Development and Characteristics of

 Twining Sweet Potatoes

 Franklin W. Martin
 Research Horticulturist, USDA-ARS
 South Atlantic Area
 Tropical Agriculture Research Station
 Mayaguez, Puerto Rico 00709


 Sweet potatoes do not generally twine, but twining can be
induced by shade. Twining sweet potatoes were produced by
selection and polycrossing. Frequency of climbing sweet
potatoes increased in four successive populations from 0.7 to
33, 56, and 48%. Twining sweet potatoes produce normal
storage roots, and can be selected for other characteristics. The
foliage is modified. Most twiners have entire leaves, long, thin
vines with long internodes, thin basal vines and under-
developed crowns. Vine tops tend to grow vertically and twine
in a counter-clockwise direction. Propagation of twiners under


optimum conditions is restricted by the ease with which the
thin stems wilt, and by reduced rooting. Most twiners are
susceptible to "virus" disease. The clone, whether propagated
from stems or from sprouts, is less vigorous than the seedling
generation. Principal symptoms are small, rugose leaves and
slow growth. After one or two generations it becomes imprac-
tical to continue. Twiners are still vigorous under test on sup-
ports and in relay with corn. Stable twining varieties should be
useful in multiple cropping.


 The sweet potato, Ipomoea batatas (L.) Lam. belongs to the
Convolvulaceae family, which consists chiefly of twining herbs.
The species of Ipomoea most closely related to sweet potato (sec-
tion batatas) are twiners, including I. trifida, I. leucantha, and I.
littoralis. They are very closely related in origin to the sweet
potato (Nishiyama, et al., 1975), I. trichocarpa, I. ramoni, I.
tileacea, and I. gracilis. Nevertheless, the sweet potato is not
usually a twining plant. In his survey of the variation of sweet
potato in Ecuador, Peru, and Pacific Islands, Yen (1961) does not
even mention twining behavior. The varieties of sweet potato
used as food throughout the tropics vary from running vines to
compact bushes. According to Yen (1968), "One of the most
striking variations in I. batatas is its growth habit, for it ranges
from a compact bush plant, little more than two feet across at
maturity, to a long sprawling vine in which individual stems have
been measured at 15 feet."
 Nevertheless, some sweet potatoes can climb by twining. Plant
breeders, working with large numbers of seedlngs, observe twin-
ing individuals (Jones, 1967). Gollifer (1973), observing tenden-
cies to twine in some varieites, provided stakes, and spontaneous
twining occurred in the variety Faunalea. Staking this variety in-
creased the yields of roots. Austin (1983), in searching for new
variation in the sweet potatoes, reports that twining varieties are
frequently found in home gardens in western South America.
The author has heard accounts in various countries of twining
varieties produced in isolated parts of tropical America. Thus, it
appears entirely feasible to develop twining varieties.
 Twining varieties might have several advantages over non-
 twining in some situations. They might be able to climb and sub-
 due some weeds. When planted with corn, they might be able to
 climb the stalks and thus obtain more light. They might be able
 to obtain sunlight more effectively when positioned on trellises
 and thus yield more.
 This study was made in order to ascertain the feasibility of
 developing twining varieties of sweet potato and to determine the
 effects of twining on other characteristics.


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MATERIALS AND METHODS
 The initial materials for this study were 3,000 sweet potato
seedlings from which the twiners were selected. Twiners were also
selected from three generations of progeny of crosses among
twiners. In addition, 50 non-twining seedlings were propagated
by stem cuttings and grown in pots in three environments, full
sun, 20% shade, and 80% shade in order to study the effects of
light on twining.
 Twiners were identified by observing field-grown plants for
twining tendency. A bamboo stake of one meter length was plac-
ed in the foliage of such plants. Plants that climbed these stakes
were twiners.
 The tuberous roots of twiners were harvested and evaluated at
5.5 months of age if started from seeds, or at 4.5 months of age if
from cuttings. Normal, terminal cuttings, 30 cm long, were taken
from the tips of the vines for transplanting and propagation
trials. Three consecutive generations of seedlings segregating for
twining were produced in polycrosses. Twenty or more twiners
were propagated from cuttings, permitted to climb by twining,
and cross-pollinated by honey bees in the polycross.

RESULTS
 Fifty seedlings, selected at random, showed no twining
 tendency when grown in pots in full sun. When grown in 20%
 shade sarann cloth) six seedlings showed a tendency to twine and
 one twined up a bamboo pole. When grown in 80% shade
 (fiberglass roof), 33 of the seedlings showed a tendency to twine
 and eight twined up bamboo poles.
 Polycrossing among twiners increased their frequency among
 seedlings (Table 1). Even one polycross increased the percentage
 of twiners by a factor of 47, and the percentage of twiners was in-
 creased to 57 by the second polycross. It is obvious that by
 polycrossing, large percentages of twiners are easily recovered.
 Of 171 tip cuttings taken from 57 twiners from polycross I pro-
 geny, 161 (94.2%) rooted normally under optimum conditions.
 However, in subsequent trials the thin cuttings of twining

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