Investigation of the Radicle Length Threshold of the Cool Germination Test to Improve Field Predictability

The cotton (Gossypium hirsutum L.) cool germination test is conducted to provide information regarding how seed lots will likely perform in suboptimal conditions. One aspect of the cool germination test is the use of a 4-cm radicle length threshold for a seedling to be counted as germinated, with little data to support its use. The objective of this study was to correlate cool germination test results using different radicle length thresholds with in-field emergence parameters. Germination tests were conducted to determine cool germination percentages for 12 seed lots using various radicle length thresholds. Field trials consisting of 12 seed lots were used to determine in-field emergence and vigor under suboptimal conditions. Linear regression was used to generate R² values between the percentage cool germination using various radicle length thresholds and in-field emergence parameters. These R² values were used to compare how well different radicle length thresholds explained variation in emergence and seedling vigor data. Across site-years and in-field parameters the radicle length threshold that maximized R² was under 3 cm, with variation between parameters and field sites observed. The 4-cm radicle length threshold used commercially in cool germination testing did not maximize R² value at any location for any field data collected. These results suggest that using a shorter radicle length threshold than the 4-cm standard when conducting the cool germination procedure would improve predictability of a seed lot’s performance in field conditions that are suboptimally cool.