Genetic mapping of the cassava genes involved in cyanogenesis

Danish title: Genetisk kortlægning af de gener i cassava der er involverede i dannelse og nedbrydnng af cyanogene glucosider. 

 

A molecular genetic map for cassava is being developed for cassava at Centro Internacional Agricultura Tropicale (CIAT), Cali, Columbia. Genes controlling various traits of agronomic interest, including resistance to disease, pests and early yield have been identified on the map. The development of this map has been possible through support from Danida. We now want to locate the genes responsible for cyanogenesis in cassava on this map to provide a basis for molecular breeding towards cassava varieties with reduced cyanogenic glucoside content.

The effort to map and associate the two cytochrome P450 genes CYP79D1 and CYP79D2 with linamarin content has been initiated using an S1 family, AM320, derived from the high cyanogenic glucoside variety MTAI8. The use of an S1 family ensures that all possible gene actions are captured in the search for QTLs and markers associated with Cyanogenic Potential (CNP). Currently, the S1 family AM320 derived from MTAI-8 is being genotyped with more than 800 DArTs markers and 200 SSRs markers for gene tagging and QTL analysis of cyanogenic glucosides. The frequency distribution of cyanogenic content (measured as CNP) in the leaves and roots suggests a polygenic control of the trait. In the leaves, 5% of individuals have below 1075 ppm, 85% have between 1075-3048 ppm, and 10% 3049-5071 ppm. In roots, 11% have below 258 ppm, 76% between 259-878 ppm and 13% 880 - 1294 ppm.

The restriction enzyme EcoRI revealed polymorphism in the parent MTAI-8 that segregated in the progeny AM320 for both CYP79D1 and CYP79D2. Simple regression analysis with the cyanogenic glucoside trait phenotype and genetic mapping is ongoing. About 80 SSR markers have been mapped in the progeny while additional SSR and DArT marker analyses are in progress. Once the map has been completed, QTL analysis of cyanogenic potential (CNP) and a search for association between the cytochrome P450 genes and CNP will be conducted. Markers found associated with CNP will be used to select early and more efficiently for the trait in breeding programs to reduce the amount of cyanogenic glucosides in cassava.

In a parallel approach, genetic crosses of high protein cassava varieties are being made to elite parents of the CIAT cassava gene pools for breeding high protein content and for QTL mapping studies. Further classical breeding will take place at CIAT and in Mozambique.

 

Researchers involved: Kirsten Jørgensen, Birger Lindberg Møller

 

Foreign collaborators: Edgar Barrera Sabogal, Ana Maria Correa Morales and Martin Fregene, all from Centro Internacional Agricultura Tropicale (CIAT), Cali, Columbia 

 

Financial support: Research Council for Technology and Production, Danida, Danish National Research Foundation