Relationship between tuber and leaf growth in radish (Raphanus sativus L. var. sativus), analysed as result of an optimal process

The relationship between the growth of the shoot and a storage organ was studied in radish (Raphanus sativus L. var. sativus). To quantify the relationship the ratio r of the relative growth rates of the tuber dry mass and the leaf area was used. On the basis of growth data, measured on twenty-four crops in the field and growth chamber, a system analysis was carried out to test whether the determined values of this ratio can be explained as result of an optimal process. The following hypothesis was examined: The adjustment of tuber and leaf growth occurs in such a way, that the harvest stage, defined here by a certain tuber dry mass, is attained in shortest length of time. For theoretically deriving the ratio a simple growth model and optimisation procedures were used. Inputs were the measured values of net assimilation rate and specific leaf mass. In the case of describing the growth with a mean value of ratio r during the growth interval from seedling stage to harvest, the calculated values were in good accordance with the measured. But, if the ratio was allowed to vary over time only the general response could be confirmed by the calculation: at first predominant leaf growth and then transition to predominant tuber growth. In order to achieve a sufficient quantitative accordance additionally several constraints (e.g. a upper Emit of the relative growth rate of the tuber) were necessary. Conclusions for further investigations were drawn from the results.