J. Plantation Crops. 29: 10-15 (2001).
Breeding for rust resistance in coffee: The gene pyramid model
In the international trade of commodities, coffee occupies a place of pride, next to petroleum, in trade volume and money value. For India, coffee exports earn about Rs.15 billion annually. Many third world economies depend on the earning from this important crop. Leaf rust caused by Hemileia vastatrix is a disease of economic significance on Arabica coffee. About 32 races of this pathogen are known. Almost all coffee research institutions in the world are engaged in breeding rust resistant strains of Coffea arabica. There are nine known genes (symbolized SH1 – SH9), which condition race specific resistance of the host plant. Many combinations of these genes were already known to have been overcome by races of the rust fungus. Hibrido de Timor (HDT) is the singular genotype that remained resistant to all known races. It has a unique genotype (SH6,7,8,9) which is the probable cause of this manifestation. Gene pyramiding is conceived to be able to impart long lasting resistance to this classic disease, and a model combining all known and unknown resistance genes is presented in this paper. Involving a variety of interspecific hybrids manifesting resistance conditioned by the elements of vertical resistance, and wild arabicas with horizontal resistance, and dwarf/semi-dwarf genotypes conditioned by dominant genes, is proposed to derive a resistant plant population carrying the necessary genetic diversity and uniform plant type. Integrating vegetative multiplication in the breeding scheme makes this commercially viable by way of eliminating segregation for plant type as well as resistance.