Dennis M. TeKrony

Species differences in seed water status during seed maturation and germination

Maize ( Zea mays L., cv. B73 × Mo17), wheat ( Triticum aestivum L., cv. Clark), and soybean ( Glycine max L. Merrill, cv. Elgin 87) were grown in the field and seed samples were collected at frequent intervals for the determination of seed fresh and dry weight and water potential of excised embryos (maize and wheat) and axes (soybean). Seed water concentration declined during seed development and the concentration at physiological maturity (PM, maximum seed dry weight) was highest in soybean (550–590 g kg −1 FW), lowest in maize (326–377 g kg −1 ) and intermediate in wheat (437 g kg −1 ). The embryo/axis water potential was relatively constant during much of seed filling before decreasing rapidly as the seeds approached PM and there was little variation among species (soybean −1.52 to −1.63 MPa, maize −1.61 to −1.99 MPa and wheat −1.66 MPa). Seed water concentration when 10% of the seeds germinated (radicle ≥3 mm) was highest in soybean (514 g kg −1 ), lowest in maize (332 g kg −1 ) and intermediate in wheat (345 g kg −1 ) while the water potential of the embryo/axis varied from −2.07 to −2.20 MPa across the three species. There was little variation in the water potential of the embryo/axis among species at the end of seed growth (PM) or at the beginning of germination. This similarity is consistent with the suggestion that the water status of critical seed structures may play a regulatory role in seed growth and germination.

Temperature during soybean seed storage and the amount of electrolytes of soaked seeds solution

ABSTRACT: The electrical conductivity test measures the electrolytes that leach out of seeds whenthey are immersed in water and this leakage is an indication of seed vigor. The level of standardizationreached by the procedures of this test is such that the test is recommended for pea seeds andsuggested for other large seeded legumes, including soybean Glycine max (L.) Merrill]. This study[was conducted to contribute to the standardization of this test for soybean seeds by verifying whetherthe seed storage temperature influences the composition of the leachate from soaked seeds solution.Two soybean seed lots of distinct physiological potential were stored in moisture-proof containerseither at constant temperatures of 10°C and 20°C or at the temperature of 20°C during the first sevenmonths of storage followed by a change to 10°C for the rest of the storage time (nine months). Thechemical composition of the soaked water was evaluated every three months from January to October1998. The highest amount of leakage was observed for potassium, followed by calcium and magnesium,iron and sodium regardless of temperature and storage period. The amount of electrolytes in thesoaked water increased as the period of time and the temperature of storage increased. On the otherhand the amount of leakage decrease along the time for those seeds stored at 10°C or transferred fromthe temperature of 20 to that of 10°C. The temperature at which soybean seeds remain during storagemay affect the amount of electrolytes in the soaked water and consequently the results of the electricalconductivity test.Key words:

Sensitivity cycling to physical dormancy break and seed vigour of two Ipomoea species (Convolvulaceae).

Department of Plant and SoilSciences, University of Kentucky, Lexington, KY 40546, USA(Received 11 February 2009; accepted after revision 19 May 2009)AbstractThe physically dormant seeds of Ipomoea lacunosaand of I. hederacea undergo sensitivity cycling(insensitive

Relationship of Seed Vigor to Crop Yield: A Review

sensitive) to dormancy-breaking treat-ment. Sensitivity cycling is important to seeds withphysical dormancy in sensing appropriate environ-mental conditions for germination. Seed vigour is alsoimportant to seedling establishment, but no study hascompared changes in vigour (or not) with changes insensitivity. This study was conducted to determinethe relationship between sensitivity cycling and seedvigour in I. lacunosa and I. hederacea. The seedmoisture contents of insensitive and sensitive seeds ofI.lacunosaand of sensitive seeds of I.hederaceaweremeasured, and several vigour tests were performed.Vigour of sensitive seeds of I. lacunosa decreasedmore rapidly than that of insensitive seeds. Nosignificant change in vigour was observed in eitherpermeable or impermeable seeds of I. hederacea.Weconclude that sensitivity cycling to physical dormancybreak is important in maintaining vigour of I. lacunosaseeds in the soil seed-bank.Keywords: Ipomoea hederacea, Ipomoea lacunosa,physical dormancy, seed vigour, sensitivity cyclingIntroductionDormancy cycling in seeds with non-deep physiologi-cal dormancy (i.e. dormancy caused by low growthpotential of the embryo; Baskin and Baskin, 2004) hasbeen shown to occur in seeds of numerous species(Baskin and Baskin, 1985, 1998). There are claims thatseeds with physical dormancy (i.e. dormancy causedby a water-impermeable seed or fruit coat; Baskin andBaskin, 2004) can cycle between dormancy and non-dormancy (Rolston, 1978; Norsworthy and Oliveira,2007). However, this does not seem to be possible sincedormancy break of physically dormant seeds occursthrough formation of mechanical breaks in a specialmorpho-anatomical area in the seed or fruit coat, thewater gap (Baskin et al., 2000; Baskin, 2003; Jayasuriyaet al., 2007a).Sensitivity cycling to dormancy break of physicallydormant seeds has been shown to occur in Fabaceae[Trifolium subterraneum (Taylor, 1981, 2005), Ornithopuscompressus (Taylor and Revell, 1999) and otherpapilionoid legumes (Van Assche et al., 2003)] and inConvolvulaceae [Ipomoea lacunosa (Jayasuriya et al.,2008a), Cuscuta australis (Jayasuriya et al., 2008b),Jacquemontia ovalifolia (Jayasuriya et al., 2008c) andIpomoea hederacea (Jayasuriya et al., 2009b)]. Insensitivity cycling, seeds cycle between insensitiveand sensitive states. Sensitivity cycling allows theseeds to germinate in favourable conditions forseedling establishment and prevents germinationwhen conditions are unfavourable.Sensitivity cycling of physically dormant seeds isdriven either by temperature only or by the interactionof temperature and soil moisture (Jayasuriya et al.,2009a). I. hederacea is a good example of sensitivitycycling driven solely by temperature. Sensitivity ofI. hederacea seeds is induced by storing them wet or dryat high temperatures (

Air Temperature During Seed Filling and Soybean Seed Germination and Vigor

158C) and reduced by storingthem wet or dry at low temperatures (#58C)(Jayasuriya et al., 2009b). I. lacunosa is a good exampleof sensitivity cycling driven by the interaction oftemperature and soil moisture. Sensitivity of I. lacunosaseeds can be induced by storing them wet at moderatetemperatures (30/158C), and sensitivity is reduced bystoring them dry at high temperatures (

Effect of drought and defoliation stress in the field on soybean seed germination and vigor

258C) or dryor wet at low temperatures (#58C) (Jayasuriya et al.,2008a). Dormancy in sensitive seeds of I. lacunosa can