36 



AGRICULTURE HANDBOOK 495, U.S. DEPT. OF AGRICULTURE 



minishes the starch reserves of the 

 tuber and reduces flavor. 



The storage of yams in piles is 

 common but should be discouraged. 

 In piles, rotting can spread rapid- 

 ly, and since it is hidden, it cannot 

 be controlled. Leaving the tubers 

 in the sun for extended periods 

 severely reduces storage life. 



Storage life can be increased by 

 chemicals. The most effective is 

 MENA, the methyl ester of alpha- 

 naphthaleneacetic acid (7) . Tubers 

 are packed in papers treated with 

 the chemical at the rate of 100 

 milliliters reagent in 100 milliliters 

 acetone applied to 250 grams of 

 packing paper. Although rate of 

 water loss is not affected to any 

 great extent, tubers remain in 

 edible conditions from li/o to 2 

 months longer than normal. The 

 tubers develop a warty surface 

 after 6 months. Results are about 

 the same if the tubers are treated 

 at harvesttime or 2 or 3 months 

 thereafter. The cost of the treat- 

 ment, however, may limit its use. 



In addition, preliminary small- 

 scale experiments have shown that 

 dipping tubers in weak solutions 

 of gibberellic acid can delay germi- 

 nation 2 to 3 months. Experiments 

 are needed with this hormone, 

 which acts powerfully even at low 

 concentration, to see if some type 

 of treatment similar to that with 

 MENA can be devised, in which 

 the active chemical is constantly 

 available to the tuber. 



Storage of wing-stemmed yams 

 at 10° to 12° C or less results in a 

 characteristic low-temperature in- 



jury (11). When tubers are re- 

 turned to normal temperatures, 

 death of tissue, internal break- 

 down, foul odor, and decomposition 

 follow rapidly. The cause of the 

 disorder has not been determined. 



A problem in marketing, in in- 

 dustry, in the kitchen, and in the 

 design of scientific experiments is 

 the great variability of Z). alata 

 tubers, not only among varieties of 

 the species but also within the 

 same variety. Undoubtedly, this 

 variation has led different investi- 

 gators to different conclusions. 

 The problem of variation is asso- 

 ciated with many factors, such as 

 source and size of the seed piece 

 and virus disease in the tuber. In 

 a few cases clonal selection has re- 

 duced variation, probably by elimi- 

 nation of heavily diseased tubers. 

 The best assurance of high uni- 

 formity, however, is growing 

 plants under optimum conditions 

 in loose soil, where they can reach 

 their full potential in size and 

 shape. 



POTENTIAL USES 



The wing-stemmed yam has a 

 bright future throughout the Trop- 

 ics wherever subsistence agricul- 

 ture is practiced and rainfall is 

 sufficient. Because of the excellent 

 flavors of yams, they will probably 

 always be more popular than other 

 roots and tubers. Nevertheless, be- 

 cause they need special attention, 

 especially staking, they may not 

 complete well with cassava, sweet- 

 potatoes, and aroids. The wing- 

 stemmed yams may thus play a 



