Category: Breeding

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Maize aguafiestas

From Jacob van Etten.

Uncorking a big bottle of agrobiodiversity, that is what Mexico’s first farmers did when they domesticated maize. Not only is maize enormously malleable, genetic diversity also goes everywhere through cross-pollination. That is in traditional farming systems. Modern maize improvement has been about sorting out this abundance by “freezing” it into breeding lines, to get some control over the diversity feast. But what happens when the hybrids are released into the dance room again?

An Italian study just out quantifies the gene flow from hybrids to traditional varieties. It finds different degrees of purity in the traditional varieties, but no genetic erosion. This is an interesting finding in the light of writings about “creolisation” in Mesoamerican agriculture. Creolisation, the mixing of modern and traditional varieties, is thought to lead to plants that combine their benefits. I have always wondered if the creolised varieties of Mesoamerica are not modern varieties “creolised” by selection instead of mixing with traditional varieties. Something similar to the Italian study would be needed to find this out.

The question is only one step removed from the issue of gene flow from transgenic crops to traditional varieties. Perhaps you remember the Quist and Chapela paper published in Nature in 2001 on the presence of transgenes in Mexican traditional maize, and the controversy it generated. A new study confirms the presence of transgenes in Mexico with an improved study design. Through genetic population simulations it also explains why detection of transgenes is erratic and prone to giving false negatives. The distribution of the transgenes is likely to be very skewed. A few fields will have much of them, but most will have very few. This has to be taken into account and therefore authors call for more rigorous sampling methods to detect transgene presence.

There is little discussion or speculation about the effects of transgenes on maize diversity. Will the transgenes just add to the existing diversity, like the hybrids in Italy? Will they perhaps produce some benefits, like the creolized varieties? Or will, in some Monty Python-like scenario, the big seed companies pick up the message about rigorous sampling and start to trace transgenes in Mexico in order to charge farmers for unlicensed use of their technology?

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A citrus species in need of research?

It seems that citrus canker, a nasty bacterial disease, has been officially eradicated in Australia. Good news, but there is a bit of a dark lining. Along with 495,000 commercial citrus trees and 4000 residential trees, the eradication programme has included destroying a lot of trees of native Citrus glauca in the affected area. Desert Lime is well-known bush tucker, as well as a potential resource for Citrus breeding. It’s not currently considered endangered, but there’s not really all that much research about it ((That’s a bit of a casual way of introducing the fascinating Australian New Crops Web Site. Thanks to Danny for the tip.)), so that might be optimistic. There are only 8 germplasm accessions worldwide (page 29), apparently. That sounds inadequate to me. Especially given the historic proportions of the current drought, which is affecting the whole of SE Australia, including areas of C. glauca.

LATER: See also a map of the latest spate of bushfires in Australia. A threat to this and other crop wild relatives?

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Nibbles: Wolf, Conservation agriculture, ODI, Food policy, Stress, Sustainability

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Nibbles: Coffee, Barley, Sheep, Diary, Ancient chocolate, South African wine, Pleistocene Gibraltar, Roads

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New and worse (nutritionally speaking)

Speaking of heirloom tomatoes, everyone will tell you that the tomatoes of their youth tasted better than they do today. Depends on the tomato, I’m sure, but in general that seems a safe bet, especially if you’re comparing something ugly fresh-picked from the garden with a supermarket beauty. Now, it seems, the older variety may have packed a superior nutritional punch too.

A fascinating paper to be published in HortScience Review by Donald R. Davis, who recently retired from the University of Texas, compares the mineral content of fruits and vegetables over the past 50 years or so. Davis looks at three types of evidence. First, the so-called dilution effect: the more yields increase, thanks to fertilizers, irrigation and other external inputs, the lower the concentrations of many minerals in the harvested part. Secondly, looking at historical food composition tables, older measurements tend to be higher than new ones, for many fruits and vegetables. Third, and most interesting, side-by-side comparisons of old and new varieties, grown today and measured in identical fashion, also show declines from old to new. This is effectively a “genetic” dilution effect. The increase in yield has been achieved by genetic selection, not environmental inputs, but the impact seems to be the same.

These last are perhaps the most convincing. Alas, they are also the most scarce. Broccoli varieties show a decline in calcium and magnesium. Wheat varieties likewise showed a decline in minerals, protein and oil from older varieties to newer. And three amino acids were lower in modern maize varieties than in older selections. Davis writes:

Recent studies of historical nutrient content data for fruits and vegetables spanning 50 to 70 years show apparent median declines of 5% to 40% or more in minerals, vitamins, and protein in groups of foods, especially in vegetables. Although these apparent declines in individual nutrients may be confounded by systematic errors in historical data, the broad evidence is consistent with more definitive studies and seems difficult to dismiss.

Without getting into the reasons for these results — almost certainly they relate to the fact that recent breeding efforts seldom target nutrients — one thing seems clear. More data would be useful. Would it be too much to ask genebanks, who often regenerate a time-series of accessions in a single year, to consider making part of the harvest available for detailed chemical analysis?