Five seed-quality indices based on individual seed electrolyte leakage tests were evaluated. Zea mays L. seeds were soaked for 6 hours, and individual seed leachate conductivity values were obtained. A total of 100 cells were scanned, one seed per cell, at 5-minute intervals for the first 30 minutes, followed by 15-minute intervals for the remaining 330 minutes. Seeds were allowed to dry for 5 to 7 days at room temperature and then were tested for germinability at 25C for 7 days. Radicle lengths were measured after 72 hours. The Richards function was fitted to cumulative frequency distributions of μAmps to obtain internal slope (IS), mean μAmp, and median μAmp values for each scan. Initial leach rate (ILR) was estimated after fitting hyperbolic functions to μAmp vs. soak time data. Average leach rate (ALR) was also derived from fitting the Richards function to μAmp vs. soak time data. Linear regression of seed quality on IS, mean, and median μAmp values after 5 hours of imbibition yielded r2 values of 0.91, 0.81, and 0.86 for predicting viability and 0.56, 0.46, 0.52 for predicting radicle length. Thus, IS was the best seed quality predictor, followed closely by median and mean μAmp values. ILR and ALR were not correlated with seed quality.
K.G.V. Davidson, F.D. Moore III, E.E. Roos, S. Nath, and S. Sowa
Seeds are coated for ease of handling, singulation, precise placement, and the incorporation of beneficial chemicals or microbials. Coated seeds are accepted widely as a standard product for many crops. Quality demands for seed suitable for coating have improved knowledge of physiological seed quality. Higher, better-defined quality standards in the seed and coating industry, combined with additional quality demand for enhanced seed, will continue to improve stand establishment potential for growers.
Cyrus Samimy and A.G. Taylor
Deterioration of snap bean (Phaseolus vulgaris L.) seed quality during accelerated aging at 42°C and 100% relative humidity was accompanied by a decline in germination, radicle emergence, hypocotyl length, and ethylene production. Field emergence of 5 seed lots had a highly significant correlation with ethylene production rates when measured after 22 to 23.5 hours of imbibition at 25°. Seed lots that produced low levels of ethylene emerged poorly in the field. Results indicate that determination of ethylene production of imbibed seeds might be a useful method for detecting changes in seed vigor.
W. F. Tracy and John A. Juvik
Acceptance of shrunken-2 (sh2) sweet corn (Zea mays L.) hybrids is limited by poor seed quality and seedling emergence, especially in cold soils. The conductivity of the electrolytes leached from imbibing seeds, a rapid measurement of seed quality, is highly correlated with field emergence among sweet corn hybrids. Our objective was to determine if conductivity is related to field emergence in a sh2 population that had undergone selection for improved field emergence for 10 cycles. The response of conductivity to indirect selection was linear, and the linear trend accounted for a large portion of the variation in conductivity (r 2 = 0.70). Conductivity ranged from 82.0 dS·m–1 in cycle 0 to 35.3 dS·m–1 in cycle 8, with cycle 10 not differing from cycle 8. High conductivity indicates greater electrolyte leakage. At P ≤ 0.01, conductivity was negatively correlated with all seed performance ratings; field emergence (r = –0.82), plant height (r = –0.81), uniformity (r = –0.92), and relative emergence (r = –0.85).
David W. Still and Kent J. Bradford
With many seed crops, the most difficult production decision is when to harvest. In indeterminate crops such as Brassica species, early harvests result in immature seed of low vigor while late harvests risk seed deterioration and seed loss due to shattering. To provide a biological basis on which to determine harvest timing, we have characterized seed development in rape seed (Brassica napus L. `Weststar') and red cabbage (Brassica oleracea L. Group Capitata) using population-based hydrotime and ABA-time models. These models provide information relevant to assessing physiological maturity, and therefore, seed quality. The hydrotime and ABA-time models quantify germination rate, the uniformity of germination, viability, and the sensitivity of germination to water potential and ABA. Indices derived from these models, along with maximum germination and t50 values, were used to determine physiological maturity (maximum seed quality) of the seeds during development. The overall trends in seed development were similar in both species: as seeds matured, germination became more uniform and less sensitive to low Ψ and externally applied ABA. The models accurately described germination time courses and final germination percentages except for seeds imbibed at very high concentrations of ABA. In rape seed, physiological maturity was attained several days after maximum seed dry mass, while in red cabbage physiological maturity occurred at or after maximum seed dry mass. Vigor indices were correlated with easily discerned traits such as moisture content and silique phenotypic characteristics. The results of these experiments suggest that hydrotime and ABA-time models can be successfully used to provide a biological basis on which to determine harvest in brassicas.
P. Kataki and A.G. Taylor
The production of ethanol under anaerobic and aerobic conditions is suggested as a sensitive indicator of seed aging. Seeds of sweet corn (Zea mays L. `Jubilee') and lettuce (Lactuca sativa L. `Salinas') were aged at 75% relative humidity and 45C to obtain five aged seed lots and compared to a nonaged control sample. The percent germination decreased while percent abnormal seedlings initially increased with seed aging. Anaerobic treatments were induced either by immersing seeds in distilled water for sweet corn or in a solution of 50 mM glucose and 5 mM KPO4 buffer adjusted to pH 5.6 for lettuce. Aerobic treatments were performed by placing seeds in a plastic chamber filled with a known amount of glass beads sufficiently moistened to allow imbibition. Ethanol was measured after 12 and 24 hours from lettuce and sweet corn, respectively. Aqueous extracts were analyzed by immobilized enzyme technology and verified by gas chromatography. Anaerobiosis induced large amounts of ethanol production compared to aerobic treatments. The amount of ethanol decreased with seed aging duration under anaerobic conditions while these trends were generally reversed under aerobic conditions. The ratio of ethanol produced under anaerobic compared to aerobic conditions was best able to separate differences in seed quality due to aging.
J.J. Steiner, R.B. Hutmacher, A.B. Mantel, J.E. Ayars, and S.S. Vail
Seed yield and quality of carrot (Daucus carota var. sativa DC.) were influenced by a wide range of water application regimes and levels. Irrigation treatments were imposed beginning at the time of extension of the primary umbel and extending throughout the reproductive development period. The three application regimes used were: 1) a high-frequency, low water deficit treatment [100% of daily accumulated crop evapotranspiration (ETc)]; 2) a series of five low-frequency (irrigated after 30 mm of accumulated ET,) application treatments with a range of water deficits from moderate to minimal (40% to 120% of ETc applied); and 3) a series of three treatments that had rapidly developing water deficits applied by terminating irrigation at 7, 5, and 2 weeks before harvest after being grown under low-stress conditions. Pure live seed (PLS) yield was optimized by different treatments within each of the three application regimes. Maximum yields were achieved with short-term (2-week) rapidly developing water deficits near harvest, moderate deficit irrigation with 60% to 80% of ETc applied after 30 mm of ETc, or with a low water deficit, high-frequency application. Seed germination percentage decreased as the amount of applied water increased. This effect was more pronounced in the later-developing umbel orders. However, seed quality measured as seedling root length was improved with increasing water application.
Mustafa M.A. Elballa and D.J. Cantliffe
The effect of temperature on seedstalk development, seed yield and quality in carrot (Daucus carota L.) was investigated in growth chambers at constant day/night temperatures of 33/28, 28/23, 25/20, 23/18, 20/15, and 17/12 °C. Days to flowering, seedstalk height, number of umbels, and seed yield decreased linearly with increasing temperature from 17/12 to 33/28 °C. Continuous high temperature (33/28 °C) had a detrimental effect on germination as measured by a standard germination test and an accelerated aging test. Optimum germination of the progeny occurred at 20/15 °C; however, germination rate was faster when seeds matured at 23/18 °C. Seeds that developed at 33/28 °C produced seedlings with the lowest vigor, while those which developed at 20/15 °C produced seedlings with the highest vigor. Brief exposure of plants to 33/28 °C during anthesis or early seed development was as detrimental to seed yield as continuous exposure to 33/28 °C. Exposure to high temperature (33/28 °C) during late seed development had less effect on seed yield, and seed quality was improved. Progeny vigor was reduced greatly by seed development at continuous high temperature (33/28 °C), but was unaffected by brief exposure to 33/28 °C at anthesis, early, or late in seed development. These results suggest that high (33/28 °C) day/night temperatures during pollination, fertilization, or early stages of seed development can greatly reduce carrot seed yield and seed quality.
Mark A. Bennett, Luther Waters Jr., and John H. Curme
To understand early development of seed quality, seed lots of sweet corn (Zea mays L.) inbred PGG-27B were harvested from an increase field at 10 stages of maturity, beginning when kernel moisture was at 59% and continuing to 19% kernel moisture content (42 to 103 days after pollination, respectively). Seed lots were dried, hand-shelled, sized, and tested for standard germination and subjected to the seedling growth cold test (SGCT). Endosperm, embryo, and kernel dry weights, and endosperm : embryo (END:EMB) ratios were monitored as the seed matured. Field tests were planted to determine the influence of kernel maturity, grade, and hydration on stand establishment and early seedling growth. Seeds were partially hydrated by mixing with moist vermiculite and screening from the substrate when seeds had reached 30% moisture content. Results from hydrated seeds were compared to those from seeds at ≈10% seed moisture to determine the effect of presowing seed hydration on seedling establishment. The seed hydration effect depended on the environment, but seed size was shown consistently to influence emergence and early seedling dry weight. Seed harvested at 45% to 54% moisture had better stand establishment than seed harvested at the more typical moisture of near 35%. The stage of maturity, determined by kernel moisture, at which PGG-27B was harvested had little effect on standard germination. Hydrating the seed prior to the SGCT improved seedling growth for all early kernel maturities and all seed grades. Embryo dry weight of composite samples increased steadily up to the fifth harvest period (38% seed moisture), then leveled off. Kernel and endosperm dry weights were more variable at the fifth harvest than at others, but followed the same general pattern. The ratio of END:EMB dry weight decreased from the first to the fifth harvest, where it continued at a value near 4.9 through harvest 10. Seed moisture at harvest, seed size, and presowing seed hydration were shown to influence the seed quality of PGG-27B.
Ute Albrecht and Kim D. Bowman
. L. asiaticus infection on seed quality and seedling development and whether seedlings grown from affected fruit develop HLB disease. Two experiments were conducted using either seeds from rootstock source trees of six different genotypes or seeds