High seed quality is required to obtain optimal plant stands and to achieve maximum yield potential. Onion seeds are commonly coated and treated with an insecticide and fungicide to control early season insects and diseases. The seed treatments may cause phytotoxicity in standard germination tests, and thus reduce the percent germination of a seed lot. The objective of this study was to examine the effect of seed quality on seed storage, stand establishment and yield. Two seed lots of two long-day onion varieties were pelleted and treated with the seed treatments Trigard and Pro-Gro. Standard germination and saturated salt aging tests were performed on each seed lot, indicating a high and lower quality seed lot for each variety. Aging was conducted by equilibrating pelleted seeds at 35% relative humidity and aging at 25 °C for up to 12 months. Aging decreased germination with time, especially for the lower quality lots. Field studies were conducted in two locations in upstate New York. The plant stand was greater in the high compared to the lower quality lots in both varieties at both locations. Yield was reduced in the lower quality than high quality lot; however, the response differed by variety and location. Overall, the initial seed quality had an impact on seed storagability, stand establishment and yield.
Alan G. Taylor
Yuliya A. Salanenka and Alan G. Taylor
The seedcoat permeability, uptake, and transport of model fluorescent tracers were investigated in snapbean (Phaseolus vulgaris), pepper (Capsicum annuum), tomato (Solanum lycopersicum), onion (Allium cepa), cucumber (Cucumis sativus), and lettuce (Lactuca sativa) seeds. Nine fluorescent tracers and one vital stain were selected to represent a diversity of physicochemical properties (lipophilicity, electrical charge, etc.) and to simulate behavior of applied seed treatments. To study seedcoat permeability, tracers were applied to seeds as dry powders, and treated seeds were sown in moistened sand at 20 °C and removed after 18 to 24 h, a time before visible germination. Imbibed seeds were dissected and fluorescence (staining) was observed in embryos with a dissecting microscope under ultraviolet (365 nm) or visible radiation. Seedcoat permeability of species to solutes was grouped into three categories: 1) permeable—snapbeans; 2) selectively permeable—tomato, pepper, and onion; and 3) non-permeable—cucumber and lettuce. Systemic tracers that failed to permeate seedcoats during seed imbibition were taken up by roots or hypocotyls after visible germination.
Yuliya A. Salanenka, Martin C. Goffinet, and Alan G. Taylor
The perisperm–endosperm (PE) envelope surrounding the embryo of cucumber (Cucumis sativus) acts as a barrier to apoplastic permeability and radicle emergence. The envelope consists of a single cell layer of endosperm whose outer surface is covered by noncellular lipid and callose-rich layers. We compared the structure and histochemistry of the radicle tip and chalazal regions of the envelope, because these regions differ in permeability. Seeds were treated with coumarin 151, a nonionic, fluorescent tracer with systemic activity. Treated seeds were imbibed and on seedcoat removal, the root tip area of the membrane-covered embryo accumulated the fluorescent tracer, but the tracer could not penetrate the envelope that bordered the cotyledons and chalazal region. The cone-shaped remnant of tissue opposite the micropylar region of the envelope was identified as nucellar tissue, the “nucellar beak.” The cuticular membrane and callose layer of the PE envelope were interrupted in the nucellar beak as well as in the chalazal region. Their role in permeability is apparently substituted by the presence of thick-walled suberized cells in the beak and chalaza. A canal was observed in the center of the nucellar beak that likely provided a conduit for the tracer to diffuse from the environment to the embryo. This canal was the remnant of pollen tube entry through the nucellus and was plugged with several cells, presumably residue of the suspensor. These cells degenerated just before cucumber seed germination. This remnant of the pollen tube canal presumably offers less mechanical resistance in the nucellar beak that might help facilitate radicle protrusion during germination. Cells of the outermost and basal regions of the nucellar beak as well as the walls of endosperm cells contained pectic material. Significant pectin methylesterase activity was found in the lateral and cap regions of the PE envelope long before seed germination. Lack of callose in the envelope at the radicle tip suggests that callose does not act as a barrier to radicle emergence during cucumber seed germination.
Corinne F.J. Rutzke, Alan G. Taylor, and Ralph L. Obendorf
A seed quality test developed by measures the anaerobic-to-aerobic (ANA) ratio of ethanol production and the relationship of the ANA ratio index-to-seed quality has been tested in several species. To expand the usefulness of the ANA ratio index and to optimize the test conditions, a series of studies was performed using cabbage (Brassica oleracea L. var. capitata L.) seeds as a model. It was hypothesized that ethanol production in cabbage seeds would be influenced by aging treatment, hydration level, seed integrity (grinding), and oxygen availability. Cabbage seeds were subjected to controlled aging treatments (40 °C at 70% relative humidity for 0, 7, 14, 21, and 28 d). Seed samples were incubated with a glucose (50 mm) potassium phosphate buffer (5 mm, pH 5.6) at 25 °C for 24 h (shorter than the time required for germination). The water concentration levels tested in the current study were 0.18, 0.22, 0.54, 0.80, 1.22, 1.86, 3.00, 5.67, and 10.0 g of H2O per gram of dry seeds. Ethanol production was measured in the supernatant of seed extracts using immobilized enzyme technology. The experiments were performed in ambient oxygen conditions and under nitrogen. Ethanol production was greater in aged than nonaged intact seeds at all water concentrations tested. Nonaged seeds under nitrogen had reduced ethanol production at ≤0.54 g of water per gram of seeds, indicating that low seed water concentration limited ethanol production. Nonaged seeds in ambient oxygen at ≥1.22 g of water per gram of seeds had elevated ethanol production, indicating that a hypoxic environment was created by excess seed water. Thus, a water concentration between these values is recommended for the ANA ratio index test for cabbage seeds. The opposite trend of lower ethanol production in aged than nonaged seeds was measured if seeds were ground before the hydration. Seed integrity experiments suggest that lower ethanol production observed in aged ground seeds may be attributed to hypoxia resulting from rapid hydration damage that results with loss of seed-coat integrity.
Masoume Amirkhani, Anil N. Netravali, Wencheng Huang, and Alan G. Taylor
This research presents a novel method of using plant-derived protein hydrolysates as seed coating materials. The objective of this study was to develop seed coating formulations using soy flour, a sustainable, inexpensive, and green source, as a biostimulant using broccoli as the model system. A 10% suspension of soy flour was used as the seed treatment binder in all coatings. The solid particulate filler was composed of mixtures of soy flour, cellulose, and diatomaceous earth, together termed as SCD. All SCD components were homogenized in water, then dried and ground to a fine particle size <106 µm. The SCD coatings were applied with rotary pan seed coating equipment at 25% of the seed weight. Increasing the proportion of soy flour increased the seed coating strength and also the time for the coating to disintegrate after soaking in water. As a result, the seed coatings reduced the percentage germination and the germination rate compared with the nontreated control. However, the 10-day-old seedling root and shoot growth showed significant improvement for all SCD coating treatments compared with controls. Plant growth and development was also measured after 30 days in the greenhouse. Fresh weight (FW) and dry weight (DW), leaf area, plant height, leaf development, Soil-Plant Analyses Development (SPAD) index (chlorophyll measurement), and nitrogen (N) per plant were all greater from coatings with 30%, 40%, and 50% soy flour than the noncoated control. Nitrogen, from the soy flour applied in the seed coatings, ranged from 0.024 to 0.073 mg per seed, while the enhanced N per plant ranged from 1.7 to 8.5 mg. The coating treatment with 0.063 mg N per seed resulted in the greatest plant leaf area and highest N content. Nitrogen applied in the seed coating only accounted for 1% to 2% of the enhanced N in the plants, indicating the soy flour acted as a biostimulant rather than a fertilizer.
Leslie S. Katzman, Alan G. Taylor, and Robert W. Langhans
Rapid, synchronized, and high percentage of germination is required for commercial spinach (Spinacia oleracea L.) production using hydroponic techniques. Seed treatments examined to improve seed germination were: 1) decoating; 2) leaching in water; and 3) soaking seeds for 4 hours in 0.5% NaOCl, leaching for 15 hours in water, and sowing in 0.3% H2O2 (this treatment will be referred to as NaOCl/H2O2). Germination studies were conducted on four cultivars at a constant 18 °C (optimal) or 30 °C (inhibitory). At 18 °C, germination rate (T50) was maximized by both hydration treatments, but uniformity of germination (Tsd) was greatest for decoated seeds; final germination was ≥89% for all treatments. At 30 °C, decoating resulted in greatest uniformity of germination. The NaOCl/H2O2 treatment resulted in highest germination (94%) at the high temperature, whereas decoating was least effective (69%). Reduced germination of decoated seeds was attributed to atypical germinants. Cultivars differed in response to the treatments at both temperatures. Component analysis of the NaOCl/H2O2 treatment was studied with two slow-to-germinate cultivars. Treatment with H2O2, with or without NaOCl, improved the rate, uniformity, and percentage of germination of seeds of both cultivars, but NaOCl alone did not. Pericarp removal or pericarp removal plus NaOCl/H2O2 treatments reduced variability in germination time and enhanced speed of germination at 30 °C, but decoating produced a higher percentage of atypical seedlings than did other treatments. Therefore, the NaOCl/H2O2 treatment is recommended for growers who are unable to maintain cool germination temperatures and/or cannot afford the costs associated with cooling. If growers can maintain a germination temperature of ≈18 °C, decoated seeds are preferable, based on the high uniformity of germination.
Alan G. Taylor, C.J. Eckenrode, and R.W. Straub
Conventional methods to control the onion maggot or onion fly, Delia antiqua (Meigen), have relied on in-furrow applications of the toxicant pesticide, chlorpyrifos. The objective of this research was to develop an onion (Allium cepa L.) seed treatment that utilizes a new chemistry compound that is environmentally safe. Cyromazine is an insect growth regulator with a mode of action different from traditional pesticides used to control onion maggot. Cyromazine has low mammalian toxicity and is relatively nontoxic to other insects, including beneficials. High seed loading rates (50 g·kg-1 active ingredient) are required for optimal efficacy, and conventional slurry methods are inadequate to apply these high loading rates. Film coating and pelleting were performed at Cornell Univ. to apply cyromazine and a registered fungicide (a formulation of thiram and carboxin) to onion seeds. Results of field studies performed over several years revealed that stand losses due to the onion maggot ranged from ≈20% to 60%. Cyromazine applied by either film coating or pelleting decreased the loss by onion maggot from 1% to 8%, and efficacy was comparable to an in-furrow application of chlorpyrifos. Cyromazine was registered as a seed treatment and is commercially used in the northeastern and midwestern United States, where onion maggot is a serious pest. Field emergence was not negatively affected by cyromazine coated onto the seeds when onion seeds are sown in organic (muck) soils. There is other evidence, however, that cyromazine seed treatments may cause phytotoxicity to germination and seedling growth. Testing seed quality in sand or on roll towels revealed a high percentage of abnormal seedlings. Retarded root growth was observed in seeds treated with cyromazine, resulting in an increase in abnormal seedling classifications. A finely ground sphagnum peatmoss applied over the seeds in a roll towel test ameliorated the abnormal root growth symptoms, and seedlings had robust growth. Collectively, film coating and pelleting were effective delivery systems for the application of plant protectants required at time of sowing. Modification of the standard germination test was needed to accurately assess onion seed quality. Moreover, this project was successful due to a team effort of a university seed scientist and entomologists working with onion growers and industry. Future registrations on small acreage, high-value horticultural crops are envisioned to require similar multi-partner approaches. Chemical name used: N-cyclopropyl-1,3,5-triazine-2,4,6-triamine (cyromazine).
Christopher B. Cerveny, William B. Miller, and Alan G. Taylor
Ranunculus asiaticus (L.) is an ornamental geophyte with some commercial production challenges presumed to be related to the storage of its desiccation tolerant tuberous roots (TRs). We investigated the influence of temperature and relative humidity during storage on viability of R. asiaticus TRs. The TRs were stored in specialized chambers for controlling relative humidity under flow-through or closed systems. In the flow-through system, air was bubbled through glycerol–water solutions to create relative humidities of 20%, 40%, 60%, 80%, or 100% and then passed through storage chambers held at 5, 20, or 35 °C for up to 20 weeks. In closed storage, tissue was equilibrated to a given moisture content (fresh basis) at 15 °C by suspending TRs over glycerol–water solutions (35%, 60%, or 85% relative humidity) with fans to circulate air. These containers were closed for 4 weeks and then tissue was transferred to sealed jars for up to 17 weeks at 5 or 25 °C. In both systems, TRs held with elevated temperature and relative humidity had the largest decrease in percent survival when planted after storage. Flow-through storage gave greater variability in TRs moisture content than closed storage. Tuberous roots at 25 °C had higher respiration rates than at 5 °C under closed storage; elevated moisture content also led to increased respiration. From these results it can be concluded that R. asiaticus dry TRs should be stored cool and dry for long-term viability.