Lettuce seeds were germinated at 20 C in the dark in water and sampled at various intervals during the first 18h of germination to determine quantitative and qualitative differences in proteins. The soluble protein fraction was partitioned into albumins and globulins by dialysis and the proteins of the globulin fraction were visualized by SDS-PAGE. Heat stable proteins were obtained by boiling the proteins, cooling on ice, and resuspending in buffer.
The soluble protein content remained constant during the first 8h of germination. Thereafter protein content decreased and was 6% of the amount present in unimbibed seed in 21 day old seedlings. The ratio of heat stable to heat unstable proteins decreased during the germination process. No differences in banding patterns were observed when the soluble protein fraction were run on SDS-PAGE. However, on gels run with the globulin fraction a 57 kD protein appeared 4 and 8 h after imbibition and had disappeared by 12 h after imbibition. The role of proteins and heat-stable proteins during germination and prevention of dessication during early seedling growth is discussed.
Anthocyanins (Antho) are the source of red color in plants and the intensity of redness is an important quality parameter in red leaf lettuce. Despite the importance of Antho in leaf lettuce, little information is available regarding the effects of major production-related factors, such as planting date, on their levels. To address this issue, field studies were conducted in 2002 and 2003 in which Antho levels were measured in nine lettuce varieties planted in early and late summer (ES and LS, respectively) using a RCB design. Leaf tissue was sampled 30 d after transplanting. Data for three strongly related Lolla Rossa-type varieties (`Lotto', `Valeria', `Impuls') are reported here. The planting date × variety interaction was significant; however, Antho concentrations were higher following planting in LS than ES, regardless of variety. Planting date effects were more pronounced in 2002, when differences in average daily temperature between ES and LS plantings tended to be larger. Regardless of planting date and year, Antho levels followed the pattern `Impuls' (three genes) > `Valeria' (two genes) > `Lotto' (one gene). Correlations between human visual and two types of instrumented assessments of color are being tested in samples from the same study.
Big vein (BV) disease of lettuce is caused by soil borne fungal vectored viruses, and reduces marketability through head deformation. Tolerant cultivars reduce BV frequency, but no resistant cultivars exist. L. virosa L. is highly resistance. The objectives were to 1) determine if L. virosa P.I.s exhibit variation for resistance, and 2) determine if resistance is transferable to lettuce. Seedlings were inoculated with root macerate of BV infected plants, transplanted to BV infested soil, and greenhouse grown for 3 months. Twelve plants in each of 1,2, or 3 reps of Great Lakes 65 (GL65-susceptible), Pavane (Pav-tolerant), L. virosa (11 accessions), and BC1 F2 through F5 families of lettuce cultivars x L. virosa accession IVT280 were tested. The percentage of BV afflicted plants was recorded. In hybrid families, BV free plants from tolerant families were selected and advanced. No BV was found in L. virosa. Variation for tolerance was observed in BC1 F2 and F3 families; 33% had greater tolerance than Pav (17% afflicted). Additional tests identified 11 BC1 F3 families (14%) with greater tolerance than Pav (42% afflicted). Subsequent BC1 F4 and F5 generations however, were more susceptible than Pav. Lactuca virosa is highly resistant, but resistance did not transfer to hybrid progeny. Variation for tolerance was observed in BC1 F2 and F3 families, but later generations were susceptible. Interactions or linkage of genes for developmental processes and BV resistance may hinder introgression. Introgression will continue using congruity backcrossing and a greater diversity of L. virosa.
Greenhouse experiments were conducted in the Dominican Republic to determine the effect of methanol and nitrogen (N) on the yield of `Black Seeded Simpson' lettuce. Plants were individually grown in plastic containers filled with loamy soil and treated with combinations of methanol, folcysteine. N rates (70, 105, 140, and 175 kg/ha) were applied at planting, and aqueous solutions of either ethanol or methanol (0%, 5%, 10%, 15%, and 20%) were applied as a foliar spray when the plants had five true leaves. Plants were harvested 50 days after planting. There were no significant effects of ethanol or methanol on lettuce yield. Lettuce yield was significantly influenced by N rates, with yield increasing as N rates were higher.
Among the factors affecting germinability of a seed lot are the environmental conditions under which the seeds are produced. The objective of this study was to determine the effects of temperature during seed development on seed quality of two Asteraceae species. Seeds of lettuce cv. Tango and Helianthus debilis cv. Vanilla Ice and sp. cucumerifolius were produced in a greenhouse under one of two treatments: i) hot (27, 40, and 20 °C temperatures average, max, and min, respectively), and ii) cool (23, 33, and 18 °C temperatures average, max, and min, respectively). In both species, heavier seeds were produced under the cool conditions and no differences were observed in standard germination. In lettuce, germination percentage and rate were both affected by increased levels of exogenous ABA concentrations and reduced water potential (PEG solutions), and, in both cases, seeds from cool treatments were more affected. Germination at 30 °C and constant light was higher for seeds from the hot treatment. Lettuce seed showed a strong light requirement for germination. However, seeds from the hot treatment gave better dark germination at 13 and 19 °C. Seeds of H. debilis did not required light for germination, and the germination percentage and rates were evaluated at 13, 21, and 29 °C. For both lines, seeds from each treatment behave similarly; however, the germination of H. debilis cv. Vanilla Ice at 29 °C was higher when seeds were produced in the hot conditions. The results showed that temperature during seed development affected aspects of seed quality that are not detectable by the standard germination, but by germination at suboptimal conditions. Within the Asteraceae family, differences varied among and within species.
An-assay was developed to determine the level of resistance to the herbicide glyphosate in trangenic seedlings of lettuce. Results of the seedling assay were correlated to results of a similar assay using callus lines of the identical transgenic plants. Transgenic plants were found to be a 32-fold increase in tolerance to glyphosate when compared to wild type plants. This was similar to the response of these transgenic lines in the callus line assay.
`South Bay' lettuce transplants were grown in F392A styrofoam Speedling® flats at different levels of N to evaluate the effect of N on transplant quality and subsequent yield and head quality in the field. Plants were irrigated eight times over a 4-week growing period by floating flats for 30 min in nutrient solution containing eight 0, 15, 39, 45, or 60 mg·liter–1 N supplied from NH4NO3. Dry shoot mass, leaf area, and plant height increased linearly with increasing N rates and dry root mass and stem diameter increased in a quadratic fashion. Transplants with the greatest plant biomass were, therefore, produced with 60 mg·liter–1 N. Plants from the 15, 30, 45 and 60 mg·liter–1 N treatments were planted in sandy soil in plastic-mulched beds under drip irrigation. To optimize lettuce head maturity among the treatments, plants from the N treatments were harvest 53, 56, and 59 days after transplanting (DAT). The optimum time to harvest was determined to be 56 DAT. There was no yield response (measured in terms of head mass) or quality response (measured in terms of head height, head diameter, head compactness or core length) to N applied during transplant production. This indicated that transplants produced with 15 mg·liter–1 N gave equally good yield to those produced with 30, 45, or 60 mg·liter–1 N when N was applied via flotation irrigation.
Three field studies on high-organic-matter soils were conducted to determine the zone of influence of spiny amaranth on lettuce head quality. Spiny amaranth reduced lettuce head firmness at all distances from the weed, ≤105 cm. Lettuce ribbiness increased at 15 and 45 cm compared with the weed-free control. Untrimmed lettuce head weight was not affected by spiny amaranth presence beyond 45 cm. Trimmed lettuce head weight was reduced at all distances compared with the control. Stem diameter and core length were not affected by spiny amaranth competition. The presence of a single spiny amaranth plant significantly influenced some lettuce quality traits at ≤105 cm.
Abstract
Lactuca sativa seed, cvs. ‘Imperial 847’, ‘Imperial 456’, ‘Imperial 44’, ‘Fulton’, and ‘Oswego’ were stored at a wide range of temperature and relative humidity, to determine their effect upon development of red cotyledons (physiological necrosis).
Red cotyledons did not develop equally (rate or amount) in seeds of all cultivars at any given storage condition. More red cotyledons developed at a low than at a high relative humidity at the same temperature. However, longer storage at the low relative humidity was required before red cotyledons developed.
Storage at −12°C/70% relative humidity prevented red cotyledon development in all cultivars tested for 210 weeks. Storage at 10/90, 10/70, 4/35 and −1/40 prevented red cotyledon development in all cultivars for 157 weeks and in some cultivars for 210 weeks.
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.