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Phasic Development of Rice Seedlings

Rice-FACE Project, Natl. Inst. of Agro-Environmental Sciences, Sciences, 3-1-1 Kannondai, Tsukuba, Ibaraki 305, Japan;
Agric. and Biol. Engr. Dep., Univ. of Florida, Frazier Rogers Hall, P.O. Box 110570, Gainesville, FL 32611-0570;
Dep. of Agric., Univ. of Reading, Earley Gate, P.O. Box 236, Reading RG62AT, England.

^* Corresponding author (msalam{at}ss.niaes.affrc.go.jp).

A better understanding of growth and developmental processes of rice (Oryza saliva L.) seedlings is necessary for crop management and modeling perspectives. This experiment was conducted to identify preautotrophic phases of rice seedlings, quantify seed dry matter mobilization and utilization, characterize dry matter partitioning during early growth, and observe if these processes are affected by cultivar and seed size. Seeds of two cultivars, each separated into two seed sizes, were sown in a greenhouse using field soil, and observations on seed weight loss and seedling weight gain were recorded daily for 27 d. The durations of heterotrophic and transition phases were determined as 74 and 247 thermal units (base temperature 9°C), respectively. Seeds lost 0.79 ± 0.010 g g–¹ during the preautotrophic phases, while 0.42 ± 0.023 g g–¹ seed weight accumulated in the seedling. Partitioning of dry matter was equal between root and shoot up to 37 thermal units, then allocation to root reduced curvilinearly until a constant root-to-shoot ratio (15:85) was reached at 148 thermal units and maintained thereafter. Shoot dry matter partitioning between cuim and leaf was almost equal throughout the experiment except for the initial 37 thermal units when all dry matter accumulated in the culm. Early developmental processes in rice seedlings were independent of cultivar and seed size in this study. Although seed dry matter loss in proportion to the initial seed dry matter was significantly higher for larger seeds, the utilization pattern remained unaffected by seed size. This indicates that larger seeds were less efficient than smaller seeds in the utilization of reserves.

Received for publication July 31, 1996.