Seed Quality & Packaging
By Shantibaba
Many people think seed packaging is colourful, gimmicky and intended for marketing a seed strain from a specific company only!
In recent years and with the increase cross section of the population all lining up asking for medical seed, there is an increased importance for all companies to abide by a set of standardized rules that protect the growers and farmers who buy seed.
A lot of mails/letters have arrived over the years asking me to deal with the problem of storing seed and how seed packaging influences the shelf life of the contents. So in recent times I have been reading quite some articles related to the grain and vegetable seed world; their ideas behind why they choose certain materials for packaging and how the influences that prey on seed should be dealt with.
Considering Cannabis seed is very much part of agriculture and its applications and storage as well as its testing (which is something missing to this date), there are strong parallels drawn from the vegetable, seed and sprout industry.
Across the sprout, vegetable and grain industry it is unanimous that seed storage and how the seed is packed can and does have a huge impact on the seed ultimately used as a food source, fodder or genetic storage unit for the future. So it is a major influence on the health of the dormant embryo inside the shell and therefore it is imperative that certain guidelines are adhered to.
Throughout the world farmers and growers have clear demands of the seeds they sow and purchase. First they want the species and variety to be consistent with what they believe they have bought. Secondly they want that seed to achieve uniform and successful establishment of a weed free crop that will develop well and harvest without harmful diseases from seed- borne infections.
WHAT IS SEED QUALITY AND HOW TO MEASURE IT?
Variety Testing
There are two aspects to variety testing. The first is to ensure that a sample is the required species or variety and the second to ensure the purity of the variety, that is, that the variety is not contaminated by the seed of other varieties. The Morphological methods; where the charac- teristics of the seeds may be compared for example, differences in seed colour my reveal that varieties have been mixed. Alternatively the char- acteristics of seedlings may be observed in the laboratory or in the field, or other plant or fruit characteristics may be observed in the field.
More modern methods of variety testing can involve a range of bio- chemical and molecular techniques.
Analytical Purity
The analysis of the analytical purity of the seed exam- ines the extent to which a seed sample is contaminat- ed with other seeds (weeds and other crops) and other plant and inert material. It therefore reveals the extent to which the seed that a farmer buys is actual- ly the desired seed.
Germination Tests The aim of a germination test is to provide ideal con- ditions for germination so that the maximum poten- tial of the seed is revealed. The ideal conditions for germination of different
species may differ in terms of the substrate, temperature and time. The substrate for germination may be sand, an organic medium, on top of paper or between papers. Temperatures for germination are either constant or alternating, where one temperature is applied for a spec- ified length of time, followed by another temperature for the rest of a 24-hour period. Finally the time allowed for germination in agricultural and vegetable species can range from as short as five days for jute (Cochorus olito- rius and C. sativum) to as long as 35 days for Tetragonia tetragonoides (New Zealand spinach).
Another characteristic of seed to be considered in a germination test is seed dormancy. In many plant species the presence of dormancy means that the viable seeds will not germinate even when the ideal conditions are present unless they have received a specific environmental cue. This evolutionary trait is a survival strategy which
ensures that seed will only germinate when the environ- mental conditions are suitable for seedling growth and plant establishment and also spreads the germination over a period of time.
The requirements for a germination test, the pre-treat- ments necessary to break the dormancy of many species have also been identified. Treatments to break physiolog- ical dormancy include dry storage, which usually applies to species that have a short period of dormancy; moist pre-chilling, usually at temperatures of 5-10oC for agri- cultural and vegetable seed and 1-5oC for tree seeds; pre-heating; light; and potassium nitrate or gibberellic acid provided during germination. Physical dormancy arises due to a hard seed coat that prevents the uptake of water at the beginning of germination. This so called ‘hard-seededness’ can be broken by soaking in water for 24-48 hours, mechanical scarification or acid scarifica- tion.
Dormancy is not often seen in many crops, having been selected out by the act of cultivation over thousands of years. There can be problems however in years when the weather causes problems during harvest or in species brought into cultivation more recently.
At the end of a germination test, a seed is said to have germinated successfully if it has developed to the stage where the appearance of the seedling indicates whether or not it is able to produce a satisfactory plant in favourable field conditions. Such a seedling is described as a normal seedling. If a normal seedling is not produced, the seedling is described as abnormal and would
not be expected to produce a plant in the field. The result of a germination test is reported as a percentage of normal seedlings, abnormal seedlings, hard (unimbibed), fresh (i.e. moist but firm) and dead seeds.
Tetrazolium Tests
The tetrazolium test is a biochemical test that provides a rapid assessment of the viability of the seed by assessing the degree to which the tissue of the embryo of the seed is living by using a stain.
Vigour Tests
Germination tests are the primary assessment of the ability of seed to germinate and emerge in the field. However, although the results of the standard germina- tion test give a good correlation between germination and field emergence in favourable conditions, germina- tion can fail to indicate the ability of a seed lot to estab- lish a crop in poor field conditions, for example, cold, wet soils. There have been instances described in a wide range of species where seed lots having equally high laboratory germinations show wide differences in field emergence.
This failure of the germination test to predict differences in field emergence, particularly in poor field conditions, suggested that there is a further physiological aspect to seed quality, which has come to be referred to as seed vigour. Seed lots having high germination, but poor emergence are referred to as low-vigour seeds, where- as those giving good emergence are termed high-vigour seeds. Vigor is also reflected in the rate of germination and seedling growth, in both favourable and unfavourable conditions for germination and emer- gence. Low-vigour seeds germinate slowly over a long period of time to produce a range of seedling sizes, whereas high vigour seeds germinate rapidly and syn- chronously to produce large and uniform seedlings. Furthermore, high vigour seeds have good storage potential while low vigour seeds lose the ability to ger- minate more rapidly during the storage period.
The results of a vigour test give a farmer more information about the potential of a seed to perform in a range of soil conditions; seed company information for managing its seed stocks, both in store and in marketing; a seed producer guidance regarding where seed quality may be reduced and how this can be minimized.
Seed Health Tests
Seed health tests to detect whether seeds are contami- nated with or infected by a plant pathogen are impor- tant for a number of reasons. The presence of seed- borne inoculums may cause disease within a crop giving an opportunity for very rapid spread of disease, may introduce a new disease into new regions or countries and may reduce the germination of seeds by reducing the percentage of normal seedlings produced. In addi- tion, the results of testing can indicate the need for seed treatments.
The term “seed health” includes the incidence in the seed lot of fungi, bacteria, viruses, and animal pests such as nematodes and insects.
Seed Moisture Content
The moisture con- tent (MC) of the seed is an additional characteristic that does not have an immediate, direct effect on quality, but is highly important.
Tests of seed MC fulfil three main purposes.
Firstly to prepare the seed for long- and short-term stor- age, secondly, the seed MC will influence the price paid for a weight of seed and thirdly the MC will determine the response of seeds to dormancy breaking techniques and vigour tests. The most significant effect of MC is on the rate of seed aging and hence the rate of decline in seed quality dur- ing storage. Thus, as the seed MC increases, the rate of aging also increases. As a rough guide, suggestions that an increase in seed MC of 1% will double the rate at
which germination declines! During storage the MC of the seed moves into equilibrium with the relative humidity (RH) of the store, therefore the RH during stor- age has a crucial effect on the MC and seed aging. In addition the storage temperature affects the rate of aging, with an increase of 5o C doubling the rate of aging . The impact of MC and temperature on seed quality are therefore of particular significance in tropical countries where ambient conditions will tend to lead to rapid loss in seed quality.
An
increase in the storage
RH not only leads to more
rapid seed aging, but the activity
of saprophytic fungi, insects and mites also increases as the RH and seed MC increase.
Uniformity in Seed Testing
Having a standardized test or series of tests in place will only aid all those who use produce or sell seed. If the same tests are recognized by the buyer of seed and asked for before purchase it will make seed producers and resellers be aware that inferior seed in the market place will be found out and reputation will be at stake.
Concluding Comments
Seed quality is the sum of multiple components. The most important of these are species and cultivar purity, analytical purity and germination, while other significant components of seed quality are seed vigour, seed health and moisture content. Assessments of seed quality are possible through field tests and a range of laboratory tests to ensure the reliability and uniformity of test results from different laboratories. The completion of such tests provides information about a seed lot that is useful to the seed producer, the seed company and the farmer, to guide decisions during seed production, marketing and storage with the ultimate aim of achieving successful and efficient crop production.
SEED PACKAGING:
What aspects to look out for to tell if the company is looking out for you the grower.
Seed companies who are serious about selling good quality seeds that pass all the tests for storage and longevity in shelf life do not expose the seeds to sunlight.
In other words seeds that are stored in unbreakable vessels within humidity controls, out of direct sunlight and sealed in temperature controlled material will be far likely to have better germination levels and seed vigour. The companies who expose their seeds to direct sunlight or allow the seeds to be seen in pack- ets will be more prone to lower germination levels even when the seed is produced fresh and stored well before being packed.
Generally seed should have a 2-5 year shelf life from the time of production if all goes accord- ingly and if stored in cool shaded areas. It is important to be able to see this date the seed is made or packed as it is a prerequisite for all other industries to show a use by date for products.
If Cannabis seed is to follow the rules set by the seed industry it must comply with certain basic requirements for a grower to know before purchasing.
Seed can be stored in a freezer and in an air tight contained to disallow humidity to infiltrate it…but it is advisable to only store seed in a freezer one time then in a fridge after that if the seed is still unused.So buyer beware of any companies who have seed visible and hanging in shops without a batch number (that can be checked for a date) or a date packed printed on the back…especially in hotter climate countries.
It is possible you are buying old seed stock (if no date is printed on it) as well as the possibility of buying dead seed since it may have been exposed to sunlight and heat inside the shop while it awaits the buyer. Seed packets should be kept in a cool environment with low humidity and it is advisable to keep sealed in a fridge if not in use. Sealed or resealable packaging is idea if you intend to use half a packet and store the other half.
Seed needs to be kept in sealed packets to avoid contamination from air borne pathogens.
It is difficult to argue with a com- pany if the seed is sold in sealed units and vacuum sealed in an alu- minium foil zip lock just as the vegetable seed is sold in supermar- kets. To claim a company made an error in seed storage and packag- ing can only be justified if the company does not vacuum seal the seed and keep it out of visibility to the sun.
Other important aspects of seed packaging to consider are indirect sunlight, heat extremities, temperatures, relative humidity, chemicals, X-rays, irradiation exposure, rollers in post office sorting points, time in transit, length of time held in stock, age at the time of planting.
Many take for granted that seed will germinate no matter what, but all these facets will cause disturbing influences on the percentage germination and type of plant that will grow from compromised seed.
There are so many aspects to take into consideration in the seed industry and behind the scenes. A fancy and colourful seed packet may be a perfect distraction to the real point of purchase. But in the end `the proof is in the seed’ and once the grower decides to germinate the seed the answers will follow.
It is therefore a big responsibility for a seed company to do testing and hygienic seed production and packaging to maintain the integrity of their product, and the time it can be used with success. The onus for the grower is to do their best to educate themselves on what constitutes a good seed company who will support their own products all the way through to harvest!
