Agriculture Reference
In-Depth Information
The molecular biology of dormancy control
Advances in techniques of molecular biology have opened
new opportunities for understanding biological systems,
and have led to a major international effort to increase our
understanding of control of dormancy at the molecular
level. Major changes in gene expression dormancy pro-
gression have been demonstrated (Bachem
et al
. 2000;
Ronning
et al
. 2003), and transcripts and proteins unique to
either dormant or growing meristems have been identified.
Extensive survey of the potato transcriptome using
expressed sequence tags (Ronning
et al
. 2003) has facili-
tated the identification and further study of key genes
expressed during dormancy and sprouting (e.g. Faivre-
Rampant
et al
. 2004). Discussion of the findings is outside
the scope of this chapter. However, these approaches open
up the possibilities of genetic manipulation to produce, for
example, cultivars with extended dormancy.
its biology, minimising the storage conditions that favour
its growth and limiting the spread from diseased to healthy
potatoes are important in preventing any problems
becoming worse.
Some diseases, in particular some fungal and bacterial
infections, can very quickly cause extremely severe dam-
age leading to the breakdown of an entire pile. Vigilance in
monitoring for problems and accurate identification can
minimise losses. Knowledge of the diseases in the post-
harvest (pre-stored potato) will help direct storage condi-
tions. For example, fungicides and disinfectants may be
applied to tubers during store loading to protect against
development of some diseases. Other diseases are poten-
tially sufficiently serious to avoid storage altogether.
Below are very brief descriptions to aid identification of
some of the major pests and diseases of potato storage,
defined here as those organisms whose activity increases to
the detriment of the tuber, and store manager, during
storage. More detailed information can be obtained from
local and national agronomic pathology services and
informative websites are listed at the end of this section.
In some cases a very general indication has been given
of the general susceptibility of the pests and pathogens to
chemical agents. However, given the diverse sets of regula-
tions and licenses that apply in different countries and the
local specific resistances to particular chemical agents,
further information should be obtained locally.
TUBER STORAGE DISEASES
AND DISEASE PREVENTION
Potato production was estimated as 320 million tonnes in
2007 and essentially all of this production must be stored
for at least a short time. However, this semi-perishable crop
is subject to many pests and diseases during both cultiva-
tion and storage which threaten its value as a food and as a
commodity. Here, we describe some of the major pests and
diseases of potato storage and their management.
Storage diseases of potato are not curable so active
prevention of diseased tubers from entering storage is a
priority. Disease-free seed with best cultural practices and
fungicide programmes to manage diseases all reduce the
percentage of diseased tubers being stored. In particular, as
most of the pathogens are opportunistic and gain entry to the
tuber through wounds, careful harvest and handling, with a
view to avoiding physical damage to tubers, is particularly
effective. Prior to storage, a good drying and curing regime
should be followed, to allow wounds to heal effectively.
Stores should be clean, free of previous year's debris and
perhaps disinfected before tuber loading. Storage conditions
must be controlled to minimise conditions under which
diseases and pests thrive. Surveillance for potential prob-
lems should be maintained throughout the storage period.
Problems should be identified quickly and appropriate
management strategies to limit pathogen spread and disease
development implemented. Early marketing may be the best
option available to preserve the value of the crop.
MAJOR POST-HARVEST PESTS
AND DISEASES
Bacterial pathogens
Bacterial soft rots
The most serious of all potato storage diseases are bacterial
soft rots and Blackleg caused by a number of closely
related bacteria of the genera
Pectobacterium
and
Dickeya
.
The principal pathogens include
Pectobacterium carotovo-
rum
and
P. atrosepticum
(formerly
Erwinia carotovora
ssp.
carotovora
and
E. carotovora
ssp.
atroseptic
a respectively)
(Gardan
et al
. 2003) and some species in the genus
Dickeya
(formerly
Erwinia chrysanthemi
) (Samson
et al
. 2005).
The pathogens and the diseases are found worldwide and
all cultivars are susceptible.
External tuber symptoms include brownish water-
soaked areas of squashy tissue usually outlined by brown
to black margins. The margin between infected and healthy
tissue is sharp (Plate 16.1). Although the rot is initially
nearly odourless it typically progresses to a pale, foul-
smelling mass. Under advantageous conditions for pathogen
Pathogen identification
Pathogen identification enables effective store manage-
ment decisions. Recognising the pathogen, understanding
