Spatial distribution of Raffaelea quercivora hyphae in transverse sections of seedlings of two Japanese oak species

Abstract

To compare the distributions of Raffaelea quercivora hyphae within seedlings of a susceptible species, Quercus crispula, and a resistant species, Q. glauca, we examined water conductance at transverse sections. Raffaelea quercivora was inoculated into the stems of seedlings in July (summer) and October (autumn) and observed by light and fluorescence microscopy at 1 and 2 weeks after inoculation. The hyphal distribution patterns expressed as the I d index differed between the species at each occasion. The hyphal growth was wider in Q. crispula than in Q. glauca in July inoculation, but did not differ in October inoculation. Non-conductive sapwood in Q. crispula in transverse section was wider than that in Q. glauca at each occasion. The differences of hyphal growth and hyphal distribution patterns between species as little as 1 week after inoculation reflect differences in host susceptibility to the fungus.

Extent of colonization by Raffaelea quercivora of artificially inoculated living and gamma‐ray‐sterilized seedlings of two Japanese and three American oak species

“…In the present study, inoculations with the fungus caused larger non-conductive areas compared with the controls in Q. coccinea and Q. palustris. In fact, the spatial distribution of R. quercivora hyphae was shown to coincide with non-conductive sapwood (Takahashi et al 2010;Torii et al 2011). However, little is known about the death mechanism of non-native oak species by inoculations of R. quercivora.…”

“…Ito (Ito et al 1998;Kubono and Ito 2002;Seo et al 2012), which is transmitted within mycangia of the ambrosia beetle Platypus quercivorus Murayama (Coleoptera: Platypodidae; Kinuura 2002;Kinuura and Kobayashi 2006). In fact, microscopic observation of transverse and longitudinal sections suggests that most hyphae of the fungus under both artificial and natural conditions were detected in non-conductive sapwood, irrespective of the time elapsed since the inoculation or infection (Kuroda 2001;Takahashi et al 2010;Murata et al 2011;Torii et al 2011). Although plants have various defence mechanisms against microbial pathogens and herbivores (Doehlemann and Hemetsberger 2013;Moles et al 2013), in this disease, the formation of non-conductive sapwood was suggested to be a defence response against fungal spread (Kuroda and Yamada 1996;Yamagishi et al 2013a,b).…”

“…In previously published studies, the mycelial distribution of R. quercivora in artificially inoculated seedlings and naturally infected trees was limited to tissues close to inoculation points and tunnels bored by P. quercivorus (Takahashi et al 2010;Torii et al 2011). Thus, multiple inoculations with R. quercivora or mass attacks by P. quercivorus are needed to induce lethal disease development under artificial and natural conditions Murata et al 2005;Kinuura and Kobayashi 2006).…”

“…Thus, differences in the susceptibility of trees to the fungus might be attributed to vessel arrangements (Murata et al 2007;Torii et al 2011). sieboldii (Makino) Nakai (Kuroda 2001;Yamato et al 2001;Murata et al 2011;Torii et al 2011). Hyphae of the fungus have been observed frequently in vessels of the susceptible species Quercus crispula Blume and Quercus serrata Thunb., as well as the less susceptible species Quercus glauca Thunb.…”

Comparison of Sapwood Discoloration in Fagaceae Trees After Inoculation with Isolates of Raffaelea quercivora, Cause of Mass Mortality of Japanese Oak Trees

“…In experiment 3, the sapwood discoloration widths of logs were sig nificantly larger than those of standing trees in some comparisons. In addition, the mortality of Q. crispula and Q. ser rata by the artificial inoculation of R. quercivora is influenced by the phenology of host trees (25,35,37), which tends to depend on host physiology. In addition, the mortality of Q. crispula and Q. ser rata by the artificial inoculation of R. quercivora is influenced by the phenology of host trees (25,35,37), which tends to depend on host physiology.…”