The etiology of tulip‐root disease in susceptible and in resistant varieties of oats infested by the stem nematode, Ditylenchus dipsaci (Kühn) Filipjev

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Abstract
SUMMARY: The number of pre‐adult larvae of Ditylenchus dipsaci which invaded seedlings of the oat variety Sun II growing in sand was linearly related to the number of larvae in the inoculum. In seedlings growing on pads, invasion rates were higher but were limited to about 200 nematodes per plant. The respective numbers of larvae invading the susceptible varieties Sun II and Powys and the resistant varieties Manod and Pennant were not significantly different after 3 days. Reproduction occurred in the susceptible varieties, and after 28 days the number of nematodes per plant in the susceptible varieties was about double that in the resistant ones.When the resistant variety Manod was infested at germination, 32.5% of the seedlings were killed after 14 days compared with 45% of the susceptible variety, Sun II, and this difference was significant at the 5% level. Oat and lucerne seedlings were invaded by larvae of both the lucerne and oat races of D. dipsaci but only in the compatible host did reproduction occur. More larvae invaded the pseudostems of oats than the root systems and this difference was significant at the 0.1% level. The nematode reproduced only in the pseudostems.A method for classifying plants attacked by stem nematodes is proposed based on the reaction of the tissues and the multiplication of the nematode within them.