DAR ES SALAAM, Aug. 23 (Xinhua) -- Scientists at the International Institute of Tropical Agriculture (IITA) have identified the genetic markers associated with resistance to two deadly cassava viral diseases in two varieties of the crop from Tanzania, the IITA said in a statement on Wednesday.
The two cassava varieties, Namikonga and Albert, grown by farmers in Tanzania, are known to be able to withstand the devastating Cassava Brown Streak Disease (CBSD) and Cassava Mosaic Disease (CMD), respectively.
The statement said a team of IITA scientists that has been studying the DNA of the two cassava varieties have successfully identified the genetic markers linked to their resistance to each of the viral disease.
"The markers can be used to speed up the often long and expensive conventional breeding for cassava varieties with dual resistance to the diseases," said the statement.
Namikonga and Albert, which are genetically related, have been grown by farmers in areas that are hotspots for the two viral diseases for many decades and have shown high resistance despite being subjected to the diseases for a long period, said the statement.
It said Namikonga was tolerant to CBSD but highly susceptible to CMD while in contrast, Albert was highly susceptible to CBSD but resistant to CMD.
The statement said the international team, drawing scientists from Tanzania, Kenya, South Africa, and the United States, crossed the two Tanzanian varieties and studied a large population of the progeny over two seasons in two disease hotspot areas in the country.
They detected the main resistance to CBSD on chromosomes 2 and 11 and that of CMD on chromosome 12. The statement also said several other genomic regions in different chromosomes had a minor influence on the expressed resistance.
CMD and CBSD are among the greatest constraints to cassava production crop in East, Central and Southern Africa where cassava is a major crop for both food and income for millions of small-holder farmers as nearly all cassava varieties grown by farmers are susceptible to either one or both diseases.
In Tanzania, the second largest producer of cassava in East Africa after Uganda, the diseases have reduced cassava yield from 10.5 tonnes per hectare to only 5.5 tonnes in the last twenty years, said the statement.
Efforts to control the diseases in East Africa were initiated in the early 1930s at the East African Cassava Research Institute at Amani in northeastern Tanzania.