The Effect of HPP on Silver Scurf Disease in Three Potato var. During Storage
U. Afek,1 Janeta Orenstein1 and J.J. Kim2
The effect of HPP (hydrogen peroxide plus) on silver scurf disease caused by the fungus Heliminthosporium solanai Durieu and Mont in 3 potato (Solanum tuberosum) var. during storage was tested. After 6 months of storage, the percentage of infected tubers in the var. ‘Mondial? ‘Avondale?and ‘Cara?following 5 treatments with 10% HPP by fogging the storage rooms via the Shira Aeroponics System, was 1%, 4% and 6% compared with 35%, 39% and 43% in the non-treated control, respectively. Percent decay after a single treatment with 10% HPP 6 months post harvest was 14%, 21% and 26%, respectively. Furthermore, Treatments with HPP controlled the progress of the fungus on the skin of infected harvested tubers.
Key Words: Potato; Solanum tuberosum; storage; HPP; silver scurf; Heliminthosporium solanai.
1Department of Postharvest Science of Fresh Produce, Agricultural Research Organization, Gilat Experiment Station, Mobile Post Negev 2, 85280, Israel.
2The Research Institute of Agricultural Resources Development, Konkuk University, Seoul 143-701, Korea.
Contribution from the Agricultural Research Organization, The Volcani Center, Bet Dagan, Israel. No. 403-00
INTRODUCTION
One of the major reasons for storage loss of potato is decay caused by various pathogens. Among them the fungus H. solanai which causes silver scruff (2,8,10,11). This important disease spreads during storage with no solution to control it.
HPP (hydrogen peroxide plus) stabilized with a mixture of substances (G.A.T.S. Biology, P.O. Box 652 Nes Ziona 74106, Israel), is an environmentally friendly disinfectant, whose activity is based on oxidation of fungi and bacteria was successfully control vegetable pathogens during storage (2,5,7). HPP was also found to inhibit potato sprouting during storage (3,4). Curing of potatoes prior to storage is a standard procedure to protect the tubers against pathogens (9).
The present study examined the effectiveness in preventing silver scurf disease during storage of potatoes by HPP. It was applied with Shira Aeroponics System fogger. This device is based on ultrasonic nebulizers, and produces very small droplets of less than10 m which have a very small mass. Such minute droplets carrying the compound behave as a weightless gas and cover every potato in the storage rooms.
MATERIALS AND METHODS
Plant material and storage procedure
Three potato var.; ‘Mondial? ‘Avondale?and ‘Cara?tubers were harvested from the northern Negev, Israel, cured for 12 days at 13 ± 1° C and 95% relative humidity (RH), and then stored for 6 months at 8 ± 1° C and 95% RH in 6 rooms. Each room (15 x 15 x 7 m3) contained 5 perforated ducts (70 cm in diameter) which were positioned on the floor from the plenum to the opposite wall. These ducts were covered with 750 tons of potatoes, piled 5 meters high (6). For each treatment, 5 sacks, each comprising 25 kg potatoes, were buried at random in each pile. In order to establish infection of the stored potatoes with H. solani, 20 actively tubers infected with this pathogen were mixed randomly among the potatoes in each sack. Additionally, the infected areas were marked to test the effect of HPP on the fungus progress on the tuber skin. The sacks, which had been attached to ropes to help extricate them, were removed from the piles once a month, and the infected tuber percentages were determined. This was repeated for 6 months per year over a three-year period.
Application of HPP
On the first day after curing, the potatoes in rooms A (Mondial), B (Avondale) and C (Cara) received treatment with 10% HPP (sole a.i.) for 10 h. The HPP was applied with the Shira Aeroponics System. Three fans (one m diameter) forced the combination of humidified air and HPP into the bottom of the plenum; this fog reached the perforated ducts, and was then pulled up through the potato pile to the vacuum space produced above the pile (1).
Rooms D (Mondial), E (Avondale) and F (Cara) were the control: the Shira Aeroponics System produced humidified air in the control as described in rooms A, B and C but no HPP was added to the water. In all of the rooms CIPC was applied to the cured potatoes in accordance with standard commercial practices (3,4).
After the treatments, the temperature in the storage rooms was reduced to 8 ± 1° C , and the RH adjusted to 95%; these settings were maintained for 6 months. The treatments were repeated every month for a total of five treatments.
Additionally, following the first treatment, the same number of sacks with tubers as described above were sampled from each pile, and stored under the same conditions as in the source treatments; this helped evaluate the effects of a single treatment with 10% HPP on the disease.
Statistical analysis
The experiment was conducted during 3 years in a randomized block design and a year was considered as one replicate. Each block comprised 15 sacks that was considered as 5 sub samples of 3 sacks for each treatment each month for a total of 90 sacks.
Data were analyzed by ANOVA procedures by means of the Statistical Analysis System (SAS) package (Cary, NC, USA).
RESULTS AND DISCUSSION
Silver scurf disease caused by the fungus H. solanai is a major pathogen that causes storage loss of potatoes. The disease spreads during storage and damages the potato skin. (1,8,11). The potato damage is expressed in 2 ways: First, decreased quality of the tubers. Second, increased weight loss and shrinkage of the potatoes following evaporation of water through the damaged skin.
No technology has been found to control this important disease during storage.
In this study we report in the first time that it is possible to control silver scurf disease of potatoes during storage. Results of the present study showed that the decay percentage after 6 months of storage, after disinfecting the tubers 5 times within storage rooms by fogging with 10% HPP using the Shira Aeroponics System, was 1%, 4% and 6% in the var. Mondial, Avondale and Cara compared with 35%, 39% and 43% in the non-treated control, respectively (Tables 1-3). Similarly, Afek et al.,1999 (2) reported that it is possible to control soft rot disease of stored potatoes caused by the bacterium Erwinia carotovora by using the same technique. Percent decay 6 months post harvest after a single treatment with 10% HPP was 14%, 21% and 26%, respectively (Table 1-3). The fungus progress on the tuber skin of the 3 var. following 5 treatments with 10% HPP was completely stopped. The rate of the fungus progress in the nontreated control was 6-9 mm per month. In the 3 var., after a single treatment with 10% HPP, there was no progress of the fungus in the first month. The rate of the fungus progress on the tubers after the first month was 2-5 mm per month.
Disinfecting by means of the Shira Aeroponics System makes The droplets produced by this fogger are of less than 10 micron diameter, with minimal mass, and leave no condensation on the roots, even in RH up to 98%. This fogger produces a sort of "dry cloud" containing the disinfectant which covers the potatoes without wetting them. This reduces the number of pathogens that could develop on wet tubers.
Disinfection by fogging is easy to implement and is conducted in a closed room, thus eliminating danger to the workers. This new technique opens a new avenue to prolonging the storage life of potatoes with minimal waste. We believe that this technique can be effective for additional stored crops and against other pathogens.
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Tables
Table 1. Decay percentage of potatoes (var. ‘Mondial? following a single or 5 treatments with 10% HPP during 6 months of storage at 8 ± 1° C and 95% RH.
|
|
1 month | 2 months | 3 months | 4 months | 5 months | 6 months |
| 5 treatments | 0 aa | 0 a | 0 a | 1 a | 1 a | 1 a |
| 1 treatment | 0 a | 2 b | 5 b | 7 b | 11 b | 14 b |
| Control | 3 b | 7 c | 11 c | 18 c | 26 c | 35 c |
Different letters within a column indicate significant differences among the
numbers according to Fisher's protected least significant difference test
(P=0.05).
Table 2. Decay percentage of potatoes (var. ‘Avondale? following a single or 5 treatments with 10% HPP during 6 months of storage at 8 ± 1° C and 95% RH.
|
|
1 month | 2 months | 3 months | 4 months | 5 months | 6 months |
| 5 treatments | 0 aa | 0 a | 1 a | 3 a | 3 a | 4 a |
| 1 treatment | 0 a | 3 b | 7 b | 10 b | 15 b | 21 b |
| Control | 5 b | 9 c | 14 c | 21 c | 30 c | 39 c |
Different letters within a column indicate significant differences among the
numbers according to Fisher's protected least significant difference test
(P=0.05).
Table 3. Decay percentage of potatoes (cv. ‘Cara? following a single or 5 treatments with 10% HPP during 6 months of storage at 9 ± 1° C and 95% RH.
|
|
1 month | 2 months | 3 months | 4 months | 5 months | 6 months |
| 5 treatments | 0 aa | 1 a | 2 a | 5 a | 6 a | 6 a |
| 1 treatment | 0 a | 3 b | 8 b | 13 b | 19 b | 26 b |
| Control | 4 b | 8 c | 16 c | 24 c | 33 c | 43 c |
Different letters within a column indicate significant differences among the
numbers according to Fisher's protected least significant difference test
(P=0.05).
Note: Published with author's permission