The distribution of closely related large genets of Heterobasidion parviporum in a Todo fir (Abies sachalinensis) stand in Hokkaido, Japan

Abstract

The distribution of genets of a root and butt rot pathogen Heterobasidion parviporum was studied in a 68-year-old Abies sachalinensis plantation in Japan. A total of 33 pure cultures of H. parviporum were isolated from diseased Todo fir stumps after clear-felling. Individual genets of the fungus were identified by three different methods: somatic incompatibility test, random amplified polymorphic DNA, and DNA microsatellite analyses. The combined results of the three analyses identified at least eight genets within a 60 · 100 m plot. One genet, consisting of only one isolate, was genetically differentiated from the other genets by all three methods; the other 32 isolates, however, were grouped with minor discrepancies, into seven genetically close genets. The genetic differentiation was lower than that recorded previously in Europe. A single genet infected 1-15 trees in the plot. The longest distance of the two most isolated trees of a single genet was 51 m. The close genetic relationship between genets and their large sizes suggest that basidiospores from restricted sources (just a few fruiting bodies) infected the site before establishment of the present Todo fir stand and that the disease has spread mainly by vegetative growth of the mycelia through root contact. Absence of fruiting bodies of the fungus in the study plot also suggests the greater importance of vegetative growth than spore dispersal for the spread of this fungus.

Biology, Epidemiology, and Control ofHeterobasidionSpecies Worldwide

“…In old forest sites and in second or later rotation stands, larger genets may develop as the result of the spread of mycelium through root contacts. The two largest genets ever reported measured 50 and 57 m and were caused by H. parviporum in Japan and H. abietinum in Spain, respectively (123,140). In most cases, the largest diameter of individual H. annosum s.l.…”

“…H. annosum s.s. is found all over Europe, except in the very northern regions, and its distribution area extends east to the Altai region in southern Siberia (3,17,68). H. parviporum occurs from the most northern parts of Europe to the southern Alps and from western Europe to China, Japan, and southern Siberia (17,18,68,69,140). H. abietinum is found in central and southern Europe and in the Mediterranean Basin (24, 68,73,81,123).…”

“…Disease incidence is reported to increase with stand age (139) at rates that depend on host species and silvicultural management techniques (140). Site location, soil type, and site history have all been reported to affect disease incidence.…”

The use of mycoviruses in the control of forest diseases

“…This fungal infection causes the death of trees (especially on pines and junipers), severe root and butt rot, general decay and decreased diameter growth in boreal forest and plantations, making it a major threat to timber production and the forest industry. Infection can occur in two ways: primary infection is caused by airborne basidiospores, while secondary infection takes place through colonisation of mycelia after contact with roots or grafting between infected and healthy trees (Asiegbu, Adomas, & Stenlid, 2005;Thor, Ståhl, & Stenlid, 2005;Tokuda, Ota, Hattori, Shoda-Kagaya, & Sotome, 2011;Woodward, Stenlid, Karjalainen, & Hüttermann, 1998).…”