Disease Testing

Diseases 

Dry Rot (NL test): (Fusarium coeruleum and F. sulphureum, separate test conducted for each pathogen):  tubers are wounded and inoculated with a suspension of spores and incubated at 12-15oC. The degree of internal rotting is assessed.

Foliage Late Blight (NL test): greenhouse-grown plants at or near flowering are sprayed with a known R-gene complex isolate(s) of Phytophthora infestans.  Leaf area blighted is scored after 7 days incubation.

Foliage Field Late Blight (IVT test):  test plants grown in small field plots are exposed to spores of known R-gene complex isolate(s) from adjacent infected plants of a susceptible variety.  Leaf area blighted is assessed on at least 3 ocassions.

Tuber Late Blight (NL test):  the rose-end of field-grown tubers is sprayed with a known R-gene complex isolate(s) of Phytophthora infestans.  The number of blighted tubers is counted after 10-14 days incubation.

Common Scab (NL test):   tubers are planted in pots containing artificially infested compost and kept dry during tuber initiation. Severity of common scab is assessed on daughter tubers.

Powdery Scab (NL test):  tubers are planted in pots in compost infested with scab peelings and kept wet during tuber initiation.  Severity of powdery scab is assessed on daughter tubers.

Blackleg (NL test):   tubers are inoculated at heel end with Pectobacterium atrosepticum and planted in an irrigated field trial. The incidence of blackleg is assessed at least 3 times during the growing season.

Black Dot (IVT test):  tubers are planted in a greenhouse in pots filled with a compost infested with mycelia and spores of Colletotrichum coccodes.  The severity of black dot is assessed on daughter tubers after 6 weeks incubation.

Black Scurf (IVT test):  tubers are planted in a greenhouse in pots filled with a compost infested with mycelia of at least 3 isolates of Rhizoctonia solani.  The severity of black scurf is assessed on daughter tubers.

Silver Scurf (IVT test):  tubers are planted in artificially infested compost of Helminthosporium solani and planted in a polytunnel.  The severity of silver scurf is assessed on daughter tubers after 4-5 months incubation at 12-15oC.

Skin Spot (IVT test):  tubers are dipped in a suspension of spores and mycelia of Polyscytalum pustulans and planted outdoors in compost in pots.  The  severity of skin spot is assessed on daughter tubers after 5-6 months incubation at 5-8oC.

Pests

Potato Cyst Nematode (Globodera spp.) (NL test, Separate tests are conducted for G.rostochiensis pathotype Ro1 and G.pallida pathotypes 2/3 and 1):  tubers are planted in pots in  compost infested with a standard concentration of PCN eggs.  Cyst multiplication on roots is assessed. View

Damage

Damage, external (splitting) and internal (bruising) (NL test):  a standard force is applied to the heel end of field grown tubers.  Tubers for ‘splitting’ test are stored at 4-6oC and the incidence of splitting at the point of impact is recorded. Tubers for ‘bruising’ test are stored at 9-11oC and the depth of damage at point of impact measured.

Tuber Quality

External tuber defects:  The weight of tubers >35 mm and < 35 mm is recorded in kg, unmarketable tubers are divided into 10 categories: growth cracks, greens, mis-shapes,mechanical damage, cutworms, common scab >25% surface area covered, late blight, wet rots and other faults. The weight of each category is recorded in kg.

Internal tuber defects:  The number of tubers with hollow heart, internal blemishes or other defects is recorded by cutting, initially, 25 tubers. If any faults are found in this sample, a further 25 tubers are cut.

View the official Value for Cultivation and Use (VCU) protocols and procedures documents on the Fera website.