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CROP PHYSIOLOGY & METABOLISM

Preflowering Abortion Reduces Spikelet Number in Upland Rice (Oryza sativa L.) under Water Stress

^a Field Production Science Center, Graduate School of Agricultural and Life Sciences, Univ. of Tokyo, Nishitokyo, Tokyo 188-0002, Japan
^b Asian Natural Environmental Science Center, Univ. of Tokyo, Nishitokyo, Tokyo 188-0002, Japan

^* Corresponding author (junya{at}fm.a.u-tokyo.ac.jp).

Spikelet number per panicle is a major target trait for improving rice (Oryza sativa L.) yield in upland fields and is strongly affected by water stress. The rice panicle consists of rachis branches and spikelets, in which preflowering spikelet abortion often occurs. We investigated the effect of timing and intensity of water stress at the early reproductive stage on the morphology of rice panicles in field and pot experiments. In the field experiment, water stress caused high rates of preflowering spikelet abortion, and spikelet number was reduced by 48% on average. Pot experiments revealed the effects of water stress on panicle morphology were dependent on the developmental stage, and water stress at the meiosis stage (10–20 d before heading) induced the highest frequency of preflowering spikelet abortion. At the meiosis stage, a mild water stress (no visible effect and less than 20% reduction in biomass production) was sufficient to cause a considerable increase in secondary rachis branch abortion (70%) and resulted in a 40 to 45% reduction in spikelet number per panicle. Reduction in plant water status under drought conditions was related to preflowering spikelet abortion, suggesting that the drought avoidance mechanism is effective for maintaining spikelet number in upland rice.

Abbreviations: DAH, days after heading • PB, primary rachis branches • SB, secondary rachis branches • SB/PB, the ratio of the number of SB to the number of PB • SSPP, survived spikelets per panicle • TLS, terminal and lateral spikelets on each primary rachis branch