Agriculture Reference
In-Depth Information
has focused on the potential for breeding potato cultivars
with extended dormancy.
A number of sprout suppressants have been identified
for use with potato. Of these, CIPC (isopropyl N-(3-
chlorophenyl carbamates, chlorpropham) is the most effec-
tive in current use for ware potatoes. This is an inhibitor of
cell division, and requires only a single application.
With CIPC treatment early maturing varieties can be stored
for 6-10 months, and late maturing varieties for up to
12 months (Kleinkopf
et al
. 2003). However, there are
human health concerns relating to CIPC usage. A recent
Environmental Protection Agency mandate, from the
requirements of Food Quality Act (FQPA) of 1996,
resulted in a reduction in allowable CIPC residues on fresh
potatoes in the United States from 50 ppm to 30 ppm.
(Kleinkopf
et al
. 2003).
For storage of seed potatoes, where sprout inhibition
must be reversible the most commonly used commercial
sprout suppressants are dimethylnaphthalene (DMN) and
Carvone (a natural product that can be isolated from
caraway seeds) (
Federal Registry
1995; Brown
et al
. 2000).
Given the concerns over the use of CIPC, new methods
of sprout control using non-chemical methods, or natural
chemicals, are being continually sought. Recently continu-
ous ethylene treatment during storage has been used to
control potato sprouting. This has been registered for
commercial use in the UK since 2003 (Prange
et al
. 2005).
Table 16.3 gives a list (not exhaustive) of sprout
suppressant treatments presently used or being investigated
for use for potato.
Given the economic importance of potato, research into
the control of dormancy is much more advanced than for
other root crops. Dormancy is considered to begin at tuber
initiation (Burton 1989). The buds (eyes) from which
sprouts will eventually grow, are present from an early
stage. Buds near the apex are dominant (apical dominance)
such that lateral buds will only develop if apical buds are
removed, or the tuber is cut into smaller seed pieces. The
control of dormancy maintenance and dormancy break is
very complex. This is illustrated by the observation using
methods of Quantitative Trait Loci (QTL) analysis that
dormancy is controlled by at least nine distinct genetic loci
(van den Berg 1996). As a consequence, the results of
scientific research are sometimes confusing and apparently
contradictory.
Table 16.3
Chemicals or Treatments Effective as
Suppressants of Sprouting in Potato.
Treatment
Reference
CIPC (isopropyl N-(3-
chlorophenyl carbamates,
chlorpropham)
Kleinkopf
et al
. 2003
Substituted naphthalenes e.g.
1,4-dimethyl naphthalene
(1,4 DMN), 2,6
diisopropylnaphthalene and
alpha-naphthalene acetic acid
Lewis
et al
. 1997
Suttle 2003b
Ethylene
Suttle 2003b
Essential oils: carvone, spearmint,
peppermint and eugenol
Kleinkopf
et al
. 2003
Hydrogen peroxide Prange
et al
. 1997
Irradiation Kleinkopf
et al
. 2003
Note: Some references given are reviews and not
necessarily the most definitive work on that particular
treatment.
been studied including: auxins, gibberellins, cytokinins,
abscissic acid and ethylene.
The role of auxins is confusing. Early bioassay data
suggested that a key auxin, indole acetic acid (IAA) was
low in dormant tubers and increased during sprout growth,
indicating a role in sprout stimulation, although contrary
evidence was presented by Sorce
et al
. (2000). On the other
hand, high doses of IAA, or of the auxin, 1-naphthalene
acetic acid have been shown to inhibit sprouting. Auxins
are therefore postulated to be involved in control of sprout
growth (Suttle 2004a). Dimethylnaphthalene, which is
used as a commercial sprout suppressant has an auxin-like
structure and may bind to auxin receptors.
The identification of hundreds of gibberellins makes
interpretation of their role complicated. Suttle (2004b)
conducted a study to determine the effects of post-harvest
storage duration on the endogenous content and bioactivi-
ties of selected gibberellins in relation to the dormancy sta-
tus in Russet Burbank potatoes. The conclusion from this
study was that endogenous gibberellins are not intimately
involved with tuber dormancy control, but play a critical
role in sprout stimulation at dormancy break. Gibberellins,
specifically (GA
3
) are used to promote sprouting of seed
potato for seed certification programmes.
Cytokinins are defined by their ability to release G1 cell
cycle blocks, and bud meristematic cells are arrested in this
phase. Recent immunological techniques have allowed
confirmation of earlier bioassay work, indicating that
Hormonal control of dormancy
A large volume of work has been conducted to understand
the hormonal control of tuber dormancy (reviewed in Suttle
2004a). The role of the different classes of hormones has
