Crop lmprovement 37 (2) : 93-99 (2010) STRATEGIES TO IMPROVE POSTFLOWERING DROUGHT TOLERANCE IN FIAB'SORGHUM FORPREDICTED CLIMATE CHANGESCENARIO H.S.TALWAR-, PRABHAKAR, M. ELANGOVAN, ARUNAKUMABI,S.S. RAO. J.S. MISHRAAND J.V. PATIL Directorate of SorghumResearch, Rajenderanagar, Hyderabad, SO0 OS0 ' ta lwa r @ so rg hum.res. n ABSTRACT The experiments were conducted.durlng rabiseasone of 2007-08, 2oog-09 and 2oog-10 to screen the promlsing germplasm, advanced breedlng -llnes and landraces to iden ty the new sources "nj1;i" """o"1"t"0 ,itl, posttlowering drought iolerance in sorghum. Th6crop r"" "oiln underlrrigated "na un.ii.ls"iJ condition to examine thepotential ot sorghum-genotypes to-.adapt 6 theposttlowering drought. lmproved sources (pEc12, Ep 87'EP 57'sLB 9, sLR andRSLG 2€2) for postftowering arougtrt iolerance have been identilied In terms of higher grain yield, biomass and gre€n lear area retentlon. sigrilficant-and positive relationships of spAD chlorophy meter reading (scMR) with totaldry mater (R'i=0.67) andg-raln yietd 1*'=o.az1 suggests thii set-"iion-u"ing scMRwitl have 42-67'/' ptobabitity In selecting genotypes withtrlgh"r tot"t dry .ater rnd grain yield. Most appropriate stage to screen for postflowering drought tolelance_on theba-isof green Laf area tet -ntion ist"y g;i iia'it) is arouna so days after flowering. spectfic leaf welght (slw) increaseo stg-nifltanily unoer un-trrigJtea'ai'coifireo to irag"teo conditions in all the genotypes suggestlng increas€ In leatihickn;ss und6r molsture stress condiuons. posiiive relationships between percent increase in SLwunder stress conditions ano yietd components Indicatethat increase in leafthlckness is anlmportant adaptlve traitto postttowering drought. Thes" r""uitJ"on"iu j""l-ri"l-scr,,rn ""n o" used as a surogate measurement ot staygrean traitandincrease ii stw unoer resiauai moisturelonoitions is a potential selectlon criteria tor postflowering drought tolerance in rabi sorghum. Key words: Postflowering drought, SpAD chlorophy meter reading, speciric lea, weight, sorghum. Sorghum (Sorghum bicolor(L ) Moench)ranks fifth among the world'smost important crops. lts current world production stands at 64.6 million tonnes while in India current production is 7.4 million tonnes. In India, sorghum is cultivated in both rainy and postrainy (rabi) season, mainly as a rainfed cropwithabout gS% of the production concentrated in Maharashtra, Karnataka and Andhra Pradesh. The national average productivity of sorghumis very low (880 kg/ha). During postrainy season, sorghum is cultivated predominanily on residual soil moisture. Postflowering drought is a regular feature and is the majorproduction constraint that adversely affects the cropgrowth and grainyield. with the threat of climate change looming large on the crop productivity, the most vulnerable regions of the world are the tropics particularly the semi-arid regionswhere higher temperature and increase in rainfall variability would aggravate the situation and would lead to frequent droughts. Climate changeimpact on rabi sorghum is projected to reduce the yield upto 7yo by 2020, upto 11o/o by 2050 and upto gO% by 20g0. superior genetic resources are required to reduce the risk of lossesin productivity due to postflowering drought. This requires the identification of easily measureable and costeffective traits related to terminal drought tolerance. staygreen or delayed senescence is a trait associated withpostflowering droughttolerance (Subudhi et al. 2000). Sorghum genotypes with staygreen traitcontinue to fill theirgrain normally even underwater deficit conditions (Borrel et al.2000). Previously, superiorsources of staygreen trait have been identified (Mahalaxmiand Bidinger zooz)and this trait is currently usedfor erl identification in sorghum. Stay-green has been described as the best characterized trait contributing to the adaptation of sorghum to terminal drought conditions, i.e. conditions of water deficitthat usuallyoccur duringand after f lowering (Rosenow and Clark, 1gg1). yet, the physiological mechanisms behind the expression of a stay-green phenotype are stiil not clear. Further,