TABLE 1. Frequency of climbers among seedlings.


 NUMBER OF NUMBER OF FREQUENCY OF
 GENERATION SEEDLINGS CLIMBERS CLIMBERS (%)
 PARENTS: UNSELECTED 3000 21 0.7
 SEEDLINGS FROM
 VARIOUS SOURCES
 POLYCROSS I PROGENY 178 59 33.1
 POLYCROSS II PROGENY 105 60 56.6
 POLYCROSS III PROGENY 134 65 48.5



varieties often wilted readily. When nine selected twiners were
propagated by resprouting tuberized roots, all showed virus
symptoms. These were so severe that eight of the nine selections
were effectively lost. We have seen virus symptoms when
tuberous roots are resprouted and interpret this as an increase in
titer of normally occurring viruses due to propagation technique.
Some sweet potatoes do not outgrow these conditions. What is
unusual is that such a large proportion of twiners displayed such
behavior.
 A total of 205 twiners were produced and evaluated over a
three-year period. From these, 14 selections were made as ten-
tative varieties. All seedling twiners were evaluated for foliage,
kitchen, and physiological characteristics. Twiners tended to
share the following characteristics as compared to non-twiners:
long, thin vines with long internodes; long running vines that
climb on encountering a support; thin basal vine (crown);
tendency of the tips of the vines to grow vertically (in contrast to
horizontally, as in the case of running vines); twining by a
counter-clockwise movement, as seen from above; leaves usually
cordate and seldom lobed; low to intermediate anthocyanin pro-
duction in the leaves and stem; early and out of season (long day)
flowering; and a tendency to exhibit virus symptoms (smaller,
rugose, cuspid leaves, sometimes with a light mosaic appearance).
 When climbers, without symptoms, as a group were compared
to non-climbers, no differences were seen in root form, internal


or external root color, root yield, or in quality characteristics, in-
cluding texture, flavor, sweetness; and fiber of the cooked root.
 Virus symptoms increased rapidly in the selections. Once the
 vines showed virus symptoms, vigor was lost, growth and climb-
 ing ability were reduced, nodes were shorter, propagation from
 stem tip cuttings became more difficult, and yields were drastical-
 ly reduced. Some of the selections were lost due to their poor
 viability, and after one year, only one of nine vigorous and
 relatively disease-free selections was maintained. However, five
 more selections have since been made. Those remaining selec-
 tions are under trial in several production systems.
 There is a suggestion that mass selection for twining has also in-
 creased virus susceptibility. This could occur if the traits are
 genetically linked.
 Twining is a specialized form of stem growth that leads to
climbing. It is not necessary for stems to touch an object in order
to twine, for in several species, twining tendency can be iden-
tified by the coiled growth of stems not touching any object. The
causes of this phenomenon were subjects of concern for early
plant physiologists (Pfeffer, 1905). Twining resembles tropisms
in that it is due to a growth curvature of the stem. Such growth
appears to be due to the unequal distribution of auxin in the
elongating cells of the young stem (Schrank, 1950).
 In common beans, Phaseolus vulgaris L., twining tendency has
been shown to be controlled by the phytochrome pigment system
(red, far-red light response) (Kretchmer, et al., 1977). A single
gene controls the twining trait and determines whether the par-
ticular plant can climb or not (Kretchmer, et al., 1978). Never-
theless, minor genes and environment modify these effects. The
system of control of twining in sweet potato is still far from
elucidated, but rapid increase in this trait through selection and
polycrossing suggests that relatively few genes are involved, and
the influence of shade suggests a strong environmental compo-
nent as well.
 The effort to develop climbing sweet potatoes is still young.
Nevertheless, results thus far show that while development of
twining sweet potato is feasible, we have still to learn how to han-
dle them.


References
 1. Austin, D. 1983. Personal communication.
 2. Gollifer, D.E. 1973. Staking trials with sweet potatoes. Tropical Agriculture
50:279-284.
 3. Jones, A. 1967. Should Nishiyama's K123 (Ipomoea trifida) be designated
I. batatas? Econ. Bot. 21:163-166.
 4. Kretchmer, P.J.,J.L. Ozbun, S.L. Kaplan, D.R. Laing, and D.W. Wallace.
1977. Red and far-red effects on climbing in Phaseolus vulgaris L. Crop Science
17:797-799.
 5. Kretchmer, P.J., D.H. Wallace and D.R. Laing. 1978. Inheritance and mor-
phological traits of a phytochrome controlled single gene in beans Phaseolus vulgaris
L. Crop Science 18:334-339.
 6. Nishiyama, I., T. Miyazaki, and S. Sakamoto. 1975. Evolutionary
autoploidy in the sweet potato (Ipomoea batatas [L.] Lam.) and its progenitors.
Euphytica 24:197-198.


 7. Pfeffer, W. 1905. The physiology of plants. Clarendon Press, Oxford. 451
pp.
 8. Schrank, A.R. 1950. Plant tropism. pp. 59-74. In: Arnon, D.I., and L.M.
Machlis (Editors). Annual Review of Plant Physiology. Vol. 1. Annual Reviews,
Stanford, CA. 364 pp.
 9. Yen, D.E. 1961. Sweet potato variation and its relation to human migration
in the Pacific. Tenth Pacific Science Congress. Bernice Pauahi Bishop Museum,
Honolulu. pp. 93-117.
 10. Yen, D.E. 1968. Natural and human selection in the Pacific Sweet Potato.
Ellen T. Drake (Editor). Evolution and Environment. Yale University Press. New
Haven, CT. pp. 387-412.


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