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. 1: Primary stem infection

Fig. 2: Sprouting of an infected tuber

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
cArtificial inoculation of potato tubers

Artificial inoculation of potato tubers

Fig. 4: Zoospores being released into water

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.
Tab. 1: Numbers of infected tubers in different seed lots (Storage 2007)
SamplesNumber of tubersVisible symtomsPositive PCR-ResultsTotal infected tubers
1940/9435/9437.2%
2951/951/952.1%
3940/946/946.4%
4940/940/940%
5951/950/951.1%
6950/9510/9510.6%
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).
Tab. 2: Emergence of latent infected tubers depending on infection severity in field trials (Site Puch 2003, variety Agria)
Inoculated withEmergence
50 zoospores77.5%
500 zoospores12.5%
1000 zoospores2.5%
Tab. 3: Emergence of latent infected tubers in field trials (average of 6 trials per year [=2 sites: Puch + Straßmoos, 3 planting times])
YearvarietyinoculatedEmergence
2004Agria50 zoospores97.0%
2005Agria50 zoospores80.6%
2006Agria50 zoospores81.5%
  Average86.4%
YearvarietyinoculatedEmergence
2004Quarta200 zoospores86.8%
2005Quarta200 zoospores53.5%
2006Quarta200 zoospores58.0%
  Average66.1%
Fig. 5: Effect of copper seed treatment on primary stem infection (48g/t Cu)

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)

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