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  • Author or Editor: D.H. Paine x
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The purpose of this project was to study factors that influence the leakage rate and develop methods to enhance leakage of sinapine from Brassica seeds. Six seedlots (two seedlots of one cultivar each of cabbage (Brassica oleracea L., Capitata group), broccoli, and cauliflower (B. oleracea L., Botrytis group) were studied. Leakage was quantified spectrophotometrically by measuring the absorbance of the soak water at 330 nm. The onset of sinapine leakage was determined from single seeds by the visual presence (yellow soak water) caused by soaking seeds in a biological buffer adjusted to pH 10. The leakage pattern from heat-killed seeds of all seedlots was sigmoidal with a distinct lag phase followed by a rapid efflux and final slower rate. The duration of the lag phase and the total amount of sinapine leaked after 24 hours was not the same for all seedlots after adjusting for seed count, seed weight, or sinapine content. Therefore, another factor was responsible for differences measured in leakage. Embryos or seeds with cracked testas leaked faster than intact seeds, and the leakage pattern without testa integrity was biphasic. From these studies, we conclude that the testa was a major factor regulating sinapine leakage. Pretreating heat killed seeds, with up to 1.0% NaOCl for 10 minutes, accelerated the onset of leakage. The time for 50 percent of the seeds to leak (T50) decreased as NaOCl concentration increased. Leakage uniformity, as measured by the standard deviation of the distribution, generally increased as NaOCl concentration increased. The sigmoidal leakage pattern from heat-killed Brassica seeds may be attributed to seedcoat cracking associated with imbibitional swelling. A NaOCl pretreatment may have increased the permeability of the testa and, thereby, enhanced the leakage rate.

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The purpose of this study was to develop a procedure to determine seed moisture content from intact pelleted seeds. Samples of `Sentinel' onion and `Salinas' lettuce were pelleted by the following companies; Asgrow, Germains (Seed Systems), Harris Moran, Incotec, Peto and Seed Dynamics. Physical characteristics of the various pellets were quantified including weight, volume and density. Measurements were made on intact pellets and densities ranged from 0.84 to 1.67 g/cc. Seed drying curves were obtained on the different pellets under controlled environmental conditions. Pellets were first equilibrated at 85% RH, and then dried at 25C and 18% RH. In general drying rates were similar among pellet types within crops. With regards to seed moisture content determination, neither the electronic moisture meter, based on measuring capacitance, nor oven methods were able to accurately measure seed moisture from intact pellets. Measurement of the head space RH from pre-equilibrated intact pellets (water activity) resulted in an accurate method to assess seed water status for all samples. The actual seed moisture content could be determined by using the moisture isotherms for each seed lot at a given temperature.

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High-quality seed lots are required for successful establishment of horticultural crops. Testing methods are needed that can detect the early phases of aging prior to a significant loss in germination. Quality was assessed using both germination speed and uniformity on non-primed and primed, as well as non-aged and aged, lettuce (Lactuca sativa L.) seed. Speed and uniformity were quantified using time to 50% (T50) germination and one standard deviation (Tsd), respectively. Embryo elongation was developed as a rapid test by first soaking seeds for 2 hours, then cutting and removing the distal one-third of the seed, and finally observing the percentage of visibly elongated embryos from the seed coverings over time. The mild aging conditions employed in this study (45 °C and 50% relative humidity for up to 21 days) had little influence on viability (germination in all treatments was >98%), but reduced germination rate (increased the time for T50 and Tsd). Primed seeds aged faster than non-primed seeds under the same aging conditions. The percentage of elongated embryos was calculated at hourly intervals after cutting, and treatment differences were observed after a total hydration period of 5 hours. The embryo elongation test detected aging in both primed and non-primed treatments.

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