TROPICAL YAMS AND THEIR POTENTIAL, PART 3 



35 



whereas red forms occur chiefly 

 in the foliage and in the cortex of 

 the tuber. The occurrence of antho- 

 cyanins is somewhat related to 

 taxonomic grouping of the vari- 

 eties. More advanced and highly 

 selected varieties contain little or 

 no anthocyanin. When foliage is 

 free of anthocyanins, so are the 

 tubers. Varieties with high antho- 

 cyanin content are often prone to 

 polyphenolic oxidation, and their 

 tubers are usually much branched 

 and agronomically inferior. 



Although the yellow pigments of 

 D. alata have not been well studied, 

 there is no reason to believe they 

 are different from those in other 

 species of yams, which contain 

 principally xanthophylls and their 

 esters, although the vitamin A con- 

 tent is sometimes high enough to 

 be of nutritional significance. 

 Good yellow-fleshed varieties of D. 

 alata would be desirable for vita- 

 min content. 



STORAGE 



Some say wing-stemmed yams 

 store well; others say they have 

 poor storage characteristics. These 

 conflicting points of view probably 

 reflect experiences with different 

 varieties or with different storage 

 methods. It is well recognized that 

 injured tubers can be readily in- 

 fected with fungi and that fungus 

 diseases can destroy entire tubers, 

 often in a short time. Further- 

 more, once started in a tuber, fungi 

 are almost impossible to eradicate. 

 Therefore, tubers that are dam- 

 aged at harvest should be used as 



soon as possible and should not be 

 stored. 



The first week after the harvest 

 is crucial to the storage life of 

 tubers. Curing under humid condi- 

 tions invariably results in rapid 

 fungal growth. Curing by hot, dry 

 air permits the development of a 

 layer of dead cells that protects 

 against fungal infection (fig. 13). 

 Cut surfaces do not develop a new 

 meristematic layer, and a wound 

 periderm is not formed. The dry 

 cells are not suberized. If the dry- 

 air treatment is too long, excessive 

 moisture loss leads to cracking, 

 permitting severe fungal infection. 

 After curing, moderate humidities 

 and cool temperatures (15°- 

 17°C) can give a storage life of 

 a year or more. 



Storage practices vary. Storage 

 in the ground (delayed harvest) is 

 common, but insect damage in- 

 creases, the risk of loss from rats, 

 pigs, and humans must be con- 

 fronted, and early rains may im- 

 pede later harvest or lead to 

 premature sprouting. Neverthe- 

 less, the quality of tubers stored 

 in the ground is as good as that of 

 tubers harvested and stored else- 

 where. 



Tubers are often stored by piling 

 them in pits, tying them to walls, 

 or placing them on shelves in yam 

 barns. They can keep well under 

 these conditions. Free circulation 

 of air around the tubers helps 

 avoid rot. Under these conditions 

 tubers begin to germinate when 

 their normal season of regrowth 

 occurs. Sprouting rapidly di~ 



