Old barley may hold key to drought resistance
27 July 2009, by Sara Coelho
A long-lost barley variety farmed for thousands of years in ancient Egypt may hold the key to drought-resistant crops as scientists uncover the secrets of its ancient DNA.
Dr Robin Allaby.
The extinct barley variety was rediscovered in the ruins of Qasr Ibrim, located between the first and second cataracts of the River Nile, south of Aswan. The barley was cultivated by the Qasr Ibrim farmers as cattle fodder for 3,000 years up until the early 19th century.
But while elsewhere in Africa farmers preferred the high-yielding six-row variety, generations of Qasr Ibrim settlers grew barley with two-rowed spikelets. Six-row barley evolved from the two-row variety 8,000 years ago, owing to a single mutation in the Vrs1 gene. Thanks to this small change, six-row barley produces up to 3 times as many grains as its ancestor and has higher protein content, making it more appealing as a crop.
'This study can lead to the development of new crop varieties better prepared to deal with today's climate change challenges.'
Dr Robin Allaby,
University of Warwick
The reasons for the Qasr Ibrim preference for two-row barley, consistent over millennia, were a mystery. Dr Robin Allaby, who researches the evolution of domesticated plants at the University of Warwick, was gripped by the puzzle.
To find the answer, Allaby and his team extracted DNA from two-row barley grains sampled from all stages of the Qasr Ibrim occupation - Napatan, Roman, Meroitic, Christian and Islamic. They were able to recover DNA from 2,900 year-old samples because the dry climate of the area protected the grains from rot.
The results were 'surprising': the team found that the Qasr Ibrim's two-row barley is unique because it evolved from a six-row ancestor. These grains carry a gene that cancels the effect of the previous mutation, which led to the growth of six-rowed spikelets. This is the first ever report of two-row barley evolving from a six-row variety.
'Since six-row barley is more prolific and produces much more grain, it's difficult for the two-row plants to prevail, unless there is strong natural selection pressure to favour this condition,' says Allaby.
It's unlikely that the farmers wilfully decided to grow two-rowed barley, because the six row variety produces much higher yields, so the reasons behind the selection must be related to local environment, he suggests. One possibility is water stress.
Allaby explains: 'Qasr Ibrim is located in the upper Nile which is very arid relative to the lower Nile where six-row remains are found, and we know from previous studies that two-row barley can survive water stress better than the six-row variety.'
The findings, published last week in the journal PLoS One, have an important implication: 'If these ancient crops are indeed better adapted to arid conditions,' says Allaby, 'the study of their DNA can lead to the development of new crop varieties better prepared to deal with today's climate change challenges.'
Palmer SA, Moore JD, Clapham AJ, Rose P, Allaby RG, 2009 Archaeogenetic Evidence of Ancient Nubian Barley Evolution from Six to Two-Row Indicates Local Adaptation. PLoS ONE 4(7): e6301. doi:10.1371/journal.pone.0006301. Available online 22 July 2009
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