A comparison of tuber slice and whole tuber tests for the assessment of potato resistance to tuber blight Phytophthora infestans (Mont.) de Bary

The resistance of potato tuber tissues to colonization by Phytophthora infestans was compared in 10 selected cultivars in two trials: on tuber slices and whole tubers with cut rose ends. When resistance to sporulation was used as the discriminating criterion, the selected cultivars segregated in a distinctly different order than when arranged according to other resistance components. Both the tuber slice test and the whole tuber test allowed resistance to sporulation to be assessed in the tested group of cultivars. The results obtained in both trials were reproducible and both criteria, i.e. the percentage of mycelium-covered area as well as sporulation intensity were equally useful for the assessment. No significant influence of the fungal growth though the tuber slice tissue was observed on the assessment of sporulation in comparison to the whole tuber test where the fungus grew directly on the wounded tissue after inoculation. Assessment of the percentage of the area of the tuber slice exhibiting visible necrosis was found to be useless due to the lack of correlation with two criteria of resistance to colonization used in the whole tuber test, i.e. the rate and depth of penetration. The most useful parameter of the whole tuber test appeared to be assessment of the depth of penetration of the tuber tissues. This parameter showed the least variability and good correlation with other criteria used to evaluate resistance to colonization