The impermeable seed‐coat trait in soybean [Glycine max (L.) Merr.) is of interest to researchers because impermeable seeds retain viability better than permeable seeds. The objective of this study was to determine how water stress during seedfllling may influence impermeable seed expression. A 2‐yr experiment was conducted outdoors with potted plants of two soybean genotypes that carried the impermeable seed‐coat trait. Starting at the R6 growth stage, one‐half of the plants were water stressed by imposing successive wilting cycles that consisted of withholding water until all plants in the treatment were wilted and then immediately rewatering until the soil was saturated. The control plants were watered daily. At maturity, seeds from water‐stressed plants were 15 to 33% smaller by weight, 8 to 22% smaller by volume, had a lower percentage of ruptured seed coats, a higher percentage seed coat, and 6 to 37% more impermeable seed (after 72 h of soaking) than well‐watered control plants over both years. The higher impermeable seed percentage (after 72 h of soaking) in the water‐stressed treatment was significantly correlated (r = −0.92**, significant at the 0.01 probability level) with the incidence of ruptured seed coats when data were combined over genotypes and years. Scanning electron microscopy suggested that ruptured seed coats were caused by the cotyledons expanding against the seed coat. The incidence of ruptured seed coat was positively associated with seed weight (r = 0.73*, significant at the 0.05 probability level), seed volume (r = 0.83*), and seed width (r = 0.92**). These data indicate that high soil moisture availability during seedfill will reduce impermeable seed expression by disrupting seed‐coat integrity.
The Ellis-Roberts seed viability equation is accepted as an accurate predictor of seed longevity over a range of storage temperatures and moisture contents (MC). One application of this model is to identify different combinations of seed MC and temperature that can result in similar seed storage lifetimes. The present study was conducted to determine whether the reduction in storage life of primed seeds is consistent with the predictions of the Ellis-Roberts equation across a range of seed MC and temperatures. Seeds of two lettuce (Lactuca sativa L.) varieties (a romaine and a crisp-head type) were primed with polyethylene glycol and along with untreated seeds were adjusted to two different MCs (6% and 9%) and then aged in two different temperature environments (48°C and 38°C, respectively). Control seeds in both storage environments conformed to the Ellis-Roberts equation. Primed seeds aged faster than non-primed seeds but also exhibited different rates of viability loss between the storage environments. Primed seeds stored at 6% MC and 48°C aged slower than those stored at 9% MC and 38°C. These data suggest that priming causes lettuce seed to have a heightened sensitivity to the adverse effects of moisture during storage. To further investigate this observation, the moisture absorption properties of primed and non-primed seeds from both varieties were examined by equilibration over saturated NaCl solutions in sealed containers at 20°C. Primed seeds tended to have higher MC than non-primed seeds, although differences were seldom significant. Thus, an alteration of the RH/MC relationship for primed seeds could not be confirmed as a cause for the differential aging rates between equivalent environments. In conclusion, the predictable effects of MC and temperature on nonprimed lettuce seeds as described by the Ellis-Roberts equation may not hold true for primed seeds.
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