Fine Mapping the High Endosperm Digestibility Trait Using near-Isogenic Lines in Sorghum.

Sorghum (Sorghum bicolor (L). Moench) is used for human consumption in parts of Africa and Asia and as an animal feed mainly in the U.S. Though sorghum grain contains higher amounts of protein than other cereal grains such as wheat and corn, it is not as readily available for enzyme degradation in humans and animals. Starch in the sorghum grain is bound by protein body matrix, it is also less digestible for biofuel production. The reason for the poor protein digestibility is thought to be due to high cysteine residue composition and high degree of disulphide bonds found in the g- kafirins that reside on the periphery of the kafirin containing protein bodies. Sorghum line P850029 has higher protein digestibility (HD) compared to other normal grain sorghum lines, which might be due to rearrangement of kafirins. In the HD line, the γ-kafirins are rearranged in the seed endosperm and the amount of γ-kafirin in the grain is also reduced. A Population derived from P850029 X ‘Sureno’, recombinant inbred lines (RILs) were developed and used in HD QTL identification. A single QTL was identified on chromosome 1 between Xtxp43 and Xtxp329. There are some problems associated with further analysis of the identified QTL in RIL population. QTL resolution is limited and there is confounding effect of other phenotypic traits that are still segregating in the RIL population. To solve these problems QTL identified will be fine mapped using near-isogenic lines (NILs). QTL location can be narrowed to a smaller interval by evaluating a number of NILs that differ for overlapping regions of genome indicated by QTL analysis. NILs contrasting at a QTL can be developed by selection within heterogeneous inbred families (HIFs).  HIFs are lines derived from an inbred that has not reached a high level of homozygosity. Fine mapping on HD QTL on NILs will aid in map based cloning of the HD trait in future.