Potato haulm resistance to Phytophthora infestans

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Abstract
SUMMARY: Haulm susceptibility to Phytophthora infestans (Mont.) de Bary of fourteen widely differing potato varieties was compared in laboratory and field tests with the maincrop variety Majestic as a standard. These two tests gave similar results except that the early varieties Viola and Arran Pilot were more resistant in the laboratory than in the field.The sequence of infection within the crop canopy was the same in susceptible and resistant varieties, starting first mainly on the lowest leaves on the stem, then the middle and finally the uppermost. This sequence was lost when haulm became prostrate. Varieties differed in the rate that infection spread and leaves were destroyed, some being attacked more rapidly, and others more slowly, than Majestic.In the field the fungus spored on different varieties as in the laboratory test; the annulus was wide and sporulation intense on susceptible varieties, but narrow and sparse on resistant ones.