TEMPERATURE NEED - DISCUSSION
In what sense is the root restriction effected by high temperature favourable? Is is root restriction or a more favourable sprout/root ratio?
I have not, as yet, made any detailed study of the root systems of high and low temperature plants, but from observation on a few plants it seemed that at high temperature the roots were generally thin and fibrous, while at low temperature a larger number of thick, fleshy roots seemed apparent.
If its is subsequently shown that real differences in root structure do result from temperature treatment in these early stages of growth then it would be logical to except that differences in shoot development would follow as a result. I have used the term "root restriction" to indicate a possible restriction of the influence of the root on shoot development. It is of interest that early high temperature treatment and physical restriction of the root system appear to have similar advantageous effects on inflorescence development when light conditions are poor.
What were the effects of high temperatures which increased the leaf area ratios and consequent photosynthetic activity, on later flowering, fruiting and total yields of tomatoes?
Some information has already been published (Calvert 1964 - in references). With January sowing, high temperature (68°F) maintained up to first anthesis advanced flowering over low temperature (60°F) by 13 days with varieties "Aila Craig" and "Potentate" and by 11 days with "Ware Cross".
Early yield records, i.e. harvest in first month, also show an advantage from high temperature treatment up to first anthesis. It is, however, unlikely that total yield would be significantly affected by these "propagation" treatments.
No attention has been given as to what part of the tomato plant is subjected to the temperature regimes. We have found that root temperature primarily determines flower number in the fruit cluster, while top temperatures play the dominant role in the determining of the position of the fruit truss.
Normally the difference between two inflorescenses is three leaves. If you give the tomatoes lower temperatures to realize an earlier first inflorescence, did you get a greater number of leaves between the first and second truss and did you know the reason?
Yes, I have found that when low temperature induces a minimal leaf number before the first inflorescence there is tendency for five leaves to form between trusses one and two. This may be also related in some way to the formation of the branched truss at low temperature. I am, however, unable to offer an explanation of why this happens.
Did you find differences between the largeness of the cotyledons of plants grown under low and high temperature conditions?
The size (area) of the cotyledons is reduced when temperature is increased, but the area of the true leaves increases with temperature.
In past planting stage — at what temperature did yield fall off, was it at 68°F or at higher temperature?
Yield increased with temperature up to 68°F and decreased above that level. Higher temperatures increased eartly but not total yield.
In Guernsey temperatures of 60°F and 70°F day or 65 night and day had given similar but earlier yields than 60/65, and higher yields than 65/70. Commercially 60/65 was too late; 65/70 reduced yields too much.