Sorghum genome to help improve dryland crops

February 2, 2009
By Syed Akbar
Hyderabad: Unraveling of the sorghum genome will help improve dryland crops
The announcement of the unraveling of the genome of sorghum, one of the mandate crops of the International Crops Research Institute for the Semi-Arid Tropics (ICRISAT), will strengthen the Institute’s research for the improvement of sorghum and other food crops.

The sequencing of the sorghum genome was announced in a scientific article published on 29 January 2009 in the journal Nature. The global team of scientists that reported the genome sequencing was led by Prof Andrew Paterson of the University of Georgia, USA, and included ICRISAT’s Cereal Breeder, Dr C Tom Hash.

Sorghum is the second food crop from the grass family to have its genome fully sequenced. The first one was rice. Sorghum is the first crop with the more efficient C4 photosynthesis system to be sequenced. Sugarcane, maize and pearl millet are other grasses with the C4 photosynthesis system that should benefit from this.

Plants that have a C4 photosynthesis system have a competitive advantage over plants possessing the more common C3 carbon fixation pathway under conditions of drought and high temperatures. While a significant portion of the water taken up by C3 plants is lost through transpiration, this loss is much lower for C4 plants, demonstrating their advantage in a dry environment.

According to Dr William Dar, Director General of ICRISAT, the unraveling of the sorghum genome is the first such breakthrough for a dryland agricultural crop that is adapted to drought. “The sequence of sorghum genome will provide us a better understanding on genes that make sorghum, as compared to other cereals, more drought tolerant.”

ICRISAT will combine the new knowledge on the sorghum genome sequence with its expertise on molecular-marker assisted crop selection and breeding to develop improved sorghum varieties and hybrids for desirable traits, say with improved drought tolerance or improved disease resistance.

Candidate genes identified for drought tolerance or pest resistance can be used to understand natural variation in ICRISAT’s sorghum germplasm collection comprising of more than 36,000 accessions with a final objective to identify superior variants for using in breeding crops.

The genome sequence is already contributing to development of additional molecular markers for economically important sorghum traits, and for identification of specific genes that control them. This in turn is leading to more efficient crop breeding methods – particularly those based on marker-assisted selection for naturally occurring genetic variation – which will reduce the time required to develop grain, forage, and sweet sorghum varieties and hybrids having improved agronomic performance, stress tolerance, pest resistance and product quality.

The availability of genome sequence data should enhance genomics-assisted breeding in sorghum. For instance, a few hundred molecular markers, genomics tools that are used in marker-assisted selection, were available in sorghum until 2 to 3 years ago; genome sequence data has now provided more than 71,000 microsatellite marker candidates.

“We believe that availability of genome sequence combined with modern genomics approaches should boost our breeding activities to develop the desirable breeding lines. Genes identified in sorghum would not be useful only for sorghum but other cereal/plant species as well, especially for enhancing drought tolerance,” Dr Dar said.

The paper published in Nature shows that different cereals such as rice, wheat, barley, maize, sorghum and pearl millet show similarities in gene number and gene order, since they derived from a common ancestor. This allows the use of genomic resources from one cereal species to improve another species. For instance, based on the sequence data of sorghum and rice, molecular markers have been developed and are being used in pearl millet, another mandate crop for ICRISAT.

Sorghum, a mandate crop of ICRISAT, is the fifth most important and relatively drought tolerant cereal crop that is the dietary staple of more than 500 million people in more than 30 countries of semi-arid tropics. It is grown on 42 m ha in 98 countries of Africa, Asia, Oceania, and the Americas.

ICRISAT has been working for more than three decades for improving sorghum for food and feed proposes. Furthermore, sweet sorghum has emerged as a feedstock for ethanol production. It gives food/feed, fodder and fuel, without significant trade-offs in any of these uses in a production cycle. ICRISAT has pioneered the sweet sorghum ethanol production technology, and its commercialization.

Having the genome sequence of sorghum is significant landmark of genomics research for sorghum community in particular and biofuel community in general