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Zeolite vs Silica Gel: Deathmatch

zeoliteThe Horticulture Collaborative Research Support Program at UCDavis has a nice factsheet out about Zeolite Desiccant Beads. Why?

Zeolite beads, used with airtight containers, are a simple, inexpensive and widely adaptable method for drying horticultural seeds and maintaining high seed‐quality during storage. The beads can be reused by baking between use.

And of course we know that’s important:

In tropical climates, high humidity causes rapid seed deterioration, resulting in poor stand establishment, lower productivity, less value and disincentive to invest in improved seeds.

Although farmers seem to be the clients here, I thought perhaps this might be a good, relatively low-cost solution for genebanks too, so I ran the factsheet past some seed experts at Kew and IRRI. Thanks to both of them for allowing me to quote them.

It turned out that Fiona Hay, formerly at the Millennium Seed Bank at Kew and now at IRRI, has had quite a lot of experience with zeolite.

Indeed, we have done some work on these zeolite (=molecular sieve) drying beads on rice … in collaboration with the company, Rhino Research, in Thailand that is marketing them (and holds the patent — I’m not sure in which countries). See attachment..

Yes, they are a good desiccator, my concerns are that they could be too good and that they don’t appear to work as described — they don’t take up the same amount of water from the seeds as they do when they are placed over water. This means that is isn’t obvious how to calculate the right quantity of beads to use to dry seeds to a required moisture content. This is based on our work on rice (three different fresh seed lots), but seems to be at odds with what Kent Bradford (UC-Davis) has found for horticultural crops.

In terms of their use by farmers — I don’t think this technology is what they need. If the HORTCRSP project helps them to understand the need to dry seeds, OK; but there may be cheaper, simpler options.

They could be of more use in a genebank situation — once we know how to use them optimally. We are doing more work on this. One of Rhino’s latest products using the beads are bins containing a core of beads which is in contact with some indicating silica gel. Seeds are put in the bin and the silica is used to know when to regenerate the beads. This could be useful for genebanks without proper drying and/or storage facilities. I’d like to get hold of a couple of these to try them out.

Robin Probert at the Millennium Seed Bank then added:

What annoys me most about the USAID fact sheet promotion of Zeolite beads is that it brags the value of Zeolite beads over silica gel for small farmers drying seeds for sowing. We have known for decades that the problem facing local farmers is the rapid loss in viability that can occur if seeds remain at high ambient relative humidity combined with warm temperatures. We also know that if farmers were able to dry seeds from say 80% equilibrium relative humidity (eRH) to below 50% eRH, seed longevity would be improved by several fold. This could mean the difference between seeds surviving for only a few months to a few years.

The fact sheet boldly states (with a nice graph to make the point) that ‘Zeolite beads are more effective than silica gel in absorbing water at low relative humidity’. But this could be written another way: ‘silica gel is more effective than Zeolite beads in absorbing water at high humidities’. Fiona’s work published in Seed Science and Technology last year [Fig 5 in Hay et al (2012) SS&T 40, 374-395] elegantly confirms this.

What this means is that a farmer would need less silica gel than Zeolite beads to dry seeds from ambient humidity to a safe moisture content for short-medium term storage (≤ 50% eRH). But what about cost? The USAID leaflet states that Zeolite beads can be bought for 10-20 US $ per Kg. We buy silica gel beads that we use in our drying drums designed for small-scale seed drying for less than 10 US $ a Kg.

Using Zeolite beads to dry seeds down to very low moisture contents for long-term storage is a different matter and as Fiona’s paper demonstrates, Zeolite beads may have it over silica gel for this purpose. However, as the paper also points out, calculating the weight of Zeolite beads needed is not straightforward and compared to silica gel there is a much greater risk of over drying.

All in all, I know where my money is.

So it turns out that, on balance, according to these experts at any rate, the Zeolite beads may actually be more promising as a solution for resource-strapped genebanks around the world than for seed-saving farmers in the humid tropics. Which was, however, presumably not the aim of the USAID-supported project that came up with that factsheet. But let me tweet this to HortCRSP and see what they say. Stay tuned…

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Banter about cucurbits

Mary Beard, classics professor at Cambridge and effective general-purpose public intellectual, knows how to get your attention:

Sikyonians … were a sort of Greek footwear, but also a famous variety of cucumber and so a comic term for a phallus, and the ‘scarlets’ are a suspicious match for the scarlet dildo…

That’s from a review, enticingly entitled Banter about Dildoes, 1 of a book on Roman shopping with a much more boring title. 2 Well, I defer to Prof. Beard on Greek footwear and Roman sex toys, but I’m not so sure about that cucumber.

To see why, let’s turn to a 2007 Annals of Botany paper The Cucurbits of Mediterranean Antiquity: Identification of Taxa from Ancient Images and Descriptions, by Jules Janick et al.:

Many of the Renaissance botanists identified the cultivated sikyos of the Greeks as cucumber. Observers of more recent times, including de Candolle (1886), Sturtevant (Hedrick, 1919) and Hyams (1971), have concurred. However, as de Candolle (1886) admitted, the origin of cucumbers is the foothills of the Himalayas. Although Roberts (2001) identified two ancient mosaic images as depicting cucumber (see Figs 3E and ​and 4B) the former is clearly Cucumis melo, as evidenced by the longitudinal split in the fruit, and the latter is Lagenaria siceraria, as evidenced by the obviously swollen peduncular ends of the fruits. Archaeobotanical records include findings of several seeds purportedly of cucumber, but it is extremely difficult, even for experts, to differentiate between the seeds of C. sativus and C. melo (Bates and Robinson, 1995). Possibly, an identification of the species of these seeds could be accomplished by analysis of ancient DNA (Gyulai et al., 2006). In this survey of Mediterranean iconography and verbal sources of Roman times, we have found no hard evidence of the presence of cucumbers. There is some linguistic evidence that they became known in the region during the early Middle Ages (Amar, 2000) but the earliest European image known to us of what can be unquestionably identified as cucumber is from approx. 1335, post-dating the Mongol invasions. Renaissance depictions of cucumbers, although very common, show much less variation than do those of melons, which is suggestive of their being more recently introduced or of their lesser culinary appreciation or economic importance.

I think it is worth reproducing those mosaic images. Hopefully Annals of Botany won’t mind. Here’s 3E, the slitty Cucumis melo.

cucurbit

And here’s 4B, the knobby Lagenaria.

cucumber1

So, one can understand the mistake, but, pace Prof. Beard, that “famous variety of cucumber” was probably a famous variety of something else, either a muskmelon 3 or a bottle gourd. Though, as you can see from the illustrations, 4 that wouldn’t affect its comic potential. On the contrary…

PS Incidentally, since we’re talking funny-shaped cucurbits in history…

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How to fix plant breeding

Big Picture Agriculture is a great source of stories about, er, the big picture in agriculture. Catching up with Kay I came across this beaut:

GM labeling activist movements are misguided. Fred Kaufman explains that the real problem lies in U.S. plant patent laws which have done more harm than good, overall. Food patent laws stand in the way of good scientific research.

The most direct and efficient way to undermine the food industrialist monopoly of the molecular seed business is to reform these laws (particularly the utility patent law of 1985), and make food property rights less exclusive, less lucrative, and less enduring. … Instead of tilting at the windmill of food labels, food nonprofits should hire a fleet of I.P. lawyers and send them to Washington to demand reform of the Plant Patent Act. When there’s less profit in genetic modification, things will get better for consumers, farmers, and scientists—pretty much everyone except corporate executives.

I really have nothing to add.

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Quinoa in Pakistan

Heralding the International Year of Quinoa, here’s an odd video of quinoa in Pakistan.

Don’t freak, as I did, if it looks a little odd if you open it in a browser; that’s just the 3D out to get you. There’s a link to get rid of that annoyance, but not to improve the rest of the production.

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The history of the tomato

One reason to love the internets, back into which, fully refreshed, we plunge, is this comment:

[T]he plant Galen mentions is the λυκοπέρσιον, lykopersion, not lykopersikon. The name means ravager or slayer of wolves, like our wolfsbane. The transition to the “wolf-peach” happened sometime later, probably a scribe’s error. Liddell-Scott’s Greek-English Lexicon describes it as an Egyptian plant with strong-smelling, yellowish juice and identifies it as Hyoscyamus muticus, one of the very poisonous, tropane-bearing Solanaceae. There are plenty of other seriously deadly Solanaceae in Egypt but this is as good a guess as any.

That’s from Pat the Plant 5 in response to this (very familiar) bit in a long and fascinating post about the tomato from Hollis at In the Company of Plants and Rocks.

“Lycopersicum” means “wolf peach”, and probably was selected by Linnaeus from the classical literature. Lycopersicon was a plant described by the Roman physician Galen as being both delicious and dangerous — appropriate for the tomato during Linnaeus’s time (see discussion below). No one has figured out what Galen’s lycopersicon actually was, and there’s no reason to think it was the tomato of the Americas, given that he lived in Europe during the second century AD. (“Wolf peach” is sometimes attributed to German were-wolf legends, for example here).

I found Hollis’ post, somewhat belatedly, via the latest Berry go Round, hosted by Susannah at On the other hand. Being partly responsible for BGR, I feel bad that it has been a little hit and miss lately, and glad that Susannah is going to feed and water it going forward until it is once again bursting with the best botany blogging the internets can offer. Why not submit your own work?