New Delhi: It took the best scientific minds from
20 nations, including India, to scale what is considered as the "Mt.
Everest of the genome world".
After 13 years of painstaking effort, a global community of scientists has decoded the gigantic bread wheat genome (Chinese Spring variety), a feat that breeders hope will help address the productivity and climate resilience issues, especially in India, which is the world's second-largest producer of the grain.
The group of scientists known as the International Wheat Genome Sequencing Consortium (IWGSC) published in August 2018 a detailed description of the genome of bread wheat, the world's most widely cultivated crop.
Wheat is the staple food of more than a third of the global human population and accounts for almost 20 percent of the total calories and protein consumed by humans worldwide, more than any other single food source. It also serves as an important source of vitamins and minerals, according to a IWGSC press release.
The reference genome provides a roadmap to improve and innovate the crop just like the advances that rice (Oryza sativa L.) had witnessed, following the unravelling of its genome in 2005. Rice was the first crop genome that was sequenced.
"The high quality reference genome generated by the global community will help in better understanding of the basic biology of wheat plant and identifying genes underlying important traits," Kuldeep Singh, senior molecular geneticist and director of National Bureau of Plant Genetic Resources, told Mongabay-India.
This achievement will enhance the wheat breeders' toolbox and pave the way for development of wheat varieties with higher yields, enhanced nutritional quality, improved sustainability and varieties that are better adapted to climate challenges, said Singh.
Singh (formerly with the Punjab Agricultural University), Nagendra Singh at ICAR-National Research Centre on Plant Biotechnology, New Delhi and J.P. Khurana at the University of Delhi, spearheaded the Indian effort (comprising 18 scientists) to sequence chromosome 2A of the genome.
Wheat cultivation in India has been traditionally dominated by the northern region.
Singh explained that the major challenges to wheat productivity in future in India will pertain to enhancing yields by 2050 and accelerating the breeding of climate-resilient wheat varieties.
"One challenge is to improve its yields by 60-70 percent in next 32 years (by 2050) when India's population stabilises at 1.66 billion. This translates to roughly two percent per annum and our current rate of improvement is 1-1.5 percent," Singh said.
The other aspect is developing varieties which, during their growth period, can tolerate higher and more erratic temperatures due to climate change, are resistant to emerging diseases and insects, require less water and other inputs including major and micronutrients and are nutritionally richer.
The challenge of ozone pollution
In addition, ozone pollution is also identified as a "significant challenge" to global food production, including wheat growth, in a recent multinational study led researchers from the UK-based Centre for Ecology & Hydrology (CEH).
For the state with the highest wheat production, Uttar Pradesh, predicted percentage yield losses due to ozone were in the range of 15 percent to 20 percent in most of the wheat-producing areas.
"We show that the impact of ozone on wheat yield is at a comparable level to pressures from other stresses in some areas of India. Also, the area of highest ozone impacts on wheat production coincided with an area with high levels of heat stress too," CEH's Katrina Sharps and co-author of the study told Mongabay-India.
The authors identified practical, short-term actions such as breeding new varieties of crop that are more resilient to ozone, better timing of irrigation and the development of non-toxic agrochemicals, that farmers and growers can take to improve crop yields.
In this regard, Kent Burkey, of the United States Agricultural Research Service (USDA-ARS) and a co-author of the ozone pollution study, said, knowing the wheat genome sequence could contribute to breeding more ozone resilient varieties by helping to identify specific genes located in the genome near known DNA markers associated with ozone tolerance.
"Manipulating the function and regulation of these specific genes would be a targeted approach to enhance ozone tolerance. However, this may not be a straightforward process because the ozone-tolerance trait may involve more than one gene," Burkey said.
Climbing Mt. Everest
Cracking the genome itself came with its own set of hurdles: the enormity of the genome and its complexity. At 17 Giga bases, the bread wheat genome is five times as large as the human genome and 40 fold larger than the rice genome.
This is because bread wheat essentially is three species rolled into one, said Singh.
Bread wheat is an allopolyploid - which means it has evolved in nature by the natural crossing of three different but very closely related species, each contributing seven pairs of chromosomes which are referred to as A, B and D genomes, making a total of 21 pairs of chromosomes.
"Hence major challenges were to bring together larger number of countries and resources for undertaking this gigantic task. However, technological advances in flow cytometry-based sorting of individual chromosomes, high throughput DNA sequencing techniques and improved algorithms made it possible for the international community to achieve this task at a cost much lower than it was achieved for in human or rice genomes," Singh explained.
Adding precision to India's wheat breeding programme
For India, which has a robust wheat breeding programme and more than 500 varieties, the genome sequence adds precision to the breeding programme.
Singh highlighted that India has different agroecological zones and different climatic conditions and therefore varieties suited to specific zones and climate.
"For example, we have northwestern plains (Punjab, Haryana, parts of Rajasthan) that have a different variety, for eastern India we have a different variety and so on and so forth," Singh noted.
"Because of the agroecological zones and climate and our robust wheat breeding programme we have all sorts of varieties such as high input irrigation condition, rain fed conditions. So far we have more than 500 varieties. With the genome sequence, use of new technologies would add precision to the breeding programme and it makes it possible to bring together genes which was not possible with conventional breeding," Singh elaborated.