Seed viability and vigor directly affect the performance of seeds planted to regenerate the crop. Although seed quality can influence many aspects of performance (e.g., total emergence, rate of emergence), the objective of this review was to examine the relationship of seed vigor to one aspect of performance: crop yield. Reductions in yield can be indirectly related to low seed vigor if plant populations are below a critical level. Thus, we have reported only on the direct effects of seed vigor on yield in the absence of population differences. Only those references where seed vigor was measured or where seed lots were evaluated following natural or artificial storage (both reduce seed vigor) were included. Annual crops were subdivided into those harvested during vegetative growth (eight species), early reproductive growth (four species) or full reproductive maturity (nine species). Seed vigor affects vegetative growth and is frequently related to yield in crops that are harvested vegetatively or during early reproductive growth. However, there is usually no such relationship in crops harvested at full reproductive maturity, because seed yields at full reproductive maturity are usually not closely associated with vegetative growth. The use of high‐vigor planting seed can be justified for all crops, however, to ensure adequate plant populations across the wide range of field conditions that occur during emergence.

A gronomy J our n al • Volu me 10 0 , I s sue 4 • 2 0 0 8 ABSTRACT Th e widespread adoption of glyphosate [N-(phosphonylmethyl)-glycine]-resistant soybean [Glycine max (L.) Merr.] and the increased cost of soybean seed have generated interest in determining the minimum plant population needed for maximum yield. Th e objective of this study was to determine yield and economic return responses to plant population for normal and late planting dates. Cultivars with relative maturities of 2.8 to 4.9 were planted at fi ve seeding rates (43,000 to 560,000 seeds ha -1 ) in May and/or June in 38-cm rows during 2003 to 2005. Th e eff ect of plant population on both yield and economic return was explained with a variation of a Mitscherlich equation. Optimum plant population (OPP) and economically optimum plant population (EOPP) were defi ned as those resulting in 95% of the estimated yield or estimated economic return, respectively, at the maximum plant population. Optimum plant population ranged from 108,000 to 232,000 plants ha -1 for May planting dates and 238,000 to 282,000 plants ha -1 for June planting dates. Economically optimum plant populations were 7 to 33% less than OPPs. Complete canopy cover at R1 produced maximum yield in 8 of 10 comparisons. Th ese results suggest that seeding rates below those that are currently recommended could lower seed costs without reducing yield.

seed quality (Dornbos et al., 1989;Smicklas et al., 1992; Heatherly, 1993), but Vieira et al. (1991Vieira et al. ( , 1992 found no High temperature stress during seed filling in controlled environeffect on germination or vigor in field and greenhouse ments reduces soybean [Glycine max (L.) Merrill] seed germination experiments when the stress did not produce shriveled and vigor, but the effect of high temperature in the field has not been and abnormal seeds. Dry conditions at harvest may indetermined. Seeds of two soybean cultivars (Hutcheson, maturity group [MG] V, and DP4690, MG IV) were produced in the field crease physical injury and reduce quality if seeds are in Kentucky, Mississippi, Arkansas, and Texas in 2000 to 2002. Air handled at low moisture levels (TeKrony et al., 1987). temperature during seed filling was monitored and brown (mature) Temperature extremes during seed development also pods were harvested, hand threshed, and all shriveled and abnormal affect soybean seed quality. Freeze injury before physioseeds were removed before determining standard germination and logical maturity caused large reductions in germination vigor (accelerated-aging germination). Mean maximum temperatures and vigor (Judd et al., 1982). High temperatures also during seed filling (growth stage R5 to R7) ranged from 24.0 (Kenreduced seed germination and vigor in growth chamber tucky) to 37.6؇C (Texas). When seed lots infected with Phomopsis and phytotron experiments (Keigley and Mullen, 1986; longicolla (Hobbs) were removed from the analysis, standard germi-Dornbos and Mullen, 1991; Zanakis et al., 1994; Gibson nation and accelerated-aging germination (AA) decreased as mean and Mullen, 1996; Spears et al., 1997; TeKrony et al., maximum temperature during seed filling increased, but the decrease was significant (P ϭ 0.05) only for Hutcheson. Standard germination 2000; Egli et al., 2005). Temperatures of 33/28ЊC (day/ of Hutcheson declined linearly (r 2 ϭ 0.49) from near 100% at 24؇C night) (Keigley and Mullen, 1986), 35ЊC (Dornbos and to 85% at 36؇C, while the decrease in AA was curvilinear (R 2 ϭ 0.86) Mullen, 1991), 35/30ЊC (Gibson and Mullen, 1996), 38/ and germination reached 11% at 36؇C. Seeds of Hutcheson were more 33ЊC (Spears et al., 1997), and 38/27ЊC (TeKrony et sensitive to high temperature than seeds of DP4690 and seed vigor al., 2000;Egli et al., 2005) during seed filling reduced (AA) was much more sensitive to high-temperature stress than was

No abstract

The quality of soybean [Glycine max (L.) Merr.] seed at harvest is dependent on the field production environment during development, maturation, and storage on the plant. These investigations were conducted to evaluate the effects of field weathering after physiological maturity (maximum dry seed weight) on seed viability and vigor. Five production environments were compared for two cultivars (‘Cutler 71’ ‐ 1973, ‘Kent’ and Cutler 71 ‐ 1974 and 1975). Seed was hand‐harvested at physiological maturity, harvest maturity (first time the seed dried to less than 14% moisture content), and at regular intervals for up to 3 months after harvest maturity. All seed were evaluated for viability (standard germination test) and vigor (accelerated‐aging germination test). Physiological maturity occurred at a seed moisture content of approximately 55% for both cultivars. The time interval from physiological maturity to harvest maturity (desiccation period) ranged from 10 to 20 days and was closely related (R2 = 0.88) to the mean open pan evaporation during the period. Seed viability and vigor were highest at physiological maturity and remained high (>80% germination) until harvest maturity for all but one production environment. Viability was maintained at these high levels for 1 to 2 months following harvest maturity for four of five production environments. However, seed vigor declined rapidly, reaching levels that were significantly (α = 0.05) less than those at harvest maturity within 4 to 39 days after harvest maturity. In four of the production environments, seed vigor reached a level of less than 50% germination within 1 month of harvest maturity. The time required for seed vigor to significantly decline following harvest maturity was closely related to mean air temperature (R2 = 0.90), mean minimum relative humidity (R2 = 0.94), and precipitation per day (R2 = 0.75). The wide range in seed vigor observed shortly after harvest maturity emphasizes the importance of timely harvest of seed fields and evaluation of seed viability and vigor soon after harvest.