Accelerator effect

Producing high-quality seeds is one of the main challenges for seed producers. The rapid and uniform establishment of seedlings in the field is a fundamental prerequisite for achieving a good stand and achieving guaranteed productivity and quality of the harvested product. The performance of seeds after sowing is mainly determined by their physiological and sanitary quality, which will determine the adequate establishment of plants in the field or in the nursery, a fundamental aspect for achieving satisfactory levels of productivity and final quality of the product.

To meet these requirements of vegetable producers, several companies have been offering seeds with extra characteristics, seeds with high vigor, good health, pelleted, osmotically conditioned, film coated, etc. This can differentiate the product from the seed company, as well as offering advantages in germination and crop establishment.

One of the main problems when using seeds from various plant species is the lack of uniformity in germination, as within the same batch of seeds, during the hydration process, there are individuals from different phases of the imbibition curve, causing germination to occur. heterogeneous. In this sense, delays in seedling emergence can reduce plant uniformity at harvest and production. Obtaining an adequate and uniform population of plants in the field is one of the main factors determining the final quality of the vegetable product. The effects of seed vigor on stand establishment can be especially critical for crops that require spatial distribution of plants to maximize their yield such as lettuce, cabbage, onions and cauliflower.

To improve this situation, the osmotic conditioning technique has been used, mainly in vegetable and flower seeds, with the aim of increasing germination speed, improving seedling uniformity and in some cases increasing the germination percentage.

During osmotic conditioning, the seeds are subjected to pre-soaking in water or in a solution of known osmotic potential, during determined time intervals and temperatures, allowing the control of water supply, i.e., it consists of controlled hydration of the seeds , in order to promote pre-metabolic activities, without the emission of the primary root. Afterwards, the seeds can be dried or used immediately. In this way, at the end of conditioning, all seeds would be in the same phase of the imbibition curve, without reaching the radicle protrusion phase (phase III).

There are conflicting reports on the effects of osmotic conditioning on germination percentage and speed. Some authors reported that the main effect of this type of treatment is to increase the germination percentage. Others mention that the success of osmotic conditioning depends, among other factors, on the initial quality of the batch. In general, batches of high physiological quality do not respond satisfactorily to treatment. However, osmotic conditioning has reinvigorated seed lots of low physiological quality of some species. In a batch of cabbage seeds of low physiological quality, which initially had 71% germination, reached 82% germination when the seeds were conditioned for six days without drying, a value that is above the minimum germination standard established for commercialization. of cabbage seeds which is 80%.

Several studies demonstrate that physiological conditioning improves the performance of seeds from different species, such as: eggplant (Solanummelongena), cauliflower (Brassicaoleracea), asparagus (Asparagusofficinalis L.), carrot, tomato (Lycopersicun esculentum L.), lettuce (lactuca sativa L.), cucumber (Cucumis sativus) and pepper.

The increase in germination speed provided by osmopriming has also been verified for seeds such as melon, lettuce and parsley. In osmoprimed “Brazilian” pumpkin seeds, germination was faster when compared to unprimed ones. In carrot seeds, it is possible to improve germination through conditioning with PEG 6000, using the aerated solution method. However, in cauliflower seeds, cultivar Sharon, there was no effect of physiological conditioning on the percentage of germination.

Osmoprimed cauliflower seeds showed superior seedling emergence results when the seeds were from lots with lower physiological potential. Osmoprimed carrot seeds showed greater seedling emergence in the field in all tested lots. This situation is advantageous because it leads to a shorter period of exposure of seeds to adverse environmental factors after sowing.

Cabbage seeds of high physiological quality subjected to osmotic conditioning for six days, followed or not by drying, resulted in longer, that is, more vigorous, seedlings. However, positive effects of osmotic conditioning on seed germination and vigor were more evident in batches of lower physiological quality, increasing first count values ​​by approximately 20%. Regarding radicle length, a negative effect of osmotic conditioning on this characteristic was observed, that is, in most treatments there was a reduction in radicle length. Drying seeds after osmotic priming may decrease the beneficial effects of osmopriming on cabbage seeds.

The beneficial effects of osmoconditioning can be attributed to membrane repair, increased protein synthesis and more efficient mobilization of sugars and proteins. However, the seeds reach high water contents at the end of osmoconditioning, which is inadequate for the conservation of physiological potential during storage.

Therefore, an important step after physiological conditioning is drying, since the techniques used to reduce the water content of the seeds can reverse the beneficial effects of conditioning and reduce the storage potential of the seeds. The aim of drying was to interrupt the metabolic processes that would cause the primary root to be emitted, but when placed in conditions favorable to germination, this would occur more quickly and uniformly.

There are controversies related to the effect of drying immediately after osmotic conditioning. In some studies, drying reversed the beneficial effects of osmopriming, but in some the results were favorable. Primed seed responses appear to be species specific and dependent on drying conditions.

The vigor of dried and non-dried eggplant seeds after osmopriming, where the values ​​of aerial part length and seedling dry matter, were higher in the lot with higher physiological quality, regardless of drying. The hypocotyl and root length of cucumber seedlings were reduced by conditioning the seeds in PEG 6000 at a potential of -1,2MPa, without subsequent drying of the seeds, when compared to the unconditioned control.

In summary, it is possible to conclude that the physiological seed conditioning technique is a useful tool capable of practical application for the vegetable seed industry, enabling the provision of seed lots to producers with a uniform level of physiological performance, thus providing opportunities , to obtain more homogeneous production standards, adding value and quality to the products offered to consumers.