Testing the Efficacy of Agrigold for the control of Erwinia
Mieke Daneel
ARC-Institute for Tropical and Subtropical Crops,
Private Bag X11208, Nelspruit 1200
August 2012
BlueGold Water and Chemicals
Fairland
2195
Introduction
Erwinia rot is a serious problem in the potato industry and a limited amount of effective sanitizing agents are available to control the bacterium in wash water during the packing process. Erwinia spp. can spread very fast in wash water making it even more important to find effective sanitizing agents that can kill the inoculum and prevent further spread of it. This will extend shelf life of potatoes extensively.
Aim
Tests were conducted to determine the efficacy of Agrigold in controlling Erwinia development on petri dishes.
Material and Methods
Two hundred and fifty mℓ solutions, with different concentrations of Agrigold, were prepared in Erlenmeyer flasks using autoclaved water as shown in Table 1. The pH of the solutions was then adjusted to pH 6 using either a NaOH or HCℓ solutions. One mℓ of an Erwinia bacterial suspension containing ~109 cfu per mℓ mixture of bacteria, from an Erwinia culture obtained from cucumber, was then added to each flask. Serial dilutions were made from each flask after 1 hour and then again after 3 hours and plated on bacteriological medium. Bacterial colony counts were made after an incubation period of one day. Each dilution was plated three times. The trial was repeated three times over time under similar conditions.
Table 1 Treatment numbers, active ingredients and dosages tested.
| Treatment | Solution description | Dosage (mℓ /250 mℓ) |
| 1 | Water | – |
| 2 | 1/10000 Agrigold | 0.025 mℓ |
| 3 | 1/5000 Agrigold | 0.05 mℓ |
| 4 | 1/2500 Agrigold | 0.1 mℓ |
| 5 | Sanitizer (QAC) (1000 ppm) | 0.25 mℓ |
Results
The effect of the different treatments on the bacterial viability of Erwinia is shown in Table 2 and 3. From both tables it is clear that Agrigold is able to prohibit growth of Erwinia. At a one hour interval after treatment, in Test 2 a small amount of Erwinia colonies was observed in the 1/10000 Agrigold solution which was still observed in the counts at 3 hours interval. However in the other tests the 1/10000 solution did seem to control Erwinia growth. In Test 1 1/5000 Agrigold also showed a bacterial colony count however this was not seen in the 3 hour interval count or in the other tests executed. It might therefore be considered a contamination.
In the 1/2500 Agrigold, no colonies were observed in any of the tests both at 1 hour and 3 hour intervals.
Table 2 Treatments and bacterial counts at one hour interval after treatment
| Treatment | Test 1 | Test 2 | Test 3 |
| 1 | 7.8 108 | 1.03 107 | 1.62 107 |
| 2 | 0 | 67 | 0 |
| 3 | 2300 | 0 | 0 |
| 4 | 0 | 0 | contaminated |
| 5 | 0 | 0 | 0 |
Table 3 Treatments and bacterial counts at 3 hours intervals after treatment
| Treatment | Test 1 | Test 2 | Test 3 |
| 1 | 2.6 109 | 1.2 108 | 5.8 108 |
| 2 | 0 | 1500 | 0 |
| 3 | 0 | 0 | 0 |
| 4 | 0 | 0 | 0 |
| 5 | 0 | 0 | 0 |
Conclusion
- It can be concluded that Agrigold is effective in controlling Erwinia bacteria at 1/5000 and 1/2500 concentrations.
- This should be tested in the field to confirm the tests done on petri dishes.
Agrigold seems to be an effective sanitizing agent against Erwinia rot.