Seed conservation of banana crop wild relatives (Musa L. spp.) is limited because of lack of knowledge about their germination ecology. Musa acuminata Colla, the most important banana crop wild relative, is distributed in tropical and subtropical Asian and Pacific rainforests and colonizes disturbed sites. The role of temperature in stimulating/inhibiting germination to detect disturbance when canopy gaps are formed is not well known. We assessed seed germination thermal requirements of three subspecies of M. acuminata using nine seed accessions which had been stored in the Millennium Seed Bank. Diurnally alternating temperature cycles were almost completely essential for germination compared with constant temperatures. Germination was optimal when the upper temperature of a diurnal cycle was at 35°C; the lower temperature of the cycle was less important. Subspecies occurrence coordinates were used to extract climate temperature data which were then compared against the temperature requirements for germination from our experiment results. Maximum temperatures of the warmest month across subspecies ranges were close to but below optimal germination temperatures, as were diurnal ranges, suggesting soil-warming at the micro-climate level following gap creation is important for M. acuminata seed germination. Additionally, pre-treatment for 3 months at 60% relative humidity at constant 25°C improved germination from 14 ± 10 (mean, standard deviation) to 41 ± 29% suggesting a period in the soil seed bank under the canopy may increase sensitivity to alternating temperature cycles. Overall viability was low (49 ± 28%), and considerable variance was caused by the different accessions. Germination remained somewhat inconsistent.

Purple nutsedge is among the most troublesome weeds of vegetables in the Southeast US and a substantial impediment in the search for methyl bromide alternatives. Greater understanding of the environmental cues that regulate tuber sprouting may assist in improved nutsedge management. Experiments were conducted to evaluate the effect of diurnal temperature variation on sprouting of purple nutsedge tubers. Two temperature regimes were evaluated: the first averaged 28 C, with daily fluctuations ranging from 0 to 19.5 C; the second temperature regime averaged 16 C, with daily fluctuations ranging from 0 to 18.5 C. When average temperature was 28 C, cumulative tuber sprouting ranged from 88 to 92%, with no detectable differences among diurnal fluctuations. The high average temperature in the first study may have negated any type of enforced sprouting suppression. However, when average temperature was lowered to 16 C (simulating early spring diurnal fluctuations under polyethylene mulch), there was a positive linear correlation between maximum tuber sprouting and temperature variation. With an average temperature of 16 C, the absence of temperature variation resulted in 52% purple nutsedge sprouting, while 87% sprouting occurred when daily temperature varied 18.5 C at the same average temperature. The use of various types of mulching material can affect average soil temperatures and diurnal variations, potentially shifting nutsedge emergence. Further studies are needed to determine if these data on tuber sprouting in response to alternating temperatures can facilitate more efficient weed management.

A better understanding of the persistence of jointed goatgrass seed in soil and its dormancy will lead to the development of more effective weed-management strategies. Three populations of jointed goatgrass were collected from winter wheat fields in Oregon, and grown together with the winter wheat variety ‘Madsen’ in nurseries at Moro and Pendleton, OR. Germination responses of jointed goatgrass and wheat seed were recorded over 14 d at 5/5, 15/10, 15/15, 25/15, 25/25, and 30/20 C day/night temperatures and a 12-h photoperiod. Because jointed goatgrass spikelets often contain two seed, primary and secondary seed germination values were recorded. Secondary seed germination was defined as 3-mm radicle protrusion, and primary seed germination was defined as 5-mm emergence of the second coleoptile. Jointed goatgrass secondary seed germinated when exposed to all temperature regimes. Jointed goatgrass secondary seed germination occurred 3 d earlier in temperature regimes involving 15 C compared to germination at 5/5, 25/25, and 30/20 C. Final germination values for jointed goatgrass secondary seed were greatest when seed were incubated at 25/15 C. Wheat seed germinated at all temperature regimes, although the onset of germination occurred 1 to 1.5 d later at 5/5 C compared to other temperature regimes. Jointed goatgrass primary seed germinated only at 15/10, 15/15, and 25/15 C, and maximum germination occurred at 25/15 C. Dormancy in jointed goatgrass might prevent germination of seed within freshly shattered spikelets until autumn when temperatures are low and moisture is available. Because final germination percentages in jointed goatgrass primary and secondary seed were less than 100%, additional research on factors regulating dormancy is needed.

Common teasel is an invasive and widespread weed in Argentina. Germination experiments were carried out from 2011 to 2014 to determine the effect of various environmental factors on germination and emergence. Germination of recently dispersed seeds was 12% in darkness at constant temperature. In contrast, seed exposure to light and alternating temperatures enhanced germination to 95%. The requirement of light and alternating temperatures suggest that common teasel has physiological dormancy. Several experiments were carried out to determine whether (1) seed responses to light and alternating temperatures have a hormonal basis, (2) seed coats can suppress germination, and (3) time and thermal conditions during seed storage reduce light and alternating temperature requirements. Germination was reduced (≤ 13%) by a gibberellin synthesis inhibitor. In contrast, the presence of gibberellins and an abscisic acid synthesis inhibitor increased germination to 95 and 38%, respectively. Results suggest that a higher ratio among gibberellins and abscisic acid (GA/ABA) leads to a break in dormancy. Germination was 100% when embryos were excised, suggesting that seed coats may suppress germination by mechanical restriction. Likewise, germination was enhanced by hydrogen peroxide (70%). This compound is known to increase GA/ABA ratio in agreement with a hormonal control of dormancy proposed for common teasel. An increment of storage time reduces light and alternating temperature requirements, allowing seeds to germinate in darkness. Taking these results together confirms that common teasel has physiological dormancy. Seedling emergence was progressively reduced from 70 to 8% by increased burial depth from 0 to 3 cm. Information from these experiments may facilitate development of effective management for common teasel.

Temperature has a key influence over seed dormancy and germination, allowing wild plants to synchronize their life history with the seasons. In this review we discuss the signalling pathways through which temperature is integrated into seed physiology and the control of primary and secondary dormancy, with an emphasis on understanding maternal effects and responses dictated by the zygotic tissues. A key emerging paradigm is that temperature signalling in seeds must be understood in relation to whole plant genetics and physiology, as overlapping pleiotropic roles for temperature sensing and hormone signalling pathways are commonplace.