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‘Black Seeded Simpson’, ‘Buttercrunch’, and ‘New York 12’ lettuce.(Lactuca sativa L.), Plant Introductions (PI) 261653 of Lactuca saligna L., and Acc. No. 500–4 of L. serriola L. regenerated plants from cell suspensions originated from leaf callus. Liquid cultures of these Lactuca spp. in either B5 or Murashige and Skoog (MS) basic medium amended with alpha-naphthaleneacetic acid (NAA) and 6-benzylamino purine (BA) developed roots, shoots, and complete plants when transferred to agar plates of B5 with several concentrations of BA under 16 hr of fluorescent illumination. Shoots were induced to produce a root system when cultured in B5 agar medium amended with NAA. Variation in response between cultivars and between species was observed, with L. serriola and ‘Black Seeded Simpson’ responding best to treatments.

Open Access

Six genes controlling flowering time or bolting time in Lactuca L. have been reported. Several crosses between parents differing in time to opening of first flower were made to ascertain the inheritance of additional flowering time traits in Lactuca species. The parents in the crosses were of five flowering classes: very late (VL), late (L), early (E), very early (VE), and very, very early (VVE). Segregation from a cross between C-2-1-1 (VL) (L. sativa L.) and `Vanguard 75' (L) confirmed that `Vanguard 75' flowering was controlled by the previously identified gene Ef-2ef-2. Mutant line 87-41M-7 (VVE) was crossed by D-3-22M (VE) and segregated 3VVE:1 VE, indicating a dominant allele, Ef-3, that decreased flowering time an additional 7 days. Cos-like line 796 (VE) was crossed to cultivars Salinas (VL) and Vanguard 75. Segregation indicated a gene Ef-4ef-4, with lateness dominant. PI 175735 (E) (L. serriola L.), crossed with C-2-1-1 produced an F2 population with a bimodal distribution, segregating 3 E:1 VL, indicating a single gene Ef-5ef-5. PI 236396 (E) and PI 250020 (E) were crossed to `Salinas' and `Vanguard 75'. Segregation and morphological similarity indicated the same gene in both PI lines, Ef-6ef-6, with earliness dominant.

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Abstract

Data for resistance in Lactuca serriola L. to turnip mosaic virus (TuMV) and downy mildew were obtained from 5 F2 progenies of crosses between TuMV-susceptible, mildew-resistant, and TuMV-resistant, mildew-susceptible parents. The F1 progeny were TuMV and mildew-resistant. Of 1,103 F2 plants assayed 823 were TuMV-resistant and 280 TuMV-susceptible. A total of 834 mildew-resistant plants were observed, and 269 mildew-susceptible. Resistance to TuMV and mildew are each controlled by a single dominant allele, designated Tu and Dm, respectively. The TuMV gene, Tu tu, is linked with the mildew gene, Dm dm. In the repulsion phase, the crossover value was 12.0% ± 2.9. F2 progenies of crosses between TuMV-susceptible, mildew-resistant L. serriola and TuMV-susceptible, mildew-resistant L. sativa cv. ‘Calmar’ or ‘Imperial 410’, and crosses among cv. ‘Calmar’, ‘Imperial 410’, and ‘E-4’, indicated they possessed the same dominant allele for mildew-resistance, and the same recessive allele for TuMV-susceptibility.

Open Access

Lettuce aphid ( Nasonovia ribisnigri Mosley) has affected lettuce ( Lactuca sativa L.) production in Europe since the 1970s and became a serious problem on lettuce in British Columbia, Canada, in 1981 ( Forbes and MacKenzie, 1982 ). It was

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-type cultivars, 12 leaf-type cultivars, 12 romaine-type cultivars, and one latin-type cultivar. In addition to cultivated lettuce, three accessions each of two wild-type species Lactuca serriola and Lactuca saligna were also included in the analysis. The 60

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Lactuca serriola accession PI 491093 and L. virosa accession PI 274378. Materials and Methods This work was done using controlled infestations in greenhouses (13 experiments) and field cages (one experiment) and natural infestations in open fields (two

Free access

largely centered on root qualities. Jackson (1995) reported differences in root architecture in cultivated L. sativa cv. Salinas and its wild progenitor ( Kesseli et al., 1991 ) Lactuca serriola . Cultivated L. sativa tends to produce more lateral

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Abstract

Lactuca saligna L., Lactuca serriola L., and Lactuca virosa L., which are cross-fertile with cultivated lettuce (L. sativa L.) were tested for resistance to lettuce infectious yellows virus in greenhouse and field tests. Fifteen of 25 L. saligna accessions were resistant, whereas 50 accessions of L. serriola and seven accessions of L. virosa were susceptible.

Open Access
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three wild species ( L. serriola , L. saligna , and L. virosa ) and primitive lettuce have thermoinsensitive genotypes. The observed thermotolerance in UC96US23 ( Lactuca serriola ) was consistent with previous results of Argyris et al. (2008a , 2008

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Abstract

A mosaic disease of Lactuca sativa L. is described and the causal agent identified as turnip mosaic virus (TuMV). Extensive infection reduces the yield appreciably or may destroy entirely the value of the crop. A survey of L. sativa cultivars indicated that TuMV susceptibility is restricted to mildew resistant: crisphead types: ‘Calmar’, ‘E-4’, ‘Imperial 410’, ‘Imperial Triumph’, ‘Valrio’, ‘Valtemp’, and ‘Valverde’. Circumstantial evidence indicates that TuMV susceptibility in cv. ‘Calmar’, ‘Imperial 410’, ‘Valrio’, ‘Valtemp’, and ‘Valverde’ stems from the mildew resistant L. serriola L. (P.I. 91532). TuMV and mildew resistant cultivars are: butterhead type ‘May King’, ‘Meikoningin’, ‘Proeftuin’s Blackpool’, ‘Ventura’; leaf type ‘Red Salad Bowl’, ‘Salad Trim’; cos type ‘Valmaine’. Seed collections of L. serriola from the Santa Clara and Salinas Valleys of California produced plants that fell into 3 classifications: a) TuMV-resistant, mildew-resistant; b) TuMV-resistant, mildew-susceptible, and c) TuMV-susceptible, mildew-resistant. No plants in L. sativa or L. serriola were susceptible to both TuMV and mildew. Extreme resistance to TuMV was demontrated in L. sativa and L. serriola. TuMV-susceptible L. sativa cultivars showed differences in tolerance to symptom expression and resistance to infection. In L. serriola a resistance connected with a hypersensitivity reaction was observed. All isolates of TuMV collected were capable of infecting susceptible L. sativa cultivars. L. sativa cv. ‘Calmar’ and ‘Valverde’ systemically infected with TuMV did not transmit the virus through the seed. L. serriola systemically infected with TuMV failed to produce seed.

Open Access