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A series of experiments on ethylene-insensitive (EI) petunia plants (Petunia ×hybrida Hort. Vilm.-Andr.) generated in two genetic backgrounds were conducted to determine the involvement of ethylene in horticultural performance. Experiments examined various aspects of horticultural performance: days to flower, flower senescence after pollination and without pollination, fruit set and ripening, and adventitious root formation on vegetative stem cuttings. The development of EI plants was altered in several ways. Time from seed sowing to first flower anthesis was decreased by a week for EI plants grown at 26/21 °C. Flower senescence in nonpollinated and self-pollinated flowers was delayed in all EI plants compared to wild-type plants. Fruit set percentage on EI plants was slightly lower than on wild-type plants and fruit ripening on EI plants was delayed by up to 7 days. EI plants produced fewer commercially acceptable rooted cuttings than wild-type plants. There was a basic difference in the horticultural performance of the two EI lines examined due to a difference in the genetic backgrounds used to generate the lines. EI plants displayed better horticultural performance when grown with day/night temperatures of 26/21 °C than 30/24 °C. These results suggest that tissue-specific ethylene insensitivity as well as careful consideration of the genetic background used in transformation procedures and growth conditions of etr1-1 plants will be required to produce commercially viable transgenic floriculture crops. EI petunias provide an ideal model system for studying the role of ethylene in regulating various aspects of plant reproduction.
The effects of six applied N treatments differing by rates and frequencies of application on the yield and quality of pepper (Capsicum annuum var. annuum L. `Anaheim Chili') grown for seed was studied. The timing of N applications was based on crop phenology, leaf petiole nitrate-nitrogen concentrations (NO3-N) minimum thresholds, and scheduled calendar applications of fixed amounts of N. Solubilized NH4NO3 was applied through a trickle-irrigation system to ensure uniform and timely applications of N. Rate of mature (green and red) fruit production was unaffected by any treatment except weekly applications of 28 kg·ha-1 of N, which stopped production of mature fruit before all other treatments. Early season floral bud and flower production increased with increasing amounts of N. The two highest total N treatments produced more floral buds and flowers late in the season than the other treatments. Total fruit production was maximized at 240 kg N/ha. Differences in total fruit production due to frequency of N application resulted at the highest total N level. Red fruit production tended to be maximized with total seasonal applied N levels of 240 kg·ha-1 and below, although weekly applications of N reduced production. Total seed yield was a function of red fruit production. Pure-1ive seed (PLS) production was a function of total seed production. Nitrogen use efficiency (NUE) for red fruit production also decreased with N rates >240 kg·ha-1, but PLS yield and NUE decreased in a near-linear fashion as the amount of total seasonal applied N increased, regardless of application frequency. Season average NO3-N (AVE NO3-N) values >4500 mg·kg-1 had total seed and PLS yields less than those treatments <4000 mg·kg-1. Six-day germination percentage was reduced with weekly N applications of 14 kg·ha-1. Seed mass was reduced with weekly N applications of 28 kg·ha-1. Final germination percent, seedling root length and weight, and field emergence were unaffected by any of the N treatments. These findings indicate that different N management strategies are needed to maximize seed yield compared to fruit yield and, therefore, there may be an advantage to growing `Anaheim Chili' pepper specifically for seed.
The influence of two drying regimes and two storage temperatures of primed asparagus (Asparagus officinalis L.) and tomato (Lycopersicon esculentum Mill.) seeds on germination after storage up to 3 months was examined. Seeds of `Mary Washington' asparagus and `Ace 55' tomato primed in synthetic seawater (-1.0 MPa, 20C, 1 week, dark) were surface-dried at 20C and 50% relative humidity (RH) for 2 h (42% to 49% moisture) or dried-back at 20C and 32.5% RH for 48 h (moisture = 13% tomato and 22% asparagus). These and nonprimed seeds were stored in tight-lidded metal cans and heat-sealed plastic pouches at 4 or 20C for up to 3 months before germination at 20C. After 3-month storage, primed surface-dried asparagus seeds stored at 4C had greater germination percentage and rate than nonprimed seeds, surface-dried seeds stored at 20C, or primed dried-back seeds. Dried-back primed tomato seeds had higher germination percentage than surface-dried primed seeds after 2 or 3 months of storage, with storage temperature having no effect on germination perecentage or rate. In a further study, primed surface-dried and primed dried-back seeds stored at 4 or 20C for 1.5 months in sealed containers were germinated at 15, 25, or 35C under low (-0.05 MPa) or high osmotic stress (-0.4 MPa). Primed surface-dried asparagus seeds stored at 4C, compared to nonprimed seeds, surface-dried seed stored at 20C, or primed dried-back seeds, had greater germination percentage at 15 and 35C and low osmotic stress, and higher germination rate at 15 or 25C. Primed tomato seeds had greater germination percentage than nonprimed seeds only at 35C and low osmotic stress, and higher germination rate at 15 or 25C. Storage of primed tomato seeds at 4C rather than 20C increased germination rate at 15 or 25C, and increased germination percentage at 35C and low osmotic stress. For maximal seed viability and germination rate after 1.5 to 3 months of storage, primed asparagus and tomato seeds should be stored at 4C rather than 20C; however, asparagus seeds should be surface-dried, and tomato seeds should be dried-back.
We investigated the effects of variation in ambient air temperature on seed production in the field during the reproductive development phase of `Salinas' head-type lettuce (Luctuca sativa L.) in the central San Joaquin Valley of California where daytime maxima may exceed 38C for many consecutive days during reproduction. Florets were tagged daily for 41 days and harvested seeds were sampled to determine temperature-sensitive periods during seed development. The number of seeds per inflorescence (NOS), seed mass (SM), and seedling root length (SRL) were reduced and percentage germination (GERM) increased with increasing minimum (LT) and maximum (HT) temperatures. Daily HT > 35C greatly reduced NOS. Increasing LT reduced SM and SRL, but to a lesser extent than NOS (r2 = 0.23 and 0.40; P = 0.01 and 0.001, respectively). The advantage of increasing HT on GERM (r2 = 0.20; P = 0.01) was overshadowed by the severe reduction in NOS and the vigor components SM and SRL. The periods of greatest sensitivity to high air temperature for NOS, SM, GERM, and SRL were - 1 to +1, - 4, +1, and - 4 to - 3 days from anthesis, respectively. The hours of peak sensitivity for these variables occurred during the same days at - 36, - 101, + 15, and - 83 hours from anthesis, respectively. Using Box-Jenkins time series analysis, diurnal periodicity in temperature sensitivity for the four variables was determined.
Abstract
The effect of drought and salinity stress on emergence of six Guayule (Parthenium argentatum Gray) cultivars was investigated. Final percent emergence declined an average of 62% from optimum conditions to those of moderate stress. Whereas the effect of either stress was nearly equivalent on final percent emergence, drought had a slightly greater effect on maximum emergence rate and salinity a greater effect on inflection time (time to maximum emergence rate) in most cultivars. Cultivars had no effect on final percent emergence, but they did affect maximum emergence rate and inflection time. Germination of cultivar 11619 was more stress-tolerant than others, since it had a higher maximum emergence rate and lower inflection time under stress. Within cultivars, variability was high for final percent emergence and maximum emergence rate and low for inflection time.
Abstract
The influence of four temperatures (25°, 30°, 34°, and 37°C), five osmotic potentials (0, −0.3, −0.7, −1.1, and −1.5 MPa) and three salts (NaCl, KCl, and Na2SO4) on the germination of three guar [Cyamopsis tetragonoloba (L.) Taub] cultivars (Kinman, Lewis, and Santa Cruz) was tested under laboratory conditions. The results show that germination decreased with increasing salt concentrations. A temperature-salinity interaction was observed with the greatest suppression of germination at the high temperatures (34° and 37°) and salt concentrations (−1.1 and −1.5 MPa). The response varied according to the type of salt, with the lowest germination rate for all three cultivars in Na2SO4 at −0.7 to −1.5 MPa osmotic potentials. The three cultivars showed significant differences in their germination response to salt stress; ‘Kinman’ performed better than either of the two other cultivars in low salt concentrations (0 to −0.7 MPa), but, at high concentrations (−1.1 and −1.5 MPa), the differences were not significant.
Abstract
Salvia (Salvia spendens, F. Sellow ex Roem & Schult.) seeds imbibed in distilled water at 6C for 6 days germinated earlier and with fewer days to 50% of total germination (T50) than non-imbibed seeds. Drying imbibed seeds for 1 to 5 days at 5C and 45% RH before sowing signficiantly reduced seed viability. Priming seeds in a hypertonic osmotic solution of aerated polyethylene glycol 8000 (PEG) at —0.8 MPa for 10 days at 15C improved germination of the three cultivars tested. In laboratory and plant growth chamber trials, seeds primed with PEG 8000 and nonprimed seeds had similar total germination at 20 and 25C, but primed seeds had significantly higher germination at 10, 15, and 30C. At 35C, PEG-primed seeds had 44% to 65% germination, while nonprimed seeds failed to germinate. Alternating 10 and 20C or 20 and 30C diurnally at 12-hr cycles did not increase total germination regardless of seed treatment. Seeds primed with PEG had lower T50 than nonprimed seeds at 10, 15, 20, 25, and 30C, with the largest difference at the most unfavorable temperatures for germination. Primed seeds stored at 5C for 1 to 16 weeks reduced total germination and the potential capacity for rapid germination.
counteract the effects of ABA and increase early seed germination rates. Two hormones in the ethylene pathway, ethylene and its precursor ACC, have been found to increase seed germination percentages of both apple ( Malus × domestica ) and grape ( Vitis
Gibberellins are phytohormones that promote important aspects of growth, such as seed germination, leaf expansion, stem elongation, flowering, and fruit development ( Davies, 1995 ). In woody plants, many GA-mediated processes are agriculturally
Abstract
Tolerance of carrot seeds (Daucus carota L.) to heat treatments that could eradicate seedborne pathogens was investigated. Germination and emergence of seedlings from seeds treated in hot water at 35, 40, 45, 50, or 55C from 4 to 20 min were not affected, but seeds treated at 60C for 8 min or more were affected adversely. At 45 and 50C, treatment durations as long as 48 min did not affect emergence, but >20 min at 55C reduced emergence. Similar results were obtained when seeds were treated at the same temperatures in water containing 1.1% sodium hypochlorite (NaOCI). Emergence of seeds treated in hot water or 1.1% NaOCl and planted within 5 days generally was similar to that of treated seeds stored for 90 days at 20C in 60% RH before planting. Any existing differences were small and not clearly related to temperature–duration treatment combinations. Percent emergence from seeds of 19 out of 25 hybrid cultivars treated at 50C for 15 min was reduced by an average of 2.9%, but differences for untreated seeds ranged from −13.3% to +4.8%. Emergence from hot water-treated seeds was reduced after 6 weeks of storage at 70% and 80% RH, but not at 20% to 60% RH. Prolonged treatment and the higher temperatures were particularly effective in reducing populations of seedborne Alternaria dauci.