Abstract: Field trials were conducted in Hartland, New Brunswick, Canada to study the effect of in-storage treatment of seed potatoes with hydrogen peroxide (H2O2) on emergence and yield parameters of Dark Red Norland potatoes. The trials included: (1) an untreated control; (2) control untreated with H2O2 in storage but sprayed with a mixture of H2O2 and water at a rate of 1:100 before planting; (3) potatoes treated with H2O2 in storage at 1:50 rate for 16 weeks and (4) potatoes treated with H2O2 in storage at 1:50 rate for 16 weeks and then sprayed with H2O2 at 1:100 rate prior to planting. Plant emergence was assessed and percent emergence was calculated 45 days after planting. Potato tubers were graded for total yield, tuber size, tuber weight, tuber number and miss-shaped tubers. Tuber sizes included the following categories: <1.75``, >1.75``<=2.0``, >2.0``<=2.25``, >2.25``<=2.75``, >2.75``<=3.0``, >3.0``<=3.25`` and >280 g. Marketable yield which included all tubers measuring >2`` in diameter was also calculated. Among these treatments, application of H2O2 in storage and then treating seed pieces before planting with H2O2 at the rate of 1:100 resulted in significantly higher percentage of seedling emergence and total and marketable yields compared to other treatments. The remaining three treatments did not differ significantly among each other with respect to percent seedling emergence and total and marketable yields. Results of this study indicated that under the conditions followed in these trials, H2O2 had no negative effect on sprouting, seedling emergence or yield. This is the first study of its kind to examine the effect of storage treatment of potatoes with H2O2 before planting on yield parameters of potato, including emergence, yield, size and weight of harvested tubers.
INTRODUCTION
Significant post-harvest losses of potatoes (Solanum tuberosum L.) are caused by the invasion of fungi, bacteria and other organisms and losses caused by post-harvest diseases of fruits and vegetables are cited to be of severe nature (Snowdon, 1990, 1992; Waller, 2002). Microorganisms attack fresh products easily and spread quickly, as such products lack natural defense and possess a reservoir of nutrients and moisture to support microbial growth. Losses in potato storages are mainly due to decay caused by various pathogens (Meijers, 1987a; Snowdon, 1992; Afek et al., 1999). Storage diseases are difficult to control due to the scarcity of registered chemical products for post-harvest use. The prevalence of favorable atmospheric conditions in storages is congenial for the spread of post-harvest potato pathogens.
Generally, fruits and vegetables are prone to infection in the field during crop development. Although growers grade out infected fruits and tubers before storage, some symptoms in their early stages of development go unnoticed. In some cases the infection that does occur in the field is usually latent and the actual development of rot or decay takes place after harvest and during storage period.
Post-harvest rots are more prevalent in fruits and vegetables that are bruised or otherwise damaged than in undamaged products. Bruises and other mechanical damage not only detract from the appearance of the product, but are good avenues of entrance for decay organisms. In storage, humid and warm storage conditions encourage the growth of microbial contaminants. The losses under storage conditions are caused by diseases such as silver scurf, soft rot, dry rot, pink rot and others (Snowdon, 1992; Afek and Warshavsky, 1998; Secor and Gudmestad, 1999; Carnegie et al., 2003) and it is necessary to prevent storage losses by use of post-harvest treatments. Curing potatoes before storage is one of the important procedures performed by potato growers in order to protect tubers from disease causing pathogens (Meijers, 1987b). Products such as chlorine dioxide, ozone and hydrogen peroxide have been reported to inhibit the growth of certain storage pathogens (Afek et al., 1999, 2001; Olsen et al., 2000; Norikane et al., 2001; Al-Mughrabi, 2005a, 2006). The use of such products in storage could provide alternative tools that help achieve disease suppression.
Hydrogen peroxide is an environmentally friendly surface disinfestant whose activity is based on oxidation of fungi and bacteria (Aharoni et al., 1994; Fallik et al., 1994; Afek et al., 1999). The product is effective in controlling early blight in potato storage and pink rot and late blight pathogens in vitro (Al-Mughrabi, 2005a, b, 2006). The present study examined whether storage treatment of potatoes with H2O2 before planting has a negative effect on yield parameters of potato, including emergence, yield, size and weight of harvested tubers.
MATERIALS AND METHODS
H2O2 Application in Storage
OxiDate™ (27% hydrogen peroxide; H2O2), a clear,
colorless liquid with a pungent odor (freezing point, -30°C; specific gravity,
1.09; pH, 1.33; solubility, complete) was supplied by BioSafe Systems, CT, U.S.A.
and used in this study. Two post-harvest treatments: (1) untreated control and
(2) treatment with H2O2 and water applied at the rate
1:50 (v/v) were applied to seed potato tubers (cv. Dark Red Norland) in storage
daily for 2 weeks (8 h day-1) and then once (8 h week-1)
for 14 weeks. Each treatment was carried out in a separate storage bin to prevent
cross contamination. Bins were set at approximately 50°F and 90+% RH. The
control treatment was treated with sterile distilled water. All treatments were
applied using a fogging system connected to a 5 hp air compressor (Al-Mughrabi,
2005a). Airflow (1.25 CFM/100 cwt) was turned on at the same time as the
fogging system to allow the fog to spread through the tubers. The fogging system
consisted of a 14-gallon water tank, timer, fogging controller and air and water
solenoids mounted on a free standing wooden support frame. Air and water hoses
were placed under a 1 ft high pallet next to the plenum. The fogging system
was calibrated to emit an amount of 4-gal/8 h. The storage trials were conducted
in 2003 in Wicklow, New Brunswick, Canada.
Seed Preparation and Treatment
Storage-treated potato seed pieces (control and 1:50 H2O2)
weighing 50-65 g each were exposed to one of four treatments: (1) untreated
control; (2) control untreated with H2O2 in storage and
sprayed with H2O2 at 1:100 rate before planting; (3) H2O2
treated potatoes in storage at 1:50 rate for 16 weeks and (4) H2O2
treated potatoes in storage at 1:50 rate for 16 weeks and sprayed with
H2O2 at 1:100 rate prior to planting.
Experimental Setup
The experiments were designed as one-way completely randomized block with
four treatments that were replicated four times. Each replicate consisted of
25 ft long row and the seed pieces were planted with a spacing of 10''. The
distance between the rows was maintained at 3 ft. Agricultural practices commonly
performed by potato growers in New Brunswick were followed throughout the growing
season (Bernard et al., 1993). The field trials
were conducted in 2004 in Hartland, New Brunswick, Canada.
Data Collection and Analysis
Plant emergence was assessed and percent emergence was calculated 45 days
after planting. Potatoes were graded for total yield, tuber size, tuber weight,
tuber number and miss-shaped tubers. Tuber sizes included the following categories:
<1.75'', >1.75''≤2.0'', >2.0''≤2.25'', >2.25''≤2.75'',
>2.75''≤3.0'', >3.0''≤3.25'' and >280 g. Marketable yield which
included all tubers measuring >2'' in diameter, was also calculated. Potato
tubers <2'' in diameter and miss-shaped were excluded when marketable yield
was calculated. Data were statistically analyzed using CoStat (CoHort Software,
Monterey, CA, USA) and the means were separated using LSD test at p = 0.05.
All data were pooled and presented.
RESULTS AND DISCUSSION
Effect of H2O2 Treatment on Emergence
The effects of treatments on seedling emergence were variable. Seed treated
with H2O2 in storage for 16 weeks at 1:50 rate and sprayed
with H2O2 at 1:100 rate before planting was significantly
different from all other treatments and recorded the highest percent seedling
emergence (84.17%). The other three treatments did not differ significantly
at p = 0.05 (Table 1). The effect of H2O2
on seedling emergence was higher when it was used both during storage
and before planting. Hydrogen peroxide aided in protecting seed tubers from
seed- and soil-borne pathogens and consequently improved emergence. The role
of hydrogen peroxide in plant disease response in the form of having antimicrobial
effect (Wu et al., 1995), structural changes
in the plant’s cell wall (Dean and Kuc, 1987; Brisson
et al., 1994), production of toxic, lipid free radicals (Keppler
and Baker, 1989) and activation of phytoalexin synthesis (Chai
and Doke, 1987; Apostol et al., 1989) are
reported earlier.
Effect of H2O2 Treatment on Total and Marketable Yield
Tubers treated with H2O2 both in storage and at planting
recorded significantly higher total tuber yield (219 cwt/acre) compared to the
other three treatments (Tabe 1). Treatment of seed tubers with H2O2
in storage for 16 weeks at 1:50 rate and spraying with H2O2
at 1:100 rate before planting was significantly different from all other
treatments resulting in highest marketable tuber yield of 202 cwt/acre. The
other three treatments did not differ significantly from each other at p = 0.05
(Table 1). Application of H2O2 resulted
in higher emergence and higher plant stand, which played a role in the increased
tuber yield. The higher tuber yields are due to the reduction in inoculum’s
level on the seed and also seed tubers protection against soil-borne pathogens.
In studies reported by Afek et al. (1999) where
H2O2 was applied in storage using a fogging system, potato
decay was 4% compared to 26% in non-treated control. Other studies indicated
that H2O2 applications reduced or inhibited potato diseases
in storage and potato pathogens in-vitro (Afek et
al., 1999, 2001; Olsen et
al., 2000; Norikane et al., 2001; Al-Mughrabi,
2005a, b, 2006).
Effect of H2O2 Treatment on Tuber Size and Knobby
Tubers
The treatments had significant effect on the number of tubers of different
sizes except for tubers sized >2.75''≤3.0'', >3.0''≤3.25'' and 280
g (Table 2). The number of tubers was higher in the treatment
with H2O2 both in storage and before planting and was
significantly superior to other treatments (Table 2). Tubers
of different sizes did not differ significantly among treatments with regard
to weight of tubers excluding tubers of >1.75''≤2.0'' and >2.25''≤2.75''
size (Table 3). Seed treatments with H2O2
were significantly superior to other treatments with respect to tuber weight.
| Table 1: | Effect of H2O2 treatments on potato seedling emergence, total yield and marketable yield |
| 1C = Untreated control; OP = No H2O2 in storage + seed treatment with H2O2 at planting (1:100 rate of H2O2 to water v/v); OS = Seeds treated with H2O2 in storage (1:50 rate); OS + OP = Seeds treated with H2O2 in storage (1:50 rate) and at planting (1:100 rate). 2Each value is the mean of four replicates. Within each column, means followed by same letter(s) are not significantly different from each other at p = 0.05 | |
| Table 2: | Effect of H2O2 treatments on number of tubers produced |
| 1C = Untreated control; OP = No H2O2 in storage + seed treatment with H2O2 at planting (1:100 rate of H2O2 to water v/v); OS = Seeds treated with H2O2 in storage (1:50 rate); OS + OP = Seeds treated with H2O2 in storage (1:50 rate) and at planting (1:100 rate). 2Each value is the mean of four replicates. Within each column, means followed by same letter(s) are not significantly different from each other at p = 0.05 | |
| Table 3: | Effect of H2O2 treatments on weight (g) of tubers produced |
| 1C = Untreated control; OP = No H2O2 in storage + seed treatment with H2O2 at planting (1:100 rate of H2O2 to water v/v); OS = Seeds treated with H2O2 in storage (1:50 rate); OS + OP = Seeds treated with H2O2 in storage (1:50 rate) and at planting (1:100 rate). 2Each value is the mean of four replicates. Within each column, means followed by same letter(s) are not significantly different from each other at p = 0.05 | |
None of the treatments had a significant effect on the weight of knobby tubers (Table 3). The weight of knobby tubers was higher in the untreated control treatment while the number and weight of knobby tubers were less in the treatments that received H2O2 (Table 2 and 3). The treatments which involved applications of H2O2 reduced the number and weight of knobby tubers compared to untreated control.
This study indicated that treatment of seed potatoes with H2O2 during storage and again before planting proved to be very effective in improving seedling emergence and resulted in higher total and marketable yields. The treatment with H2O2 recorded less number and weight of knobby tubers compared to control and indirectly was able to produce larger number of tubers. The higher yields were obtained due to the suppression of potato pathogens on or around the seed tubers at planting. This is the first study of its kind that involves the application of H2O2 during ‘potato’ storage and prior to planting and its effect on emergence and yield parameters. The results of the current study suggest that using H2O2 in a proper manner did not inhibit sprouting or germination.
ACKNOWLEDGMENT
This project was financially supported by BioSafe Systems, Inc., CT, USA. Excellent assistance of René Poirier and Vikram Appanna is appreciated.