Identification of Quantitative Trait Loci (QTLs) Conferring Dry Matter Content and Starch Content in Cassava (Manihot esculenta Crantz)

Abstract

Cassava tubers are an excellent source of carbohydrate and a competitive source of starch most traded internationally. It is a highly desirable raw material for food and industrial purpose due to its high dietary carbohydrate content. The economic value of cassava products lies in the DMC (dry matter content). Cassava roots contain up to 80-90 per cent of carbohydrate by dry weight and 80 per cent of carbohydrate is starch. Increasing world population, limited land area, changing climatic condition and food scarcity demanded the need for improved cassava starch. Yield of cassava tubers is related to both tuber volume and DMC and thus DMC can be improved by cassava breeding. Thus QTL mapping of DMC is very much relevant to understand the genetic effects controlling the traits. The current study focused on QTL mapping for DMC and SC (starch content) to identify and study the favourite alleles using Windows cartographer version 2.5. Single marker analysis (SMA) identified seven marker alleles associated with DMC and eight marker alleles associated with SC. Using interval mapping, a single QTL for DMC was identified in chrom21 flanked by SSRY110b and SSRY182b. On the other hand, five QTLs for SC were identified by simple interval mapping (SIM) and a single QTL in chrom17 with R2 value of 12% and at a LOD value 5 using composite interval mapping (CIM). The exact position of the QTLs and its interactions were studied using MIM and the genetic effect of QTLs controlling DMC was found to be over-dominance. But in the case of SC, the QTL interaction was identified and found to be additive x additive epistatic interaction.