Environmental Engineering Reference
In-Depth Information
31
Sweetpotato
Karine Zinkeng Nyiawung, Desmond Mortley, Marceline
Egnin, Conrad Bonsi, and Barrett Vaughan
Tuskegee University
contents
31.1 Introduction ....................................................................................................................... 737
31.2 Sweetpotato as Feedstock for Ethanol ................................................................................ 738
31.2.1 Starch .................................................................................................................... 739
31.2.2 Starch Biosynthesis ............................................................................................... 741
References ...................................................................................................................................... 743
31.1 IntroductIon
Sweetpotato,
Ipomoea batatas
(L.) Lam., is a root crop that belongs to the family Convolvulaceae,
the morning glory family. It is a creeping dicotyledonous plant and an important crop, widely grown
in tropical, subtropical, and warm temperate regions. It ranks as the world's seventh most important
crop, with an estimated annual production of approximately 122 million metric tons (Collado et
al. 1999; FAO 2006). On the basis of analysis of morphological characters of sweetpotato and the
wild
Ipomea
species, the center of origin of
I. batatas
was thought to be somewhere between the
Yucatan Peninsula of Mexico and the mouth of the Orinoco River in Venezuela (Austin 1987).
Recent evidence revealed by the use of molecular markers suggests that Central America is the
primary center of diversity and most likely the center of origin, considering the richness of the
wild varieties of sweetpotato (Haung and Sun 2000; CIP 2006). Sweetpotato is especially valued
because it is highly adaptable and tolerates high temperatures, low fertility soil, and drought
(Yencho et al. 2002).
The growth cycle of sweetpotato is generally from 3.5 to 7 months and takes place in three
phases:
1. From planting to formation of storage roots (40-60 days),
2. From storage root formation to the time of maximal leaf development (60-120 days), and
3. From maximum leaf development to the total development of storage roots (45-90 days).
Normally the cycle is completed within 100-150 days for the short-term varieties, at which
time the plant can be harvested (Ramirez 1992). A temperature range between 15 and 33°C is
required during the vegetative cycle, the optimal temperature being 20-25°C. The highest yields
are obtained when temperatures are high during the day (25-30°C) and low at night (15-20°C);
low night temperatures favor the development of storage roots, and high day temperatures favor
vegetative development. Storage root development only occurs within a temperature range of
20 -30°C; 25°C is optimal, and growth stops below 10°C (Ramirez 1992).
Sweetpotato is a short-day plant that needs light for maximum development, although the growth
of storage roots appears not to be influenced by photoperiod alone. It is most likely that temperature
and fluctuations in temperature, together with short days, favor the development of storage roots and
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