Abstract
AbstractPine wilt disease, caused by the pine wood nematode (PWN), Bursaphelenchus xylophilus, has been devastating pine forests in Japan for a century but an effective method for controlling the disease is still needed. Pre-inoculation of the host plant with an avirulent pathogen can induce resistance against subsequent infection with virulent pathogens; this is called 'induced resistance'. Host pine trees have this type of resistance against pine wilt disease but the detailed mechanism is unknown. In this study, 1-year-old potted seedlings of the susceptible Japanese black pine, Pinus thunbergii, were pre-inoculated with an avirulent isolate of PWN (C14-5), as well as an avirulent fungus, Botrytis cinerea, to induce host resistance against PWN. One, 2, 3, 4 and 5 weeks after inoculation, the seedlings were challenged with a virulent isolate of PWN (S10), and the survival of these seedlings was estimated by their external symptoms. Pre-inoculation with either C14-5 or Botrytis delayed the symptom development caused by subsequent inoculation with S10, suggesting that pre-inoculation induced host resistance against PWN. The resistance induced by pre-inoculation with C14-5 lasted for at least 5 weeks, while that induced by Botrytis weakened with time. It has been reported that the PWN survives inside the host seedlings for a long period without causing any symptoms under certain conditions, but Botrytis survives only for a while in the seedlings. Thus, the duration of host resistance induced by pre-inoculation may vary with the viability of the inoculum used for pre-inoculation. In order to obtain durable induced resistance, it may be necessary to repeat inoculations of avirulent microbes to be able to control pine wilt disease.
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