Thermal Time For Germination Research Articles

Cardinal Temperatures and Thermal Time for Germination of Sarawak Traditional Rice

Germination of two rice landraces, namely Bario Sederhana and Biris, was determined from twelve temperatures (12.5 – 40 ºC) in a series of incubation experiments. The cardinal temperatures and thermal time for germination were estimated from a ‘broken-stick’ linear model. Both landraces had a Tb of 10 ºC, Topt between 32 – 33 ºC, and Tmax of 43 ºC. At the sub-optimal temperatures, the thermal time for germination was 62 ºCd for Bario Sederhana and 53 ºCd for Biris. Within the supra-optimal range (Topt to Tmax), both landraces required 27-29 ºCd for seed germination. The maximum final germination for Bario Sederhana was 93% at 30 ºC while Biris had 100% seeds population germinated at 27.5 ºC.

Genotypic variation in cardinal temperatures and thermal time for germination and seedling emergence of pigeonpea (Cajanus cajan [L.] Millsp.)

Abstract In this study, we define the cardinal temperatures and thermal time for germination and emergence of pigeonpea genotypes. Seeds of six genotypes were subjected to constant temperatures ranging between 5 and 50°C in petri dishes with filter paper (germination) and with media (emergence) were placed in a thermal gradient plate. A nonlinear bent-stick model fitted to the rate of development to germination and emergence resulted in parameters predicting cardinal temperatures including base (Tb), optimum (To), maximum (Tm), and thermal time. Estimated Tb for 50% germination and emergence were 8.4 and 10.8°C, respectively, with no significant differences between genotypes. Optimum temperatures were 33.8 and 37.9°C for germination and emergence, respectively, with genotypes differing significantly. Thermal time for 50% germination and emergence varied significantly among genotypes. The results suggest that genotypic responses to the temperature are typical for their tropical origin and hence their suitability for cropping in summer dominant rainfall regions insubtropical Australia.

Simple

A model predicting seedling emergence is described and applied to sugarbeet (Beta vulgaris L.). The input variables are the soil surface texture, soil temperature, rainfall, aggregate size distribution and position in the seedbed, sowing depths, characteristics of the seeds (initial seed mass distribution, germination time, and hypocotyl elongation distributions). A three‐dimensional seedbed layer is created where the aggregates and seeds are placed. Soil water content is assumed not to limit sugarbeet emergence (sowing conditions in northern Europe). The time needed to reach the soil surface is calculated using germination thermal time, soil temperature, the presence or absence of aggregates, and the hypocotyl elongation function. The ability of seedlings to break through the soil surface is a function of crust development and moisture. The seedling growth after emergence is calculated with reference to seed mass distribution, emergence delay, and the presence or absence of mechanical obstacles. The emergence prediction was tested in field experiments with four seedbeds, from fine earth to cloddy structure, and a sowing depth of 17 to 35 mm. The predicted number and sizes of clods encountered by seedlings and the calculated hypocotyl length were not significantly different from measured ones. Predicted germination times were longer than the observed ones (differences <5°C d); final rates were well predicted. Predicted vs. measured final emergence rates differed by less than 10%; changes with time differed from 15 to 30°C. This was due to the hypocotyl elongation functions, which must be improved. Further improvements will be to predict soil water content variations and effects on emergence via water stress and soil strengthening.