Thermal time requirements for germination, emergence and seedling development of adventive legume and grass species

Abstract

Thermal time (Tt, °C days) was used to quantify germination, emergence and leaf appearance of temperate grassland species from natural and commercial seed populations. Germination requirements of six clovers (Trifolium arvensis, T. dubium, T. glomeratum, T. striatum, T. subterraneum, T. repens) were determined from constant temperatures from 5 to 35°C. The base temperatures (T b ) were all less than 2.5°C, except for B. erectus (5.8°C). The four grasses had slower rates of germination and a wider tolerance of high temperatures than the clovers. All five annual clovers had a lower thermal time requirement for emergence and seedling development than the perennial T. repens. For four of the species used, the internationally recommended seed testing procedures that requires prechilling was found to be unnecessary and for two others the currently recommended optimum temperatures are higher than the optimum found. The thermal time approach has provided a robust summary of large datasets generated from controlled and field conditions. These easily transferable coefficients can be used to quantify seed and seedling responses to temperature for individual species and should form the basis for redefining seed testing regimes.

Thermal time requirements for germination of four annual clover species

“…These values were consistent with those reported by Monks (2009) and Lonati (2009) and therefore suggest that future work in annual clover species could assume a T b of 0°C for germination.…”

“…In addition, 'Cefalu' arrowleaf, 'Bolta' balansa, 'Prima' gland and 'Mihi' Persian clovers germinate quicker than subterranean and white clovers (Moot et al 2000). The thermal time requirements for germination of 'Cefalu' arrowleaf, 'Bolta' balansa, 'Prima' gland and 'Mihi' Persian clovers were similar (Table 1) to the adventive clovers (Boswell et al 2003;Lonati et al 2009). Their similarity in temperature response and germination rate suggests that 'Cefalu' arrowleaf, 'Bolta' balansa, 'Prima' gland and 'Mihi' Persian clovers may be suitable for over-sowing in hill and high country where the adventive clovers are abundant (Maxwell et al 2010).…”

“…Cardinal temperatures for germination of 'Cefalu' arrowleaf, 'Bolta' balansa, 'Prima' gland and 'Mihi' Persian clovers showed that these species are adapted to a broader range of temperatures compared with subterranean clover and the adventive annual clovers namely, haresfoot (Trifolium arvense), suckling (T. dubium), cluster (T. glomeratum) and striated (T. striatum) clovers (Boswell et al 2003;Lonati et al 2009). This means that 'Cefalu' arrowleaf, 'Bolta' balansa, 'Prima' gland and 'Mihi' Persian clovers could inhabit the same ecological niche as the subterranean clover and adventive clovers, and also germinate in warmer areas where some other species cannot.…”

“…Thermal time has been used to quantify germination of some annual clover species (Moot et al 2000;Boswell et al 2003;Lonati et al 2009;Monks et al 2009). In most cases, the thermal time was species dependent and unaffected by cultivar.…”

Germination in Cool‐Season Forage Grasses under a Range of Temperatures

“…The base temperature for germination in most commercially available temperate pasture and field species is £4.5°C (Lonati et al, 2009). The optimum temperature for germination of most cool-season grasses is reported to be in the range of 10 to 30°C (Sprague, 1943;Odabaş and Mut, 2007;Lonati et al, 2009;Monks et al, 2009;Schellenberg et al, 2013;Zhang et al, 2013). Adaptability and germination of seeds under a broad range of temperatures is important for early seedling emergence and establishment of a full crop stand (Brar et al, 1991).…”