three plants treated with the second extract began to turn green.
Several explanations came to mind: (1) The osmotic pressures of these
extracts were much different (we did not measure osmotic pressure); (2) the
stem and hypocotyl contribute something harmful to young tl plants (only leaves
were used in the extracts of mature plants); (3) young tomato plants produce a
toxic substance not found in older plants. We are not sure that these extracts
will have any effect upon seedlings of normal genotype; only tl seedlings were
used as test plants. I no longer have the time nor facilities to pursue these
possibilities. Perhaps someone else will take an interest in solving this
dilemma.
Since the photosynthetic
compensation temperature for
potato is much lower than that for tomato, potatoes do not survive through the
Arkansas summer, whereas tomatoes do. It was felt that by grafting tomato scion
on potato stock we would have a plant that could continue to produce potato
tubers through the heat of the summer. In the summer of 1974 some 30-40 grafts
onto field planted potatoes were attempted. Only two survived, and they did not
grow. In the spring of 1975, potatoes were started in flats inside the
greenhouse, and grafts established before transplanting to the field. Red
Pontiac and Red Cherry tomatoes were the varieties used.
At the time of transplanting in early June, the tubers which had formed in
the seed trays were removed, so that every tuber harvested on August 19 was
formed during the summer months. As can be seen in Table 1, in spite of the
fact that the grafted plants were also producing tomatoes in their upper parts,
they slightly out-produced the ungrafted potatoes in both number and size of
tubers. An even greater difference occurred in the % survival, with grafted
plants (65%) doing much better than ungrafted (37%). These results, while only
those of a single, small test, indicate that it is the foliage, not the tuber
which is important in the inhibition of growth at high temperatures.
As a practical result, we can see from Table 2 that for the home gardener
who has only a few plants in his summer garden, the chance of having a good
tuber producing plant is greater with the grafted plants than with the
ungrafted potatoes -- at least under the climatic conditions of north west
Arkansas.
Reeves, A. F. Tomato-potato grafts.
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