Temperature gradient plate for seed germination efficacy testing

Applications of a temperature gradient plate in seed germination studies at The University of Reading, U.K.

Overcoming seed dormancy
Dormant seeds often require moist storage (stratification) to help break their dormancy. Prolonging the moist storage treatment often results in decreased germination. A temperature gradient plate was used recently by Kebreab & Murdoch (1999a) to quantity temperature effects in seeds during warm stratification.

Germination at constant temperatures
The investigation just described relates to seed dormancy. Other experiments are needed to examine the effects of temperature on germination of both dormant and non-dormant seeds. The temperature gradient plate allows germination tests over a very wide range of temperatures. Interactions with other factors such as water stress and chemicals can also be studied. For example, seeds of Orobanche aegyptiaca were tested with the temperature gradient plate operating in a single direction. The effects of a range of constant temperatures with the modifying effect of water stress were then observed and modelled (Kebreab & Murdoch 2000).

Germination at alternating temperatures
The plate will also operate with the temperature gradient for part of the day in one direction and then at right angles to that direction for the rest of each day. Using such a programme, the Grant temperature gradient plate provides 196 different thermal environments. Using an 8h/16h time cycle and a system with 169 thermal environments, the effects of constant and alternating temperatures at two thermoperiods have been quantified and modelled in several species (Kebreab & Murdoch 1999b).
In Orobanche seeds, alternating temperatures did not promote either loss of dormancy or germination. Many small-seeded species, however, show positive effects of alternating temperatures and it is here that the temperature gradient plate provides an extremely powerful tool. (Murdoch et al., 1989) Optimum temperatures for germination are easily identified and sufficient data is available to understand and model the responses to temperature. Interactions with other dormancy-relieving factors may be investigated by, for example, exposing the seeds to potassium nitrate solutions during the germination tests. In such cases, it has been found helpful to place the seeds in small polystyrene boxes to ensure that the chemical concentration remains constant during the germination test (which may last for a month or more).

Germination rates
Such applications concern the final germination of the seeds. Often, the time taken for seeds to germinate (or the rate of germination) is of interest because the thermal time required for germination can then be evaluated. The temperature gradient plate has been found invaluable in such studies. Examples include Ellis & Barrett (1994) and Kebreab & Murdoch (1999c).

Other applications
Apart from the constraint that the plate cannot really be used for items bigger than about 30 mm in diameter, uses are only limited by imagination. For example, parasitism of insects by nematodes has been tested (Ratnasinghe and Hague, 1998).

Dr Alistair Murdoch
Department of Agriculture,
The University of Reading

Seed-based approach for identifying flora at risk from climate warming

ANNE COCHRANE,1* MATTHEW I. DAWS2† AND FIONA R. HAY3
1Department of Environment and Conservation, Science Division, Locked Bag 104 Bentley Delivery
Centre,Western Australia 6983, Australia (Email: anne.cochrane@dec.wa.gov.au); 2Royal Botanic
Gardens, Kew, Seed Conservation Department,Wakehurst Place, Ardingly,West Sussex, UK; and 3TT
Chang Genetic Resources Center, International Rice Research Institute, Metro Manila, Philippines

Abstract
In obligate seeding species, the germination niche is crucial for colonization and population survival. It is a high-risk phase in a plant's life cycle, and is directly regulated by temperature. Seeds germinate over a range of temperatures within which there is an optimum temperature, with thresholds above and below which no germination occurs. We suggest that abrupt changes in temperature associated with a warming climate may cause a disconnect between temperatures seeds experience and temperatures over which germination is able to occur, rendering obligate seeding species vulnerable to decline and extinction. Using a bidirectional temperature gradient system, we examined the thermal constraints in the germination niche of some geographically restricted species from the low altitude mountains of the Stirling Range, southern Western Australia, including seedlots from lowland populations of four of these species. We demonstrated that high temperatures are not a limiting factor for germination in some restricted species, signifying a lack of relationship between geographic range size and breadth of the germination niche. In contrast, we identified other restricted species, in particular Sphenotoma drummondii, as being at risk of recruitment failure as a consequence of warming: seeds of this species showed a strong negative relationship between percentage germination and increasing temperature above a relatively low optimum constant temperature (13°C). We found some ecotypic differences in the temperature profiles between seeds collected from montane or lowland populations of Andersonia echinocephala, and while specific populations may become more restricted, they are perhaps at less risk of extinction from climate warming. This seed-based approach for identifying extinction risk will contribute tangibly to efforts to predict plant responses to environmental change and will assist in prioritizing species for management actions, directing limited resources towards further investigations and can supplement bioclimatic modelling.

http://onlinelibrary.wiley.com/doi/10.1111/j.1442-9993.2010.02211.x/abstract

Biology and survival of broom corn millet (Panicum miliaceum) seed

T.K. James1, A. Rahman1, C.R. McGill2 and P.D. Trivedi3
1AgResearch, Ruakura Research Centre, Private Bag 3123, Hamilton 3240, New Zealand 2Massey University, Private Bag 11 222, Palmerston North 4442, New Zealand 3University of Waikato, Private Bag 3105, Hamilton 3240, New Zealand
Corresponding author: trevor.james@agresearch.co.nz

Abstract

The wild type of broom corn millet (Panicum miliaceum) is a serious emerging
weed, currently prevalent in New Zealand sweet corn (Zea mays) crops. This study shows its seed is nearly twice the weight of other common grass weeds and can germinate in the temperature range 16-34°C, with 50% germination at 26°C and greatest germination occurring at 31°C. At 15°C it took 8 days for seedlings to emerge but required only 4 days at 25°C. Seed was able to emerge from depths of up to 170 mm in a range of soils. Experiments showed that broom corn millet seed can persist in the soil for longer than 2 years in the field but is killed in silage stack and bales. Immersion in stock effluent for up to three months
reduced seed germination to less than 40%. These characteristics are discussed in relation to herbicide and management control options for this weed.

http://ww.nzpps.org/journal/64/nzpp_641420.pdf

Climate warming and the germination niche

A. Cochrane
Department of Environment and Conservation, Bentley, WA. Email: anne.cochrane@dec.wa.gov.au

Introduction
Germination is an important life history phase for obligate seeding species. Seeders need to germinate to persist in the environment after disturbance, with favourable environmental conditions required to ensure recruitment success. Failure to germinate after disturbance events may mean local population extinction.
Temperature is arguably one of the most important climatic variables influencing seeds since it synchronises germination to environmental conditions most suitable for seedling establishment. Seeds will germinate over a range of temperatures, with thresholds above and below which little or no germination will occur. Under climate warming scenarios temperatures are forecast to rise between 2-5°C.  If species have specific temperature requirements for germination then climate warming could cause a mismatch between temperatures that seeds experience and temperatures over which germination is able to occur. Such a mismatch in the germination requirements of obligate seeding species could render them vulnerable to decline and extinction. Species that occupy specialised habitats and those inhabiting cooler and wetter climates are likely to be more susceptible to change.

Read more at:
http://www.anbg.gov.au/anpc/apc/19-3_cochran.html

Germination Responses of Terminalia superba Engl. and Diels Seeds on the 2-way Grant`s Thermogradient Plate

Joseph M. Asomaning, Moctar Sacande and Nana S. Olympio, 2011. Germination Responses of Terminalia superba Engl. and Diels Seeds on the 2-Way Grant’s Thermogradient Plate. Research Journal of Seed Science, 4: 28-39.

Abstract

The goal of the study was to take a more comprehensive look at germination responses of the species to a broad range of alternating or constant temperatures on the thermogradient plate. Terminalia superba seeds were placed in Petri dishes containing a gel of 1% agar for germination over a period of 30 consecutive days. Petri dishes were arranged 8x8 units on the 2-way Grant’s thermogradient plate (a bi-directional incubator). The instrument allows for germination testing of seeds over a wide range of single temperature and alternating temperature regimes over a time continuum, given 64 temperature combinations (regimes) (5 to 40°C). Conditions were 40/40°C (day/night temperature) on the high end of the plate and 5/5 °C (day/night temperature) on the cool end. Dried out agar in petri dishes located at the hot end of the plate were replaced periodically. Two temperature gradients ranging from 5 to 40°C were used. The first gradient, progressing from left to right on the thermogradient plate in dark, was alternated every 12 h with the second progressing from front to back of the thermogradient plate with light. The study was repeated two times. Twenty seeds were used in each replication. The various temperature combinations had significant effect on final germination percentage, mean germination time, time for first germination and rate of germination. Alternating temperatures improved overall germination. The best germination at a constant temperature was at 35/35°C (88%). The best temperature combinations for seed germination at alternating temperatures were 35/40°C (100%); 35/15°C(95%); 40/25°C(95%); 20/40°C (92.5%) and 40/30°C (92.5%).

Full article is available here:

Germination Responses of Terminalia superba Engl. and Diels Seeds on the 2-way Grant`s Thermogradient Plate.pdf