multiparent advanced generation intercross (MAGIC)

It’s all about water and weakness – or strength. The Greek legend has it that Achilles was dipped into River Styx by his mother, Thetis, in order to make him invulnerable. His heel wasn’t covered by the water and he later died of the wound from an arrow that struck his heel.

In our times, this analogy can be applied to chickpeas, where this streetwise tough customer in the crop kingdom that thrives on the most rugged terrains is hamstrung if there is no rain at the critical grain-filling period – its sole Achilles’ heel, when it cannot take the searing heat in the drylands it otherwise thrives in.

But before you read on about the latter-day borrowing of this ancient legend, and science’s quest to heal the hit from heat and to cure the crop’s fatal flaw on water, first, an important aside…

Who’s now calling the shots in chickpea research?

Molecular breeding in Phase I was led by ICRISAT, with country partners in a supporting role. In Phase II, activities are being led by country partners, which also assures sustainability and continuity of the work. ICRISAT is now in a facilitating role, providing training and data, while the research work is now in the hands of country partners.” – Pooran Gaur, Principal Scientist: Chickpea Breeding, ICRISAT.

The facts
Chickpeas are an ancient crop that was first domesticated in central and western Asia. Today, this crop is cultivated in 40 countries and is second only to common beans as the food legume most widely grown by smallholders. The two main types of chickpeas – desi and kabuli – are valuable for both subsistence and cash.

Even for the hardy, times are tough
“Chickpeas are well-known to be drought-tolerant,” says Rajeev K Varshney, Principal Investigator of the project to improve chickpeas work in the Tropical Legumes I Project (TLI). He explains, “The plants are very efficient in using water and possess roots that seek out residual moisture in deeper soil layers.” However, he points out that, with changing climatic conditions, especially in drier areas, terminal drought – when rain does not fall during grain-filling – is the crop’s Achilles’ heel, and principal production constraint.

“Chickpeas are such tough plants that, even for conditions of terminal drought, yields can be increased by improving root characteristics and water-use efficiency,” says Rajeev. The research team has identified several lines with superior traits such as drought tolerance, after screening a set of 300 diverse lines selected based on molecular diversity of large germplasm collections.

VIDEO CLIP: Recipe for chickpea success

Enhancing the genetic makeup to beat the heat
The team went on to develop genomic resources such as molecular markers. With these markers, the team developed a high-density genetic map, and identified a genomic region containing several quantitative trait loci (QTLs), conferring drought tolerance. “QTLs help pinpoint, more specifically, the location of genes that govern particular traits like root length” explains Rajeev.

Longer roots will naturally give the plants a deeper reach into the water table. Root length is the difference between survival and perishing, which is why trees will be left standing on a landscape otherwise laid bare by prolonged drought.

Q for ‘quick’: QTLs speed things along from lab to field, and running with the winners
The discovery of QTLs makes identifying tolerant plants not only easier, but also cheaper and faster. “This means that better-adapted varieties will reach farmers faster, improving food security,” says Rajeev.

Pooran Gaur, GCP’s Product Delivery Coordinator for chickpeas, Principal Scientist for Chickpea Breeding at ICRISAT, and an important collaborator on the TLI project, adds, “We began marker-assisted selection backcrossing (MABC) in Phase I. By 2011, lines were already being evaluated in Ethiopia, India and Kenya. We are now at the stage of singling out the most promising lines.”

Putting chickpeas to the test: Rajeev Varshney (left) and Pooran Gaur (right) inspecting a chickpea field trial.

What was achieved in Phase I, and what outcomes are expected?
Phase I run from mid-2007 to mid-2010, during which time 10 superior lines for improved drought tolerance and insect resistance were identified for Ethiopia, Kenya and India. As well, a total of 1,600 SSR markers and 768 SNPs on GoldenGate assays were developed, along with an expanded DArT array with more than 15,000 features. A high-density reference genetic map and two intraspecific genetic maps were developed.

“We now have materials from marker-assisted backcrossing by using the genomic resources we produced in Phase I. These materials were sent to partners last year [2011]. And because in most cases we have the same people working in TLI as in TLII, this material is being simultaneously evaluated across six to seven locations by all TLI and TLII partners,” says Pooran.

“Preliminary analysis of data is quite encouraging and it seems that we will have drought-tolerant lines soon,” adds Rajeev.

Future work, and who’s now calling the shots in the field
In Phase II, 1,500 SNPs on cost-effective KASPar assays have been developed that have been useful to develop a denser genetic map. In collaboration with University of California–Davis (USA) and the National Institute of Plant Genome Research (India), a physical map has been developed that will help to isolate the genes underlying the QTL region for drought tolerance. A novel molecular breeding approach called marker-assisted recurrent selection (MARS) has been adopted. Over the remaining two years of Phase II, the chickpea work will focus on developing chickpea populations with superior genotypes for drought tolerance through MABC and MARS.

Pooran adds, “Molecular breeding in Phase I was led by ICRISAT, with country partners in a supporting role. In Phase II, activities are being led by country partners, which also assures sustainability and continuity of the work. ICRISAT is now in a facilitating role, providing training and data, while the MABC and MARS aspects are both in the hands of country partners.”

“Another important activity in Phase II is development of multi-parents advanced generation intercross (MAGIC) population that will help generation of genetic populations with enhanced genetic diversity,” says Rajeev.

Partnerships
The chickpea work is led by the International Crops Research Institute for the Semi-Arid Tropics (ICRISAT), working with partners at the Ethiopian Institute of Agricultural Research, Egerton University in Kenya, and the Indian Agricultural Research Institute. Additional collaborators in Phase I included the University of California–Davis (USA), the National Center for Genome Resources (USA) and DArT P/L (Australia).

For more information on the overall work in chickpeas, please contact Rajeev K Varshney, Principal Investigator of the chickpea work.

Video: Featuring Rajeev and partners Fikre Asnake (Ethiopia) and Paul Kimurto (Kenya)