Evaluation of drought tolerance in forage sorghum (Sorghum bicolor L. Moench) promising lines

To evaluate the drought tolerance in forage sorghum promising lines, a filed experiment was conducted as split plot arrangement using randomized complete block design (RCBD) with three replications at the Research Farm of Seed and Plant Improvement Institute, Karaj, Iran, in 2011 and 2012 growing seasons. Main plots consisted of three irrigation regimes (irrigation after 60, 120 and 180 mm evaporation from class-A Pan) and sub-plots included five forage sorghum promising lines (KFS2, KFS3, KFS12, KFS17 and KFS18). Combined analysis of variance showed that the effect of irrigation regimes on fresh and dry forage yield and plant height was significant (P ≤ 0.01). Under sever drought stress the highest forage yield was obtained from KFS3, KFS2 and KFS18 lines (112.3, 97.5 and 95.9 t.ha-1 respectively). Results revealed that stress tolerance index (STI), geometric mean productivity (GMP) and mean productivity (MP) indexes had significant positive correlations with forage yield under stress and non-stress conditions and were identified as suitable indices for screening of forage sorghum promising lines. The results of biplot analysis indicated that KFS3 line with the highest STI (1.18) had high forage yield potential and low susceptibility to drought stress. The results of multivariate biplot analysis and correlation of indices using forage yield data under stress and non-stress conditions showed that MP, GMP and STI were the suitable indices for predicting forage yield of sorghum promising lines and superior genotypes could be selected based on these indices. KFS3 promising line was identified as highly adpated forage sorghum genotype to drought stress condition.