The period from booting to flowering is the most sensitive stage to high temperature stress (HTS) in rice. The present study was aimed to improve the high temperature stress tolerance in Improved White Ponni. QTLs controlling spikelet fertility under HTS namely qHTSF 1.1 and qHTSF 4.1 was targeted for introgression from a tolerant donor Nagina 22 (N22) into Improved White Ponni (IWP) through marker assisted breeding. Number of spikelets opened per day and total flower count was taken at the time intervals (09.00 am, 11.00 am and 01.00 pm). Time taken to complete flowering was studied under control and stress conditions. The QTL introgressed lines had maximum flowering at 09.00 am and quickened the flowering period under high temperature stress which was induced using open top chambers maintained at temperatures ranging from 37.10ºC to 41.20ºC. Rice lines (# 295, 277 and 246) which contained both the QTLs for spikelet fertility had very less spikelet sterility percentage.
Key Words: Rice, High temperature stress, QTLs, Spikelet fertility, Yield