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Storage solutions for indigenous vegetable seeds

When stored at sub-zero temperatures seed germination rates in bitter gourd fall to less than 4% (© AVRDC)
When stored at sub-zero temperatures seed germination rates in bitter gourd fall to less than 4%
© AVRDC

Protecting the diversity of our food plants is a vital tool in coping with climate change and other crop challenges. The Taiwan-based genebank of AVRDC - The World Vegetable Center, for example, houses and maintains more than 12,000 accessions of 200 traditional vegetable species from South Asia, Southeast Asia and Africa. Many of these species are high in micronutrients and vitamins, and adapted to growing in less favourable environments, without costly inputs. As such, they represent a significant opportunity for achieving food and nutrition security in a sustainable way. But ongoing research suggests that many species are at risk, even in the genebanks designed to conserve them.

In theory, bitter gourd (Momordica charantia) belongs to the category of 'orthodox' seeds that can be dried to low seed moisture levels and stored at low temperatures to preserve their viability. However, recent research at AVRDC has found that, when stored at sub-zero temperatures (-15°C) - the typical practice for long-term storage - seed germination rates in bitter gourd fall to less than four per cent. Though not yet described in literature, the germination problem has been confirmed by two seed companies who performed their own germination tests.

This has major implications for safe germplasm conservation and storage. If long-term sub-zero storage is not possible, frequent regeneration cycles of seed lots will be necessary (cultivating plants to the fruiting stage, and collecting and re-storing the resultant seed), but this is labour-intensive, costly, and if not done properly can threaten the integrity of the genetic diversity in the seed lot. In response, AVRDC is now carrying out detailed physiological studies to define optimal seed drying and storage conditions for bitter gourd seeds.

Too dry, too hard

Seed of stored okra varieties often show poor germination and growth in the field (© IFAD/Christine Nesbitt)
Seed of stored okra varieties often show poor germination and growth in the field
© IFAD/Christine Nesbitt

In the case of okra (Abelmoschus esculentus), it is seed moisture content for long-term storage that is the subject of the scientists' attention. While drying and storing okra seeds at sub-zero temperatures is known to extend their viable lifespan, seed of stored okra varieties often show poor germination and growth in the field, which AVRDC scientists are linking, in part, to hardseededness. "This occurs when seeds develop an impermeable seed coat, which prevents them absorbing moisture and leads to germination failure, says Andreas Ebert, genebank manager for ARVDC. "This is a problem which tends to be exacerbated in genebanks, where seeds are dried to a very low moisture content to extend their storage life." The AVRDC team are now researching optimum drying levels for both okra and a third traditional vegetable, water spinach (Ipomoea aquatica).

But hardseedness does not only cause a headache for genebank scientists. For farmers who grow the three vegetable species, it's also a major cause of poor germination and low crop yields. Hence, AVRDC is also testing simple seed priming techniques that small-scale farmers could use to improve germination rates and plant vigour. The methods include: soaking seeds in water for 24 hours; soaking in household vinegar for two hours; soaking in potassium nitrate solution for one hour; and partial mechanical removal of the seed coat. In bitter gourd, soaking for an hour in potassium nitrate solution proved the most successful method of seed priming, resulting in 76 per cent normal seedling growth. Studies for okra and water spinach are ongoing, but all the results will need to be validated in further trials scheduled for 2014, to assess seasonal effects and confirm the observed trends.

Seed setting studies

Slippery cabbage is quick and easy to cultivate (© AVRDC)
Slippery cabbage is quick and easy to cultivate
© AVRDC

A fourth traditional vegetable under scrutiny is slippery cabbage (Abelmoschus manihot). Despite its unappetising name, the plant is quick and easy to cultivate, nutritionally rich, and a popular food in the Pacific Islands, Northern Australia, East Asia, and parts of Southeast Asia. As such, AVRDC is keen to assess and conserve its extensive diversity in order to produce improved varieties. However, the scientists hit a major barrier when they found that plants grown at AVRDC's fields in southern Taiwan would not flower or set seed. In response, the Centre has entered into collaboration with Crop-Innovations, a UK-based organisation based at the universities of Warwick and Bath that promotes under-utilised crop species. "Crop-Innovations provides expertise and research capabilities to solve problems with the seed of under-utilised crops, these problems can range from difficulties with production of high-quality seed to ensuring optimal seed size," says Heather Sanders Crop-Innovations operation manager. "In the case of slippery cabbage, we are contributing experience in plant developmental biology, and a number of possible causes for the flowering and fruit-setting failure are under investigation."

Date published: November 2013

 

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Slippery cabbage is widely distributed throughout India, tro... (posted by: Andreas Ebert)

This kind of commodity slippery cabbage in not a well-known ... (posted by: fed launio)

 

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