The sweetpotato is a staple for millions worldwide, particularly in sub-Saharan Africa, where its tolerance to climate extremes supports food security. Researchers have now decoded its complex genome, providing new tools for targeted crop improvement.
Unlike humans, who have two sets of chromosomes, sweetpotatoes have six. This genetic condition, known as hexaploidy, has long complicated sequencing efforts. A team led by Professor Zhangjun Fei at the Boyce Thompson Institute, as reported in Nature Plants, has now completed the first fully phased genome of 'Tanzania', a variety valued in Africa for disease resistance and high dry matter content.
The main challenge was to map the plant's 90 chromosomes into their six original haplotype sets. "Having this complete, phased genome gives us an unprecedented level of clarity," said Fei. "It allows us to read the sweet potato's genetic story with incredible detail."
Analysis revealed that the sweetpotato genome is a mosaic from multiple wild ancestors. About one-third originates from Ipomoea aequatoriensis, a wild species from Ecuador, thought to be a direct descendant of one progenitor. Another portion resembles the Central American species Ipomoea batatas 4x, though the exact donor has not yet been identified.
"Unlike what we see in wheat, where ancestral contributions can be found in distinct genome sections," said Shan Wu, the study's first author, "in sweetpotato, the ancestral sequences are intertwined on the same chromosomes, creating a unique genomic architecture."
This genetic structure supports the classification of sweetpotato as a segmental allopolyploid, a hybrid from different species that functions genetically as if it originated from one. The recombination of multiple genomes may contribute to its adaptability and disease resistance. Fei noted that having six chromosome sets allows for multiple versions of important genes, providing redundancy that can help the plant withstand drought, pests, and varying environmental conditions.
The researchers note that to fully understand sweetpotato's genetic diversity, further sequencing of varieties from different regions will be necessary, as some genetic traits may have been lost in certain lines.
The genome mapping is expected to help plant breeders more precisely locate and use genes controlling yield, nutritional value, and resistance to drought and disease. The methods applied in this work also have relevance for other polyploid crops such as wheat, cotton, and banana.
As climate change and pest pressures increase, such genomic insights may assist in developing improved cultivars for food production systems.
Source: BTI Science