NL9001892A - METHOD FOR ACCELERATING AND SYNCHRONIZING SEED GERMINATION. - Google Patents

Description

Title: Method for accelerating and synchronizing seed germination.

For at least the past fifty years, there has been an interest in the possibilities of improving seed performance, particularly with regard to improved germination and seedling establishment. Seed treatments that initiate or complete the germination process under controlled conditions prior to sowing would have a number of practical advantages, especially if the germination were synchronized as well as accelerated. Rapid establishment of a uniform population of seedlings enhances the ability of the crop to control weeds, and further economic benefits are achieved in a uniform population of plants, including improved yield uniformity in harvesting. Rapid germination following sowing can reduce erosion by quickly stabilizing bare slopes, and can bring playing fields such as golf greens to playable levels in less time using less seed. Rapid germination can reduce the exposure of the planted seed to infection, reducing the need for extensive chemical control of the conditions, such as rotting. In fact, the growing season for a given crop can be effectively extended by at least the number of days normally required for soil germination.

Attempts to accelerate germination have included the use of physical or chemical treatments intended to shorten the seeding period following seed formation. Such treatments include exposure of seed to light, exposure of seed to cold, Humidity conditions (stratification), mechanical breakdown, and treatment with chemicals such as gibberellic acid, potassium nitrate, thiourea, hydrogen peroxide or ethylene.

Seed hardening, the practice of subjecting seeds to water suction followed by air drying, has been studied for years with inconclusive results. Several methods of planting pre-germinated seeds have also been developed, but remain problematic due to the tendency of newly-germinated seeds to dehydrate and their susceptibility to mechanical damage. Seeds have also been subjected to osmotic conditioning, including hydrating the seeds in salt or polyethylene glycol solutions. These treatments can reduce the slumber period, while preventing the occurrence of root germ or primary root.

Therefore, there is a need to reduce the germination time of seeds after planting ("in situ") and to increase the amount of synchronous germination of said seeds.

The present invention provides a method of accelerating the germination processes of a population of seeds before planting, so that the seeds germinate faster and with a higher degree of synchronization after planting than an untreated population of the same seeds. According to the present method, the seeds are "cycled" to a critical point just prior to germination by applying thereto controlled humidification and drying cycles, during a period termed the "critical fluctuation period". The seeds reach physiological synchronization at the end of the critical fluctuation period and then germinate quickly following a subsequent water exposure. Therefore, the present invention provides a method of accelerating and synchronizing seed germination comprising: (a) contacting an initial population of seeds with liquid water so that the moisture content of the resulting hydrated seed population is higher than the initial moisture content of the initial population of seeds; (b) removing the hydrated seed population from contact with liquid water and dehydrating them so that their moisture content is reduced to a level above the initial moisture content of the initial seed population; and (c) repeating steps (a) - (b) at least once to obtain a population of seeds with a moisture content that is above the moisture content of the initial population, and preferably also above that of the population of seeds is as produced by the previous dehydration (drying) step.

Preferably, the moisture content of each population of hydrated seeds is above that of the previously hydrated population. Thus, preferably, the moisture content of both the hydrated and dehydrated populations is incrementally increased above the moisture content of the initial population until the moisture content of the hydrated population reaches a critical point where germination will occur. Upon subsequent exposure to liquid water, said final population of dehydrated seeds will hydrate and germinate with significant synchrony and in a time period following said subsequent rehydration which is considerably shorter than the time required to germinate said initial population upon contact with water. For example, upon re-exposure to liquid water under ambient conditions, the germination time of the population cycled according to the present invention can be reduced to about 16 hours or less, with germination of at least about 90%, e.g. about 97.5-100% , of the viable seeds. For some grass seed types, two hydration / dehydration cycles (e.g. ab; a'-b ') will be sufficient to achieve effective synchronization and germination acceleration, while others will require 16-20 (a) - (b) cycles to achieve critical complete fluctuation.

Surprisingly, the present method can be used to improve the ability of older seed to germinate, and the present method can rejuvenate low strength seeds. The seeds produced according to the present invention can also withstand further drying to air-dry moisture content while maintaining an improved synchronization. The rapid germination of the subject seeds also reduces their exposure to rotting organisms, such as Pythium spp., Thereby reducing or eliminating the need to apply fungicides or other chemical treatments to the seeds.

The present invention will also be useful in replacing one type of ground cover with a second type of ground cover, especially in situations where maintaining an intact layer of cover is important, for example, for the protection or use of the surface.

For example, in the case of golf courses, it is often necessary to switch from one grass variety to another in order to adapt the characteristics of the grass to seasonal changes in the weather. Conventionally, this is accomplished by overseeding the old grass carpet so that the new grass variety uniformly replaces the previous variety, and at a sufficient density. However, due to the wide variation in germination times within the seed population being applied, much seed is wasted. The present invention achieves a population of seed that is pre-synchronized with respect to germination, which will germinate in a reduced time, advantageously shortening the time that the web cannot be used. The seeds of the present invention are also useful when it is desired to quickly cover a bare area of soil, for example, to protect it from erosion or from leaching hazardous residues. The area to be protected can be seeded and then exposed to water for one preselected period of time to effect the germination of the seeds and initiate the growth of the seedlings.

Although the invention has been described primarily with respect to grass seeds, the invention is expected to be generally applicable to the seeds of monocotyledons such as grains, for example, corn, wheat, barley, oats, rice, sorghum millet, and rye. Also, the seeds of plants such as orchard grass, freesia, cashews and fescue, and processed plants such as soybeans, beets, carrots, sellerie, tomatoes, onions, lupins, sunflower and cotton can be improved by the present process. The invention will be particularly effective in species where there is a significant time interval between maturation and germination of the seeds under natural conditions.

In the following, a more detailed description of the invention will be given by description of some embodiments.

Seed synchronization has been achieved with four genotypes of lolium perenne (perennial rye grass) and with different genotypes of poa annua (annual spring meadow grass). Generally, seeds stored under different conditions are cycled between aqueous environments with a liquid and vapor phase. The hydration phase (ψ = 0 MPa) is achieved by placing seeds in continuous contact with free water.

It is preferred to dehydrate the seeds at a high humidity under conditions where the seeds are not wetted. This can be achieved by placing seeds in an environment where humidity is strictly controlled. Since the relative humidity in the air of a chamber that also contains saline solutions corresponds to a particular water potential, a specific vapor pressure gradient above the liquid can be achieved, preferably at a water potential of about ψ = -5 MPa to -10 MPa at ambient conditions ( 25-27.5 ° C). Preferably, the relative humidity at about 26.5 ° C can be about 90-97%. This gradient provides a controlled drying rate and predictable seed moisture content at any time following introduction of the seeds into the vapor (drying) phase environment. It should be noted that a temperature control is used to prevent condensation due to temperature reduction rather than prevent temperature increase. Ambient air pressures are applied.

Seeds are alternated between the two environments for preselected durations, typically about 8-24 hours. Repeated hydration / dehydration cycles under the appropriate conditions synchronizes seed germination.

Example 1

Fifty seeds of "DelRay" residual rye (Northrup King) were subjected to hydration / dehydration cycles at 26.5 ° C. Following 16 hours of hydration on water-saturated tissue paper, the seeds were transferred to a sealed jar where they floated on a raft on a saturated aqueous potassium nitrate solution (RH = 93%, ψ = -10 MPa) for 8 hours at 26.5 ° C. Repeating this procedure twice fulfills the critical fluctuation period (2.0 cycles) and 100% of the viable seeds germinate upon re-exposure to water at 26.5 ° C overnight.

Example 2

Figure 1 summarizes the results of repeated hydration / dehydration cycles on lolium perenne (rye) seeds. The hydration (liquid) cycles were performed at 26.5 ° C for 16 hours. Dehydration (vapor) cycles were performed for 8 hours at ψ = -10 MPa (26.5 ° C) and at 97% and 93% relative humidity (R.H.), respectively.

The control seeds were continuously hydrated with liquid water at 26.5 ° C and germinated between 40 and 72 hours. The arrows in the figure indicate the point where the first seed germinated. All of the cycled seeds wetted at 93% (curve 16.8.93) germinated during the hydration step between 48 and 62 hours.

Example 3

Repeated hydration / dehydration cycles on poa annua (field grass) were also performed. The hydration cycles (liquid) were performed at 26.5 ° C. The dehydration cycles (vapor) were performed at 26.5 ° C (-10 MPa) and at 93% R.H., respectively. The control seeds were continuously hydrated with liquid water at 6.5 ° C.

Table I below summarizes the observed germination percentage for poa annua seeds that were cycled according to the present invention during two hydration / dehydration (liquid / vapor) periods.

TABLE I

TREATMENT CYCLES REDUCING Germination of P & anmia SEEDS (cycle = liquid / -10 MPa) LIQUID / VAPOR ----------------- Germination (%) * ----- ------------

(hours) DURING CYCLES FOLLOWING CYCLES

8 / 16a 0 * 81 8 / 24b 0 * 72 * Indicates a significant difference from the control, which had 75% germination between 56-136 hours of hydration. a Thirteen hydration / dehydration cycles, followed by less than 32 hours of hydration.

b Ten hydration / dehydration cycles, followed by less than 32 hours of hydration.

The data in Table I demonstrate that the present method is effective both to delay germination prior to planting and to synchronize germination with continuous hydration following cycling.

The invention has been described with reference to various specific and preferred embodiments and techniques. It will be understood, however, that many variations and modifications can be made within the spirit and scope of the invention.

Claims (6)

A method of accelerating and synchronizing seed germination, comprising, prior to sowing: (a) contacting an initial population of seeds with liquid water until the moisture content of the resulting population of hydrated seeds exceeds the initial moisture content of said population; (b) removing the hydrated seeds from contact with the liquid water and dehydrating them so that the moisture content is reduced to a level above the moisture content of the initial population of seeds; and (c) repeating steps (a) - (b) at least once to reach a population of dehydrated non-germinated seeds. A method according to claim 1, characterized in that the moisture content of the dehydrated seeds obtained after step (c) is also higher than that of the previous dehydration step. A method according to claim 1, characterized in that the moisture content of each population of hydrated seeds as produced in step (c) is above that of the previous hydrated population. Method according to claim 1, characterized in that the steps are performed under ambient temperatures. A method according to claim 4, characterized in that the dehydration is carried out at a water potential of about -5 MPa to -10 MPa. The method of claim 1, characterized by exposing the dehydrated seed population of step (c) to water to germinate substantially all of the viable seeds.