Effect of desiccation temperature on viability of immature dandelion (Taraxacum agg.) seeds dried in mowed inflorescences

Abstract

After flowering has ceased, dandelion (Taraxacum agg.) capitula close to enable maturation of seeds. In late summer the period of seed maturation lasts for 9 days. The capitula mowed later than 4 days after the start of this period and desiccated at 25°C produce viable seeds. If cut and prostrated on insolated ground inflorescences can experience temperatures exceeding 50°C which may impair seed viability. We determined the effect of desiccation temperature (5, 15, 25, 35, 45 or 55°C) on viability of ripening seeds using inflorescences harvested on September 5, 2008 at Prague-Ruzyne (50°05'N, 14°18'09 E), five days after flowering ceased (about 4 days before seed dispersal). As control, ripe seeds were collected at dispersal on the same day and desiccated at identical temperatures. Desiccated seeds were germinated at constant 17°C. Ripening seeds of maturing capitula only remained germinable if desiccation temperatures were ≤ 35°C (optimum 25°C) and were killed at 45 and 55°C. The viability of ripe seed was not affected by any of the desiccation temperatures. Time of germination of 50% seeds that germinated was significantly shorter in ripe than ripening seeds. Exposure of mowed dandelion inflorescences on insolated ground (solarization) may thus decrease production of viable seeds because of high temperatures experienced during desiccation.

Geographic differentiation of adaptive phenological traits of barnyardgrass (Echinochloa crus-galli) populations

“…At~50 C, the proportion of germinating seeds can increase in a few days to >90% (Taylorson and Brown 1977). Because the temperature of the insolated soil surface often exceeds 40 C (Bonan 2002;Martinková and Honěk 2010), the dormancy of freshly ripened E. crus-galli seeds may be terminated in late summer and early autumn of the same year in which the seeds have ripened. These seeds can germinate, and seedlings will emerge before the onset of winter.…”

Plasticity of the thermal requirements of exotherms and adaptation to environmental conditions

“…1). This temperature, which is lethal for seeds that had started to germinate, was not lethal for dormant nongerminating seeds and certainly not for dry seeds (Martinkova and Honek 2010). Using these derived characteristics, we calculated (iv) the width of the thermal window ( W T  =  t d max  −  t d min ), (v) thermal range over which germination occurs ( t d let  −  t d min ), and (vi) “skewness” of the germination response, which is the percentage of thermal range over which germination occurs taken up by the width of the thermal window, which is (SKEW = [( t d max  −  t d min )/( t d let  −  t d min )*100]).…”