POTATO YIELDS.

New Zealand Herald, Volume LXVI, Issue 20383, 11 October 1929, Page 7

POTATO YIELDS.

QUESTION OF TUBERISATION;

TREATMENT BY X-RAYS.

LIMITED EXPOSURE BENEFICIAL. ,-TT "" A recent claim that increase^.tuborisation of potatoes results from X-ray treatment of tho seed is partially dis-:., credited by scientists who record con-r troverting experiences in a late issue of Science (United States). In that journal Mr. Howard B. Sprague, of the Agricultural College, Rutgers University, and Mr. Maurice Lenz, of Montcfiore Hospital Radium Clinic, New York* who collaborated in experimentation on the subject, state that results contrary to those claimed by a previous investigator attended their efforts. They found that while limited exposure to the rays produced beneficial effects, prolonged. exposure was definitely detrimental. Tho subject of. their experiments was certified seed of both Irish Cobbler and. Green Mountain varieties, and two dosages of X-ray were employed. Ono half of each tuber was irradiated, the. other portion remaining untreated for control purposes. Portion of the irradiated half-tubers was treated for ten minutes and a second lot for only five , minutes. Sprouts were 'just commencing to develop at tho time of exposure, and the tubers wore planted on the following day. Each seed piece was cut to a weight of thirty grams using tho budend, and the pieces were spaced nine> inches -in tho rows, the corresponding' treated and untreated pieces being planted in adjoining rows 32 inches apart. Results of Irradiation. The soil was o sandy loam of good fertility, but a &8-7 fertiliser was employed at the rate of 10001b. to the acre. Ordinary tillage operations were, followed and for the purpose of controlling tho potato beetle the plants were periodically dusted with arsenate of lead. Harvested by hills after the vines had died, each tuber was carefully and separately weighed. ; ■. Plants from the lot of tubers receiving; tho ten-minute exposure produced only 84.4 per cent, as many timers of all sizes as the untreated controls, and only 89.6 per cent.- as many tubers weighing over forty-five grains each. Although the total weight of all tubers was re-. duccd 6.0 per cent, by the .the total weight of tubers weighing over forty-five grams was increased 6.1 per cent. Tho average weight per tuber of marketable stock (over forty-five tfhuns. per tuber) was 81.6 grams for the lot irra- L diated ton minutes, as compared with 68.9 grams for tho untreated lot. Plants from tho lot of tubers irradiated five minutes produced 104.7 per cent. aB many tubers ol all sizes as the con- ; " trols; and 10-5.1' per cent, as many tubers weighing over forty-five grams each. Tho total weight of all tubors was' increased 3.0 per cent, by the treatment, and tho total weight of marketable, tubers was increased 3.8 per cent. Ti% : average weight' per tuber of marketable stock was 74.7 grams for the lot treated five minutes, as compared with 73.7 grams for the corresponding untreated lot. Effect on Foliage. The ten-minute irradiation caused the first leaves of tho plants to assume a peculiar, shape. The leaf tips appeareg; to have been injured and the blade pinched-in as it approached theso lesions'." The margins .of the leaf curled downwards, and the leaf in general seemed to be more glossy than normal leaves. Subsequent leaves of these plants were normal. After formation of normal leaves the plants were vigorous, and remained green several days later than untreated plants at tho time of maturity. No strik- ' ing abnormalities resulting .from irradiation were noted in the harvested tubers. Irradiation for five minutes* produced no apparent modification of plants or tubers. "Those results that strong dosages which cause definite lesions on leaves may also reduce tho number of tubers formed; but such tubers may attain a greater size, so .that yields of marketable stock are not lowered,' tho investigators state.'."lt seems likely that still stronger dosages may - reduce tuberisation still further, and perhaps the yield of marketable stock as wcil.