Biology Reference
In-Depth Information
Chapter 15
Marker-Assisted Breeding for Cassava
Mosaic Disease Resistance
E.Okogbenin,I.Moreno,J.Tomkins,C.M.Fauquet,G.Mkamilo,and M.Fregene
Abstract
Cassava, grown primarily for its starchy tuberous root, is the third most important source of calories
in the tropics. Cassava mosaic disease (CMD), caused by cassava mosaic geminiviruses (CMGs),
is the most important viral disease and a major constraint for cassava production in Africa and in
India. The emergence of new viral diseases and the increasing evolutionary capacity of the viruses
and their vectors to adapt and remain highly virulent is a huge challenge to breeding programs.
Molecular markers are valuable tools for understanding the genes and genomes underlying natural
variation. Three sources of CMD resistance have been tagged with the aid of markers ( CMD1 ,
CMD2, and CMD3 ). They have now been deployed via marker-assisted breeding (MAB), with CMD2
being the most widely used in breeding recently. MAB for CMD resistance has been used for
breeding in the absence of the pathogen in the Neotropics, broadening the germplasm base in Africa,
exploring heterosis, transfer of novel traits, and pyramiding of resistance genes, as well as germplasm
screening for parent selection in CMD-resistance breeding in Asia. Initiatives involving BAC (bacterial
artificial chromosome) sequencing for cloning of the CMD2 gene have also been initiated. The ex ante
impact assessment of MAB-developed varieties combining CMD resistance with other key farmer-
desired traits is estimated to be between US$2.89 and US$4.3 billion in Africa alone. Recent genome
sequencing projects in cassava are expected to enhance understanding of the genetic bases of CMD
resistance and allow for their effective deployment toward development of superior CMD-resistant
varieties. This chapter highlights the advances and challenges of marker-assisted breeding in the last
decade, since the discovery of genetic markers for CMD beginning in 2002, and the future prospects
for revolutionizing cassava breeding by combining advanced molecular technologies, high throughput
platforms, and innovative breeding strategies.
ica, is a major source of food for more than 800
million people, mostly in sub-Saharan Africa,
Asia, the Pacific, and South America. It is the
third most important source of calories in the
Introduction
Cassava ( Manihot esculenta Crantz, Family
Euphorbiaceae), which originates in Latin Amer-
 
Search WWH ::




Custom Search