Overview

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Cassava, a herbaceous plant of the family Euphorbiaceae, is an important food crop in the tropics and subtropics. Cassava together with potato and sweet potato is known as the world's three major potato crops, and it is also one of the top sixth food crops in the world after sugarcane, corn, rice, wheat and potato. It is praised as "the underground granary" and "the king of starch suppliers". For the fine characteristics of drought resistance, barren resistance, strong disease and insect resistance, flexible growth cycle and simple field management, cassava is better suited for field cultivation than other crops.

Geographical Distribution

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Cassava originated in South America,which cultivation can be traced back to over 4,000 years ago since it was firstly domesticated in Brazil. It was introduced into China in 1820. Nowadays, cassava is mainly planted in Nigeria, Bolivia, the Republic of Congo, Brazil, Mexico, Thailand, Indonesia and so on, mostly in African countries, which accounts for up to 60% of all areas.

In China, cassava cultivation is mainly distributed in Guangdong, Guangxi and Hainan, followed by Fujian, Yunnan, Jiangxi and Hunan provinces. And there is also a small number of trial plantings in Sichuan, Guizhou and Chongqing.

Application

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• Edible use: For the abundance of starch, cassava becomes the staple food for nearly 700 million people.
• Feed use: The whole plant of cassava, including roots, leaves and tender stems, as well as the cassava residue and peel by-products from the processing industry, can be used as raw materials for animal feed processing and production.
• Energy supply: For the impressive efficiency of alcohol productivity, cassava is widely used in the production of alcohol and fuel ethanol.
• Other industrial raw materials: There are more than a dozen processed products and deep-processed products of cassava, such as modified starch, edible alcohol, cassava protein, enzyme preparations, glucose, organic chemical products and so on.
• Health care: Cassava is rich in dietary fiber, which helps to cleanse the intestines and keep the digestive system healthy. It also provides important benefits in the prevention and treatment of constipation, coronary heart disease, hypertension, diabetes and other chronic diseases.

Genome sequencing

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The Joint Genome Institute of the U.S. Department of Energy, in collaboration with the University of Arizona and other organizations, completed the assembly of the reference genome for the inbred cassava cultivar AM560-2 in 2012. This study utilized the 454 whole-genome shotgun sequencing method, generating a total of 22.4 billion base pairs of raw sequence data, which provided approximately 29-fold coverage of the genome. Ultimately, a total of 12,977 scaffolds were assembled, 30,666 protein-coding genes were annotated, and 3,485 alternative splicing sites were identified.

The genomes of cassava wild subspecies W14 and cultivar KU50 were completed under the leadership of the Chinese Academy of Tropical Agricultural Sciences and analyzed in comparison with the previously reported AM560 genome sequence. The study utilized Illumina HiSeq2000 and Roche 454 GSFLX sequencing technologies, resulting in 76.32 Gb reads for W14 and 34.43 Gb reads for KU50. The genome sizes of W14 and KU50 were 742 Mb and 495 Mb, respectively, with sequencing coverage of 58.2% and 66.7%. The N50 values for the assembled genomes were 43 kb for W14 and 19 kb for KU50. Additionally, the study identified a total of 34,483 and 38,845 annotated protein-coding genes for W14 and KU50, respectively.

The cassava variety SC205 plays a significant role in cassava breeding in China, and its reference genome was successfully completed under the leadership of the Chinese Academy of Tropical Agricultural Sciences. The reference genome was assembled using Pacific Biosciences long reads technology with a coverage of 98.5× and Hi-C mapping technology with a coverage of 35.0×, resulting in a high-quality reference genome sequence of 710.1Mb. The study identified a total of 37,923 protein-coding genes and 50,046 transcripts in the SC205 genome. Notably, the newly assembled cassava SC205 genome exhibited a 41-fold increase in contiguity and a 38-fold decrease in the number of gaps compared to the previously published AM56 genome.

Reference

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