Time, Temperature and Germination of Pearl Millet (Pennisetum typhoidesS. & H.)

Priming and temperature limits for germination of dispersal units of Urochloa brizantha (Stapf) Webster cv. basilisk

“…Otherwise, a decrease in the base temperature (Tb) was observed in primed seeds, supporting the hypothesis that priming could improve the germination rate of U. brizantha by reducing Tb. However, the results presented here did not support our hypothesis that a priming effect on the germination of U. brizantha can be accounted for a decrease in θT (g) , as reported by Hardegree and Van Vactor (2000) in some grasses, and an increase in Tc (g) , considering that the germination rate is directly proportional to Tc (g) and inversely proportional to Tb for a given T and θ (Garcia-Huidobro et al, 1982). In onion (Allium cepa L.) seeds the major effect of priming was to reduce θ (g) at both sub-and supra-optimal temperatures (Ellis and Butcher, 1988), but this feature was not observed in the present study, suggesting such parameters may have a strong genotypic basis which is relatively unaffected by environmental factors prior the visible germination in U. brizantha.…”

“…A thermal time (or degrees-day) approach have been used to describe the distribution of the times to germination at different temperature regimes according to the models θT (g) = (T-Tb)t (g) , for suboptimal temperatures, and θT = (Tc (g) -T)t (g) , for supraoptimal ones, where θT (g) is the thermal time required for (g) percent of the seeds germinate, T is the temperature, Tb is the minimum or base temperature, t (g) is the time for (g) percent of the seeds germinate and Tc (g) is the maximum or ceiling temperature corresponding to a percentage fraction (g) (Garcia-Huidobro et al, 1982;Bradford, 1995). Once the model parameters Tb, θT (50) (median thermal time), σ θT (standard deviation in thermal time), Tc (50) (median Tc) and σ Tc (standard deviation in Tc (g) ) are known, the germination time courses at different temperatures can be normalized on a common thermal time scale which allows the germination rate at any temperature regime can be predicted (Bradford, 1995).…”

Analysis of thermal dependence on the germination of braquiarão seeds using the thermal time model

“…The thermal window within which braquiarão seeds could germinate (8 °C to 41.5 °C) was similar to that observed in several other tropical grasses, such as Pennisetum typhoydes (Garcia-Huidobro et al, 1982), Themeda australis, Chrysopogon fallax, Sorghum plumosum, Chrysopogon latifolius and Sorghums tipoideum (Mott, 1978 Figure 2. Relationship of germination rate of braquiarão for percentages 10% (■), 30% (♦), 50% (▲) and 70% (•) to temperature, both below and above the optimum (30 °C).…”

“…An initial estimate of the model parameters (Tb, Tc and θ T ) was obtained through regression analysis of the reciprocal of the times for germination of a given seed fraction on T (Garcia- Huidobro et al, 1982), with Tb and Tc corresponding to the intercepts on abscissa and 1/θ T the slopes of the regression lines. For a more accurate estimation of the model parameters, a probit regression analysis was also used assuming that at the infra optimum interval θ T (referred to as θ (G) ) is normally distributed among the seeds and Tb is constant, while in the supra optimal interval θ T is constant and Tc (referred to as Tc (G) ) is normally distributed within the seed population.…”

Does thermal time for germination vary among populations of a tree legume (Peltophorum dubium)?

“…Considering that the thermal time model employed -θ T = (T-Tb).t g -assumes that the heat sum or thermal time (θ T ) to germination of a given percentage remains constant (Garcia-Huidobro et al, 1982), an increase in temperature, as observed in the assay IV, necessarily leads to a decrease of t g (time to germination of a specific percentage g).Thus, it was expected that θ 50 did not vary with thermal conditions during the experiment, but that did not occur in P. dubium seeds from APC and, chiefly, PVH lots.…”