and resistant phenotypes could be linked with marker M1 (see Table 1) located on chromosome 8 at 2673609 bp on the reference genome SL2.40 (S. lycopersicum). 92 plants have been genotyped with 26 markers in order to flank the QTL (M2 to M27, see Table 1). Based on these results the resistance could be mapped between 53118984 bp and 57038544 bp on the reference genome SL2.40 (between M8 & M20, See Table 1 and FIG. 1).

(20) TABLE-US-00001 TABLE 1 Pos. Pos Primer name Primer sequence SL2.40 on Locus SEQ ID No. M1_F GGTACAACAATTGACCAAGG  2672994  19 M1_R GCTAATTAAAAAGGAACATCAGC  20 M2_F GCTATGGCGGAGAAGTCAAG    18124  21 M2_R AGTCACCTCCATAGTAGACC  22 M3_F GGATCCAAGTTGTGTTCGAAC   881036  23 M3_R CTTCTCATCAATGTATGTGATTTC  24 M4_F TGTATAACACCTGGTGCTCC 15384575  25 M4_R CCATTTTCTGTTACAAAATTTCAG  26 M5_F GCTTCCCAATTTATGCTGAAG 47887679  27 M5_R GAGCCTCCCACTATAGTAATC  28 M6_F AGAATTATCATTTGCAGGATCG 50957946  29 M6_R CTATGGTTCGCATGTCATGC  30 M7_F CACAACGGCAATATACCTTGC 53082561  31 M7_R TGGAAGTATTAGAAAGGTCCAG  32 M8_F CCATTGAGAATAACTACTGTAC 53118984  33 M8_R CCACAGGATGACTAACTTGG  34 M9_F TGCAGTATTGATCGCATCTTCTA 53452252  35 M9_R GTTTGTTGCTGCCCTCAAA  36 M10_F TGATCAAGAATTTTGTTTTAGCATAGA 55664335  37 M10_R TAAAGCATCAATTTTGCATTGTCT  38 M11_F TCGAAGACTAACAAAGTCCTTGTAGA 55720872  39 M11_R GACACTCCGGCAGTTCCTT  40 M12_F TTCTTATGTGAAAAATTGGGTGG 55776574  41 M12_R ACTACGCAGTCCCACAGCTT  42 M13_F TTGTTTGGTGGATCCATGTG 56448988  43 M13_R AGGGAAAGGGCAAGGATG  44 M14_F GATCTACCAATGGCTATTCATC 56781521  45 M14_R GCAAAACTTAACCGGTCTAAG  46 M15_F TCTCGATGGTTGATAATTTGTTC 56874054  47 M15_R GGAATCGATTAACACTGGTTC  48 M16_F CATCTTATTGAAGCTCTGCTG 56920720  49 M16_R CAAACAGTCCCTATTCAACAC  50 M17_F GGTCTTGCGCTAATCAAAAG 56990004  51 M17_R GCGTTGTGGTGAAAGTTTTATC  52 M18_F CTTGTTTGGATGGTTGTCAC 57003163  53 M18_R CAACAAAAAATATACAATCCGTCC  54 M19_F GAGATAGAAGGAAACTTACCG 57024614  55 M19_R CAATTATCCCCTCAGTTCTG  56 M20_F TATGCCTGTCCCTGAAAAGG 57038544  57 M20_R AGGGTCTTGGATCAAATCTTGA  58 M21_F TGTGGACTTGGAGTGGTATC 57427631  59 M21_R GTAGAAAGGGTAGGCATGTTC  60 M22_F TACCAAAGCAAACACTGCCAC 57441418  61 M22_R AGCCACGAGATATATATTGGAG  62 M23_F GATAAGACCGCCAATAACTAG 60844273  63 M23_R GTGATCTCCATGAGCAAATG  64 M24_F TGAGTTGAGATGCTGTTCTAG 61412883  65 M24_R AGTCCACCAAGACTTAAAGAG  66 M25_F GTCTGCCTTCTCTTGCATGC 62277547  67 M25_R GTTGCTCCAGACAGAATAAGC  68 M26_F CATCGAAGAGATGTGTAGGG 62418391  69 M26_R TGCAGTTGAAGTAGACTTCAG  70 M27_F TCAACGTTAGTGGTGATGCTAG 62783214  71 M27_R CAATTGCAGAAAGTGAAGCTG  72 M28_F GTGGATTCAGTTAAACCAGAAC 56924513   4076  73 M28_R GACATGTGGAACTTGACAAAAC  74 M29_F GCGAGAGAAAAGATTCTCTAC 56934501  12765  75 M29_R CATTCTTCACTCTCTCAAGATG  76 M30_F CGTTTGGTGATCTGCCTTGTCTT 56934846  13109  77 M30_R TCTTCTTGTAGGGAATCCAGAATC  78 M31_F GTGTCCTGTGCTTGTTATTCC 56935054  13317  79 M31_R CCTCAAACCTATTGCATCTGACA  80 M32_F CGGCTCAGCGAGGAAGTGCAG 56935849  14113  81 M32_R CGTTGACTGTTTTTCTTTATG  82 M33_F GTAAGCTCCTTCATGTCAGC 56941043  15893  83 M33_R CAAGTATTGTCTGCCGAGTAAC  84 M34_F GCGTACAGACATATTTATGCAAC 56942927  17777  85 M34_R GAACAGCTAAAAGTAAGAGCAC  86 M35_F GTTCATGTGTGTTTATGGACC 56943610  18416  87 M35_R CTTCACTAAATAAATAAGTGGTAG  88 M36_F TATGGATTTGTGTCTCAGAAGA 56944105  18912  89 M36_R TGTGGTCACCAAGTGGGTTTC  90 M37_F GTCTTCCAGAGCAGTTATGCAAG 56945167  19974  91 M37_R TGAGACTGCTAAGTTGACTTGTTTG  92 M38_F GTACACCAAATCACAGACATCG 56958371 101133  93 M38_R CCCAATTTGGTTTGTGTTGGAC  94 M39_F GAAATTCCTTGCCTCCTCTC 56961307 104063  95 M39_R GTGGAAGCCATAGTGTACAAG  96 M40_F CATATTATACAGTGAAAGCTTTG 56965103 107926  97 M40_R GAATTGCAGTTCACTTGCTTC  98 M41_F CCACAAAGCTAAAAAGGGATTG 56969685 112529  99 M41_R TCCATGTGAGTTTTGTGTGTG 100 M42_F GCCACATAAATTACATATAGCTG 56981278 125792 101 M42_R GAACTATTCAACAAGCATAATAC 102 M-SEQ 10_F GTCTTACAATAGTAAAATGCGCAG  36480 105 M-SEQ 10_R GCGGTTCGTTGATATTCCAAC 106 M-SEQ 11_1F AGCGAAAGCGGAAGGAGTAC  48748 107 M-SEQ 11_1R TGTGGTGAGTAAGCAATGAATC 108 M-SEQ 11_2F GTGTATAATTCGCCAGAATATACGG  52303 109 M-SEQ 11_2R CGTTTAGATAATTGTATATTACACATATG 110 M-SEQ 14F CAAATTATTACTTATGTTGTGATTTG  77410 111 M-SEQ 14R ATTAAGCCATGATACACAAATTAC 112

(21) The whole population of 782 plants have been genotyped with the flanking markers M8 & M20 in order to find the recombinant plants for further fine mapping. This resulted in 21 recombinant plants (See FIG. 1). These 21 recombinant plants have been selected and genotyped with 11 markers M9 to M19 in order to further fine map the region (Table 1). The resistance could be fine mapped between 56920720 and 56990004 (marker M16 and M17) on the reference genome SL2.40.

(22) Sequencing the resistant LYC4943 region using Oxford Nanopore sequencing technology resulted in a locus of 133.515 bp. The 21 recombinant plants have been genotyped with extra markers in this specific locus (M28 to M42) of LYC4943. Based on the recombinant plants, plants 594 and 608, it was determined that the resistant region was located between positions 56941043 and 56958371, based on the reference genome SL2.40, corresponding with positions between 15.893 and 101.133 on the LYC4943 locus (between M33 and M38, see FIG. 1).

(23) Based on the fine mapping, the size and location of the genomic sequence that was harbouring the TBRFV resistance was determined to be between markers M33 and M38 and was approximately 68.000 bp larger compared to the SL2.40 reference genome of S. lycopersicum (85.240 bp vs. 17.328 bp, respectively). It is therefore highly likely that one or more genes are located within this region, indicated in FIG. 1 as “TBRFV region”, providing the TBRFV resistance and is indicated as SEQ ID No. 3 in this application. Based on the reference genome SL2.40 and in silico prediction analysis (ITAG 2.3), at least one gene is located in the fine mapped region that encodes for a CC-NBS-LRR resistance protein. Blasting the fine mapped TBRFV region against the database of National Center for Biotechnology Information (NCBI), resulted in seven genomic fragments of which five have homology with NBS-LRR resistance proteins (SEQ ID No. 8, No. 9, No. 10, No. 11 and No. 14) and two have homology with LRR receptor-like serine/threonine-protein kinases (SEQ ID No. 12 and SEQ ID No. 13).

(24) Next, further fine mapping was performed and a recombinant selection has been performed by genotyping 668 BC2 plants ((OT9×90479-3)×OT9×OT9) with M33 and M38 in order to identify recombinant plants in the TBRFV region, which resulted in three plants 15321-02, 15321-03 and 15321-07 (see FIG. 4). These three plants were tested for resistance by inoculation with TBRFV isolate AE50. Approximately three weeks after TBRFV inoculation the plants were phenotyped by observation, and ELISA and qPCR was performed to monitor virus infection. The recombinant plants have been genotyped with markers (M-SEQ 10, M-SEQ 11-1, M-SEQ 11-2, and M-SEQ 14, respectively SEQ ID No. 105 to SEQ ID No. 112) covering the TBRFV locus and were specifically designed to eliminate candidate genes in the TBRFV locus. This approach provided insight into which of the candidate genomic sequences SEQ ID No. 1 to SEQ ID No. 18 of present invention specifically provides resistance to TBRFV. Based on the recombinant plants and phenotyping by disease tests, ELISA and qPCR, we concluded that the gene conferring resistance is encoded by genomic sequence of SEQ ID No 14, more specifically the coding DNA sequence of SEQ ID No. 115 encoding the protein of SEQ ID No. 116.

(25) Validation Tm0, Tm1 & Tm2 Strain Resistance in Plant Comprising the TBRFV Resistance Locus

(26) A tomato plant of the present invention (S. lycopersicum) comprising the TBRFV resistance locus (SEQ ID No. 1) was tested for resistance against the Tm0, 1 and 2 strains. The presence of the TBRFV resistance locus was determined by markers M16, M17 and M33. It was furthermore confirmed that the plant does not contain the Tm2.sup.2 gene (is a known gene that provides resistance against Tm0, 1 and 2 strains). In some case the plant did contain the Tm1 resistance gene. As a control, plants were selected that did not contain the TBRFV resistance locus.

(27) Eight plants (See Table 2, 1 to 8) of which six plants comprise the TBRFV resistance locus (heterozygous), and two plants (7 and 8) do not have the TBRFV resistance locus have been inoculated with the Tm0 isolate. Eight plants (See Table 2, 9 to 16) of which six plants comprise the TBRFV resistance locus (heterozygous), and two plants (15 and 16) do not have the TBRFV resistance locus, have been inoculated with the Tm-1 isolate. Eight plants (See Table 2, 17 to 28) of which four plants comprise the TBRFV resistance locus (two homozygous 17, 18+two heterozygous 19, 20), and four plants not have the TBRFV resistance locus have been inoculated with the Tm2 isolate. As control the susceptible cultivated tomato line OT95 was also inoculated with all three strains.

(28) First symptoms were typically observed after 12-14 days post-inoculation. Plants were categorized as Resistant (R) when no mosaic pattern symptoms on leaves were observed; plants displaying any of the symptoms on leaves were categorized as Susceptible (S). The phenotype of every single plant has been compared with the TBRFV genotype. Results are summarized in Table 2 below.

(29) TABLE-US-00002 TABLE 2 Plant Isolate Phenotype M16 M33 M17 Tm2 Tm1  1 Tm0 R h h h a a  2 Tm0 R h h h a a  3 Tm0 R h h h a a  4 Tm0 R h h h a h  5 Tm0 R h h h a h  6 Tm0 R h h h a h  7 Tm0 R a a a a h  8 Tm0 R a a a a h OT95 Tm0 S a a a a a OT95 Tm0 S a a a a a  9 Tm1 R h h h a a 10 Tm1 R h h h a a 11 Tm1 R h h h a a 12 Tm1 R h h h a a 13 Tm1 R h h h a h 14 Tm1 R h h h a h 15 Tm1 S a a a a a 16 Tm1 S a a a a h OT95 Tm1 S a a a a a OT95 Tm1 S a a a a a 17 Tm2 R b b b a a 18 Tm2 R b b b a a 19 Tm2 R h h h a a 20 Tm2 R h h h a a 21 Tm2 S a a a a a 22 Tm2 S a a a a a 23 Tm2 S a a a a a 24 Tm2 S a a a a a OT95 Tm2 S a a a a a OT95 Tm2 S a a a a a R = resistant, S = susceptible, a = no resistance locus present, h = heterozygous, b = homozygous
Result Tm0

(30) All plants that contained the TBRFV resistance locus were resistant. Plants 7 and 8 did not contain the TBRFV resistance locus but were also resistant. A reason that could explain the results is that the Tm1 gene is causing the resistance to ToMV isolate Tm-0. In addition, plant 1, 2 and 3, did not contain the Tm1 gene, but did contain the TBRFV resistance locus, showed to be resistant.

(31) Result Tm1

(32) The resistant phenotypes are linked with the TBRFV genotypes, providing resistance against ToMV isolate Tm-1.

(33) Result Tm2

(34) The resistant phenotypes (hetero-, homozygous) are linked with the TBRFV genotypes, providing resistance against ToMV isolate Tm-2.

(35) Determination of TBRFV Infection in Tomato (S. lycopersicum) by qPCR

(36) Tomato plants comprising the TBRFV resistance locus (heterozygous or homozygous) and plants not containing this region have been selected for TBRFV bioassay using markers (M16 and M17). Plants were infected with TBRFV and the susceptible tomato line OT9 has been included as control (OT9 non-infected and infected).

(37) After 3 weeks of inoculation, one leaf from the top of the plant of every single plant was collected in a 2 ml tube which contain a 6.35 mm metal bullet. The tube was frozen in liquid nitrogen. The tubes were shaken with high speed to pulverize the plant material. After spin down the tube, the standard RNA extraction using Macherey-Nagel™ NucleoSpin™ RNA Plant was carried out. RNA concentration was measured using DropSense 96 (Trinean) and was diluted to a concentration of 100 ng/μl. 900 ng have been used for cDNA synthesis using M-MLV Reverse Transcriptase (Invitrogen). 10 ng cDNA was used for Real-time PCR using LC green as Intercalating dye. Two primer combinations for amplifying the TBRFV strain were used, see Table 3 (SEQ ID No. 103 and SEQ ID No. 104, respectively).

(38) TABLE-US-00003 TABLE 3 qPCR primer name Sequence TBRFV-3 Fw ACCGTTCAACGGCAATTTAGC TBRFV-3 Rev CCTATACACCTTAAAACCACTG

(39) The more viral RNA present in the samples the lower the Ct value in the qPCR, since less PCR cycles are required to amplify the cDNA (of the viral RNA) and pick up a signal. The control sample (OT9 uninfected) showed a Ct value of between 35 and 40 cycles and the infected control sample (OT9 infected) showed a Ct value between 20 and 25. Therefore plants that show a Ct value above 30 cycles, preferably around 35 cycles were considered resistant, whereas plants that show a Ct value below 30 were considered susceptible (see FIG. 2).

(40) Tomato plants comprising the TBRFV resistance locus, homozygous (B) or heterozygous (H) all have a Ct value above 30 cycles and can be considered as resistant. The results are showing that the resistance is dominant. Plants that did not comprise the TBRFV resistance locus (A) showed a Ct value of between 20 and 25, indicating that the plant was susceptible to TBRFV infection.

(41) Sequencing of Genomic Sequence of Resistant Tomato Plant

(42) Genomic DNA was isolated from a resistant plant (S. lycopersicum) of the present invention, i.e. comprising the TBRFV resistance locus, according to the protocol as published on 27 Apr. 2018 in Nature, Protocol Exchange (2018), Rachael Workman et al,. “High Molecular Weight DNA Extraction from Recalcitrant Plant Species for Third Generation Sequencing”. The sequencing libraries were prepared using the PCR free, no multiplex, DNA Ligation Sequencing Kit-Promethion (SQK-LSK109). The isolation procedure resulted in high quality sequencing libraries to be used in the Oxford Nanopore system for sequencing (ONT sequencing). Promethion Flowcell Packs (3000 pore/flowcell) version R9.4.1. were used for sequencing.

(43) Furthermore, to further resolve the TBRFV locus and identify the gene providing the TBRFV resistance, we performed ONT sequencing on a resistant line (LYC4943). Sequencing of the entire transcript isoforms of the resistant LYC4943 line was done using the Iso-Seq analysis application (Pacific Biosciences of California, PacBio). This resulted in only one candidate resistance transcript/gene located in region between markers M33 and M38, more specifically the TBRFV resistance gene of SEQ ID No. 115. This transcript was predicted to encode for a CC-NBS-LRR resistant protein of SEQ ID No. 116.

(44) Gene Validation Using VIGS

(45) To confirm that the TBRFV resistance gene (SEQ ID No 115) was indeed the gene conferring resistance to TBRFV, a Virus Induced Gene Silencing (VIGS) analysis was performed. Tobacco rattle virus (TRV)-derived VIGS vectors have been abundantly described to study gene function in plants such as Arabidopsis thaliana, Nicotiana benthamiana, Lycopersicon esculentum and other plants (see for example Huang C, Qian Y, Li Z, Zhou X.: Virus-induced gene silencing and its application in plant functional genomics. Sci China Life Sci. 2012; 55(2):99-108).

(46) As such, two VIGS constructs were developed (Table 4), one construct VIGS-01a to specifically target SEQ ID No 115 and a control construct VIGS-01b that targets SEQ ID No. 7, i.e. a sequence also located within the previously identified TBRFV locus.

(47) TABLE-US-00004 TABLE 4 VIGS construct Sequence VIGS-01a GGAAGATTTTAATGAAAAGAGGTTGATAAAGA (SEQ ID No. 113) AAATTGTAGAATCTATTGAAGAAAAGTCACTT GGTGACATGGACTTGGCTCCACTTCAAAAGAA GCTTCAGGACTTGCTGAATGGAAAAAAATATT TGCTTGTCTTAGATGATGTTTGGAATGAAGAT CAAGATAAGTGGGCTAAGTTAAGACAAGTCTT GAAGGCTGGAGCAAGTGGTGCTTATGTTCTAA CCACTACC VIGS-01b AGAAGATTTTGATGAGAAGAAGTTGATAAAGG (SEQ ID No. 114) CAATTGTTGAATCTATCGAAGGAAACCCACTT GGTGACCACATGGATTTGGCTCCACTTCAAAA GAAGCTTCAGGACATGTTGAATGGAAAGAGAT ACTTTCTCGTTTTGGATGATGTTTGGAATGAA AATCAAGAAAAGTGGGATAAGATAAAAGCAGT CTTAGAGGTTGGAGCACGAGGTGCTTCTGTTC TAACCACCACT

(48) The VIGS fragments were synthesized (IDT, gBlocks) and subsequently cloned into a TRV vector. The DNA sequences were confirmed by Sanger sequencing. The vector contained all sequences encoding for proteins that are required for a functional TRV particles including the target sequences. The VIGS vectors including the VIGS-01a and VIGS-01b constructs were transformed into Agrobacterium tumefaciens strain GV3101 and used in VIGS experiments to reduce endogenous mRNA levels in tomato plants used in this experiment. A homozygous TBRFV resistant line (15322-04) as well as a susceptible control line (OT9) were used in the VIGS experiment, in which plants were Agrobacterium infiltrated at seedling stage (cotyledons) followed by TBRFV isolate E50 inoculation three weeks after Agrobacterium infiltration. Two weeks after TBRFV inoculation the individual plants were phenotyped by ELISA and qPCR and this revealed that susceptibility was found in resistant plants infiltrated with construct VIGS-01a whereas no susceptibility had been detected in resistant plants infiltrated using construct VIGS-01b. Results of the ELISA and qPCR are shown in FIGS. 5 and 6, and results have been summarized in Table 5.

(49) TABLE-US-00005 TABLE 5 VIGS- TBRFV # S # R Plants # plants construct infection plants plants R line 15322-04  7 VIGS-01a Yes 7  0 R line 15322-04  6 VIGS-01b Yes 0  6 R line 15322-04 10 No Yes 0 10 S line OT9  6 No Yes 6  0

(50) In the OT9 line all plants were susceptible, as expected. The R line which was shown earlier to be fully resistant became susceptible to TBRFV in cases where the suspected TBRFV resistance gene was silenced using the VIGS-01a construct designed to specifically target this gene, whereas silencing using the VIGS-01b construct (control construct) did not result in any susceptibility of the plants tested. Based on these results it can be concluded that gene SEQ ID No 115 is the conferring resistance to TBRFV.