Fusarium dry rot of potato in
South Africa I: Fungicide
treatment of seed pieces
Article: Dr Fienie Niederwieser, Potatoes South Africa
(Article is based on the report written by C Millard on work done by DJ Theron in the 1990’s)
Introduction
As the cost of potato seed tubers represents the greater
part of the production cost of potatoes, the use of tubers
cut into seed pieces, is a customary planting practice with
some farmers. This cutting process can, however, lead to
the spread of tuber-borne pathogens throughout the seed
lot and to the soil, causing considerable losses during
the growing season or thereafter and exposing tuber
tissue to desiccation and bacterial and/or fungal seed-
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CHIPS • Maart/April 2016
piece decay. Bacterial decay, e.g. soft rot, caused mainly
by Pectobacterium spp. and fungal decay, e.g. dry rot
caused by Fusarium spp. and their combinations are the
primary cause of decayed potato seed pieces. Total or
partial decay of seed pieces, reduction of plant vigour and
poor stands are symptomatic of seed-piece decay. Often
single sprouts emerge from partly decayed seed pieces,
developing in small, slow growing plants more susceptible
to other diseases, resulting in low yields. Cut seed tubers
contaminated with Fusarium spp. will increase soil
Tegniese Nuus • Technical News
contamination and is an important source of contamination
of progeny tubers, resulting in high levels of Fusarium dry
rot in storage.
The objectives of the study were:
• To determine the value of fungicide treatments to reduce
seed piece decay.
• To determine whether wound healing may have any
benefit.
• To determine whether planting time has any effect on
the treatments above.
a randomised block design. Each replication consisted of
one row, 9 m long. Intra-row spacing was 30 cm and inter
row spacing, 75 cm. Border rows were planted between
treatment rows using uncut tubers of Up-to-Date.
Plant stands were determined 3 – 6 weeks after planting
and yield were determined after harvest, 15 weeks after
planting. The data were statistically analysed using the
Genstat 5 PC Program (Genstat 5 Committee, 1987) and
the means compared using Tukey’s test (p ≤ 0.05).
Results
Materials and methods
Effect of planting season
Six trials were carried out in 1990, ’91 and ’92 at
Roodeplaat. Three were planted in the autumn (February)
and three in the spring (August). The soil inoculum
potential for Fusarium dry rot was determined for all six
plots. Certified seed tubers weighing 100 – 150 g of the
cultivar Up-to-Date were used in each trial. Tubers were
cut and subsequently dip-treated for five minutes with eight
fungicide treatments. Two controls were included, namely
cut tubers dipped in water for five minutes and uncut
tubers weighing 50 – 75 g each. To determine the effect
of wound healing, tubers were planted one day after they
were cut and dip-treated, or planted 14 days after diptreated, dried and stored 25oC and RH 65 – 75% in the
dark. Three replications of each treatment were planted in
% PLANT STAND / YIELD (T/HA)
90
80
The mean temperature during the growing season of spring
plantings was 3.8oC higher than the mean temperature of
autumn plantings. However, the mean temperature during
the first seven days after planting of spring plantings,
was 9oC lower than during the same period in autumn
plantings. During the autumn plantings significantly poorer
(p ≤ 0.05) plant stands (Figure 1) and lower yields were
obtained than during the spring plantings. This was possibly
caused by the temperatures during the growing period,
especially the temperatures during the first seven days after
planting, which could enhance seed piece decay.
STAND
70
STAND
60
YIELD
50
40
30
YIELD
20
10
0
Spring
Autumn
Spring
Autumn
Figure 1. Plant stand and yield of spring and autumn planted seed.
CHIPS • March/April 2016
• Page 31
The calculated potential for Fusarium dry rot was clearly
higher in autumn than in spring (Table 1). High soil
temperature is known to be favourable for Fusarium dry rot
and was probably the cause of the higher potential values
during autumn indicating a high risk for Fusarium seed
piece decay during autumn plantings.
Table 1. Soil inoculum potential for Fusarium dry rot in spring and autumn plantings in 1990 – 1992.
Soil inoculum potential for Fusarium
dry rot (%)
1990
1991
1992
Average
Spring plantings
13
15
10
19
Autumn plantings
36
43
35
38
Effect of time of fungicide treatment
Results indicated that wound healing, by cutting and
% PLANT STAND / YIELD (T/HA)
90
80
70
STAND
treating seed pieces 14 days before planting, did not result
in better stand and yields compared to cutting and treating
seed pieces one day before planting (Figure 2).
STAND
60
50
YIELD
40
YIELD
30
20
10
0
After 14 days
After I day
After 14 days
After 1 day
Figure 2. Mean % plant stand and yield of seed pieces cut and treated 1 or 14 days before planting
Effect of season and time of treatment
yields than those treated 14 days prior to planting.
During the autumn plantings, plant stands derived from
seed pieces treated 14 days prior to planting did not differ
significantly (p ≥ 0.05) from those treated the day prior to
planting (Figure 3). However, seed pieces treated one day
prior to planting resulted in significantly (p ≤ 0.05) higher
During the spring plantings, significantly better (p ≤ 0.05)
plant stands and yields were derived from those seed
pieces treated the day prior to planting than from those
treated 14 days prior to planting allowing for wound
healing.
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CHIPS • Maart/April 2016
Tegniese Nuus • Technical News
% STAND / YIELD (T/HA)
120
100
80
STAND
STAND
60
STAND
STAND
YIELD
YIELD
40
0
YIELD
YIELD
20
Spring, 14
days
Autumn, 14 Spring, 1 day
days
Autumn, 1
day
Spring, 14
days
Autumn, 14 Spring, 1 day
days
Autumn, 1
day
Figure 3. Mean % plant stand and yield of seed pieces cut in spring and autumn and spring, 1 or 14 days before planting.
Effect of fungicide treatments
Figure 4 shows that uncut, untreated tubers gave the best
overall results over six seasons. Throughout all three autumn
plantings the uncut, untreated seed tubers resulted in
significantly better (p ≤ 0.05) plant stands and yields than
100
STAND
the treated seed pieces, irrespective of the time of treatment
prior to planting (results not given). During the spring
plantings the uncut, untreated seed tubers did not perform
significantly (p ≥ 0.05) better than most of the seed pieces
treated the day prior to planting, but both stand and yield
was higher (results not given).
YIELD
80
60
40
20
0
FUNGICIDE TREATMENTS (1 - 8) and controls
Figure 4. The mean % stand and yield of fungicide treated, cut tubers and controls
(water treated and uncut tubers) over 6 seasons.
CHIPS • March/April 2016
• Page 33
Tegniese Nuus • Technical News
Fungicide treatments, planting time and wound
healing
Spring planting proved to be more suitable for cutting of
seed potatoes than autumn plantings (Figure 5). As a result
of the high soil inoculum potential values for Fusarium rot
in autumn, cutting of seed must be discouraged during this
period.
120
% STAND / YIELD (T/HA)
100
STAND
AUTUMN PLANTING
STAND
80
STAND
60
STAND
40
YIELD
YIELD
YIELD
20
0
YIELD
Uncut
Cut&treated, Uncut
14 days
Cut&treated,
1 day
Uncut
Cut&treated,
14 days
Uncut
Cut&treated,
1 day
120
% STAND / YIELD (T/HA)
100
STAND
STAND
80
SPRING PLANTING
STAND
STAND
YIELD
YIELD
60
YIELD
YIELD
40
20
0
Uncut
Cut&treated,
14 days
Uncut
Cut&treated,
1 day
Uncut
Cut&treated,
14 days
Uncut
Cut&treated,
1 day
Figure 5. % Stand and yield of cut and uncut, treated and water treated seed tubers and tubers cut and treated
1 and 14 days before planting in spring and autumn.
Conclusions and recommendations
•
•
Cutting of seed for planting in autumn cannot be
recommended as stand and yield of cut seed is lower
than in spring planting when soil is cooler during and
after planting
Treatment of cut seed pieces with fungicides did not
improve stand and yield
Page 34 •
CHIPS • Maart/April 2016
• Wound healing for14 days before planting did not
improve results. C
Source
Final report: Fusarium dry rot on potato in South Africa.
A report written by C Millard on work done by DJ Theron
in the 1990’s. Report available on www.potatoes.co.za/
research/final reports.