ABSTRACT

Sorghum [Sorghum bicolor (L.) Moench] is the 5th most important cereal crop globally after wheat, maize, rice and barley (FAO, 2003; FAO and ICRISAT, 1996). This C4 grass is grown in more than 80 countries, mostly in tropical and sub-tropical regions. The average annual sorghum area cultivated amounts to 44 M ha, with an average annual grain production of 63 M tons, and average grain yield of 1.4 t ha-1 (FAO, 2003; FAO and ICRISAT, 1996). Sorghum was domesticated in Ethiopia and part of Congo, with secondary centers of origin in India, Sudan and Nigeria.

Production of sorghum in semi-arid regions of the world is limited by drought. Developing plants that have an advantage under water-limited conditions is a major challenge for sorghum improvement programs globally. There are three distinct stages in which drought affects sorghum: Vegetative (GS1); Pre-Flowering (GS2); and Post-Flowering (GS3). The best characterized form of drought stress tolerance in sorghum during this post-flowering stage of growth is called “stay green.” Stay-green is a drought-tolerance trait in grain sorghum. When water is limited during the grain filling period, genotypes possessing this trait maintain more photosynthetically active leaves compared with genotypes not possessing this trait.

Putative QTL for stay-green trait from B35 have been identified in five recently published studies (Tuinstra et al, 1997: Crasta et al 1999; Xu et al, 2000; Tao et al, 2000 and Subudhi et al 2000); Using the linkage map developed by Bhattramakki et al (2000) identified six genomic regions associated with stay green trait in B35 parent. The identification of these QTL provided us an opportunity for marker assisted breeding (MAB) for introgression of QTL from B35 to recurrent parents.

We aimed at transfer of QTL from B35 to recurrent parents. S35 and ICSV111. Both recurrent parents have been advanced to BC3 and BC4 generations for introgresstion of QTL from donor parent using SSR maker assisted selection (MAS), targeting six QTL detected. In this study, all genotypes in two generations from each recurrent parent were screened with foreground markers to identify the genotypes for QTL of our interest and also screened with background markers to select the genotypes for all other loci from recurrent parent. Selected individuals are advanced to next generation.