Relative Contribution of Hetero-and Auto-trophic Growth to Genotypic Variation of Seedling Vigor in Rice (Oryza sativa L.)

To elucidate the major physiological process to cause genotypic variation in the seedling vigor of rice, we analyzed the dry matter accumulation in the seedling for diverse cultivars distinguishing hetero- and auto-trophic growth. Four cultivars in Exp. 1 and 63 cultivars in Exp. 2 were grown in a glasshouse by hydroponics for about three weeks. In Exp. 1, heterotrophic dry weight (DWh) was regressed against thermal time (T, ºC d) by logistic functions, in which the final heterotrophic dry weight (DWh.Max) was considered the primary determinant of heterotrophic growth rate. The increase of autotrophic dry weight (DWa, DWt (total DW)-DWh) was regressed to the exponential function of T with a fairly stable parameter, relative growth rate (RGR). The variation of DWt among cultivars and seed-sizes was well represented by combining the DWh and DWa models. In Exp. 2, DWt varied among cultivars from 51 to 116 mg pl-1. The effects of cultivar-specific parameters, DWh.Max (final DWh) and RGR, were evaluated by calculating the standard DWt with the mean DWh.Max and RGR, and then substituting one of the two cultivar-specific parameters for every cultivar. The results showed that those cultivars whose superior DWt was attributable to DWh.Max were limited to very large-seed cultivars. If they were excluded, the estimated effect of RGR (autotrophic process) on DWt was evidently greater than that of DWh.Max (heterotrophic process).