Obtaining advanced generations from <Emphasis Type="Italic">Solanum peruvianum</Emphasis> PI 126944 in the genetic background of <Emphasis Type="Italic">S. lycopersicum</Emphasis> by immature seed culture

The accession Solanum peruvianum PI 126944 has been reported as resistant to different biotic and abiotic stresses. In previous works of the group, advanced generations were derived from two interspecific hybrids, including up to pseudo-F₆ generations and backcrosses to the cultivated species of some of the pseudo-F_n generations. Moreover, resistance to Tomato yellow leaf curl virus (TYLCV) and Tomato spotted wilt virus (TSWV) was confirmed in some of the plant materials obtained. Here we describe the development of some advanced backcross generations between the cultivated tomato and S. peruvianum. Three backcross assays were carried out. In the first assay, 16 plants belonging to pseudo-F₄, pseudo-F₅ and pseudo-F₆ generations were backcrossed as male parents to cultivated tomato. Immature seeds from the 408 fruits obtained were platted and 77 plants were regenerated. A total of 21 descendants obtained in the first assay were backcrossed as male parents in the second assay, which allowed the obtaining of 599 fruits and regeneration of 365 plants. The 19 male parents used in the third assay were obtained either in the first or in the second one. Seventeen of them were obtained in the first assay and two in the second. A total of 339 plants were regenerated from 519 fruits. A high number of the plants obtained in these assays has been acclimated. Some plants set fruits with viable seeds.     

Pyramiding of genes conferring resistance to Tomato yellow leaf curl virus from different wild tomato species

Tomato (Solanum lycopersicum) production in tropical and subtropical regions of the world is limited by the endemic presence of Tomato yellow leaf curl virus (TYLCV). Breeding programmes aimed at producing TYLCV‐resistant tomato cultivars have utilized resistance sources derived from wild tomato species. So far, all reported breeding programmes have introgressed TYLCV resistance from a single wild tomato source. Here, we tested the hypothesis that pyramiding resistances from different wild tomato species might improve the degree of resistance of the domesticated tomato to TYLCV. We have crossed TYLCV‐resistant lines that originated from different wild tomato progenitors, Solanum chilense, Solanum peruvianum, Solanum pimpinellifolium, and Solanum habrochaites. The various parental resistant lines and the F₁ hybrids were inoculated in the greenhouse using viruliferous whiteflies. Control, non‐inoculated plants of the same lines and hybrids were exposed to non‐viruliferous whiteflies. Following inoculation, the plants were scored for disease symptom severity, and transplanted to the field. Resistance was assayed by comparing yield of inoculated plants to those of the control non‐inoculated plants of the same variety. Results showed that the F₁ hybrids between the resistant lines and the susceptible line suffered major yield reduction because of infection, but all hybrids were more resistant than the susceptible parent. All F₁ hybrids resulting from a cross between two resistant parents, showed a relatively high level of resistance, which in most cases was similar to that displayed by the more resistant parent. In some cases, the hybrids displayed better levels of resistance than both parents, but the differences were not statistically significant. The F₁ hybrid between a line with resistance from S. habrochaites and a line with resistance from S. peruvianum (HAB and 72‐PER), exhibited the lowest yield loss and the mildest level of symptoms. Although the resistance level of this F₁ hybrid was not statistically different from the level of resistance displayed by the 72‐PER parent itself, it was statistically better than the level of resistance displayed by the F₁ hybrids between 72‐PER and any other resistant or susceptible line.     

Search in <Emphasis Type="Italic">Solanum</Emphasis> (section <Emphasis Type="Italic">Lycopersicon</Emphasis>) germplasm for sources of broad-spectrum resistance to four <Emphasis Type="Italic">Tospovirus</Emphasis> species

The genus Tospovirus was considered as monotypic with Tomato spotted wilt virus (TSWV) being the only assigned species. However, extensive studies with worldwide isolates revealed that this genus comprises a number of species with distinct virulence profiles. The Neotropical South America is one center of Tospovirus diversity with many endemic species. Groundnut ringspot virus (GRSV), TSWV, Tomato chlorotic spot virus (TCSV), and Chrysanthemum stem necrosis virus (CSNV) are the predominant tomato-infecting species in Brazil. Sources of resistance were found in Solanum (section Lycopersicon) mainly against TSWV isolates from distinct continents, but there is an overall lack of information about resistance to other viral species. One-hundred and five Solanum (section Lycopersicon: Solanaceae) accessions were initially evaluated for their reaction against a GRSV isolate by analysis of symptom expression and systemic virus accumulation using DAS-ELISA. A subgroup comprising the most resistant accessions was re-evaluated in a second assay with TSWV, TCSV, and GRSV isolates and in a third assay with a CSNV isolate. Seven S. peruvianum accessions displayed a broad-spectrum resistance to all viral species with all plants being free of symptoms and systemic infection. Sources of resistance were also found in tomato cultivars with the Sw-5 gene and also in accessions of S. pimpinellifolium, S. chilense, S. arcanum, S. habrochaites, S. corneliomuelleri, and S. lycopersicum. The introgression/incorporation of these genetic factors into cultivated tomato varieties might allow the development of genetic materials with broad-spectrum resistance, as well as with improved levels of phenotypic expression.     

New sources for high resistance of tomato to the tomato spotted wilt virus from Lycopersicon peruvianum

Mechanical inoculation and transmission by thrips in a growth chamber were used in order to screen Lycopersicon peruvianumand Lycopersicon chilense germplasm for tomato spotted wilt virus (TSWV) resistance. Two highly aggressive Spanish TSWV isolates (HA-931100 and T-941117), having different restrictotypes were used. L. peruvianum accessions PI-126935, PI-126944, CIAPAN 16, PE-18 and CIAPAN 17 showed high resistance to both isolates in mechanical and thrips transmission. Their resistance appears useful in breeding programmes.     

Tomato Spotted Wilt Virus (TSWV) resistance in tomato derived from Lycopersicon chilense Dun. LA 1938

Tomato spotted wilt virus (TSWV) resistance wasidentified in Y118 (Fla 925-2), an F₁BC₁S₆ tomato line(Lycopersicon esculentum Mill.), derived from a crosswith L. chilense Dun. (LA 1938). This line waspreviously selected for tomato mottle virus (ToMoV)resistance in Florida. Progeny from crosses betweenFla 925-2 and three different TSWV susceptible L.esculentum parents were used in TSWV resistancestudies. A total of 75 F₁ and 596 F₂ plants from allthree crosses were screened for TSWV resistance. ForF₂ plants free of TSWV symptoms, evaluations were madeusing enzyme-linked immunosorbent assay (ELISA). TenF₃ populations used for further greenhouse and fieldscreenings were selected from F₂ plants found to befree of the virus using visual and ELISA criteria ateach evaluation. One F₁ and four F₃ lines werestudied under field conditions (Stellenbosch, SouthAfrica) in which 100% of the `Flora-Dade' susceptiblecontrols were severely infected with TSWV. Theresults of the field study clearly establish that TSWVfield resistance is present in the Fla 925-2 (Y118)derived lines. Studies conducted on these linesrevealed that this resistance has the distinctcharacteristic of often `recovering' from initiallyhigh levels of virus titer in the tissue to levelsbelow detection with ELISA.     

Resistance in two Lycopersicon species to an Arkansas isolate of tomato spotted wilt virus

Summary Tomato spotted wilt virus (TSWV) was obtained from infected tomatoes in commercial fields in Arkansas in 1985. A greenhouse screening procedure for identifying tomatoes resistant to TSWV was established using an enzyme-linked immunosorbent assay (ELISA) to detect infected plants. Symptom expression was variable and symptom expression was not reliable for identifying infected plants. Germplasm evaluated for resistance to one typical Arkansas isolate (85–9) of TSWV included: twenty cultivars and breeding lines of Lycopersicon esculentum Mill, 52 accessions of L. pimpinellifolium (Jusl.) Mill and 8 accessions of L. peruvianum (L.) Mill. All cultivated accessions and breeding lines evaluated were susceptible. Some individual plants in several accessions of L. pimpinellifolium were resistant and nearly all plants of the L. peruvianum accessions that were evaluated were resistant to isolate 85–9.Dept. of Plant Pathology     

Effectiveness of combining resistance to Thielaviopsis basicola and Tomato spotted wilt virus in haploid tobacco genotypes

Black root rot (BRR) caused by Thielaviopsis basicola as well as Tomato spotted wilt virus (TSWV) are the most serious problems in tobacco growing regions. We crossed the breeding line WGL 3 carrying BRR resistance derived from N.glauca with the line PW-834 the resistance of which to TSWV was transferred from cultivar Polalta. Anthers obtained from F₁ hybrid plants were cultured to induce haploids combining resistance to Th. basicola and TSWV. Flow cytometry analysis revealed 242 haploids and 2 spontaneous doubled haploids among regenerants. All haploids were cloned and then evaluated for BRR as well as TSWV resistance. The presence of pathogens was detected by microscopic evaluation of roots or using DAS-ELISA test. Microscopic assessment showed that, 132 haploids had no symptoms of Th. basicola which, together with the absence of symptoms in the F₁ hybrids, indicated a dominant monogenic mode of inheritance. At the same time only 30 haploids demonstrated resistance to TSWV. SCAR markers associated with TSWV resistance gene detection was applied. The results indicate that small proportion of TSWV-resistant haploids is probably due to the influence of deleterious genes flanking the resistance factor that reduced vitality of gametophytes. Altogether, 24 haploids showed multiple resistance to Th. basicola and TSWV.     

A survey of Nicotiana germplasm for resistance to Tomato spotted wilt virus (TSWV)

The reaction to Tomato spotted wilt virus (TSWV) was evaluated in 94 accessions of Nicotiana, originating from the Institute of Soil Science and Plant Cultivation tobacco germplasm collection in Pu?awy, Poland. Tests for resistance were conducted under greenhouse conditions using single TSWV isolate collected from tobacco plantation in Lublin district, Poland. The presence of the virus was verified using DAS-ELISA. SCAR markers associated with TSWV resistance gene were applied. The members of the section Alatae, the genus Nicotiana: N. alata, N. forgetiana, and Nicotiana x sanderae as well as N. tabacum cultivars: ‘Polalta’ and ‘Wiktoria’ with the TSWV resistance gene introduced from N. alata, displayed the hypersensitive reaction (HR) against TSWV (grade 0 on symptom intensity scale). In some of those accessions, the virus spread from the initially infected areas eliciting systemic hypersensitive reaction (SHR). Five accessions of N. alata and three of Nicotiana x sanderae were composed of 6.3–50.0 % of plants in which SHR symptoms appeared. In all of N. forgetiana plants HR reaction was followed by systemic infection (SHR). In N. tabacum ‘Wiktoria’ 21.1 % of plants showed HR reaction, while the remaining were susceptible (S). All of the genotypes which responded with HR or SHR reaction to TSWV infection demonstrated the presence of SCAR markers linked to the resistance gene. The remaining eighty tested accessions were identified as being susceptible upon exposure to TSWV.     

Genetics of resistance in <Emphasis Type="Italic">Luffa cylindrica</Emphasis> Roem. against <Emphasis Type="Italic">Tomato leaf curl New Delhi virus</Emphasis>

Sponge gourd is a popular vegetable grown throughout India. Tomato leaf curl New Delhi virus, the causal virus of tomato leaf curl disease, has recently been reported to be associated with sponge gourd, causing up to 100% crop loss under epidemic conditions. We have collected 30 genotypically diverse genotypes of sponge gourd from different parts of India, screened these for resistance under natural epiphytotic conditions, and then confirmed the results through challenge inoculation with a purified strain of the virus under insect-proof greenhouse conditions. The minimum vulnerability index was recorded in genotype DSG-6 (3.33), followed by DSG 7 (6.0) under the challenge (whitefly-populated) inoculation conditions. Two susceptible genotypes (‘Pusa Sneha’ and NSG-1-11), both possessing desirable fruit characters, were crossed with the two most promising resistant lines (DSG-6 and DSG-7) and the disease reaction of segregating and backcross generations studied through challenge inoculation with a purified strain of virus under insect-proof greenhouse conditions. A chi-square (χ²) test of frequency distribution based on the vulnerability index of the F₂ progenies of the two resistant × susceptible crosses revealed monogenic dominant Mendelian ratio 3(R):1(S) to be the best fit in all crosses. This monogenic dominant model was further confirmed by the 1(R):1(S) ratio found to be best fit for the test cross with the susceptible parent. These results reveal that resistance to Tomato leaf curl New Delhi virus associated with yellow mosaic disease of sponge gourd is controlled by a single dominant gene in the genetic background of the resistant parents (DSG-6 and DSG-7) and that these two lines can be effectively utilized for the development of high-yielding and yellow mosaic disease-resistant varieties/hybrids of sponge gourd. This is the first conclusive identification of a resistant source and the inheritance of resistance against Tomato leaf curl New Delhi virus in sponge gourd.     

Screening for new sources of resistance to Clavibacter michiganensis subsp. michiganensis (Cmm) in tomato

Bacterial canker of tomato, caused by Clavibacter michiganensis subsp. michiganensis (Cmm), is considered the most serious bacterial threat, resulting in high damages in production areas. Worldwide, Cmm is subjected to quarantine regulations.There is no cultivar in market containing Cmm resistance genes. This project aimed to screen tomatoes or wild relatives of tomato for resistance to Cmm, to be used for starting breeding programs. We have screened 24 different wild accessions of tomato and found several new tolerant sources: Solanum pimpinellifolium GI.1554, S. parviflorum LA735 and S. parviflorum LA2072. We also confirmed the tolerance which was reported previously in S. peruvianum LA2157, S. peruvianum PI127829, S. peruvianum LA385, S. habrochaites LA407 and S. lycopersicum cv. IRAT L3. No immunity was found. Also accessions showing a low disease score still contained high titers of bacteria as determined by a dilution plating method, using tow selective media. These results were confirmed with a TaqMan real time PCR assay, which was developed to determine and quantify Cmm in planta.     

Evaluation of tomato entries with different combinations of resistance genes to tomato yellow leaf curl disease in Tunisia

Tomato yellow leaf curl virus (TYLCV) is one of the most widespread begomoviruses transmitted by the whitefly Bemisia tabaci that cause tomato yellow leaf curl virus diseases (TYLCDs). TYLCD losses can be especially severe in open‐field tomato (Solanum lycopersicum L.) crops. TYLCV is particularly well known and widespread in the Mediterranean (Med) countries where TYLCD control is mostly based on insecticidal control of B. tabaci populations. Unfortunately, Tunisian B. tabaci populations include Middle East‐Asia Minor I and the Med species that have developed resistance to many classes of insecticides. Therefore, TYLCD‐resistant cultivars are essential for sustainable disease management. Six TYLCD resistance genes (Ty) have been introgressed from wild species into cultivated tomato and are available for breeding. Information on the Ty genes or gene combinations is useful for breeding resistant cultivars. To this end, 14 tomato lines carrying different Ty gene combinations and two susceptible tomato entries were evaluated for TYLCD incidence and severity in two field trials during late season in Tunisia. Entries with Ty‐1/Ty‐3 + Ty‐2 offered the highest levels of resistance in Tunisia.     

Evaluation of seven Lycopersicon species for resistance to tomato spotted wilt virus (TSWV)

Summary One hundred eighty-eight accessions of Lycopersicon cheesmanii, L. chilense, L. chmielewskii, L. hirsutum, L. parviflorum, L. pennellii, and L. peruvianum were screened for resistance to three isolates of tomato spotted wilt virus (TSWV). All plants in an accession were initially screened for resistance to TSWV using isolate 85–9 from Arkansas. Visual symptoms were used to cull obviously infected plants, followed by enzyme-linked immunosorbent assay (ELISA) to identify uninfected plants. Cuttings were taken from uninfected plants in the first screening and the resulting plants were inoculated with isolates Glox and T-2 from Texas and Hawaii, respectively. No resistance was identified in L. cheesmanii, L. chmielewskii, L. hirsutum, L. parviflorum, and L. pennellii. However, 33 of 63 L. chilense accession produced 91 of 1268 plants that were uninfected with isolate 85–9 and 20 accessions that produced 40 of 257 plants that were not infected with any of the isolates. After screening with isolate 85–9 9 of 12 L. peruvianum accessions tested had 38 plants uninfected and 8 accessions had 25 plants that were not infected with any of the isolates.     

Morphological and chemical characteristics of doubled haploids of flue-cured tobacco combining resistance to Thielaviopsis basicola and TSWV

Thielaviopsis basicola and Tomato spotted wilt virus (TSWV) are the most important problems in a moderate climate zone. Previously obtained doubled haploids (DH) of F₁ hybrids of the flue-cured line WGL3 resistant to Th. basicola and the dark-cured line PW-834 carrying RTSW-al gene provided the research material. Biological tests and SCAR markers linked with TSWV were applied to confirm resistance of DH. Lines combining resistance to TSWV and Th. basicola were evaluated for morphological and chemical characteristics. Most of DH were significantly shorter than parents but two lines, 31/A/2 and 31/B/3, were close to the flue-cured WGL3. Usually DH possessed fewer leaves while one of them 31/B/3, exceeded parental forms. The doubled haploids flowered later than their parents. The most negative effect was reduced area of mid-position leaves of DH. It might be explained by a recombination during microsporogenesis in F₁, however the influence of ‘Polalta’-derived RTSW-al gene cannot be excluded. Extensive line to line variation for nicotine and sugars content was not associated with the genes for TSWV and Th. basicola resistance. Biological tests and field performance of DH revealed potential to overcome the negative effect of coupling between the RSTV-al gene and genes responsible for the morphological deformations.     

Sources of resistance to tomato-yellow-leaf-curl-virus (TYLCV) in Lycopersicon species

Summary Sources of resistance to tomato-yellow-leaf-curl-virus (TYLCV) were investigated in 16 accessions of three Lycopersicon species and 55 commercial tomato hybrids and cultivars. All commercial hybrids and cultivars were highly susceptible. Accessions of L. hirsutum, L. hirsutum f. glabaratum and L. pimpinellifolium showed a wide range of reactions. Those of L. peruvianum, LA 385 of L. peruvianum f. humifusum exhibited very high levels of resistance indicating their potential use in local breeding programs. In contrast to earlier findings, back indexing showed that all symptomless genotypes in this investigation were carriers of the TYLCV.     

Resistance to tomato spotted wilt virus in transgenic tomato hybrids

Summary Tomato spotted wilt virus (TSWV) causes significant economic losses in the commercial culture of tomato (Lycopersicon esculentum Mill.). Culture practices and introgression of natural sources of resistance to TSWV have only been marginally effective in controlling the TSWV disease. Recently however, high levels of protection against TSWV have been obtained by transforming tobacco with a chimaeric gene cassette comprising the TSWV nucleoprotein gene. This report demonstrates the successful application of this newly-created TSWV resistance gene in cultivated tomato. Transformation of an inbred tomato line with the TSWV nucleoprotein gene cassette resulted in high levels of resistance to TSWV that were maintained in hybrids derived from the parental tomato line. Therefore, transformant lines carrying the synthetic TSWV resistance gene make suitable progenitors for TSWV resistance to be incorporated into the breeding programmes of tomato.     

Inheritance of black leaf mold resistance in tomato

Summary Inheritance of black leaf mold (BLM) (caused by Pseudocercospora fuligena) resistance was studied in four crosses involving two resistant Lycopersicon accessions (PI134417, L. hirsutum and PI254655, L. esculentum) and four susceptible Asian Vegetable Research and Development Center tomato lines (CLN657BC₁F₂-267-0-3-12-7, CL143-0-10-3-0-1-10, CLN698BC₁F₂-358-4-13 and CL5915-93D₄-1-0-3). For each cross, six generations, i.e. P₁, P₂, F₁, F₂, BC₁F₁ and BC₁F₂ were evaluated following inoculations with isolate Pf-2 of P. fuligena. Chi-square analyses of the data based on the ratio of resistant to susceptible plants in the F₂ in three of four crosses gave a good fit to a segregation ratio of 1 R : 15 S, and BC₁F₂ data in three of four crosses gave an acceptable fit to the segregation ratio of 1 R : 63 S. The results indicate that resistance to BLM may be conditioned by two recessive genes acting epistatically in both PI134417 and PI254655.     

Interspecific crosses in the genus Lycopersicum

The use of a tetraploid tomato as a pistillate parent in the crosses with Lycopersicum peruvianum and Lycopersicum glandulosum, instead of a diploid tomato, increases about 80 times the set of hybrid seed and thus gives a broader basis for the breeding work. The results seem to indicate that in the crosses on a diploid level, only unreduced eggcells of the tomato fertilized by haploid pollen of the above wild species, develop into normal seeds, and give rise to sesquidiploid F₁ progeny.     

Evaluation of whitefly-mediated inoculation techniques to screen Lycopersicon esculentum and wild relatives for resistance to Tomato yellow leaf curl virus

For two consecutive years nine hybrids and three varieties of tomato, four Lycopersicon peruvianum and four Lycopersicon chilense accessions were screened for Tomato yellow leaf curl virus (TYLCV) resistance. Three inoculation techniques using Bemisia tabaci, the vector of TYLCV, were compared: (1) artificial mass inoculation-simultaneous infection of cultivated and wild material in greenhouses; (2) artificial cage inoculation-individual infection in insect-proof cages; (3) natural field infection. Artificial inoculations led to higher levels of infection, but different patterns of response to each inoculation technique were found depending on the resistance level. Tomato varieties showed an important fruit set reduction after both artificial and natural inoculations. In contrast, field infection was milder in tomato hybrids, in which yield was barely affected. These hybrids showed a wide range of reactions with the two artificial inoculation techniques, but infection was always more severe after mass inoculation. Extreme severity of mass infection made it difficult to differentiate among variable degrees of resistance that were more reliably detected with cage inoculation. The hybrids F3524, F3522, Fiona, and Tyking showed the highest level of resistance. F3524 and F3522 had an acceptable yield in field and cage assays, but their resistance collapsed under massive conditions of infection. Tyking and Fiona exhibited the best response in all conditions, although their yield was moderately reduced in mass assays. Mass inoculation was not adequate for the screening of wild Lycopersicon. Some susceptible plants escaped infection, probably as a consequence of non-preference mechanisms and loss of vector infectivity. Individual inoculation in cages prevented the risk of non-infection, ensuring 100% disease incidence. This technique allowed the selection of highly resistant wild sources. L. chilense LA 1969 and LA 1963 had the highest level of resistance with the three inoculation techniques. L. peruvianum PI-126944 and L. chilense LA 1932, which were only tested in mass and field conditions, also exhibited a promising response. The results proved that the inoculation technique influences the response of tomato and wild Lycopersicon spp to TYLCV. It is concluded that artificial cage inoculation, although more time-consuming, is the most efficient, adequate, and reliable technique to screen both cultivated and wild Lycopersicon species for resistance to TYLCV. This revised version was published online in July 2006 with corrections to the Cover Date.     

Response of tolerant breeding lines of tomato, Lycopersicon esculentum, originating from three different sources (L. peruvianum, L. pimpinellifolium and L. chilense) to early controlled inoculation by tomato yellow leaf curl virus (TYLCV)

Selection of tomato plants supposedly tolerant to tomato yellow leaf curl virus (TYLCV), based solely on the absence of symptoms in an infested field can be misleading. An inoculation routine was therefore established to avoid escapes and to overcome difficulties associated with the age of the plant at the time of infection. The inoculation routine was applied to a selection of resistant/tolerant individuals generated through a diallel F¹ cross and to F² segregating populations originating from three wild tomato species described as tolerant to TYLCV: Lycopersicon peruvianum EC 104395, Lycopersicon pimpinellifolium Hirsute and Lycopersicon chilense LA 1969. Clear differences were observed between susceptible symptomatic and tolerant symptomless tomato genotypes, indicating that the uncertainty resulting from escapes, from different levels of inoculum, and from the time of inoculation, can be eliminated. The genes involved in tolerance provided different levels of protection; combinations of various tolerant sources and levels in a single genotype gave a higher level of tolerance. Differences in level of protection were found between genes from the same source and between sources; none of the sources tested had complete dominance. The results obtained with the F² segregating population showed that tolerance from L. pimpinellifolium is controlled by one major gene, that from L. chilense by two genes, and that from L. peruvianum by three genes with no dominant effect. The combination of sources for resistance can thus have positive or negative synergistic effects, or no effect. We suggest that a maximal level of tolerance can be obtained by the additive effect of the partly dominant genes from L. pimpinellifolium and L. chilense.     

Transfer of powdery mildew resistance from Brassica carinata to Brassica oleracea through embryo rescue

Interspecific hybrid plants and backcross 1 (BC₁) progeny were produced through sexual crosses and embryo rescue between Brassica carinata accession PI 360883 and B. oleracea cvs Titleist’and‘Cecile’to transfer resistance to powdery mildew to B. oleracea. Four interspecific hybrids were obtained through application of embryo rescue from crosses with B. carinata as the maternal parent, and their interspecific nature confirmed through plant morphology and random amplified polymorphic DNA (RAPD) analysis. Twenty‐one BC₁ plants were obtained through sexual crosses and embryo rescue although embryo rescue was not necessary to produce first backcross generation plants between interspecific hybrids and B. oleracea. All interspecific hybrids and eight of the BC₁ plants were resistant to powdery mildew.