Marker assisted transfer of stay-green trait of sorghum to enhance terminal drought tolerance: candidate donor and recipient genotypes

Delaying leaf senescence is an effective strategy for increasing cereal production under water-limited conditions.To identify candidate donor and recipient genotypes, a set of four non-senescent (stay green) genotypes and 9 local Farmer Preferred Varieties (FPVs) of sorghum bicolor (L.) Moench were evaluated for pattern of pre and post flowering leaf senescence and molecular polymorphism. The experiment was conducted at Agricultural Research Corporation (ARC) during the off season of 2005 in split plot design with four replications. Three watering regimes were applied; frequent irrigation as recommended (control), water stoppage after 4 irrigations (pre-flowering drought) and complete water stoppage after flowering (post flowering drought). Molecular polymorphism was assessed using 15 RAPD and 20 SSR markers. All of tested FPVs and two of the stay-green donors had not survived pre-flowering drought stress. The remaining two stay-green donors (B35 and SC56) could only produce harvest after supplementary irrigation. There was significant difference among FPVs and stay-green donors in their post flowering drought tolerance. B35 and SC56 gave significantly higher tolerance index 0.89 and 0.67, respectively, while Tabat, Wad Ahmed and Arus Elrimal were intermediate with tolerance index ranging from 0.42 to 0.51. The remaining FPVs were post flowering drought sensitive with tolerance index ranging from 0.15 to 0.28. Chlorophyll content and greenness were significantly higher in B35 and SC56 after post flowering drought stress. Combination of RAPD and SSR markers indicated separate clusters of FPVs, B35 and SC56. However, 20% of the used SSRs were common. Combining drought tolerance and molecular data, Tabat and Wad Ahmed were chosen to receive the stay-green trait from B35 and SC56 as the first and second choice, respectively. F1 crosses were made to proceed for first backcrossing and genotyping using the identified polymorphic SSR markers