Analysis: Sensitivity to Heat

Laboratory Analysis TEMPERATURE 1A, 1B, 2A, and 2B

When we perform laboratory analyses of seeds, we rate them by various designations. The sample and germination designations are as follows:

  • 1A and its corresponding % germ indicates the raw seed germination percentage in 24 hours @ 23 degrees C / 72 degrees F.
  • 1B and it’s corresponding % germ indicates the ‘seed priming indicator’ germination percentage in 24 hours @ 23 degrees C / 72 degrees F.
  • 2A and it’s corresponding % germ indicates the raw seed germination percentage in 24 hours @ 28 degrees C / 83 degrees F.
  • 2B and it’s corresponding % germ indicates the ‘seed priming indicator’ germination percentage in 24 hours @ 28 degrees C / 83 degrees F.

 

Assessing how lettuce seed for hot weather environments ?

Germination temperatures in desert growing areas can often exceed 28 degrees Celcius  (which is 83 degrees Fahrenheit).But we test seeds at 28 degrees C. Why? 28 degrees C is the temperature at which thermo inhibition is first induced in most desert lettuce varieties. In addition to temperature the seed is further stressed by germination in a light-free environment. The ability of temperature to induce thermo inhibition is intensified in the absence of light. Most seed is covered with soil after planting, which limits their exposure to light.

We determined these germination protocols through many years of experience correlating laboratory results with field results. Independent research in the ensuing years demonstrated that average daily wet soil/irrigated temperatures accumulated when maximum daytime temperatures could easily exceed 45 degrees C (113 degrees Fahrenheit) was 28 degrees C.