The effect of copper seed treatment on late blight in potatoes
Primary stem infections (Fig. 1) resulting from Phytophthora infestans infected potato tubers (Fig. 2) are an increasing problem in potato production. In the project ÖKO-SIMPHYT primary stem infections should be reduced by seed treatment with copper fungicides in order to postpone the beginning of the blight epidemic as well as the start of spraying. In the field trials in 2005 and 2006 a copper seed treatment reduced primary stem infection of potato plants and furthermore it decreased infection of daughter tubers with Phytophthora infestans.
Fig. 1: Primary stem infection
Fig. 2: Sprouting of an infected tuber
Materials und Methods
To ensure the appearance of primary stem infections, artificially infected tubers (Varieties Agria and Quarta inoculated with zoospores) were planted in field trials (Fig. 3+4). Subsequently seed tubers were treated with different application methods and copper fungicides. After emergence visible primary stem infections were measured weekly and confirmed by PCR detection. Finally the daughter tubers were analysed for tuber blight by PCR
Artificial inoculation of potato tubers
Zoospores being released into water
Results
Latent infected seed tuber are becoming increasingly important in potato production, because many seed tuber lots are containing latent infected tubers. In 2007 different seed lots (from conventional and organic potato production) were examined by PCR (Tab. 1). The infection incidence ranged from 0 % - 37.2 %, whereas only one lot showed absence of tuber infection.
| Samples | Number of tubers | Visible symtoms | Positive PCR-Results | Total infected tubers |
|---|---|---|---|---|
| 1 | 94 | 0/94 | 35/94 | 37.2% |
| 2 | 95 | 1/95 | 1/95 | 2.1% |
| 3 | 94 | 0/94 | 6/94 | 6.4% |
| 4 | 94 | 0/94 | 0/94 | 0% |
| 5 | 95 | 1/95 | 0/95 | 1.1% |
| 6 | 95 | 0/95 | 10/95 | 10.6% |
Tuber infection with Phytophthora infestans significant decreased emergence depending on severity of tuber infection (Tab. 2+ 3). A copper seed treatment significant decreased primary stem infections of potato plants (Fig. 5).
| Inoculated with | Emergence |
|---|---|
| 50 zoospores | 77.5% |
| 500 zoospores | 12.5% |
| 1000 zoospores | 2.5% |
| Year | variety | inoculated | Emergence |
|---|---|---|---|
| 2004 | Agria | 50 zoospores | 97.0% |
| 2005 | Agria | 50 zoospores | 80.6% |
| 2006 | Agria | 50 zoospores | 81.5% |
| Average | 86.4% | ||
| Year | variety | inoculated | Emergence |
| 2004 | Quarta | 200 zoospores | 86.8% |
| 2005 | Quarta | 200 zoospores | 53.5% |
| 2006 | Quarta | 200 zoospores | 58.0% |
| Average | 66.1% |
Fig. 5: Effect of copper seed treatment on primary stem infection (48g/t Cu)
Fig. 6: Effect of copper seed treatment on tuber blight of daughter tubers (Site Straßmoos 2006)
In 2005 seed treatment resulted in reduced seconda-ry leaf infections. Thus, a delay of the blight epidemic as well as start of spraying were possible. Furthermore a copper seed treatment reduced tuber blight infections of daughter tubers (Fig. 6). The PCR detection applied to daughter tubers showed a decreased latent tuber infection with Phytophthora infestans.
Summary
- Infected tubers resulted in decreased emergence depending on infection severity
- Infected seed tubers can cause primary stem infection
- Copper seed treatment decreased primary stem infection significantly
- Copper seed treatment effected significant reduction of infected daughter tubers