SEEDLING INOCULATION STUDIES WITH THE ALFALFA STEM NEMATODE

Abstract

Inoculation tests were carried out to assess the importance of stage of seedling development, variety, inoculum concentration, inoculum carrier, and light treatment on infestation of stem nematodes, Ditylenchus dipsaci (Kühn), in alfalfa seedlings. Inoculation was less effective after the appearance of the unifoliolate leaf. Infestation of the shoot apex was lower in the resistant variety Lahontan than in the susceptible variety Grimm. Inoculum concentration was not a critical factor in screening tests. Carboxymethyl cellulose as an inoculum carrier resulted in high levels of infestation in cotyledons providing the seedlings were exposed to an alternating light-dark or continuous light schedule. Very little cotyledon infection occurred when seedlings were kept in darkness, presumably because the stomata remained closed. Neither inoculum carrier nor light variations influenced infestation in the shoot apex region. Improved screening techniques in the breeding program at Lethbridge have resulted from some of these findings.