PLINY THE ELDER, a Roman administrator with a sideline in philosophy, appreciated the complexities of the chickpea. In his master work, “Naturalis Historia”, he wrote of it: “This plant presents considerable differences in reference to size, colour, form and taste.” One type, he reported, came in the shape of a ram’s head. Another, the Venus pea, was white, round and smooth. A third had small, angular seeds.
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These days, chickpeas are still as varied, though the main types now recognised are the large, light-coloured Kabuli and the smaller, darker Desi. They are grown in more than 50 countries, particularly in Asia and Africa, and contribute 11.5m tonnes of protein-rich pulses to the world’s food supply, making them the third most productive leguminous food crop, after beans and peas. But their variety is under-exploited, and much of it is found in poorly studied “landraces”—local varieties that have some genetic coherence but are not as selectively bred as modern cultivars.
Recognising this, a group of researchers from the International Crops Research Institute for the Semi-Arid Tropics (ICRISAT) and 40 other organisations, led by Rajeev Varshney of Murdoch University, in Australia, have produced a comprehensive “pan-genome” derived from the cultivated plant, Cicer arietinum, and seven of its wild relatives, which they have now published in Nature. One of their purposes was to identify blocks of genes, called haplotypes, that encode particular, desirable properties, and which could be bolted together in various combinations to yield both better chickpeas overall, and chickpeas better suited to particular sets of circumstances. In a world where circumstances are changing rapidly, that matters. A study published in 2016, for example, estimated that shifts in temperature and rainfall patterns could, by 2069, decrease chickpea yield in parts of the world by almost 20%.
Building on an initial map of more than 28,000 chickpea genes, published by ICRISAT in 2013, Dr Varshney’s team sequenced 3,171 cultivated chickpeas and 195 wild examples taken from collections around the world. That added 1,582 previously unknown genes to the list, including ones that encode responses to environmental factors such as cold, acidity and oxidative stress. The result is the most comprehensive genetic map of any vegetable species.
Crucially, the samples came with useful data about the characteristics of the plants they were taken from, known in the argot as their phenotype. That allowed the team to cross-correlate between genotype and phenotype, identifying which bits of the former appeared responsible for what parts of the latter. As a consequence, they think they have identified 24 haplotypes that do useful things like increasing seed weight, improving yield per plant and reducing the time it takes for a plant to become mature enough to flower.
Looking back at the original collections, they found around 80% of cultivars lacked these beneficial blocks of genes, suggesting there was considerable room for improvement. Knowing exactly which genes are involved means the process of breeding in those improvements can be done quickly. Instead of waiting for a plant to grow and mature, you can check its genes shortly after it has germinated, and throw it away if you do not want it.
Upgrades suitably developed, the question will be how to get them into the wider world. Dr Varshney says that big agricultural and seed companies tend to have limited interest in chickpeas. That means more reliance on smaller firms and co-operatives for distribution. If this can be done, though, the humble chickpea will join the big boys like rice and soyabeans as crops whose genes have been analysed for the betterment of human nutrition. ■
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This article appeared in the Science & technology section of the print edition under the headline "Chick-please"
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