Tuberization of the Colorado Wild Potato as Affected by X-radiation.

The Colorado wild potato (Solanum jamesii) is the only species among more than 100 different kinds of plants that the writer (6) has irradiated in which a plant organ has made greater growth leading to increased weight as a result of the treatment. The growth and development of the underground parts of 22 species (7) exposed to medium doses showed detrimental effects to adventitious, fibrous, and tap roots. Corms and bulbs of certain species of Iridaceae and Liliaceae, although less sensitive than tubers of the Jerusalem artichoke, agree in showing retarded growth. The wild potato was the only species, among those in which the underground organs especially were studied, for which a dose favoring tuber production was found. JACOBSON (2) reported that by x-radiation the crop of one variety of cultivated potatoes was increased 84 per cent. in weight over the control plants, while with another variety the increase was as much as 200 per cent. He stated that not only was each tuber larger than normal but that there was an increase in the total number as well. SPRAGUE and LENZ (9) from preliminary experiments concluded that strong doses may reduce the number of tubers formed, but that such tubers attain a greater size so that the total production is not lowered. In the writer's preliminary experiments (3) with cultivated potatoes grown in the greenhouse, tubers which were given light doses of x-rays formed more young tubers per hill than did the controls, but the average weight was less than that for the controls. Consequently the average total weight per hill was practically the same for controls and experimental plants. Since only a very limited number of cultivated potatoes could be grown in the greenhouse at one time, further experiments were carried on with the Colorado wild potato which has proved to be useful in ecological experiments (8) since it requires little room and matures quickly. A summary (1) of the studies reporting stimulative action of x-radiation has pointed out that in the great majority of cases where it has occurred, light doses have been used. Experiments of two seasons, in which the use of light doses on the wild potato failed to give increased production, have been previously reported (5). Results based on 14,000 tubers obtained from the second year's experiment, indicated that the controls and experimental plants did not vary more in yield than would two groups of untreated plants.