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

Ditylenchus dipsaci caused cells to enlarge and separate in tissues of the susceptible oat variety, Sun II. Cytoplasm was withdrawn from the cells, the walls of which collapsed to form a cavity around the nematodes. In the resistant variety Manod, separation and hypertrophy were slight, but cytoplasm was withdrawn and cavities formed similar to those in Sun II; hyperplasia or necrosis was not seen.

The body and gonads in nematodes from Manod plants were shorter than from Sun II, but the de Man ratios and the ratio of males to females were the same. Fourth‐stage larvae matured to adults more slowly in Manod seedlings. Nematodes grew by a series of steps caused by alternating periods of slow growth before an ecdysis and rapid growth afterwards. In Manod, D. dipsaci grew more slowly but the form of the growth curve was as in Sun II. Gonads lengthened rapidly and continuously during the late fourth larval and early adult stages and especially during the period before the fourth ecdysis when body length stopped increasing.
RESP-4736