Hermetic enclosure extends hybrid rice seed viability

The viability of hybrid rice seeds can now be prolonged up to nine months by storing them in hermetic seed storage enclosures, according to results of a study conducted by researchers at PhilRice (Philippine Rice Research Institute) and BPRE (Bureau of Postharvest Research and Extension).

In the past, farmers were meeting problems on the low germination rate of hybrid rice seeds provided to them by the Department of Agriculture, as these were stored under ordinary storage conditions.

The germination rate of hybrid rice seeds (no lower than 85 percent) could be maintained only up to three months under ordinary storage conditions. The germination rate drops significantly when stored up to six months.

In their joint study, the researchers stored one-month old seeds of Mestizo 1 with 9.5 to 10.5 moisture content in imported Volcani Cubes or GrainPro Cocoons for hermetic storage. These were compared with seeds stored in a cold room, air-conditioned room, and ordinary storage condition.

The germination rate of seeds kept in hermetic storage for six months was comparable with those in cold room storage, and significantly higher than those stored in air-conditioned room. At nine months, however, the germination rate of seeds in hermetic storage was significantly lower than those stored in a cold room, but comparable with those kept in air-conditioned room.

The PhilRice and BPRE researchers said the low oxygen environment inside the enclosure prevents growth of fungi and creates a favorable environment to preserve seed germination capacity without refrigeration. After a few days of storage, the oxygen inside the enclosure is reduced to a level that cannot sustain insect life (one to two percent) and the carbon dioxide level rises substantially.

Results also showed that among the four methods, hermetic storage is the most effective in controlling insect infestation and in reducing weight loss. This was followed in a decreasing order by cold room storage, air-conditioned room storage, and ordinary storage.

Hermetic storage was also the best in terms of cost effectiveness per bag after six and nine months. It was followed by ordinary storage, air-conditioned room storage, and cold room storage in a decreasing order.

PhilRice researchers said the hermetic seed storage technology uses a flexible enclosure made of plastic material with low permeability to air. However, the imported seed storage enclosure (SSE) is relatively expensive. For instance, a five-ton hermetic storage enclosure, which can contain 210 bags of hybrid seeds weighing 20 kg each, costs P70,000.

To cut down on cost, PhilRice researchers designed and developed a low cost SSE with a capacity that would fit the needs of local seed producers. This locally fabricated material is made of tarpaulin, which is normally used for making tents and cargo truck cover. The local SSE is provided with simple and easy-to-fabricate zipping mechanism to attain airtight sealing.

The PhilRice-fabricated SSE compares well with the imported material in terms of maintaining low oxygen concentration inside the enclosure, seed germination rate, weevil count, and moisture content.

The design of the enclosure has been refined to make it more user-friendly and fit with the current system of handling and storing seeds practiced by seed growers. The latest prototype has a capacity of 50 bags weighing 20 kg each and costs around P4,000 each. It is much easier to open and close than the imported enclosure. – Sosimo Ma. Pablico