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Although the sensitivity of crop species to water stress during reproductive growth stages is well documented, the causes of sterility are not understood. The role of decreased panicle exsertion as a causal factor of spikelet sterility in water stressed rice ( Oryza sativa L.) was investigated. Rice cultivar IR36 was grown on a deep silty loam soil under full sprinkler irrigation for 77 days. A line source sprinkler system was then utilized during panicle exsertion and flowering to impose six continuously decreasing irrigation treatments. After the 15‐day treatment period, full sprinkler irrigation was resumed until maturity. Soil moisture extraction and plant water potential were monitored as soil and plant water stress progressed. Panicle exsertion rate was measured on tagged panicles which were later used to assess percent final panicle exsertion and percent sterility. The six irrigation treatments varied in grain yield from 5.0 t ha −1 to about 1 t ha −1 with corresponding increases in spikelet sterility of 16.6 and 74.2%. Panicle exsertion rate decreased linearly with decreasing mean daily leaf water potential. The degree of final panicle exsertion from the flagleaf sheath and percent spikelet sterility both decreased linearly with panicle exsertion rate. All spikelets left unexserted from the flagleaf sheath were sterile. Panicle exsertion rate was slightly confounded by tiller age in that late tillers in the well irrigated treatment had a slower exsertion rate and higher percent sterility than earlier tillers. The early tillers which exserted at rates of 4.5 to 5.5 cm day −1 under well watered conditions decreased to about 3.0 cm day −1 in the stressed plot and accounted for 25 to 30% spikelet sterility in the severely stressed treatment.
O’Toole et al. (Tue,) studied this question.