Ditylenchus dipsaci is well known for its “race” characteristics in terms of host range preferences. This study established isolates of D. dipsaci occurring in California in monoxenic laboratory cultures to account for different host properties as reflected in nematode growth and development. Microbial contaminants in hosts as well as seed lots varied, thus no single axenization method was found acceptable. Multiple treatments, varying in kinds and sequences of axenizing agents and duration of exposures, were required. Growth rate of all tissues were increased two-fold by the addition of casein hydrolysate and yeast hydrolysate to a literature recommended medium.

Three biotypes of the “onion race”—Mexican, French, and California—and one biotype of the “alfalfa race,” Antelope Valley biotype, were studied. In some regimes, the “type-host” response was observed for “non-type host” tissues, while in other regimes a bias towards maleness or femaleness occurred. This bias, however, was not always directly correlated with density changes. Differentiated rather than undifferentiated or callus tissue of a suitable “non-type host” was requisite for satisfactory population buildup. Blockage in callus cultures probably occurred in embryogenesis. With reduced population buildups on “non-type hosts,” as compared with “type host,” blockage in the nematode life cycle occurred at different steps depending upon the kind of host tissue—whether from the same or from different plants. Our results with two “races” of the stem and bulb nematode indicating “inter racial” and “intra-racial” characteristics in the nominal species, D. dipsaci, host-parasite complex would suggest that this phenomena occurs more generally than has been thought.