INTRODUCTION
Potato (Solanum tuberosum L.) is the world number one of non-grain food
commodity. The global production of potatoes is 324,181,889 tons grown under an
area reached about 18,596,233 hectares, and the world seed production was
31,567,656 tons (FAO, 2010). Potato has an important position among all
vegetable crops in Egypt, where about 20% of total area devoted for vegetable
production, was cultivated with it. In addition, the total cultivation of potato,
according to estimates of the Egyptian Ministry of Agriculture for the
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year 2012,reached 200 thousands feddans spread over three lugs (summer, Nili
and winter) with a total production reached more than 2 million tons, with an
average productivity about 10 tons per feddan (FAO, 2010).
In the past ten years, processing potatoes was increased in Egypt, both for
the production of potato chips or for French fries. These processes require a
number of specifications to keep the products in high quality. Among the most
important factors is the high net product ratio which is highly associated with the
percentage of dry matter and starch content, in addition to the lack of reducing
sugars. Many researches were directed to increase the quality processing. Tuber
starch is an important quality character for potato crops. Dry matter is, generally,
used as an index of starch content by growers and breeders and it is an important
factor to decide the destination of the produce (Gould and Plimpton, 1985; Estrada,
2000). Tubers with high dry matter content, for example, require less energy and
absorb less oil during frying, and have a drier texture after cooking (Storey and
Davies, 1992). Also; the acceptability of potatoes for processing is largely
dependent on the color of the end product. Color is directly related to the quantity
of sugars in the tuber. The quantity and composition of sugars in tubers are
dependent on cultivar, stage of maturity, occurrence of stress, handling and
storage management practices. Regulation of sugar levels in tubers by proper
production and storage management practices is essential acceptable processing
quality (Prichard, 1993). Delgado et al. (2005) demonstrated in their research that
field plants treated with 5 or 50 mM hydrogen peroxide significantly enhanced tuber
starch accumulation within 6.7% and 30%, respectively. Also, they found that
hydrogen peroxide treated stems were up to 27% thicker than control plants. and
explained that this result mainly due to enlarged medullar parenchyma cells.
However, this research was conducted in an attempt to improve potato plant
characteristic and tuber quality, i.e., productivity, specific gravity, starch, reducing
and total sugars contents to produce acceptable crisp at the end through spraying
the field growing plants with some different concentrations of hydrogen peroxide.
MATERIALS AND METHODS
Three potato cultivars; namely, Lady Rossetta, Valor and Mondial were
tested in this investigation during two successive winter seasons of 2010 and 2011.
The planting was conducted in the newly reclaimed area in Al-Amria region,
Alexandria governorate. This research was existed to test the effect of hydrogen
peroxide on the potato yield and tuber quality. Hydrogen peroxide was foliar
sprayed once every three days along the growing season starting from the
complete plant emergence until the crop maturing. Three doses of hydrogen
peroxide (25, 50 and 75 mM) were used in the first season, in addition to the
control treatment, which sprayed with water. In the second season, two higher
doses; 100 and 125 mM were added to the levels of tested variable. Tubers were
planted as a whole, 25 cm apart in the row, 6.25 m long and 0.70 m width.
Each treatment comprised of two rows containing 25 seed tubers each. The
experimental plot was 8.75 m2. The plots were under furrow irrigation. It was
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fertilized with 20 m3 of farm manure/ fed. added with soil preparation. It was
fertilized with 45 kg P2O5/fed. in the form of super phosphate 15.5 % added within
planting in the opened row. Potassium was added at 72 kg k2O/fed. added on there
equal doses, within planting, 45 and 60 days after planting. Nitrogen fertilizer
added to the crop in 120 kg N/fed. One quarter of the quantity was added within
planting in the form of ammonium sulphate. The rest of the quantity was added in 3
equal placements in the form of urea 48 % N at, 45, 60 and 75 days after planting.
All the agricultural practices for potato production i.e. green sprouting, irrigation,
pest disease and weed control were practiced as well. The three tested cultivars
were randomly distributed in the block and the spraying with hydrogen peroxide
was randomly distributed within each cultivar. The split-plot design in three
replicates was used, where potato cultivars were placed in the main plots, while
doses of foliar spraying with hydrogen peroxide were occupied the sub-plots.
All the agricultural practices used for commercial potato production, as
common in this area, were carried out in both years.
Measurements
Vegetative growth and yield parameters: average of ten plants/ plot was
tested 70 days after planting for measuring plant height (cm), stem diameter (mm)
and counting number of main stem / plant. At harvesting time (120 days after
planting), the following determinations were estimated: total tuber yield / feddan
(ton/ fed.); where the produced tubers per plot were weight and converted into
tons/ fed. Average number of tubers/ plant was estimated using the average 10
plants. Number of tubers/ 10 kg was determined by taking a random sample of 10
kg of tubers from the yield of each treatment then their tubers were counted. The
accepted category is that count 72-112 tubers in such treatment.
Physical and chemical characteristics: Chlorophyll content was determined
using the method of (Grodzinsky and Grodzinsky, 1973) 75 days after planting.
Tuber shape index was estimated by dividing the length over the width of the tuber.
Dry matter (%): was determined by drying the tuber slices at 70° C for 24 hr
until a constant weight by dividing the (dry weight/ fresh weight) x 100 (Haase,
2003).
Specific gravity: was determined using the method described by Dinesh et
al. (2005):
Weight of tuber in air
Specific gravity = ----------------------------------------------------------------------------
Weight of tuber in air - weight of tuber under water
Starch (%); it was determined using the method described by A.O.A.C.
(1980) on dry matter basis.
Total and reducing sugars (%): were determined using the method of
Dubios et al. (1956) method on fresh weight basis.
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Crisp net percentage (was recorded only in the first year): where some
potato slices were weight and deep fried at 170°C and the resulted crisps was
weight and related to the fresh weight. Crisps defect evaluation was calculated by
showing the size limits (1/2 cm) for sugar browning and defects using chip-check
chart method to determine the internal, external and undesirable color defects and
dividing the defects to three categories; the first green from 0 - 8 % defects are
acceptable potato chips, the second yellow > 8 – 15 % defects are acceptable
potato chips but with discarding the percentage over 8 % and the third red > 15 %
defects are rejected and not suitable for processing according to (Frito Lay
Company, 1999).
Histological examination: random samples of tubers were taken from each
treatment (three tubers) then peeled and cut with a sharp cork on sliding
microtome into slices 1 mm thickness and 10 mm in diameter. The slices were
mixed and washed with distilled water. Ten randomly slices were examined under
a compound microscope using a high power (400 x) objective to determine the
parenchyma cell diameter, in micron (μm), of potato tubers.
Statistical analysis:
All the collected data from both years were tabulated and statistically analyzed
using analysis of variance technique. Duncan's multiple range test (Steel et al.,
1997) was applied to determine the least significant difference (LSD) at p ≤ 0.05.
RESULTS AND DISCUSSION
1. Effect of hydrogen peroxide concentrations on the studied vegetative
characters:
The data presented in (Table 1) appeared that number of stems per plant
did not significantly affected with the differences in tested concentrations of
hydrogen peroxide (H2O2). Meanwhile, the interaction between the cultivars and
the concentrations of H2O2 was insignificant. Potato plant stem diameter was
positively affected with the increasing of H2O2 concentrations from zero up to 125
mM during 2010/2011 season. The data showed that there were significant
differences among the tested cultivars during the two years of the study. The
cultivars Valor and Mondial positively surpassed the cultivar Lady Rosetta in both
years of the study. The interaction between potato cultivars and the levels of H2O2
was significantly noticed in the second season only. Mean diameter of sixth
internodes of H2O2 treated plants was 27% (5 mM) and 21% (50 mM) greater than
control plants (Delgado et al., 2005). These authors discussed that these results,
mainly, taken place due to enlargement of the medullar parenchyma cells. Same
trend of results were obtained by Moussa et al. (2012).The results of plant height
character showed that spraying potato plants with increased levels of H2O2, did not
significantly affect this character. Same trend of results was, also, noticed for the
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results of the interaction between the tested potato cultivars and the H2O2
concentrations during both years. Valor cultivar, positively, surpassed both Lady
Rosetta and Mondial cultivars in plant height especially in the first season of the
study. The results of Moussa et al. (2012) appeared that no significant effect of the
concentrations of hydrogen peroxide on the plant height during both years of the
study, as well as there were no effects of these concentrations of hydrogen
peroxide on the number of branches per plant in the first year of the experiment.
The results of leaves chlorophyll content (Table 1), clearly appeared that
neither the tested cultivars, nor hydrogen peroxides treatments, nor the interaction
between both factors had the ability to affect the leaves chlorophyll content during
the first year of this research. In the second year, there were significant difference
effects among the tested cultivars. Lady Rossitta and Valor possessed highly
significant values than Mondial cultivar. The tested H2O2 levels affected the
chlorophyll content. The highest mean value was recorded with using 100 mM
H2O2 with insignificant differences effects with both 50 and 125 mM H2O2. The
levels of zero, 25, 50, 75 and 125 mM H2O2 had, significantly, lower values in
comparison with the treatment 100 mM H2O2. As in the first year, the interaction
between the cultivars and H2O2 treatments was not significant.
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Table (1): Mean values, performances of the studied vegetative traits of
tested potato cultivars during both years of 2009/2010 and
2010/2011
Seasons 2009/2010 2010/2011
Chloro
phyll
(mg/g
F.W)
Stem
diamete
r (mm)
No. of
main
stems/p
lant
Plant
height
(cm)
Chloro
phyll
(mg/g
F.W)
Stem
diamete
r (mm)
No. of
main
stems/p
lant
Plant
height
(cm)
Characters
Cultivars
Lady rosetta 41.95b* 3.68a 9.34b 1.019a 34.31b 3.49b 10.21b 1.073a
Valor 46.10a 5.15a 10.45a 1.006a 40.54a 4.73a 11.02a 1.075a
Mondial 40.06b 4.66a 10.11a 0.992a 34.07b 4.63a 10.84a 1.046b
H2O2 Concentration
Control 41.46a 4.47a 8.89d 0.991a 35.82a 4.13a 9.50d 1.053b
25 mM 43.41a 4.62a 9.62c 1.014a 36.41a 4.03a 9.76d 1.038b
50 mM 42.62a 4.40a 10.32b 1.010a 35.80a 4.69a 10.40c 1.068ab
75 mM 42.46a 4.49a 11.03a 1.010a 36.66a 4.17a 10.97b 1.045b
100 mM ---- ---- ---- ---- 36.83a 4.36a 11.71a 1.119a
125 mM ---- ---- ---- ---- 36.31a 4.32a 11.80a 1.066ab
Cultivars x H2O2 Concentration
Control 42.7a 3.8a 8.1a 1.032a 33.4a 2.8a 8.9d 1.092a
Lady rosetta
25 mM 40.4a 3.7a 9.1a 1.014a 34.8a 3.3a 8.9d 1.085a
50 mM 40.6a 3.5a 9.8a 1 .0 8 6 a 33.3a 3.9a 10.0cd 1.093a
75 mM 41.7a 3.7a 10.3a 0.947a 35.2a 3.7a 10.3c 1.054a
100 mM ---- ---- ---- ---- 34.9a 3.8a 11.3b 1.110a
125 mM ---- ---- ---- ---- 34.3a 3.4a 11.7ab 1.007a
Control 42.9a 5.3a 9.3a 1.005a 41.0a 4.9a 10.1cd 1.049a
Valor
25 mM 48.9a 5.2a 10.1a 1.005a 41.1a 4.7a 10.5c 1.045a
50 mM 45.4a 4.6a 10.9a 0.969a 38.9a 5.2a 10.7bc 1.084a
75 mM 47.2a 5.4a 11.5a 1.047a 40.5a 4.2a 11.2b 1.046a
100 mM ---- ---- - --- ---- 41.5a 4.7a 11.9a 1.117a
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125 mM ---- ---- ---- ---- 40.2a 4.7a 11.8ab 1.114a
Control 38.8a 4.3a 9.3a 0.936a 33.1a 4.7a 9.5d 1.020a
Mondial
25 mM 40.9a 4.9a 9.6a 1.025a 33.3a 4.1a 9.9cd 0.984a
50 mM 40.7a 5.1a 10.2a 0.975a 35.2a 4.9a 10.5c 1.028a
75 mM 39.8a 4.3a 11.3a 1.035a 34.2a 4.6a 11.4ab 1.036a
100 mM ---- ---- ---- ---- 34.2a 4.6a 11.9a 1.131a
125 mM ---- ---- ---- ---- 34.5a 4.6a 11.9a 1.078a
* Values with an alphabetical letter, in a comparable group of means, don ׳t differ
significantly from one another using Duncan ׳s Multiple Range Test, at 0.05 level of
significance.
----, not treated during the first year
2. Effect of hydrogen peroxide concentrations on potato yield and its
component characters:
Total potato yield (ton/ fed.) was significantly affected by the tesyed cultivar
(Table 2) during both years. In the first year, Mondial and Valor cultivars over
cropped Lady Rosseta, significantly. In the second year, the Valor cultivar
surpassed the other two cultivars, significantly. The results showed that the H2O2
concentrations did not amend the potato tuber yield, in the first season. The data of
the second season appeared that the levels 25, 50, 75 mM of H2O2 did not differ in
their productivities with the control treatment. The other two high levels (100 and
125 mM) of H2O2 resulted in lower potato yields. The interaction effect between
cultivars and H2O2 was highly significant for both seasons of this research. Moussa
et al. (2012) declared that the highest productivity was obtained as a result of
spraying H2O2 at 40 mM, followed by 60 mM. Data presented for number of tubers
per plant showed that the cultivar Valor exceeded the other two cultivars all over
both years of the study. Non- of the tested hydrogen peroxide levels in the first
season resulted in insignificant effect on number of tubers per plant. The results of
the second seasons declared that the level of 125 mM H2O2 produced the highest
number of tubers per plant without significant differences with the levels 25, 50,
75,100 mM of H2O2.The control treatment (zero level of H2O2) recorded the lowest
mean value without significant differences with the levels 25, 50, 75, 100 mM of
H2O2. No interaction effect was found to change tuber number of plants in the first
year. On the other hand, the interaction was found to be highly significant effects
on such character in the second year of this investigation. The results of Romero
and Lopez-Delgado (2009) detected that the treated plants with H2O2 and
antioxidant such as ascorbic acid lead to reduce the number of mini- tubers, while
enhancing their weights and starch content. Moussa et al. (2012) pointed that
increasing the concentration of H2O2 led to positive effect on the number of tubers
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per plant. Average tuber weight of "Lady Rossitta" cv. was the significantly lower
among the tested cultivars in both seasons of the experiment (Table 2). Nonsignificant
differences between "Valor and Mondial" cv. in the average tuber weight
in both seasons were detected.
Hydrogen peroxide levels did not show any significant difference effects on
the average tuber weight during both years of the study. No interaction effect
between H2O2 level and potato cultivar was noticed to enlarge the average tuber
weight character. Gutierrez et al. (2012) reported that H2O2 treatment induced
higher internal H2O2 concentration, which was associated with positive effects on
tuber weight, starch content and reduction tuber number. The number of tubers per
10 kg was recorded. This character indicates the suitability of potato cultivars for
chipping. There is general agreement among potato processors to use this record.
It ranks between 72-112 tubers/ 10 kg of potatoes, less than 72 tubers/ 10 kg
indicate that the tubers are too large for processing. Data of (Table 2) revealed
that in the first season of the study. All the studied cultivars were in the acceptable
range of this record, meaning that all the tested cultivars are acceptable for potato
processing, with some significant differences among them. In the second season,
all the tested cultivars did not meet the acceptable record for number of tubers/ 10
kg, in which it was above the accepted number. The interaction effect was clearly
noticed to amend the number of tubers/ 10 kg trait.
Table (2): Mean values, performances of yield and yield components of tested
potato cultivars during both years of 2009/2010 and 2010/2011
Seasons 2009/2010 2010/2011
Characters
No. of
tubers/
Plant
Avr.
tuber
weight(
gm)
Crop
yield
(ton/fed.)
Tuber
shape
index
No. of
tuber/
10kg
No. of
tubers/
plant
Avr. tuber
weight
(gm)
Crop
yield
(ton/fed.)
Tuber
shape
index
No. of
tuber/
10kg
Cultivars
Lady rosetta 9.2b* 34.5b 16.16b 0.96c 109.5a 7.9b 49.93b 5.40c 0.94c 199.9a
Valor 10.6a 53.6a 20.70a 1.12b 86.1b 8.2a 70.01a 9.20a 1.04b 121.6c
Mondial 9.9ab 66.6a 21.40a 1.44a 78.7c 7.3c 77.38a 7.02b 1.36a 135.7b
H2O2 Concentration
Control 9.8a 53.3a 19.37a 1.19a 86.7b 7.4b 60.48a 7.51a 1.10a 140.2c
25 mM 9.8a 53.2a 19.77a 1.14b 91.1ab 7.8ab 64.53a 8.03a 1.11a 156.7ab
50 mM 9.9a 49.0a 19.33a 1.18a 95.8a 7.6ab 69.38a 7.70a 1.12a 140.2c
75 mM 10.2a 50.8a 19.21a 1.18a 92.2ab 7.8ab 70.84a 7.66a 1.11a 152.0b
100 mM ---- ---- ---- ---- ---- 7.9ab 69.49a 5.77c 1.13a 153.1ab
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125 mM ---- ---- ---- ---- ---- 8.3a 59.92a 6.56b 1.10a 157.8a
Cultivars x H2O2 Concentration
Lady rosetta
Control 9.9a 35.1a 17.06a 1.02c 114.3a 7.8a 42.0a 5.34a 0.96ef 213.3a
25 mM 8.8a 33.5a 15.63a 0.87d 107.7a 7.6a 51.9a 5.94a 0.98ef 196.3a
50 mM 9.3a 34.0a 15.63a 0.99c 106.7a 7.8a 48.1a 5.51a 0.97ef 165.7a
75 mM 9.0a 35.8a 16.37a 0.99c 104.3a 8.5a 50.7a 6.38a 0.94ef 196.3a
100 mM ---- ---- ---- ---- ---- 8.7a 51.5a 4.47a 0.92ef 203.3a
125 mM ---- ---- ---- ---- ---- 7.4a 48.9a 4.95a 0.88f 214.7a
Valor
Control 10.4a 61.1a 20.97a 1.13b 79.3a 8.8a 72.0a 10.1a 1.00e 132.7a
25 mM 11.3a 59.7a 22.01a 1.09b 88.3a 8.9a 70.5a 10.8a 1.02de 133.7a
50 mM 9.7a 44.4a 19.84a 1.14b 96.0a 8.3a 74.2a 9.81a 1.10d 126.3a
75 mM 10.6a 49.6a 20.41a 1.14b 96.0a 8.7a 78.7a 10.4a 1.10d 121.0a
100 mM ---- ---- ---- ---- ---- 8.8a 75.2a 7.51a 1.10d 129.3a
125 mM ---- ---- ---- ---- ---- 8.7a 71.7a 7.25a 1.00e 128.7a
Mondial
Control 9.8a 63.9a 21.80a 1.46a 79.0a 7.2a 70.8a 7.68a 1.40b 132.7a
25 mM 9.4a 66.6a 21.93a 1.47a 77.7a 6.8a 69.1a 7.68a 1.32bc 131.0a
50 mM 10.1a 68.7a 21.84a 1.43a 75.0a 6.8a 74.3a 8.12a 1.30c 128.0a
75 mM 10.4a 67.2a 20.71a 1.43a 71.0a 5.9a 83.2a 6.51a 1.34bc 138.7a
100 mM ---- ---- ---- ---- ---- 8.1a 78.1a 5.60a 1.50a 131.3a
125 mM ---- ---- ---- ---- ---- 8.1a 80.5a 6.68a 1.40b 152.7a
*Values with an alphabetical letter, in a comparable group of means, don ׳t differ
significantly from one another using Duncan ׳s Multiple Range Test, at 0.05 level of
significance.
----, not treated during the first year
3. Effect of hydrogen peroxide concentrations on potato physical, chemical
and quality characters:
Mondial cultivar showed the biggest mean value of tuber shape index
among the studied cultivars in both years (Table 3). This means that this cultivar
has more long tubers than the others. The data recorded that in the first season 25
mM of hydrogen peroxide resulted in significant difference than the other
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treatments, in which it decreased the tuber shape index. This means that the tuber
became more round than the other treatments. In the second season, H2O2
concentrations had nothing to do with the tuber shape index. The interaction was
only significant in the second year of the study. Specific gravity of tubers of Lady
Rossitta cultivar was the highest among all the studied cultivars in both seasons
(Table 3).
Kunkel et al. (1951) and Lana et al. (1970) reported that specific gravity of
row potato is widely accepted by the potato processing industry as a measure of
total solids, starch concentration and other qualities. Neither the tested H2O2 nor its
interaction with potato cultivar had the capacity to change potato tuber specific
gravity in the study. Moussa et al. (2012) detected that the specific gravity trait was
positively affected with foliar application with H2O2 compared with the untreated
plants. Tuber dry matter was significantly affected by potato cultivar in both
seasons of the study (Table 3). "Lady Rossitta" cultivar was the significantly higher
one in dry matter content in both seasons. "Valor" cultivar ranked the second in dry
matter content after "Lady Rossitta" in the second season. This result may point to
that "Lady Rossitta" is the more suitable cultivar among the tested cultivars in
chipping industry. Duran et al, (2007) stated that dry matter is particularly important
in the production of potato chip because of greater surface area to volume ratio in
chips compared with fries. Stevenson et al. (1964) explained that dry matter
concentration of tubers is an important measure of quality to assess suitability for
processing purpose as it influence process efficiency, product yield and oil
absorption. None of the studied levels of H2O2 treatments and their interactions
with potato cultivars showed significant effect on potato tuber dry matter content
during the second year of this study. In the first year, the data of (Table 3),
appeared that spraying potato plants with 70 or 50 mM of H2O2 significantly
increased dry matter percentage compared with the control treatment. Delgado et
al. (2005) reported that H2O2 used to spray potato plants and lead to increase dry
matter. "Lady Rossitta" cv. showed the highest significant level of starch content
compared with the other tested cultivars (Table 3) during both years of this
investigation. "Valor" cv. was not significantly different than "Mondial" cv. in the first
year. In the second year, there was significantly difference between these two
previous cultivars. "Mondial" cv. came the third one in this respect. This result may
be related to the cultivars differences. This result may point to that "Valor" cv. is
more suitable than both others cultivars to be used in crisp production depending
on its starch content. Owing to its economic importance, potato tuber starch has
the subject of considerable research effort, with an accelerating rate of progress in
recent years. The data cleared that there were pronounced effects noticed as a
result of hydrogen peroxide on potato tuber starch content. Both treatments 75 and
50 mM of H2O2 produced the highest levels of tuber starch content in the first year
of the study. Spraying potato plants with 75 mM of hydrogen peroxide produced
the highly tuber starch content with significant differences among the other tested
treatment in the second year of the study. No interaction effects were found
between cultivar and H2O2 level to change tuber starch contents during both
seasons of this study. Generally, it could be calculated that spraying growing plants
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with the concentration of 75mM H2O2 gave the highest values of potato tuber
quality. Total sugars were not affected by neither potato cultivar nor H2O2
concentration or their interaction during the first season. The differences among
potato cultivars were found only in the second season, as well as the differences
among the H2O2 concentrations. The interaction was not affected significantly.
Reducing sugars content did affect neither H2O2 concentrations nor the interaction
between potato cultivar and H2O2 concentration in the present study. The
significance in total sugars was only detected among the tested cultivars. Reducing
sugars of "Valor" cv. showed higher significantly value than the other tested
cultivars in the first season of the study. "Lady Rossitta" possessed the highest
significant value for reducing sugars comparable with valor and Mondial cultivars
during the second season. Talburt and Smith (1987) claimed that level of reducing
sugars is one among of the four primary factors determining French fry quality.
French fry color is largely determine by the reducing sugars content of the potato
tuber; potatoes with high reducing sugars level make dark fries, when potatoes are
fried, the reducing sugars react with amino acids in the tuber to form dark
products in amino-enzymes browning reaction. The concentration of reducing
sugars in the potato tuber depends on cultivar, growing conditions, maturing and
storage conditions (Surmacka, 2002). As with French fries, the color of potato
chips depends on the reducing sugars content of the potato (Biedermann, 2003).
However, potato chip processors have slightly loss control over reducing sugars
levels because blenching is not option in chipping process. The net crisp product of
Mondial exceeded Lady Rossitta and Valor, significantly (Table 4). Likely, "Lady
Rossitta" produced much net crisp than Valor. This result means that the high net
crisp production cultivar is desired by the potato processors because the cost
production will be reduced. Potato crisp have been popular salty snacks for ISO
years and it sale in USA are about 6 $ billion/ year, repressing 33% of the total
sales of their market (Gurayo and Moreira, 2000 and Clarke, 2003). Applying H2O2
at 25 or 50 mM increased the net crisp production. Application of 75 mM slightly
reduced the net crisp production significantly than 25 or 50 mM treatments. The
control treatment was significantly differed than any of the tested H2O2 levels used
in this study. It gave the lowest net crisp percentage. No interaction effect was
noticed between potato cultivars and the levels of H2O2 to change the net crisp
production.
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Table (3): Mean values, performances of tuber quality characteristics of
tested potato cultivars during both years of 2009/2010 and
2010/2011
Seasons 2009/2010 2010/2011
Characters Starch%
Total
Sugars
%
Reduce
Sugars
%
Dry
matter
%
Specific
Gravity Starch%
Total
Sugars
%
Reduce
Sugars
%
Dry
matter
%
Specific
Gravity
Cultivars
Lady rosetta 14.62a* 6.8a 3.56ab 23.1a 1.089a 10.50a 11.7c 4.97a 18.8a 1.074a
Valor 12.94b 7.3a 4.10a 19.1c 1.078b 10.10b 12.5a 4.55b 18.2b 1.071b
Mondial 12.91b 7.4a 3.37b 19.9b 1.078b 9.04c 11.9b 4.27b 17.5c 1.067c
H2O2 Concentration
Control 13.13b 7.1a 3.56a 20.1b 1.081a 10.10b 12.0b 4.36a 17.9a 1.070a
25 mM 13.42b 7.0a 3.82a 20.7ab 1.082a 9.73b 12.1b 4.31a 18.2a 1.071a
50 mM 13.10b 7.1a 3.66a 21.0a 1.082a 10.10b 13.1a 4.41a 18.1a 1.070a
75 mM 14.31a 7.5a 3.67a 21.0a 1.082a 10.85a 11.8b 4.53a 18.1a 1.070a
100 mM ---- ---- ---- ---- ---- 9.15c 12.2b 5.04a 18.2a 1.071a
125 mM ---- ---- ---- ---- ---- 9.45c 11.0c 4.94a 18.3a 1.071a
Cultivars x H2O2 Concentration
Lady rosetta
Control 14.35a 6.5a 3.0a 23.3a 1.087a 10.70a 11.4a 4.51a 18.7a 1.073a
25 mM 14.55a 6.8a 3.7a 23.1a 1.087a 9.80a 11.4a 4.31a 19.0a 1.074a
50 mM 14.10a 6.9a 3.6a 23.0a 1.089a 10.70a 11.4a 4.58a 18.8a 1.070a
75 mM 15.50a 7.0a 3.5a 23.1a 1.089a 11.40a 12.4a 5.61a 18.8a 1.073a
100 mM ---- ---- ---- ---- ---- 10.00a 12.6a 5.02a 18.6a 1.073a
125 mM ---- ---- ---- ---- ---- 10.50a 11.0a 5.80a 19.0a 1.075a
Valor
Control 12.95a 7.5a 3.9a 18.6a 1.077a 10.40a 12.7a 4.18a 18.0a 1.070a
25 mM 12.60a 7.3a 3.5a 19.6a 1.076a 10.50a 13.5a 5.07a 17.9a 1.069a
50 mM 12.60a 7.4a 3.9a 19.0a 1.077a 10.20a 13.5a 4.20a 18.1a 1.071a
75 mM 13.60a 7.3a 3.7a 19.3a 1.078a 11.65a 12.7a 4.26a 18.5a 1.072a
100 mM ---- ---- ---- ---- ---- 9.15a 11.4a 4.72a 18.1a 1.072a
125 mM ---- ---- ---- ---- ---- 8.70a 10.8a 4.90a 18.3a 1.071a
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Mondial
Control 12.10a 7.4a 3.2a 18.7a 1.079a 9.20a 11.7a 4.41a 17.2a 1.066a
25 mM 13.10a 7.2a 3.4a 20.2a 1.079a 8.90a 12.1a 4.11a 17.6a 1.068a
50 mM 12.60a 7.1a 3.5a 20.5a 1.077a 9.20a 12.6a 4.45a 17.3a 1.066a
75 mM 13.85a 8.1a 3.4a 20.0a 1.078a 9.50a 11.3a 3.73a 17.1a 1.065a
100 mM ---- ---- ---- ---- ---- 8.30a 12.6a 5.38a 17.9a 1.069a
125 mM ---- ---- ---- ---- ---- 9.15a 10.7a 4.12a 17.8a 1.069a
* Values with an alphabetical letter, in a comparable group of means, don ׳t differ
significantly from one another using Duncan ׳s Multiple Range Test, at 0.05 level of
significance
----, not treated during the first year
Table (4): Means values, performances of the net crisp production of tested
potato cultivars during winter season of 2009/ 2010
Seasons 2009/2010
Characters Net crisp production
Cultivars
Lady rosetta 32.57 b*
Valor 31.33 c
Mondial 34.65 a
H2O2 Concentration
Control 31.81 c
25 mM 33.31 a
50 mM 33.39 a
75 mM 32.89 b
100 mM ----
125 mM ----
Cultivars x H2O2 Concentration
Lady rosetta
Control 32.48 a
25 mM 32.40 a
50 mM 32.90 a
75 mM 32.89 a
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100 mM ----
125 mM ----
Valor
Control 29.46 a
25 mM 32.00 a
50 mM 31.20 a
75 mM 30.52 a
100 mM ----
125 mM ----
Mondial
Control 34.06 a
25 mM 35.59 a
50 mM 34.90 a
75 mM 34.96 a
100 mM ----
125 mM ----
* Values with an alphabetical letter, in a comparable group of means, don ׳t differ
significantly from one another using Duncan ׳s Multiple Range Test, at 0.05 level of
significance.
----, not treated during the first year
4. Effect of hydrogen peroxide on both tuber parenchyma cells diameter and
tuber chipping defects:
Parenchyma cell diameter (μm) of the tubers of "Valor" cultivar was higher
significantly than the other two cultivars in the first season (Table 5). In the first
second, "Valor" and "Mondial" cvs. parenchyma cells were the significant widest
cells than "Lady Rossitta" cv. which ranked the third. In the first season, H2O2
treatments affected parenchyma cell diameter. The treatment 50 mM possessed
the highest value with insignificant different effects with the treatments zero and 75
mM H2O2. The lowest value was produced by the treatment 25 mM. In the second
season, spraying potato plants with 25 or 125 mM of H2O2 increased the diameter
of parenchyma cells. The treatment 100 mM ranked the second followed with both
the treatments 50 and 75 mM, while the unsprayed plants treatment produced the
lowest value for parenchyma cell diameter. Moussa et al. (2012) reported that
parenchyma cells diameter was affected with H2O2 concentrations. The ratio of
increasing in tuber parenchyma cell diameter reached 9.34 % as compared with
none treated plants. It is known that starch is mainly stored in cells located
parenchyma cells in tubers and thus increasing the diameter of parenchyma cells
lead to an increasing in starch content of tubers and these tubers has a positive
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impact on increasing the proportion of tubers dry matter. This result is in harmony
with that obtained by Delgado (2005) who stated that the applying H2O2 lead to
enlarged medullar parenchyma cells. The interaction effect between cultivar and
H2O2 was significant during the two years of this study.
The data of Potato chips defects are tabulated in (Table 6). This character
was tested only in the season of 2009/2010. Chips quality is a collection of many
characteristics and color is one of the most important traits. In general, yellowish
brown (Burton et al., 1992), uniform light golden (Stevenson et al., 1964), and
lighter colored (Cunningham and Stevenson, 1963) crisps are preferred. The
results showed that the tested cultivars differed significantly for potato chips
defects. It appeared that the cultivar "Lady Rossetta" pronounced the lowest
defects followed by the cultivar "Mondial" while the cultivar "Valor" gave the highest
value for chipping defects. Crisps quality is influenced by both genotypic and
environmental factors (Stevenson et al., 1964). The data presented clearly showed
that spraying potato plants with hydrogen peroxide treatment had significant effects
on the tuber chipping defects. The lowest defects were produced when the plants
sprayed with 50 mM H2O2. There were no significant differences effects between
the two treatments 25 and 75 mM H2O2. The control treatment gave the worst
result where this treatment produced highly significant level of tuber chipping
defects. This result may be related with the previous obtained results for tuber dry
matter, tuber starch content and parenchyma cell diameter where the control
treatment gave the lowest level for these traits. This research explained that the
best results for the previous mentioned traits were given when the plants were
sprayed with 50 or 75 mM of H2O2. There were no significant interactions effects
noticed between the tested cultivars and the hydrogen peroxide treatments.
Table (5): Means values, performances of parenchyma cell diameter of tested
potato cultivars during both years of 2009/2010 and 2010/2011
Seasons 2009/2010 2010/2011
Characters Parenchyma cell diameter (μm) Parenchyma cell diameter (μm)
Cultivars
Lady rosetta 208.3 b* 186.9 bc
Valor 234.4 a 217.1 a
Mondial 216.2 b 220.9 a
H2O2 Concentration
Control 219.0 ab 200.3 d
25 mM 212.1 b 216.6 a
50 mM 225.9 a 202.1 cd
75 mM 221.4 ab 205.4 c
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100 mM ---- 209.5 b
125 mM ---- 215.9 a
Cultivars x H2O2 Concentration
Lady rosetta
Control 192.5 c 194.9 bc
25 mM 207.7 bc 188.8 c
50 mM 220.6 bc 176.6 c
75 mM 212.6 bc 184.5 c
100 mM ---- 169.8 c
125 mM ---- 194.3 bc
Valor
Control 256.0 a 199.8 bc
25 mM 223.6 bc 224.2 ab
50 mM 226.7 b 232.8 ab
75 mM 224.3 bc 202.2 bc
100 mM ---- 224.3 ab
125 mM ---- 208.9 bc
Mondial
Control 212.6 bc 212.6 b
25 mM 202.2 c 233.4 ab
50 mM 223.6 bc 202.8 bc
75 mM 213.8 bc 231.0 ab
100 mM ---- 217.5 ab
125 mM ---- 235.8 a
*Values with an alphabetical letter, in a comparable group of means, don ׳t differ
significantly from one another using Duncan ׳s Multiple Range Test, at 0.05 level of
significance
----, not treated during the first year
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Table (6): Means values, performances of chips defects of tested potato
cultivars during winter season of 2009/ 2010
Seasons 2009/2010
Characters Chipping defects
Cultivars
Lady rosetta 0.28 c*
Valor 10.25 a
Mondial 4.63 b
H2O2 Concentration
Control 6.11 a
25 mM 5.07 b
50 mM 3.94 c
75 mM 5.08 b
100 mM ----
125 mM ----
Cultivars x H2O2 Concentration
Lady rosetta
Control 0.87 a
25 mM 0.2 a
50 mM 0.0 a
75 mM 0.0 a
100 mM ----
125 mM ----
Valor
Control 10.93 a
25 mM 11.27 a
50 mM 8.40 a
75 mM 10.40 a
100 mM ----
125 mM ----
Mondial
Control 6.53 a
25 mM 3.77 a
50 mM 3.43 a
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75 mM 4.80 a
100 mM ----
125 mM ----
*Values with an alphabetical letter, in a comparable group of means, don ׳t differ
significantly from one another using Duncan ׳s Multiple Range Test, at 0.05 level of
significance.
----, not treated during the first year
Conclusions
It could be concluded that spraying potato plants with hydrogen peroxide
positively affected the breadth of parenchyma cell diameter leading to increase
tubers starch content, under the conditions of this study. The final results of this
research conducted that spraying potato plants with hydrogen peroxide at the rates
of 50 or 75 mM starting from 40 days of planting twice a week until maturity stage
led to enhancement potato tuber quality which produced the highest values for
both tubers starch and dry matter, highest percentage of net crisp with lowest
percentage of chipping processing defects.
