Poster Session 17–Seed and Stand Establishment 19 July 2005, 12:00–12:45 p.m., Poster Hall–Ballroom E/F
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.
1 To whom reprint requests should be addressed. Current address: Bodger Seeds, 1851 W. Olive, Lompoc, CA 93436. Journal paper no. J-14892 of the Iowa Agriculture and Home Economics Experiment Station, Ames
Standardized seed vigor tests must be developed for greenhouse-grown flower species. Current vigor tests used to evaluate large-seeded agronomic crops are generally not useful for evaluating smaller-seeded flower species. One alternative is to use radicle length in seedlings grown under controlled environments as an indicator of seed vigor. For that purpose, a seed vigor test was developed that uses digital images taken using a flat bed scanner to measure radicle length in small-seeded flower species. A novel, cellulose substrate was used for germinating seeds. It provided similar moisture-holding properties to standard germination blotters used by commercial seed analysts, but is clear. This has allowed for quick image acquisition without removing seedlings from the petri dish. Correlations were made between seedling growth (radicle length, total seedling length, and total seedling area) with other vigor tests (saturated salts accelerated aging) and greenhouse plug flat emergence. For several seed lots of impatiens that varied in initial seed quality, radicle length after 4 days showed good correlations (>R 2 = 0.79) with other measures of seed vigor for describing seed quality. This system is an improvement over other attempts to use computer-aided assessment of digital images because it provides digital images that do not vary due to external lighting; it uses software that can evaluate radicle length in a petri dish assay that does not require a slant-board for straight radicle growth; it relies on standard germination technics used by every seed lab; it uses a clear substrate to replace the opaque blotter to allow digital images to be taken within the petri dish; and accurate measurements of seedling parts is performed in under 2 min per petri dish.
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.
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.
78 ORAL SESSION (Abstr. 497-503) CROSS-COMMODITY SEED PHYSIOLOGY I
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