Ecological Studies on Dodder (Cuscuta japonica Choisy) in Hokkaido : Seed Germination and Host-Dodder Relationship

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  • Zaroug Mohamed Saeed Ahmed
    Department of Biosystem Management, Division of Environmental Conservation, Graduate School of Environmental Science, Hokkaido University

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The present studies deal with the seed germination of the Japanese dodder (Cuscuta japonica Choisy) and the host-parasite (the dodder) relationship. The seed germination of the dodder is promoted by the pretreatments which are effective on the removal or destruction of the seed coat by submerging in conz. sulfic acid and by scarification. The germination of the acid pretreatment is 58% at 5℃ in 15 days and 98% at 30℃ in 2 days. The burial depth of seeds seems to be effective on the seed germination, paricularly in shallower depth. In the burning experiment the percentages of the seed germination at a 0.5 cm depth are from 2.6% to 5.7% for dormant seeds and 76% for non-dormant seeds. The process of the germination due to burning can be attributed to (1) the burning temperatures and heat pretreatment which break the dromancy of seeds and accelerate the germination at shallower depths and (2) the presence of non-dormant seeds which escape from the damage of fire at deeper depths and can germinate successfully in the post-fire recovery period. There are two host groups -.major host groups and minor host groups. These 2 host groupes are ientified by the author's idea based on 5 criteria and a scoring method. On major hosts, the dodder produces relatively long filaments and show high values of the survival potential; On minor hosts, the dodder produces short filaments and fails to set fruits.

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