Propagation and Effects of the Pinewood Nematode on Calli of Various Plants

Abstract

Bursaphelenchus xylophilus and its closely related species, B. mucronatus were successfully propagated well on calli of tobacco (Nicotiana tabacum), alfalfa (Medicago sativa) and several pine species. Different propagation rates or different maximum populations were recorded. Most nematodes occurred in the outer layer of the callus, in which cells appeared to be dead. Tannin accumulated in the nematode- inoculated callus tissues. The correlation of the tannin content with the number of Many studies have been done on pine wilt disease caused by the pinewood nematode, Bursaphelenchus xylophilus (STEINER and BUHRER) NICKLE. Several of these studies have focused on host resistance and on chemical components of the host that attract nematodes or promote their reproduction3' 15) as well as factors that inhibit invasion of host tissue3) or affect nematode mobilityn. FUTAI and FURUNO7 who inoculated the pinewood nematodes into young trees of 30 pine species, showed that resistance to the pinewood nematode varies among pine species. They correlated the differences in host resistance to taxonomic categories of pines (sensu CLITCHFIELD and LITTLE, 1966), but could not explain the cause of such differences. The mechanisms of pine wilt and host resistance have been studied by propagating B. xylophilus on tissue cultures of various plants. For example, TAMURA and MAMIYA13, 14) observed that B. xylophilus feeds and reproduces on the calli of Pinus densiflora and P. thunbergii, both of which are susceptible to pine wilt. TAMURA and DROPKINI1) propagated B. xylophilus on the callus of P. jeffreyi which is a resistant species to pine wilt. B. xylophilus has been propagated on calli of non-host plants such as alfalfa (Medicago sativa)12) and Japanese red cedar (Cryptomeria japonica). It is also well-known that B. xylophilus can be propagated on various fungi. These examples demonstrate the nematode's ability to feed and reproduce on various kinds of plant callus tissues and fungal cells. In the present study, the population buildup of B. xylophilus and that of non-pathogenic related species B. mucronatus were compared on calli of four pine species and alfalfa. In addition, the reproduction of B. xylophilus was also examined on calli of the F1 hybrid of P. thunbergii x P. massoniana and N. tabacum. Special consideration was also paid to the effect of nematode feeding and population buildup on callus responses, and to the way this relates to resistance shown in nursery trees. Tannin production in inoculated callus was also determined, which is known to be associated with host resistance to the pinewood nematode6). Nematode feeding and movement on callus cultures was also observed microscopically.