Gkowth and Flowering of the Tomato in Relation to Natural Light Conditions

Continuous-recording photometers were used to measure the amounts of light entering a glasshouse during certain growth periods of young tomato plants. Fresh and dry weights of the tops of the plants and the number of days between cotyledon expansion and anthesis of the first flower of the first inflorescence were related to the recorded light values as follows :

1.The relationship between log dry weight and the light-time integral was linear up to 220,000 foot candle hours, after which a marked reduction in growth occurred.

2.The departure from linearity occurred at about the same light integral even when additional nutrients were supplied to the standard volume of compost, but was delayed when a larger container was used.

3.The number of days to anthesis and the recorded light-time integrals show the following relationships : in winter, light integrals are constant (about 400,000 f.c.h.) while time is variable ; in summer, time is constant (about 40 days) while the light integrals are variable.

4.In summer, neither the reduction of the natural day-length to 9 hours nor the reduction of the light intensity to 75% normal materially influenced the number of days to anthesis.

It is concluded that in winter growth is limited by, and is therefore proportional to, the amount of available photosynthetic light, while in summer the young tomato is light-saturated and growth is limited by factors other than light.

The results indicate that the amount of photosynthetic light is the major factor determining the seasonal pattern of days to anthesis. There was no indication of any photoperiodic response.