**6. Conclusion/recommendations**

plantings, however, seed from the 21 April plantings had poor vigor and never achieved Germ80, while only GA-03 L had a Germ80 of 35 GDD for seed from the 1 June planting date. Runner-type seed produced by any planting date for Headland 2009 had very poor germination and vigor. Germination was less than 70% (**Table 4**). The maximum rate of germination (parameter *a*) for vigor was less than 75.6% for all cultivars and planting dates. Germ80 was not achieved indicating low vigor (**Figure 7**). Previous research has indicated that there can

> **Georgia Green 2009 Headland**

> > **20 April 11 May 1 June**

**AT3085RO 2009 Headland**

**AT271516 2009 Headland**

**Figure 7.** Cumulative germination patterns for runner-type peanut seed produced in 2009 at Headland Alablama, based on nonlinear regression using growing-degree day (GDD) accumulation with a base temperature 15°C. To calculate the regression equation for the respective seed lot, the parameter estimates shown in **Table 4** for the Eq. (2) were used.

**40 Growing-Degree Days 0 02 06 80**

Germination was measured on a thermal gradient.

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118 Advances in Seed Biology

All cultivars exhibited phenotypic vigor variation by planting and harvest date across years. Comparing data generated from the thermal gradient using these growth curve models provided maximum germination rates with optimal temperatures (**Tables 2**–**4**). Cold germination testing can be used as a measure to stress peanut to evaluate vigor [52], using the thermal gradient apparatus used to evaluate peanut cultivars in this study established variation in seed vigor across a wide range of temperatures simultaneously. This method of seed evaluation provided an indication of vigor which assist peanut seed producers in determining the success of the cultivar over a range of temperatures, unlike the standard peanut germination test [30]. Seed produced from mid-May plantings each year were consistent with respect to germination, Germ80, and GDD to reach maximum germination (*a*) among the five cultivars evaluated in Dawson for 2008 and 2009. Phenotypic differences were noted when these same cultivars were grown in Headland in 2009. These data assisted in determining phenotypic variation between planting dates when grown under known environmental conditions. This information will assist growers with making planting decisions based on these vigor testing methods.
