Search Results
ACC-derived ethylene production was used as an index of seed vigor of lettuce (Lactuca sativa L.), cabbage [Brassica oleracea (Capitata Group)], tomato (Lycopersicon esculentum Mill.), snap bean (Phaseolus vulgaris L.), and sweet corn (Zea mays L.) seeds. Seeds were aged at 40C and 93% relative humidity over saturated solution of KH2PO4 for various times to obtain seeds of differing vigor. Naturally aged lettuce seeds, differing in vigor, were also used. Depending on the seed type, 0.25 to 2 mm ACC (saturating dose) was needed to produce maximal amounts of ethylene. Seeds in the presence of ACC produced a much larger amount of ethylene than those in the absence of ACC, the ACC-derived ethylene could be detected before germination, and ACC had no adverse effect on germination. ACC-derived ethylene production paralleled vigor loss as determined by a decrease in percentage germination over a soak period required for complete germination of nonaged seeds (16 hours for lettuce, 24 hours for cabbage, and 48 hours for tomato and sweet corn), an increase in mean germination time (determined for lettuce only), and a decrease in seedling growth (determined for snap bean only). Second degree polynomial and logarithmic equations generated for the relationship of ACC-derived ethylene production to germination or growth parameters following seed aging, provided good to excellent fit. As a vigor test, the ACC-ethylene procedure has several advantages over the non-ACC ethylene procedure: It improves the sensitivity of the test by enhancing ethylene production, permits detection of small differences in vigor, and allows detection of ethylene before germination within a few hours of soaking. Chemical name used: 1-aminocyclopropane-1-carboxylic acid (ACC).
The cause for the differences in germination ability of large and small confection sunflower (Helianthus annuus L.) seeds was investigated over 3 years. The source-sink relationship was manipulated to better explore the differences between seeds of various sizes and to study the role of the embryo and the pericarp (hull) in controlling germination ability. Percent germination of large seeds was significantly lower than that of small seeds when tests were performed at 15 °C. Increasing the ratio of leaf area to number of developing seeds caused an increase in mean seed mass, but resulted in a lower percentage of germination. Seed vigor, as measured by mean time to germination or to emergence of hulled seeds or by rate of root elongation, was negatively correlated with embryo mass, indicating that the low vigor of large seeds is not due to the mechanical barrier imposed by the hull. Analysis of electrolyte leakage confirmed the hypothesis that the low quality of large seeds results from a disturbance during the process of seed development.
Abstract
Seed weight in lettuce was more important than seed width or thickness in predicting vigor. An air column separator was an effective way to separate seeds varying in weight. A biological assay called the slant test was developed to test vigor. The average root length after 3 days was used as a measure of vigor.
Sweet corn (Zea mays L.) and tomato (Lycopersicon esculentum Mill.) seeds were aged naturally for 18 months or artificially aged using saturated salt accelerated aging to provide seed lots that differed in seed vigor, but retained a high standard germination percentage. Seed vigor was confirmed using standard vigor tests, including time to radicle emergence, cold, and accelerated aging tests. Ethylene evolution from both sweet corn and tomato seeds during germination was positively correlated with seed quality. Differences in ethylene evolution between nonaged and aged seeds were greater in seeds germinated on exogenous 1-aminocyclopropane-1-carboxylic acid (ACC). After 36 hours, there was about a 15-fold increase in ethylene evolution from seeds treated with 5 mm ACC compared to untreated seeds. Naturally and artificially aged seeds responded similarly and showed reduced ethylene production compared to nonaged seeds. In contrast to ethylene production, endogenous ACC titers were less for nonaged compared to aged seeds. Exogenous application of ACC to artificially aged seeds reduced the time to radicle protrusion, but did not completely reverse age-related effects on vigor. The data indicate that the reduced ability to produce ethylene in aged seeds was related to ACC oxidase (ACCO) synthesis or activity. Using Northern blot analysis, ACCO mRNA was detected after 48 hours of imbibition in nonaged seeds, but was undetectable in aged seeds affirming the contention that ACCO synthesis was delayed or reduced by aging. The current study provides additional support for ethylene as a biochemical indicator of seed vigor in seed lots with reduced vigor but high germination capacity.
Abstract
Several lots of lettuce seed were separated into fractions varying in seed width and weight per seed. Seed vigor, as measured by the slant test, was found to vary in relation to seed weight. In field trials low vigor seeds emerged slower with less total emergence and produced smaller seedlings at thinning time than high vigor seeds. Head size at harvest and percent marketable heads were greater from high vigor seeds. It is suggested that seed vigor can be used to evaluate potential field performance of lettuce.
Abstract
Seeds of 2 corn (Zea mays L.) endosperm mutants, shrunken-2 (sh2) and sugary (su), were produced in the field and greenhouse and harvested 18 to 46 days postpollination (dpp). Seeds of su accumulated dry weight rapidly after 26 dpp, while sh2 seeds had nearly attained their final weight by this stage. This resulted in a larger endosperm in su. Greenhouse-grown sh2 seeds weighed more than field-grown sh2 throughout development. Germination and seedling growth of greenhouse-grown sh2 seeds under optimum conditions were greater than that of field-grown sh2 when seeds were older than 26 days. Greenhouse-grown sh2 seeds 26 days and older germinated as well as field- and greenhouse-grown su with comparable seedling growth. Germination of field-grown sh2 seeds was much higher throughout development in the cold rolled-towel test compared to the cold soil test. Viability and vigor differences between immature seeds of both genotypes were not distinguishable by the cold, rolled-towel test, but were very noticeable in the cold soil test. Under cold soil test conditions, greenhouse-grown sh2 seeds had significantly greater emergence than did field-grown sh2 38 dpp and older. Mature greenhouse-grown sh2 and su seeds were of equal viability and vigor in the cold soil test.
Abbreviations: CNS, `Crisp N' Sweet 710'; FLASS, `Florida Stayaweet'; SGCX, seedling cold growth test. 1 Graduate Research Assistant. Current address: Asgrow Seed Co., 500 Lucy Brown Lane, Box L, San Juan Bautista, CA 95045. 2 Assistant Professor
We thank Kent J. Bradford for providing the seeds for this experiment and James H. Wilson for assistance with Instron analysis. This research was funded in part by USDA research project W-168. Use of trade names does not imply endorsement of
Abstract
Slow and inconsistent germination of cyclamen, Cyclamen persicum Mill., seed appeared to be more related to seed and seedling vigor than to any type of seed dormancy. Pregermination and germination seed treatments such as immersion in hot water, still and flowing water, cool moist storage, alternating temperatures and fungicide treatments were of little value. Treatment with gibberellin (GA) solutions accelerated germination but created an expelled embryo problem. The grower is advised to surface disinfest fully imbibed seed in 5% sodium hypochlorite for 20 sec to 1 min.
Abstract
Seed vigor in sweet corn (Zea mays L.) was compared among cultivars with the triple recessive endosperm mutant gene combination amylose-extender (ae), dull (du) and waxy (wx), the shrunken-2 (sh2) gene, their sugary (su) counterparts and an open-pollinated cultivar of normal genotype. Dry weight was significantly lower for F2 kernels of the high-sugar genotypes ae du wx and sh2 than for their su counterparts or the normal cultivar. The endosperm:embryo dry weight ratio was also low in the high-sugar lines due primarily to their small endosperm. Seedling dry weight at 10 days was correlated with endosperm:embryo ratio. Comparisons were made among the cultivars for shoot, radicle, and seminal lateral root growth from intact seeds and from excised embryos on nutrient agar. The normal genotype showed superior seed vigor when evaluated by seedling growth from intact kernels, but not when embryos were grown on agar, suggesting that vigor in normal was due to large endosperms. Respiration rate (μl O2 uptake/kernel·hr) of the germinating seeds did not account for growth differences among the genotypes. Respiration at 24 hr after imbibition was negatively correlated with seedling dry weight at 10 days. Respiration at 48 and 72 hr showed no significant correlations with growth rates. Low seed vigor in high-sugar genotypes apparently was related to their small endosperms. The genotype of the embryo also was important in seedling vigor, but low vigor in high-sugar cultivars could not be attributed wholly to genetic inferiority of the embryo.