DORMANCY IN BUDS 239 



A Chemical That Inhibits Potato Buds 



In previous chapters we have mentioned that ethylene and other hor- 

 mone-like chemicals inhibit bud growth. Guthi-ie *^' *^ found a-naphtha- 

 leneacetic acid and its salts and esters very effective in inhibiting the growth 

 of buds of the potato. Fig. 90 shows the effectiveness of the potassium salt 

 of this acid in inhibiting potato buds. It also shows that ethylene chlor- 

 hydrin throws potato buds out of chemically induced dormancy, though 

 perhaps not as effectively ^^ as it does out of natural dormancy. With the 



FiGUKE 91. Irish Cobbler potato tubers stored in paper bags for five and one-half 

 months after treatment with different dosages of the methyl ester of a-naphthaleneacetic 

 acid applied in talc powder. Temperature varied from 10° to 16° C (50° to 60° F). 

 Dosages (above): check without talc, check with talc only; (below, left to right): 25 ppm 

 of weight of tuber, 50 ppm, 100 ppm of methyl ester. 



use of these two chemicals, potato buds can be thro^vn into and out of dor- 

 mancy almost at w^ill. The methyl ester of a-naphthaleneacetic acid ^^ is 

 desirable for use for potato storage because it has sufficient vapor pressure 

 to insure its entrance into the buds; the most efficient way to apply it to 

 the tubers is in a talc or clay dust on the surface of the tubers at 55° F 

 (13° C) or above so that the chemical vdW have sufficient vapor pressure. 

 Fig. 91 shows the effect of different dosages of this chemical in maintaia- 

 ing dormancy in potato buds. It is evident that 25 parts of the chemical 

 to a million parts of the tubers by weight is sufficient to maintain complete 

 dormancy. It is possible that even a low^er dosage applied by this method 

 will be effective, especially if the treatment is made at room temperature. 

 It has been showTi that only 5 ppm of the chemical is absorbed by the 

 tubers when the dosage is 100 ppm, and of the chemical absorbed four-fifths 

 is held in the skin. Unpublished experiments at the Institute have sho^\^l 

 that a-naphthaleneacetic acid and its salts and esters have low toxicity for 



